Assessment of Pulp Sensibility

One of the greatest diagnostic challenges in clinical practice is the accurate assessment of pulp status. A variety of pulp testing approaches exist, and there may be confusion as to their validity or appropriateness in different clinical situations. When tests are evaluated, there are some terms that may lead to more definitive and possibly quantifiable endodontic diagnoses. These terms are sensitivity, the ability of a test to identify teeth with disease; specificity, the ability of a test to identify teeth without disease; and predictive value, the ability of a test to foretell what the diagnosis actually is.

Pulp stimulation with cold or heat is the oldest method of evaluating the pulp’s health and its ability to respond to external stimulation, but evaluation of pulpal response must not be confused with vitality testing, which requires assessment of pulpal circulation.¹⁴⁰

Cold Tests

Cold thermal testing causes contraction of the dentinal fluid within the dentinal tubules, resulting in a rapid outward flow of fluid within the patent tubules. This rapid movement of dentinal fluid results in hydrodynamic forces acting on the Aδ nerve fibers within the pulp-dentin complex, leading to a sharp sensation lasting for the duration of the thermal test. A variety of cold tests may be employed; the major difference between them is the degree of cold applied to the tooth.¹⁴⁰

A simple means of applying a cold stimulus to a tooth is to wrap a sliver of ice in wet gauze and place it against the buccal surface, comparing the reaction between the test tooth and a control tooth. Pencils of ice can be made by filling a plastic straw with water and freezing it in an upright position in a freezer.³⁵²

Ethyl chloride (−41° C) may be sprayed onto a cotton pledget, resulting in the formation of ice crystals (Fig. 8-1) prior to application to the tooth. Dichlorodifluoromethane (DDM) (−50° C) is a compressed refrigerant spray that can also be sprayed onto a cotton pledget for cold testing (Fig. 8-2). More recently, ozone-friendly non-chlorofluorocarbon sprays have been introduced in certain countries.

FIG. 8-1 Ethyl chloride sprayed onto a cotton pledget, resulting in the formation of ice crystals.

(Courtesy Dr. R. Portigliatti.)

FIG. 8-2 Hygenic Endo-Ice.

(Courtesy Colténe/Whaledent, Cuyahoga Falls, OH.)

Another effective cold stimulus is frozen carbon dioxide (CO₂), also known as dry ice or carbon dioxide snow (−78.5° C). For testing purposes, a solid stick of CO₂ is prepared by delivering CO₂ into a custom-made plastic cylinder, and the stick is applied to the buccal surface of the tooth. This method is particularly effective when trying to assess teeth that have been restored with full-coverage metal restorations.³⁹⁷ Rickoff et al.³¹⁴ reported that CO₂ snow applied to a tooth for 5 minutes did not jeopardize the health of the pulp, nor does it damage the surface of the enamel.³⁰⁰ On the other hand, CO₂ may cause pitting of the surface of porcelain restorations when applied for as little as 5 seconds.²⁰³ When testing with a cold stimulus, the advantage of refrigerant sprays and frozen carbon dioxide is that the cold stimulus does not go into a liquid phase but rather a gas phase. This allows testing to be specific to one tooth at a time, without cold water from melted ice stimulating adjacent teeth.

Ice-cold water is another useful and inexpensive test. The tooth being tested should be isolated with a rubber dam and then bathed with water from a syringe. Cold tests should be applied until the patient definitely responds or the stimulus has been applied for a maximum of 15 seconds.¹²¹ One of the significant benefits of ice-water testing is that it can be used on any tooth regardless of the type of restoration that may be present. Overall, cold tests appear to be more reliable than heat tests,^93,341 and there is a general consensus that the colder the stimulus, the more effective the assessment of tooth innervation status.

Electric Pulp Test

The objective of the electric pulp test (EPT) is to stimulate intact Aδ nerves in the pulpal-dentin complex by applying an electric current to the tooth surface. A positive result stems from an ionic shift in the dentinal fluid within the tubules, causing local depolarization and subsequent generation of an action potential from intact Aδ nerves.²⁹²

The electric pulp tester is a battery-operated instrument connected to a probe that is applied to the tooth under investigation. It functions by producing a pulsating electrical stimulus, the initial intensity of which should be set at a very low value to prevent excessive stimulation and discomfort. The intensity of the electric stimulus is then increased steadily at a preselected rate, and a note is made of the readout on the digital display when the patient acknowledges a warm or tingling sensation. The readout is not a quantitative measurement of pulp health; it simply provides evidence that the Aδ fibers are sufficiently healthy to function.¹⁴⁰

Bipolar and monopolar are the two stimulating modes available. The bipolar mode is presumably more accurate because the current is confined to the coronal pulp, but most EPTs are still monopolar.³⁵²

The requirements of an EPT are an adequate stimulus, an appropriate application method, and careful interpretation of results (Fig. 8-3). Tooth isolation during EPT is essential. Drying the enamel, placement of an interproximal plastic strip, and use of a rubber dam can prevent the spread of electrical impulses to adjacent teeth or gingival tissue. Electric current can also be transferred between adjacent teeth through contacting metallic restorations.⁶⁴ A conducting medium should also be used to ensure that maximum current passes from the electrode to the tooth surface.²⁶¹ A laboratory study²⁴⁷ concluded that the interface medium made no appreciable difference to either the voltage or the electric current transmitted. However, a more recent study did demonstrate that different media influence the responses gained from electric testing.²⁶²

FIG. 8-3 Electronic pulp tester.

(Courtesy SybronEndo, Orange, CA.)

There are several considerations regarding optimal placement of the tester electrode. The response threshold is reached when an adequate number of nerve terminals are activated to attain what is termed a summation effect.²⁸¹ An area of high neural density should have a relatively fast and strong response and requires the least electric current. Therefore, the most desirable area of assessment in incisor teeth is at the incisal edge.³² The tester should be applied on the tooth surface adjacent to a pulp horn, the area of highest nerve density within the pulp. This position equates to the incisal third region of anterior teeth and the mid-third region of posterior teeth. The threshold for response may be influenced by the thickness of the enamel and dentin overlying the pulp. Thus, the response threshold for healthy teeth may be lowest in incisors, slightly greater in premolars, and greatest in molar teeth. A recent study has revealed that the optimum site for tester electrode placement on molars is on the tip of the mesiobuccal cusp.²²⁵

Assessment of Pulp Vascularity

Vitality testing requires the measurement of pulpal blood flow. Several devices are used to evaluate circulatory changes rather than the neural integrity of the pulp, and a number of these have been used experimentally to evaluate pulpal health.

Assessment of Cracks and Fractures

Magnification

The introduction of the operative microscope marked outstanding progress in dentistry. Magnification improves the performance of clinical procedures, and the operating microscope has dramatically improved endodontic nonsurgical treatment and periradicular surgery. The use of the operating microscope and microsurgical instrumentation have resulted in greater precision in surgical procedures, less operative trauma, improved healing, better esthetic results, and more predictable treatments. Speed, control, comfort, and adjustment are other distinct advantages.

Loupes

Magnification loupes attached to eyeglasses are relatively inexpensive, and the learning curve for their use is much shorter than for the microscope. However, there are several shortcomings to loupes compared to the operating microscope. Each loupe has a fixed magnification power (typically less than 4×) that cannot be increased or decreased. Most loupes have no integrated light source, although often they are employed with an accompanying headlamp system. There is no way to digitally document viewed images. The focus is adjusted through the movements of the clinician’s head, creating postural positions that may not be ergonomic.

Operating Microscopes

All microscope lenses are designed and installed in a telescopic system (Fig. 8-4). This means they are already focused to infinity. They send parallel beams of light to each eye, allowing the viewing of objects three dimensionally with an excellent depth impression.

FIG. 8-4 Zeiss Operating Microscope.

(Courtesy OperatingMicroscopes.com.)

Some characteristics of microscopes are: (1) wide range of magnification, (2) coaxial illumination that allows light to enter even the deepest areas of examination, (3) easy photographic and video capture documentation, (4) the capacity to make focus adjustments by moving the microscope or its parts, maintaining an ergonomic work position.

The major advantage of using light and magnification is the increased diagnostic potential. The microscope is an excellent tool for detecting cracks, additional canals, perforations, and the like.²⁵² It is important to clarify the difference between magnification and differentiation. Magnification is defined as viewing an object at a greater size; differentiation refers to making an object distinct or specialized. The microscope alone is very useful, but sometimes additional adjuncts must be employed for better differentiation. Methylene blue used in conjunction with magnification can add important information, especially for fracture detection. Additionally, some operating microscopes employ colored light sources which help in the differentiation between bone and root surfaces during apicoectomies.

Periodontal Probing

Periodontal probing is an essential part of the endodontic diagnostic process. The tooth should be evaluated interproximally and at every millimeter on both the buccal and lingual surfaces, with emphasis on the convex part of the root. Each furcation should also be explored with a periodontal or furcation probe. Periodontal probing is especially useful in helping to detect vertical root fractures (VRF). If the probe sinks abruptly into an isolated deep, narrow periodontal defect, the level of suspicion for a VRF increases. This is true especially when there is no evidence of periodontal disease associated with other areas of the tooth or adjacent teeth. If a VRF is suspected but cannot be directly visualized, magnification, illumination, and staining can be very helpful.

Elastic, plastic, periodontal probes (Premier, Plymouth Meeting, PA) (Fig. 8-5) have been advocated for better detection of defects associated with VRFs. A periodontal pocket associated with a VRF—in an otherwise periodontally intact tooth—differs from a common periodontal pocket by having a deep, narrow pocket with a small occlusal entrance. The flexibility of the plastic probes allows them to be introduced into pockets that may not permit the insertion of rigid metal probes (Fig. 8-6).

FIG. 8-5 Flexible periodontal probe (Premier, Plymouth Meeting, PA) and a conventional rigid metal probe.

FIG. 8-6 A Premier periodontal probe in a narrow and deep pocket associated with VRF. Note the blanching that indicates the narrow nature of the pocket.

Biting Tests

The Tooth Slooth (SybronEndo) (Fig. 8-7) has proved very useful for the differential diagnosis of various stages of incomplete crown fractures. The design of the device permits a chewing force to be applied selectively to one cusp at a time. When this selective force is applied to a cracked cusp of a vital tooth, the coronal dentin distorts, which is allowed by the crack and results in a painful response. This sensation is not present in other intact cusps of the same tooth. This device can be effective when cotton rolls or wooden sticks are not helpful.

FIG. 8-7 Tooth Slooth.

(Courtesy Profession Results, Inc., www.toothslooth.com.)

Transillumination

Transillumination is the transmission of light through tissues of the body. A common example is the transmission of light through fingers, producing a red glow due to red blood cells absorbing all other colors of the light. Transillumination is an excellent technique for viewing caries, fractures, narrow root canal orifices, and other clinical entities. It is used by passing an intense light through the side of the tooth and can substantially enhance the clinician’s diagnostic and treatment abilities. Healthy tooth structure has an index of light transmission greater than that of caries or calculus. A fracture line or a calcified root canal orifice also have a reduced ability to transmit light. Therefore, if an intense light is applied in direct proximity to a tooth, and other extraneous light is reduced, these clinical entities will appear as distinct dark areas in the otherwise bright structure (Fig. 8-8). The transilluminator tip is placed on either the facial or lingual surface of the tooth or the root, and the area can be viewed from the occlusal surface or the surface opposite the transilluminator. Direct vision or a dental mirror may be used for viewing, depending upon the area under examination. The exact placement of the transilluminator differs for caries, endodontics, fractures, and so forth.

FIG. 8-8 A crack in the crown of a tooth, located by using a transilluminator.

The acceptance of transillumination as a diagnostic technique has been greatly enhanced by the availability of modern devices made expressly for this purpose.¹¹⁸ These transilluminators use white light–emitting diode (LED) lamps to generate the necessary intense white light. The light is then transmitted to the working area, without heat, using a narrow fiberoptic rod or fiberoptic cables. An important feature is that a fiberoptic rod can be easily removed and autoclaved to avoid cross-contamination between patients. The small size and portability of these new devices enhances the convenient use of transillumination.

Assessment of Images

Cone-Beam Computed Tomography and Other Scans

CBCT (Fig. 8-9), ultrasound, and other emerging technologies seem to be very promising tools for determining a more accurate diagnosis of periradicular pathoses.^{67,153,246,275} The reader is referred to Chapter 29 for further information about CBCT.

FIG. 8-9 CBCT example: These series of images show an ovoid radiolucent area in the anterior right maxilla. Both teeth 1.1 and 1.2 were endodontically treated; however, given the epicenter of the entity relative to the teeth, the radiolucent area was interpreted to be a keratocystic odontogenic tumor.

(Courtesy Dr. E. Lam.)

Hand Instruments

Traditional dental hand instruments have been modified for endodontic uses. A typical set of endodontic instruments might include a front-surface mouth mirror, a D-5 explorer, a D-16 endodontic explorer, cotton pliers, a spoon excavator, a series of pluggers, a plastic instrument, a hemostat, a periodontal probe, and a ruler. The endodontic explorer has two straight, very sharp ends that are angled in two different directions from the long axis of the instrument.

The mouth mirror should be a front-surface mirror, especially when magnifying loupes or an operating microscope are used. Several types of endodontic spoons are available. These spoons have a much longer offset from the long axis of the instrument (for better reach inside constricted pulp chambers) than regular dental spoons. The spoons are used to remove carious material and to excise pulp tissue; therefore, they should be kept well sharpened (Fig. 8-10). The cotton pliers should preferably be of the locking type that can securely hold gutta-percha cones when transferred from the dental assistant to the dentist’s hand. The periodontal probe should be a flexible one (see Fig. 8-5). The exact type and number of instruments usually depend on the techniques used and clinician’s preference.

FIG. 8-10 Endodontic explorer (A) and endodontic spoon (B).

(From Boyd LR: Dental instruments: a pocket guide, ed 3, Saunders Elsevier, St Louis, 2009.)

Instruments for Cleaning and Shaping the Root Canal Space

The purposes of this section is to provide the principles necessary for the clinician to better understand the ideal design for current and future instruments. Most instructional materials mistakenly attempt to teach step-by-step techniques rather than explain the physics of the instruments. However, an increasing number of new products and their advocates have created confusion in the selection process. For this reason, the clinician must understand the basic mechanical, physical, and scientific principles of instrumentation (Box 8-1).

The two primary goals of root canal instrumentation are (1) to provide a biologic environment (infection control) conducive to healing and (2) to develop a canal shape receptive to obturation. Historically, most instruments used to shape the canal were designed to be used by hand. Recently, rotary instrumentation has gained considerable popularity and may be used in conjunction with hand instruments (Box 8-2). The information in the following sections should facilitate the most efficient use of rotary instruments, minimizing the chance of instrument or procedural mishaps and allowing the clinician to achieve ideal treatment results.

Group I: Manually Operated Instruments

Manually operated instruments are all instruments that are generically called files. Defining endodontic instruments by function, files are instruments that enlarge canals with reciprocal insertion and withdrawal motions. Reamers cut and enlarge canals with rotational motions. Before using either instrument, the clinician must make sure the canal is patent.

Files were first mass produced by the Kerr Manufacturing Co. of Romulus, Michigan, in the early 1900s, hence the name K-type file (or K-file) and K-type reamer (K-reamer). K-files and K-reamers originally were manufactured by the same process. Three or four equilateral, flat surfaces were ground at increasing depths on the sides of a piece of wire, producing a tapered pyramidal shape. The wire then was stabilized on one end, and the distal end was rotated to form the spiral instrument (Fig. 8-11). The number of sides and the number of spirals determine whether the instrument is best suited for filing or reaming. Generally, a three-sided configuration with fewer spirals is used for reaming; a three- or four-sided configuration with more spirals is used for filing.

FIG. 8-11 The two ends of a blank, tapered pyramidal wire are stabilized (top) and then one end is rotated to create a spiral shape on the file’s working surface (middle). Multiple rotations produce the final spiral shape (bottom).

(Courtesy John T. McSpadden, Lookout Mountain, GA.)

Historically, root canal instruments were manufactured from carbon steel. Subsequently, the use of stainless steel greatly improved the quality of instruments. More recently, the introduction of the nickel-titanium (NiTi) alloy in the manufacture of endodontic instruments has resulted in significant improvements in canal shaping because of its increased flexibility compared to stainless steel (this metal is described later in the chapter).

Barbed Broaches and Rasps

Dating from the early to mid-19th century, broaches and rasps were the earliest endodontic instruments used to extirpate the pulp and enlarge the canal (Fig. 8-12). Still used today, these instruments are manufactured by hacking a round, tapered wire with a blade to form sharp, projecting barbs that cut or snag tissue. Specifications have been set for both the barbed broach and the rasp (ANSI/ADA standard No. 63, ISO/FDI standard No. 3630/1).

FIG. 8-12 Barbed broach (Union Broach, York, PA).

A barbed broach does not cut or machine dentin; this instrument is mostly used to engage and remove soft tissue from the canal. It is also an excellent tool for removing cotton or paper points that have accidentally become lodged in the root canal.

K-Type Instruments

The K-file and K-reamer are the oldest useful instruments for cutting and machining dentin (Fig. 8-13). They are made from a stainless steel wire that is ground to a tapered square or triangular cross-section and then twisted to create either a file or a reamer. A file has more flutes (see Components of a File) per length unit than a reamer.

FIG. 8-13 K-file #40 (DENTSPLY Maillefer, Ballaigues, Switzerland).

K-type instruments are useful for penetrating and enlarging root canals. The instrument works primarily by compression-and-release destruction of the dentin surrounding the canal. Generally, a reaming motion (i.e., constant file rotation) causes less transportation than a filing motion (reciprocating or “watch-winding” file rotation).⁴⁰⁶ (Transportation is the excessive loss of dentin from the outer wall of a curved canal in the apical segment. This procedural error can lead to perforation of the root canal system or an inability to negotiate the canal space apical to the canal transportation.) A stainless steel K-file can be precurved to a desired form to facilitate insertion and minimize transportation. Permanent deformation occurs when the flutes become wound more tightly or opened more widely (Fig. 8-14). When such deformation occurs, the instrument should no longer be used. Instruments fracture during clockwise motion after plastic deformation.^158,345 This occurs when the instrument becomes bound while the force of rotation continues. Interestingly, although the force required for failure is the same in both directions of rotation,^205,213 failure occurs in the counterclockwise direction at half the number of rotations required for failure in the clockwise direction. Therefore K-type instruments should be operated more carefully when pressure is applied in a counterclockwise direction.

FIG. 8-14 K-files stressed to deformation by clockwise and counterclockwise twisting (arrow indicates deformed areas). These instruments are close to fracture and should be discarded.

H-Type Instruments

An H-type instrument has spiral edges arranged to allow cutting only during a pulling stroke (Fig. 8-15). An example is a Hedström file. An H-type instrument is better for cutting than a K-type instrument, because it has a more positive rake angle (see Components of a File) and a blade with a cutting rather than a scraping angle. Bending a Hedström file results in points of greater stress concentration than occurs with K-type instruments. These concentration points can lead to the propagation of cracks and fatigue failure.¹⁵⁸ Clinically, fatigue happens without any external physical signs of stress, such as the flute changes seen in K-type instruments (see Fig. 8-14).

FIG. 8-15 Hedström file #50 (DENTSPLY Maillefer, Ballaigues, Switzerland).

Currently all H-type instruments are ground from a tapered blank. Hedström files are formed by grinding a single continuous flute. Computer-assisted machining technology has allowed the development of H-type instruments with very complex forms. This process, called multiaxis grinding, allows adjustment of the rake angle, helix angle, multiple flutes, and tapers. H-files cut the canal wall when pulled or rotated clockwise; the file is relatively ineffective when pushed or rotated counterclockwise. Because the H-file generally has sharper edges than the K-file, it has a tendency to screw into the canal during rotation, particularly if the instrument’s blades are nearly parallel. Awareness of screwing-in forces is important for avoiding instrument failure.

Instrument Design Modifications

K-files and H-files can be modified into numerous designs. Often the instruments can be improved for more effective instrumentation by changing the geometric dimensions, using computerized multiaxis grinding machines. For example, changing the cross-sectional geometry of a K-type instrument from square to rhomboid enhances the instrument’s flexibility and rake angle. However, the possible geometries can complicate adherence to ISO and ANSI standards.

Tip Design

Studies have shown that tip design can affect file control, efficiency, and outcome in the shaping of root canal systems.^266,267 The tip of the original K-file resembled a pyramid (see Fig. 8-13). Instrument tips have been described as cutting, noncutting, and partially cutting, although no clear distinction exists among the three types (Fig. 8-16).

FIG. 8-16 Instrument tips arranged in order from cutting to non-cutting.

(Courtesy John T. McSpadden, Lookout Mountain, GA.)

The instrument tip has two functions: to guide the file through the canal and to enlarge the canal. A clinician who is unfamiliar with the tip design of a particular instrument is apt to do either of the following: (1) transport the canal (if the tip is capable of enlarging the canal and remains too long in one position) or (2) encounter excessive torsion and break the file (if a noncutting tip is forced into a canal with a smaller diameter than the tip). Transportation of the original axis of the canal can occur by remaining too long in a curved canal with a tip that has efficient cutting ability.

The angle and radius of its leading edge and the proximity of the flute to its actual tip end determines the cutting ability of a file tip. Cutting ability and file rigidity determine the propensity to transport the canal. The clinician must keep in mind that as long as the file is engaged 360 degrees, canal transportation is unlikely to occur. Only with overuse does the file begin to cut on one side, resulting in transportation. Most instrumentation errors occur when the file tip is loose in the canal, which gives it a propensity to transport the canal.

A good beginner’s rule is this: If the canal is smaller than the file, the prudent use of a cutting tip is more efficient. If the canal is larger than the tip, using a less-effective cutting tip can help prevent transportation (see Fig. 8-16). Much has been written about the importance of various sophisticated tip modifications to prevent such ledging, but little scientific evidence exists that any one design is better than another.^{190,308,309,316,321}

Metal Alloys

The development of nitinol, an equiatomic alloy composed of nickel and titanium,⁴¹² has proved a significant advancement in the manufacture of endodontic instruments. NiTi is called an exotic metal because it does not conform to the typical rules of metallurgy. Because it is a superelastic metal, the application of stress does not result in the usual proportional strain seen in other metals such as stainless steel. When stress is initially applied to NiTi, the result is proportional strain, but the strain remains essentially the same as the application of additional stress reaches a specific level, forming what is called a loading plateau. Eventually, of course, application of more stress results in more strain, which increases until the file breaks. This unusual property is the result of a molecular crystalline phase transformation. External stresses transform the austenitic crystalline form of NiTi into a martensitic crystalline structure that can accommodate greater stress without increasing the strain. As a result of its unique crystalline structure, a NiTi file has superelasticity, or the ability to return to its original shape after being deformed. Simply stated, NiTi alloys currently are the only readily available affordable materials with the flexibility and toughness for routine use as effective rotary endodontic files in curved canals.

Attempts to improve the NiTi alloy continue, and recent reports indicate that new NiTi alloys may be five times more flexible than currently used alloys.¹⁸⁶ Microscopic surface defects are considered a contributing factor for crack propagation and instrument fracture. Therefore, attempts to improve surface characteristics by electropolishing, surface coatings, and surface implantation have been used for this purpose.^216,310

Group II: Low-Speed Rotary Instruments

Many types of rotary instruments are used during endodontic procedures. In addition to regular burs adapted for endodontics, various types of root canal reamers are used to shape the canal space, to place or remove root canal filling materials, or to prepare a post space.

Burs

In addition to conventional burs, burs with extended shanks for low-speed contra-angle handpieces are useful for providing good visibility during deep preparation of the pulp chamber. This is particularly important when using an operating microscope when performing such procedures after access to the pulp chamber has been achieved. Straight-line access to the initial point of curvature traditionally has been accomplished using rotary instruments such as Gates-Glidden burs and Peeso instruments. These reamers are available in a 32-mm length and a 28-mm length for posterior teeth (Figs. 8-17, 8-18). Use of these instruments should be limited to the straight portion of the canal preparation. The risk of perforation with these instruments becomes a real possibility with attempts to instrument beyond the point of curvature or if the instruments are used to cut laterally. The risk of lateral cutting resulting in perforation is lower with Gates-Glidden burs than with the other instruments mentioned. This risk is especially pronounced on the furcation sides of mesial roots of molars. Gates-Glidden instruments are also available in nickel-titanium. The Peeso reamer is used mostly for post space preparation (Fig. 8-19).

FIG. 8-17 Gates-Glidden (GG) burs made of stainless steel.

(From Johnson WT: Color atlas of endodontics, St Louis, 2002, Saunders.)

FIG. 8-18 Working part of a Gates-Glidden bur made of stainless steel. Note the rounded safety tip and the lack of sharp cutting edges. The instrument has a marginal land for centering the drill in the canal and to allow safer machining of the canal walls.

FIG. 8-19 Peeso Reamer (Union Broach, York, PA). Note the safety tip and marginal lands on the machining surfaces.

Group III: Rotary Instruments for Canal Preparation

Components of a File

To make the best use of files, the clinician should be familiar with the parts of each file and understand how variations in design affect instrumentation (Fig. 8-20). The taper usually is expressed as the amount the file diameter increases each millimeter along its working surface from the tip toward the file handle. For example, a size #25 file with a #.02 taper would have a 0.27 mm diameter 1 mm from the tip, a 0.29 mm diameter 2 mm from the tip, and a 0.31 mm diameter 3 mm from the tip. Some manufacturers express the taper in terms of percentage (e.g., a #.02 taper is a 2% taper). Historically, as an ISO standard, a file was fluted and tapered at 2% for 16 mm, but now files incorporate a wide variation of lengths and tapers of working surfaces. The ability to determine cross-sectional diameter at a given point on a file can help the clinician determine the file size in the point of curvature and the relative stress being placed on the instrument.

FIG. 8-20 Components of an endodontic rotary instrument.

(Courtesy John T. McSpadden, Lookout Mountain, GA.)

The flute of the file is the groove in the working surface used to collect soft tissue and dentin chips removed from the wall of the canal. The effectiveness of the flute depends on its depth, width, configuration, and surface finish. The surface with the greatest diameter that follows the groove (where the flute and land intersect) as it rotates forms the leading (cutting) edge, or the blade of the file. The cutting edge forms and deflects chips from the wall of the canal and severs or snags soft tissue. Its effectiveness depends on its angle of incidence and sharpness. If a surface projects axially from the central axis as far as the cutting edge between flutes, this surface is called the land (or sometimes the marginal width) (Figs. 8-21 and 8-22). The land touches the canal walls at the periphery of the file and reduces the tendency of the file to screw into the canal, reduces transportation of the canal, reduces the propagation of microcracks on its circumference, supports the cutting edge, and limits the depth of cut. Its position relative to the opposing cutting edge and its width determine its effectiveness. To reduce frictional resistance, some of the surface area of the land that rotates against the canal wall may be reduced to form the relief (Fig. 8-23). The angle the cutting edge forms with the long axis of the file, called the helix angle, augers debris collected in the flute from the canal. This angle is important for determining which file technique to use (see Fig. 8-23; Fig. 8-24).

FIG. 8-21 ProFile rotary NiTi instruments, #3, #5, and #6 (DENTSPLY Tulsa Dental, Tulsa, OK). The instruments have marginal lands that guide the instrument in the center of the canals and around curvatures.

FIG. 8-22 Rotary ProFile NiTi file, #5 (DENTSPLY Tulsa Dental, Tulsa, OK). Note the instrument’s wide marginal land (arrows).

FIG. 8-23 Components of the Quantec NiTi rotary instrument (SybronEndo, Orange, CA).

(Courtesy John T. McSpadden, Lookout Mountain, GA.)

FIG. 8-24 Components of the ProTaper NiTi rotary instrument (DENTSPLY Tulsa Dental, Tulsa, OK).

(Courtesy John T. McSpadden, Lookout Mountain, GA.)

If a file is sectioned perpendicular to its long axis, the rake angle is the angle formed by the leading edge and the radius of the file. If the angle formed by the leading edge and the surface to be cut (its tangent) is obtuse, the rake angle is said to be positive or cutting. If the angle formed by the leading edge and the surface to be cut is acute, the rake angle is said to be negative or scraping (Fig. 8-25). However, the rake angle may not be the same as the cutting angle. The cutting angle, or the effective rake angle, is a better indication of a file’s cutting ability and is determined by measuring the angle formed by the cutting (leading) edge and the radius when the file is sectioned perpendicular to the cutting edge. If the flutes of the file are symmetric, the rake angle and the cutting angle are essentially the same.

FIG. 8-25 Positive and negative rack angles. Negative angle results in scraping action; positive angle results in cutting action.

The pitch of the file is the distance between a point on the leading edge and the corresponding point on the adjacent leading edge, or it may be the distance between corresponding points within which the pattern is not repeated. The smaller the pitch or the shorter the distance between corresponding points, the more spirals the file has and the greater the helix angle. Most files have a variable pitch, one that changes along the working surface. Because the diameter increases from the file tip toward the handle, the flute becomes proportionately deeper, resulting in a core taper that is different from the external taper.

The cutting angles, helix angles, and external and core tapers may vary along the working surface of the file, and the ratios of these quantities can vary between instruments of the same series. A change in any of these features can influence the file’s effectiveness or its propensity for breakage as it progresses into the canal space; this can explain why some files act uncharacteristically compared with other files in the same series. In one study, investigators using electric and air-driven handpieces with rotary NiTi instruments found no significant difference in file distortion or breakage between the two handpieces at 150 revolutions per minute (rpm).⁴⁰ Other researchers have shown that the ability to select precise rpm⁷¹ and torque¹²² settings affects the efficiency and durability of instruments (Fig. 8-26). Determining and maintaining a file’s proper rotational speed is more difficult with an air handpiece than with an electric handpiece. For this reason, the clinician would be wise to use an electric handpiece when instrumenting with rotary files. The popularity of electric handpieces among clinicians appears to support the conclusion that regardless of the design used for rotary NiTi instruments, an electric handpiece—rather than an air-driven handpiece—should be used because it allows precise speed and torque control (see Fig. 8-26).

FIG. 8-26 Torque- and speed-controlled electric micromotor and handpiece (X-Smart Endodontic Motor).

(All rights owned by and used with permission from DENTSPLY International, Inc.)

Instrument Designs

Design changes are made in endodontic instruments to help prevent procedural errors, increase efficiency, and improve the quality of canal shaping. Examples of instruments commonly used today are the ProFile and ProFile GT, the ProTaper, the Lightspeed LSX, the Quantec, the Twisted File (TF),^123,212 the RaCe, the EndoSequence, and the EZ-Fill SafeSider. For more information about these instruments and others, see Chapter 9. In many patients, the apical canal is larger than the largest file used at working length, so many design changes have been directed toward enabling the clinician to increase the size of the largest file used at working length. The following design components can be used to prevent excess stress on instruments.

1. The difference between the file’s minimum and maximum diameters can be reduced so that the torque required for rotating the larger diameter does not exceed the plastic limit of the smaller diameter.

2. The space between the tip and the maximum diameter can be reduced so that the required torque does not exceed the ultimate strength of any part of the file.

3. A zero taper or nearly parallel and fluted working portion of the file can be provided for curved canals so that the apical portion of the canal can be enlarged without undue file stress and compression of debris.

4. The continuity of the blade engagement can be interrupted.

5. The number of flute spirals can be eliminated or reduced to the smallest number necessary to prevent excessive torque, which results from the accumulation of debris.

6. A means can be provided to complete the file function before the flutes fill with debris.

7. Any land width can be minimized to reduce abrasion on the canal surface.

8. The file can be given an asymmetric cross-section to help maintain the central axis of the canal.

9. The number of flutes with similar helix angles can be reduced. When helix angles are dissimilar, screwing-in forces are reduced; when flutes have no helix angles, screwing-in forces are eliminated.

10. Positive cutting angles can be incorporated to enhance the efficiency of canal enlargement.

11. Blades can be made appendages or projections from the file shaft rather than ground into the shaft.

12. Channels can be cut along the long axis of the file to facilitate its removal if it breaks.

Group IV: Engine-Driven Three-Dimensionally Adjusting Files

Self-Adjusting File

The self-adjusting file (SAF; ReDent-Nova, Raanana, Israel) represents a new approach in file design and mode of operation.²⁶⁰ The file is a hollow device, designed as a cylinder of thin-walled, delicate NiTi lattice with a lightly abrasive surface (Figs. 8-27 and 8-28). An initial glidepath is established with a #20 K-file to allow the insertion of the SAF file. The file is proposed to be compressed from its 1.5 mm diameter into dimensions equivalent to those of a #25 K-file (Fig. 8-29). It is operated with a modified KaVo handpiece (GENTLEpower 20LP with a 3LDSY head, KaVo Dental GmbH, Biberach/Riss, Germany) that generates in-and-out vibrations with 5000 vibrations per minute and 0.4 mm amplitude (Fig. 8-30). The overall concept is that the compressed file will adapts itself to the root canal walls, applying a uniform cutting action (see Fig. 8-28) gradually removing a uniform dentin layer from the canal walls.

FIG. 8-27 The SAF instrument. The instrument is made as a hollow, thin NiTi lattice cylinder that is compressed when inserted into the root canal and adapts to the canal’s cross-section. It is attached to a vibrating handpiece. Continuous irrigation is applied through a special hub on the side of its shank.

(Courtesy ReDent-Nova, Raanana, Israel.)

FIG. 8-28 The abrasive surface and details of the lattice of the SAF instrument. The extreme elasticity is the total of the elasticity of each of the delicate NiTi segments.

(Courtesy ReDent-Nova, Raanana, Israel.)

FIG. 8-29 The SAF instrument adapted into a root canal that was initially prepared with #20 K-file. Right: A #20 K-file in the canal. Left: The SAF file in its relaxed form. Center: The SAF file inserted into the same narrow canal. It will apply delicate pressure on the canal wall, attempting to resume its original shape.

(Courtesy ReDent-Nova, Raanana, Israel.)

FIG. 8-30 The VATEA continuous irrigation unit used with the SAF instrument. The unit has two containers and provides a continuous flow (low pressure, 5 ml/min) of either irrigant (i.e., sodium hypochlorite and EDTA) through double silicon tubes that are connected to the hubs on the front of the device. It is controlled by finger-operated switches located on the handpiece.

(Courtesy ReDent-Nova, Raanana, Israel.)

As noted, the file is hollow, which allows for continuous irrigation through the file while operated in the root canal. The irrigant is delivered through a free-rotating hub to which a silicone tube is attached (see Fig. 8-30). Either a special irrigation unit (Fig. 8-31) (VATEA, ReDent-Nova, Raanana, Israel) or any appropriate dispenser-type unit may be used to deliver a constant flow of irrigant at 5 ml/min. This maintains a continuous flow of fresh, fully active irrigant that carries with its outflow tissue debris and the dentin powder generated by the file.²⁵⁶

FIG. 8-31 A micro–computed tomography (microCT) analysis of the operation of the SAF instrument in a flat canal with extremely oval cross-section. Upper: Buccolingual and mesiodistal views of the root canal reconstructed from microCT. Lower: Cross-sections at 4 and 6 mm from the apex. Red: before, blue: after treatment.

(Courtesy ReDent-Nova, Raanana, Israel.)

One file is used throughout the procedure. It is initially compressed into the root canal (see Fig. 8-29) and gradually enlarges while cleaning and shaping the canal. The unique feature of this file is that it adapts to the shape of the canal not only longitudinally, as every NiTi file does, but also to the cross-section of the canal. Consequently, the basic shape of the root canal is preserved: a root canal with a round cross-section is enlarged to one with a similar but larger cross-section, whereas a flat root canal will be enlarged to a flat root canal of bigger dimensions (see Fig. 8-31). This unique feature of the SAF file makes it different from any other currently available file system.

Because it has no rigid metal core, the file is also extremely adaptable longitudinally. The inherent tendency to straighten curved root canals and transport their apical part to the outer side of the curvature, which is typical of most other file systems, is greatly avoided. The absence of a metal core also makes the SAF extremely resistant to fracture. File separation—a major problem with other NiTi files—has not been reported to occur, and mechanical failure (a rare occurrence if it happens) is limited to local tears in the delicate NiTi lattice.²⁶⁰ It is clear that this interesting conceptual device will be subjected to extensive independent study over the next few years.

Group VI: Sonic and Ultrasonic Instruments

A radically different way of instrumenting root canals was introduced when clinicians became able to activate files by electromagnetic ultrasonic energy. Piezoelectric ultrasonic units are also available for this purpose (Fig. 8-32). These units activate an oscillating sinusoidal wave in the file with a frequency of about 30 kHz.

FIG. 8-32 P5 Neutron piezoelectric ultrasonic unit.

(Courtesy Satelec, Merignac Cedex, France.)

Two types of units, ultrasonic and sonic, are primarily available. Ultrasonic devices, which operate at 25 to 30 kHz, include the magnetostrictive Cavi-Endo (DENTSPLY Caulk, Milford, DE), the piezoelectric ENAC (Osada, Tokyo) (Fig. 8-33), the EMS Piezon Master 400 (Electro Medical Systems [EMS] Vallée de Joux, Switzerland), and the P5 Neutron (see Fig. 8-32) (Satelec, Merignac Cedex, France). Sonic devices, which operate at 2 to 3 kHz, include the Sonic Air MM 1500 (Micro Mega, Prodonta, Geneva, Switzerland), the Megasonic 1400 (Megasonic Corp, House Springs, MO), and the Endostar (Syntex Dental Products, Valley Forge, PA). Ultrasonic devices use regular types of instruments (e.g., K-files), whereas sonic devices use special instruments known as Rispi-Sonic, Shaper-Sonic, Trio-Sonic, or Heli-Sonic files.

FIG. 8-33 ENAC piezoelectric ultrasonic device.

(Courtesy Osada USA, Los Angeles, CA.)

Although similar in function, piezoelectric units have some advantages over the magnetostrictive systems. For example, piezoelectric devices generate little heat, so no cooling is needed for the electric handpiece. The magnetostrictive system generates considerable heat, and a special cooling system is needed in addition to the irrigation system for the root canal. The piezoelectric transducer transfers more energy to the file than does the magnetostrictive system, making it more powerful. Working with no water cooling becomes essential when using an operating microscope, because the water spray may obstruct visualization.

The file in an ultrasonic device vibrates in a sinus wave–like fashion. A standing wave has areas with maximal displacement (i.e., antinodes) and areas with no displacement (i.e., nodes). The tip of the instrument exhibits an antinode. If powered too high, especially with no contact with the canal wall, the instrument may break because of the intense vibration. Therefore files must be used only for a short time, must remain passive within the canal, and the power must be controlled carefully. The frequency of breakage in files used for longer than 10 minutes may be as high as 10%, and the breakage normally occurs at the nodes of vibrations.⁵

Ultrasonic devices have proved very efficient for irrigating root canal systems. During free ultrasonic vibration in a fluid, two significant physical effects are observed: cavitation and acoustic streaming. During oscillation in a fluid, a positive pressure is followed by a negative pressure. If the file’s tensile strength is exceeded during this oscillation of pressure gradients, a cavity is formed in the fluid in the negative phase. During the next positive-pressure phase, the cavity implodes with great force; this is cavitation. Under normal clinical conditions, the power of dental ultrasonic units is too low to create significant cavitation effects on the dentin walls. Acoustic streaming creates small, intense, circular fluid movement (i.e., eddy flow) around the instruments. The eddying occurs closer to the tip than in the coronal end of the file, with an apically directed flow at the tip. Acoustic streaming increases the cleaning effect of the irrigant in the pulp space through hydrodynamic shear stress. The increased amplitude that occurs with the smaller file sizes enhances the acoustic streaming.⁶ This has proved valuable in the cleaning of root canals because conventional irrigation solutions do not penetrate small spaces well.

Acoustic streaming has little direct antimicrobial effect. Both cavitation and acoustic streaming are dependent on the free vibration of the file. The limits of the space in a root canal significantly inhibit the practical utility of ultrasonic devices for root canal cleaning. Depending on size and power, the file tip may have amplitudes that require a canal size of at least a #30 file through a #40 file for free oscillation. Any contact with the root canal walls dampens oscillation. As the contact with the canal wall increases, the oscillation is dampened and becomes too weak to maintain acoustic streaming. Using a small file size with minimal contact to the root canal wall provides optimal cleaning conditions.⁷

Ultrasonic devices have proved disappointing as instruments for improving the removal of dentin from the root canal walls. They do improve the ability to clean the pulp space (Fig. 8-34) and difficult-to-débride areas through acoustic streaming.^{12,68,402,403} However, it is unclear whether this can be achieved during regular preparation when the file is actively dampened and little acoustic streaming takes place. Cleaning is further enhanced by the excellent irrigation systems some of the devices provide. Application of a freely oscillating file with sodium hypochlorite (NaOCl) irrigation for several minutes to aid pulp space disinfection is believed to be useful after complete biomechanical instrumentation of the pulp space.³⁶¹

FIG. 8-34 Start-X ultrasonic tip #2; designed for working on the pulp chamber floor and walls when looking for 2MB canals. Note the surface texture of the instrument that allows long-lasting active surface.

(All rights owned by and used with permission from DENTSPLY International, Inc.)

Sonic devices are more useful for true hard-tissue removal during root canal preparation. Because the files operate like a conventional handpiece, the file vibrations are less likely to be dampened by contact with the root canal walls. Therefore the special files used in these systems are true bulk dentin removers. New tip designs for piezoelectric ultrasonic units have also been found extremely effective in dentin removal in the pulp chamber and orifice of the canals (see Fig. 8-34).

National and International Standards for Instruments

As a result of concerns that arose nearly 45 years ago, efforts were made to standardize endodontic files and root filling materials. As mentioned previously, this resulted in an international standard for endodontic files, known in the United States as ANSI standard No. 58 for Hedström files and ANSI standard No. 28 for K-files (Table 8-1). The standards have several similarities, but some important differences exist. Fig. 8-35 shows the measurements dictated by the standards. The size designation is derived from the projected diameter at the tip of the instrument. This is an imaginary measurement and is not reflected in the real size of the working part of the instrument. The taper of the instruments is designed to be a 0.02 taper, namely a diameter-increase by .02 mm for each mm of length, starting at the tip. The working diameter is the product of the taper and the length of the tip. Three standard lengths are available at 21 mm, 25 mm, and 31 mm. The working part of the instrument must be at least 16 mm. As stated previously, tapers other than .02 and working parts of instruments less than 16 mm are now available and outside the standard.

TABLE 8-1 Dimensions of Standardized K-File, H-File, and Gutta-Percha Cones (ANSI No. 28, 58, and 78*)

FIG. 8-35 Measuring points for American National Standards Institute (ANSI) and American Dental Association (ADA) regulations #28 and #58, which cover K-type and H-type instruments. The measuring point for the diameter of the instrument (size) is imaginary (D₀) and projects the taper of the instrument at the tip. Therefore an instrument with a short tip is more true to its size than an instrument with a long tip. D₁₆ represents the diameter at the end of the working part, which must be at least 16 mm long.

This system of numbering files with at least 15 different sizes replaced the old, somewhat imperfect system that numbered the sizes from #1 through #6. Although the new standard includes many sizes, astute clinicians may include fewer instrument sizes for their special work habits.

In recent years, suggestions to change the numbering system for files with different sizes have been implemented by several manufacturers. One system has introduced “half” sizes in the range of #15 through #60, resulting in instruments in sizes #15, #17.5, #20, #22.5, and so on. Considering the fact that most manufacturers already are unable to size their instruments within the accepted range, the introduction of half sizes seems unnecessary. However, if standards are strictly adhered to, the use of half sizes seems more reasonable for instrument systems such as the LightSpeed, in which the strength of the instrument is such that full-size increments may generate stresses beyond the tolerance of the instrument. The standards are overdue for reevaluation in light of recent technologic changes.

Devices for Periapical Débridement Through a Root Canal Access

The Apexum device (Apexum, Or-Yehuda, Israel) is currently the single representative of this group^258,259 (Fig. 8-36). It represents a totally different concept than that applied by most root canal cleaning and shaping systems. The goals of most current concepts are to maintain the original apical constriction by all means and to avoid any substantial overinstrumentation past the apical foramen. The Apexum concept requires widening the apical foramen to create an opening 330 µm in diameter by passing a #30 file 1 mm beyond the apex. This may represent some enlargement of the apical foramen in certain cases, but in other cases, the natural apical foramen diameter may be larger than this.⁴³ Further instrumentation with larger instruments (#40 or #45) to a length 1 mm short of the apical foramen are then used to recreate an artificial apical stop and constriction.

FIG. 8-36 Apexum device. A, The Coarse Apexum Ablator in its NiTi sheath (arrow in C). B-C, The active part was extruded and regained its preformed shape that allows it to rotate in the periapical lesion (250 rpm, 30 sec), mincing the soft tissue without engaging the walls of the bony crypt. D, The Fine Apexum Ablator, inserted into the lesion after the Coarse Apexum Ablator is removed; rotates at 7000 rpm for 30 seconds, turning the minced tissue into a thin suspension that can be washed out.^258,259

(Courtesy Apexum, Or-Yehuda, Israel.)

Two miniature devices are then used to débride the periapical tissues through the root canal access. The first is the Coarse Apexum Ablator, which is made from a prebent memory-shape NiTi wire encased in a NiTi tube that serves as its sheath (see Fig. 8-36). The instrument, still encased in its sheath, is inserted to the artificial apical stop. Then the inner wire is gently pushed through the apical foramen and into the periapical lesion.

While in the periapical area, it regains its prebent shape (Figs. 8-37 and 8-38). It is then attached to a low-speed handpiece and rotated at 250 rpm for 30 seconds, thus coarsely mincing the periapical tissues. The first instrument is then removed, and the second instrument, the Fine Apexum Ablator, is inserted, passed through the apical foramen, and rotated at 7000 rpm for 30 seconds, turning the tissue into a thin suspension. The resulting suspension is then washed out coronally through the canal space using sterile saline solution delivered into the periapical area using a syringe and a thin, 30-gauge blunt needle.

FIG. 8-37 Apexum in clinical use. A, The Coarse Apexum Ablator in a periapical lesion of an upper single rooted tooth. Note the sheath in the root canal (arrow). B, Root canal obturation (lateral condensation) immediately after the Apexum procedure has been completed.²⁵⁸

(Courtesy Apexum, Or-Yehuda, Israel.)

FIG. 8-38 Apexum in clinical use. A lower molar with two Coarse Apexum Ablator devices in the mesial and distal periapical lesions. Note the distance from the inferior alveolar nerve canal. Both instruments were inserted at the same time for purposes of illustration.

(Courtesy Apexum, Or-Yehuda, Israel.)

The method is used as a supplementary treatment for enhancement the healing kinetics of periapical lesions for promoting faster healing (Fig. 8-39).^258,259 The Apexum procedure is applied only after completion of cleaning, shaping, and disinfection of the root canal and before root canal obturation. This interesting device will clearly be subjected to additional research over the next few years.

FIG. 8-39 Periapical healing after the Apexum procedure. A, Immediate postoperative radiograph. Note the periapical lesion. B, Three-month follow up. C, Six-month follow-up.²⁵⁸

(Courtesy Apexum, Or-Yehuda, Israel.)

Devices for Measuring Root Canal Length

Radiographs, tactile sensation, the presence of bleeding on paper points, and knowledge of root morphology have been used to determine the length of root canal systems. Sunada³⁸¹ developed the original electronic apex locator when he suggested that the apical foramen could be localized using a direct electric current. Currently the electronic apex locator is considered an accurate tool for determining working length.^114,115 One study reported that the use of electronic apex locators in a dental student clinic resulted in a higher quality of obturation length control and an overall reduction in the number of radiographs taken.¹¹⁵ However, these devices must not be considered flawless, because several variables are known to affect their accuracy. For example, immature roots can present problems.¹⁸⁰ Once the roots mature (i.e., formed a narrow apical foramen) and the instruments are able to contact the canal walls, the electronic apex locator’s accuracy greatly improves. Some investigators have found no statistical difference between roots with vital and necrotic tissue.^135,250 Because apical root resorption is prevalent in necrotic cases with long-standing apical lesions, these researchers also concluded that apical resorption does not have a significant effect on the accuracy of electronic apex locators.

Recently some clinicians have advocated the use of the electronically determined working length in lieu of working length estimations using the placement of a file in the canal and a radiograph. However, combined use of both of these techniques has been shown to result in greater accuracy.⁹⁵ Furthermore, radiographs may also add essential anatomic information that may be missed if electronic apex locators are used exclusively.

The first two generations of electronic apex locators were sensitive to the contents of the canal and irrigants used during treatment. The development of an algorithm called the ratio measurement method distinguished the third generation of apex locators.¹⁹⁷ To arrive at this method, the impedance of the canal was measured with two current sources of different frequencies, and a quotient was determined using the electrical potentials proportional to each impedance.¹⁹⁷ This study found that electrolytes did not have a significant effect on the accuracy of the unit. Some third-generation apex locators are the Endex Plus, or Apit, (Osada, Los Angeles, CA),¹⁴¹ the Root ZX (Fig. 8-40) (J. Morita, Kyoto, Japan),^114,211 and the Neosono Ultima EZ (Satelec, Mount Laurel, NJ). The Endex Plus device uses 1 and 5 kHz and provides apex location based on subtraction. The Root ZX emits currents at frequencies of 8 and 0.4 kHz and provides apex location based on the resulting quotient.

FIG. 8-40 Root ZX apex locator with lip clip and file holder.

(Courtesy J. Morita USA, Irvine, CA.)

A fourth-generation apex locator was introduced with the Elements Diagnostic Unit (see Fig. 8-44), the Apex Locator (SybronEndo), and the Bingo 1020/Ray-X4 (Forum Engineering Technologies, Rishon Lezion, Israel). The Bingo uses only one of its two frequencies at a time (8 Hz or 400 Hz). According to the manufacturer, the Elements unit (which operates at frequencies of 0.5 and 4 kHz) compares the resistance and capacitance information to a database to determine the distance between the file and the apex. When the file tip reaches the area of the apical foramen, the apex locator emits a signal.

Recently, miniaturized electronic apex locators were introduced by SybronEndo (Fig. 8-41) and MedicNRG, Kibutz Afikim, Israel (the Apex NRG^277,278) (Fig. 8-42).

FIG. 8-41 SybronEndo mini apex locator.

(Courtesy SybronEndo, Orange, CA.)

FIG. 8-42 NRG miniature electronic apex locator.

(Courtesy MedicNRG, Kibutz Afikim, Israel.)

An apex locator typically has four parts: (1) the lip clip, (2) the file clip, (3) the instrument itself, and (4) a cord connecting the other three parts. A display indicates the advancement of the file toward the apex (see Fig. 8-40).

These electrical instruments are generally safe, but manufacturers’ instructions state that they should not be used on patients with pacemakers without consulting the patient’s cardiologist.^30,113 When connected directly to cardiac pacemakers in vitro, four of five electronic apex locators did not interfere with the function of the pacemaker.¹²⁶

Instruments for Root Canal Obturation

After the root canal has been properly cleaned and enlarged, the space is obturated with a manufactured material. A number of obturation methods are practiced, but lateral and vertical compactions are the two most common. Many specialized instruments are available for every type of method. Spreaders and pluggers are the significant instruments for obturation. The spreader is a tapered, pointed instrument intended to displace gutta-percha laterally for insertion of additional accessory gutta-percha cones. The plugger is similar but has a blunt end. In smaller sizes, the spreader and plugger are often used interchangeably. These instruments are available with handles or as finger-held instruments. The instruments with handles are potentially dangerous because the tips of the working ends are offset from the long axes of the handles. This results in strong lateral wedging forces on the working ends if the instruments are not operated carefully. The risk of vertical damage to the root is greatly reduced with finger spreaders and pluggers. Each clinician must choose the appropriate spreader and plugger according to personal working preferences. Standardized instruments are available with the same taper as the files (e.g., #.02). Considering the greater taper of standardized accessory gutta-percha cones (Table 8-2), nonstandardized spreaders with a larger taper sometimes may be used to better accommodate the gutta-percha.

TABLE 8-2 Size Designations for Auxiliary Gutta-Percha Cones*

When using spreaders and accessory gutta-percha cones, the accessory cone selected must reach the depth of the penetration of the spreader. To accomplish that, the accessory cone must be thinner and/or with a smaller taper than the spreader used. If accessory cones which do not reach that depth are used, the procedure will result in voids at the apical end of each spreader penetration, leading the operator to an illusion that the root canal is properly obturated.

In recent years, spreaders and pluggers have become available in nickel-titanium. NiTi spreaders have been shown to reach deeper into canals than the stainless steel type when #.02 tapered gutta-percha is used in canals with a curvature of more than 20 degrees. When #.04 taper gutta-percha was used, the NiTi spreaders were more effective regardless of the degree of curvature.⁴²⁴

Heat carriers are used for vertical-compaction obturation techniques. Traditionally, heat carriers are handled similarly to pluggers. They are used to transfer heat to the gutta-percha in the root canal, allowing apical and lateral displacement of the gutta-percha. Electrical heat carriers are more common today, either as independent units such as Touch ’n Heat and System B (SybronEndo, Orange, CA) (Fig. 8-43), or incorporated into multifunctional systems such as Elements (Fig. 8-44) (SybronEndo). Recently, battery-charged, handheld heat carriers were introduced, such as the vibrating heat carrier DownPack⁶⁷ (Hu-Friedy, Chicago, IL) (Fig. 8-45) or HotTip (Fig. 8-46) (Discus Dental, Culver City, CA). These devices can be heated to controlled levels with a self-contained cordless unit.

FIG. 8-43 System B heating device for vertical compaction and removal of gutta-percha.

(Courtesy SybronEndo, Orange, CA.)

FIG. 8-44 Elements unit, combining a System B element with one delivering injectable gutta-percha.

(Courtesy SybronEndo, Orange, CA.)

FIG. 8-45 DownPack: hand-held heating and vibrating unit for warm gutta-percha compaction.

(Courtesy Hu-Friedy, Chicago, IL.)

FIG. 8-46 “HotTip”: hand-held heating unit for warm gutta-percha compaction.

(Courtesy Discus Dental LLC; Culver City, CA.)

A Lentulo spiral may be used for placement of the sealer, cement, and calcium hydroxide (Ca[OH]₂) dressings. The Lentulo spiral is a safe instrument if used correctly but if used carelessly, it may engage the wall of the root canal and break. It must be operated clockwise in the handpiece, inserted not rotating to working length, then retracted 1 to 2 mm to make sure it is free to rotate without engaging the canal walls. It should be started and rotated at a slow speed while being gradually withdrawn from the root canal. This instrument effectively drives the paste into the root canal. However, for optimal effect, the spiral must be as large as possible so that the paste is forced forward as the material is squeezed between the canal walls and the spiral. Endodontic files, paper points, and syringes also are commonly used to apply sealer in the root canal system, but they are all less effective than a Lentulo spiral if filling a root canal entirely with sealer is desired.

Devices for Removing Root Canal Obstructions

There are many devices available for removing natural and manufactured obstructions from within the canal. Please see Chapter 25 for details on these devices.

Chemomechanical Preparation

To increase the efficacy of mechanical preparation and bacteria removal, instrumentation must be supplemented with active irrigating solutions. Irrigation is defined as washing out a body cavity or wound with water or a medicated fluid. Aspiration is defined as the process of removing fluids or gases from the body with a suction device.

The objectives of irrigation are both mechanical and biologic. The mechanical objective involves flushing out debris, lubricating the canal, and dissolving organic and inorganic tissue. The biologic function of the irrigants is related to their antimicrobial effect.

Irrigation Hydrodynamics

The effectiveness of root canal irrigation in terms of debris removal and eradication of bacteria depends on several factors: penetration depth of the needle, diameter of the root canal, inner and outer diameter of the needle, irrigation pressure, viscosity of the irrigant, velocity of the irrigant at the needle tip, and type and orientation of the needle bevel (Box 8-3).¹⁸¹

BOX 8-3 Ideal Characteristics of an Endodontic Irrigant^58,149,390

The ideal irrigant should:

1. Be an effective germicide and fungicide.

2. Be nonirritating to the periapical tissues.

3. Remain stable in solution.

4. Have a prolonged antimicrobial effect.

5. Be active in the presence of blood, serum, and protein derivates of tissue.

6. Have low surface tension.

7. Not interfere with repair of periapical tissues.

8. Not stain tooth structure.

9. Be capable of inactivation in a culture medium.

10. Not induce a cell-mediated immune response.

11. Be able to completely remove the smear layer, and be able to disinfect the underlying dentin and its tubules.

12. Be nonantigenic, nontoxic, and noncarcinogenic to tissue cells surrounding the tooth.

13. Have no adverse effects on the physical properties of exposed dentin.

14. Have no adverse effects on the sealing ability of filling materials.

15. Have convenient application.

16. Be relatively inexpensive.

The size and length of the irrigation needle relative to the canal space dimension is of utmost importance for the effectiveness of proper irrigation. If the external diameter of the needle is too large or rigid, it may inhibit introduction of the irrigant into the more apical extent of the root canal or into areas of curved canals. The internal diameter of the needle correlates to the necessary pressure for moving the syringe plunger and the velocity at which the irrigant is expressed. Narrow needles require more pressure of the plunger and will extrude the irrigant with higher velocity than large needle diameters. Although a needle with a larger internal diameter will extrude the irrigant with a larger volume over time, the irrigant cannot be introduced as deeply. Moser and Heuer²⁷⁶ measured the pressure necessary for activation of the plunger in different sizes and types of irrigation needles. They determined lower pressure was necessary for irrigation with larger needle diameter sizes (23 to 24 gauge) compared with smaller diameter sizes (24 to 30 gauge). However, larger needles placed at a greater distance from the apex were less efficient during irrigation than smaller diameter needles placed closer to the apex.¹⁷⁴ Common injection needles have an external diameter of 0.40 mm (27 gauge), but special irrigation tips with external diameters of 0.30 mm (30 gauge) are available as well (Table 8-3). To improve safety of irrigation and prevent apical extrusion of the irrigant, some of these needles release the solution through lateral openings and have a closed, safe-ended tip (Fig. 8-47). The Stropko Flexi-Tip (30 gauge) needle is fabricated out of NiTi to improve its flexibility and penetration into curved canals.

TABLE 8-3 Sizes and Manufacturers of Needles Used for Root Canal Irrigation

Manufacturer	Product	Gauge
DENTSPLY	Max-I-Probe	21–30
Ultradent, South Jordan, UT, USA	NaviTip	29, 30
	NaviTip FX Tip (brush-covered needle)	30
	Capillary Tip	25, 28
	Endo-Eze Tip/Deliver Eze	18, 19, 20, 22, 30, 31
	Endo-Eze Irrigator Tip/Deliver Eze Spülkanüle	27
KerrHawe, Bioggio, Switzerland	NaviTip	21–30
Hager & Werken, Duisburg, Germany	Miraject Endotec	21–25
Vista Dental Products	Stropko Flexi-Tip (NiTi)	30
KerrHawe	KerrHawe irrigation probe
Transcoject, Neumünster, Germany	Spülkanülen Endo	23, 25, 27, 30

Adapted from Hülsmann M, Rödig T, Nordmeyer S: Complications during root canal irrigation. Endod Topics 16:27, 2007.

FIG. 8-47 Scanning electron microscope (SEM) image of 30-gauge safety needle.

(Courtesy Dr. F. Tay.)

Sodium Hypochlorite

NaOCl is the most commonly used irrigating solution. It is an excellent antibacterial agent, capable of dissolving necrotic tissue, vital pulp tissue, and the organic components of dentin and biofilms.³⁴³

NaOCl solution, commonly known as bleach, is frequently used as a disinfectant or a bleaching agent. It is the irrigant of choice in endodontics, owing to its efficacy against pathogenic organisms and pulp digestion, and satisfies most of the preferred characteristics stated earlier.

Chlorhexidine

The cleanliness of root canals by CHX in gel and liquid forms was evaluated using scanning electron microscopy in two separate experiments. In an in vitro study, the canals treated with 2% CHX gel were cleaner than those treated with 2% CHX liquid or 5.25% NaOCl, and it was suggested that the mechanical action of the gel might have facilitated the cleansing of the canals. Another in vitro study showed that the 2% CHX liquid was inferior to 2.5% NaOCl in cleaning the canals.⁴³¹

The antibacterial effectiveness of CHX in infected root canals has been investigated in several studies. Investigators³¹⁵ reported that 2.5% NaOCl was significantly more effective than 0.2% CHX when the infected root canals were irrigated for 30 minutes with either of the solutions.

In a controlled and randomized clinical trial, the efficacy of 2% CHX liquid was tested against saline using culture technique. All the teeth were initially instrumented and irrigated using 1% NaOCl. Then either 2% CHX liquid or saline was applied as a final rinse. The authors reported a further reduction in the proportion of positive cultures in the CHX group. Their results showed a better disinfection of the root canals using CHX compared to saline as a final rinse.⁴³⁷

In a recent study, the antibacterial efficacy of 2% CHX gel was tested against 2.5% NaOCl in teeth with apical periodontitis, with the bacterial load assessed using real-time quantitative polymerase chain reaction (RTQ-PCR) and colony forming units (CFU). The bacterial reduction in the NaOCl group was significantly greater than the CHX group when measured by RTQ-PCR. Based on culture technique, bacterial growth was detected in 50% of the CHX-group cases compared to 25% in the NaOCl group.⁴⁰⁵ On the other hand, another study based on this culture technique revealed no significant difference between the antibacterial efficacy of 2.5% NaOCl and 0.12% CHX liquid when used as irrigants during the treatment of infected canals.^356,357

Chlorhexidine as an Intracanal Medication

CHX in liquid, gel, or in a controlled-release device has been suggested as an alternative intracanal medication to replace Ca(OH)₂. This has been the focus of many in vitro^{78,199,217,354} and in vivo studies.* The results of in vitro experiments were mostly in favor of CHX regardless of its mode of application. The results have also demonstrated the potential antibacterial substantivity of CHX in the root canals.

Researchers¹⁵⁵ developed an experimental model using dentin powder particles to investigate the possible inactivation of some antibacterial medicaments when they come in contact with dentin. The medicaments tested were Ca(OH)₂, 1% NaOCl, 0.5% and 0.05% CHX acetate, and different concentrations of iodine potassium iodide (IKI). They showed that dentin powder had inhibitory effects on all medicaments tested. The effect was dependent on the concentration of the medicament and the duration of contact. The effect of Ca(OH)₂ was totally abolished by the presence of dentin powder. The effect of 0.05% CHX and 1% NaOCl was reduced but not totally eliminated by the presence of dentin. No inhibition could be measured when full-strength solutions of CHX and IKI were used.

Contradicting results have been reported when evaluating the effect of different intracanal medications on sealing of the root canals. In an in vitro study using extracted human teeth, all root canals, after 10 days of intracanal medication, were obturated and then tested for microbial leakage. The root canals medicated with CHX gel demonstrated less resistance against bacterial leakage compared to the root canals medicated with Ca(OH)₂.²³ In contrast, Wuerch et al.⁴³⁰ found no significant difference in leakage between the canals medicated with CHX and Ca(OH)₂ and reported that 2% CHX gel and Ca(OH)₂ paste did not adversely affect the apical seal of the root canal system.

In a human ex vivo model, the antibacterial efficacy of 0.2% CHX liquid applied for 24 hours was tested against a saline solution. After extraction, the infected teeth were endodontically treated using CHX or saline for irrigation and then further medicated with either of the solutions. Samples were obtained and evaluated using culture technique at each treatment step. In both groups, the numbers of bacteria were decreased after instrumentation and irrigation of the canals. However, after 24 hours of medication, it was reported that the numbers of bacteria were further decreased in the CHX group, in contrast to the saline group, where an increase was noted.⁷⁸ CHX may also have an effect on reduction of inflammatory external root resorption caused by infection. Lindskog et al.²²⁸ assessed the therapeutic effect of a 4-week intracanal application of CHX gel on inflammatory root resorption in replanted infected teeth of monkeys. They reported that the extent of inflammatory resorption was significantly reduced compared to nonmedicated teeth, suggesting that CHX may be a useful adjunct in the management of inflammatory root resorption.

These in vitro and animal studies suggest that CHX has the potential to replace Ca(OH)₂ as an intracanal medicament, but the limitations of the in vitro experiments make the conclusions obtained difficult to extrapolate to actual clinical situations. In vivo human experiments are therefore required to test the efficacy of CHX as an intracanal medication.

Compared to the number of in vitro studies, very few in vivo studies have been conducted to assess the effectiveness of CHX as an intracanal medication. An in vivo investigation²⁰ assessed the antibacterial efficacy of three different intracanal medications: camphorated paramonochlorophenol, Ca(OH)₂, and 0.12% CHX liquid by applying them for 1 week in single-rooted teeth of patients. Using a culture method, it was reported that the proportions of positive cultures were not significantly different among the tested medications, but they were slightly lower in teeth medicated with CHX (0.12%) liquid than those medicated with camphorated paramonochlorophenol or Ca(OH)₂.²⁰

Another in vivo study evaluated the antibacterial effectiveness of 2% CHX liquid as an intracanal medication in teeth with apical periodontitis.²⁹³ The results showed a moderate increase in bacterial counts during a medication period of 7 to 14 days that was similar to outcomes seen and reported for Ca(OH)₂ by Peters et al.³⁰¹ It was speculated that the CHX liquid may have partially escaped from the apical foramen, and that the higher-viscosity gel form might have been better suited as an intracanal medication.²⁹³

However, a different study²³⁹ demonstrated that intracanal medication with Ca(OH)₂, 2% CHX gel, or a mixture of Ca(OH)₂/CHX applied for 7 days did not reduce the bacterial concentration beyond what was achieved after chemomechanical preparation using 1% NaOCl. The results were not significantly different among the medication groups. Similar results were found by other investigators,²³⁸ where after a randomized controlled trial of 30 patients, they concluded that a final rinse with MTAD (mixture of tetracycline, acid, and detergent) and intracanal application of 2% CHX gel did not reduce bacterial counts beyond levels achieved by chemomechanical preparation using NaOCl.

Chlorhexidine and Calcium Hydroxide

During the last few years, researchers have studied the combination of Ca(OH)₂ and CHX, with the concept that their antimicrobial properties interact in a synergistic fashion that enhances their efficacy. The high pH of Ca(OH)₂ was unaffected when combined with CHX.²⁶ However, the results have not been conclusive. Some in vitro studies have reported an improved antibacterial action when both agents were combined,^28,102,438 while other studies reported conflicting results.¹⁵⁷

Recent animal studies have evaluated the tissue reactions to the mix of Ca(OH)₂/CHX, showing that the combination exerts good antimicrobial properties³⁶⁴ and improves healing of the periapical tissues. In vivo studies have shown that the mix is at least as good as both agents applied separately in necrotic teeth with apical periodontitis,²³⁹ as well as in previously treated cases with persistent apical periodontitis. A more recent study utilizing a CHX-based protocol of 0.12% CHX as an irrigant followed by a 7-day intracanal medication of Ca(OH)₂/0.12% CHX has shown promising results. The authors concluded that chemomechanical canal shaping using 0.12% CHX solution as an irrigant significantly reduced the number of intracanal bacteria, but it failed to render the canals bacteria free. Further intracanal medication with a Ca(OH)₂/CHX paste significantly improved the results by reducing the number of bacteria.³⁵³ Taken together, it seems that the usefulness of mixing Ca(OH)₂ with CHX remains unclear and controversial.

Chlorhexidine and Coronal Penetration of Bacteria

Because of its antimicrobial substantivity, it seems that CHX preparations delay entry of bacteria through the coronal portion of the tooth into the root canal system. A laboratory study¹³⁸ investigated the time required for recontamination of the root canal system of teeth with coronal restorations medicated with Ca(OH)₂, 2% CHX gel, or a combination of both. The canals without a coronal restoration but medicated with CHX showed recontamination after an average time of 3.7 days, the group with Ca(OH)₂ after 1.8 days, and the group with CHX + Ca(OH)₂ after 2.6 days. The canals medicated with CHX and restored with intermediate restorative material (IRM) showed recontamination within 13.5 days, the group with Ca(OH)₂ + IRM after 17.2 days, and the group with CHX + Ca(OH)₂ + IRM after 11.9 days. The group with no medication but restored with IRM showed recontamination after an average time of 8.7 days. There were statistically significant differences between the groups (P < 0.05). All groups without a coronal restoration were recontaminated significantly more quickly than those restored with IRM, except those teeth that had a restoration but no medicament. The groups with intracanal medication and a coronal restoration were not significantly different from each other.

An ex vivo study⁴⁰⁸ assessed coronal dye penetration of extracted human teeth after root canal treatment using 1% NaOCl, 1% NaOCl + 17% ethylenediamine tetra-acetic acid (EDTA), 2% CHX gel, 2% CHX gel + 1% NaOCl and distilled water. Results revealed that the least dye penetration occurred with 1% NaOCl + 17% EDTA and 2% CHX gel. NaOCl, distilled water, and 2% CHX gel + 1% NaOCl had more dye penetration with a significant difference compared with NaOCl + 17% EDTA and 2% CHX gel and compared with one another.

Lambrianidis and colleagues²¹⁰ have shown that viscous irrigants, including those containing CHX gluconate, were less soluble substances that can leave residue on root canal surfaces and potentially affect root canal obturation. The efficiency of removing Ca(OH)₂/CHX gel, Ca(OH)₂/CHX solution and Ca(OH)₂/saline pastes with the use of instrumentation and irrigation with NaOCl and EDTA solutions has been assessed. None of the techniques used in this study removed the interappointment root canal medicaments effectively. Overall, Ca(OH)₂/CHX (gel) paste was associated with significantly larger amount of residue, whereas the Ca(OH)₂/CHX mixture was associated with less residue than the other two medicaments. Overall, because of its substantivity, CHX as an intracanal medicament/irrigant may delay the coronal recontamination of the root canal system.

Interaction Between CHX, NaOCl, and EDTA

A suggested clinical protocol⁴³⁹ for treating dentin prior to root canal obturation consists of irrigation with NaOCl to dissolve the organic components, irrigation with EDTA to eliminate the smear layer, and irrigation with CHX to increase the antimicrobial spectrum of activity and impart substantivity. Although such a combination of irrigants may enhance the overall antimicrobial effectiveness,²⁰⁸ possible chemical interactions between the irrigants must be considered. Some studies have reported the occurrence of color change and precipitation when NaOCl and CHX are combined^26,439 (Fig. 8-48). Furthermore, concerns have been raised that the color change may have some clinical relevance because of staining, and the resulting precipitate might interfere with the seal of the root obturation. The formation of a precipitate could be explained by the acid-base reaction that occurs when NaOCl and CHX are mixed together. CHX, a dicationic acid, has the ability to donate protons. NaOCl is alkaline and can accept protons from the dicationic acid. This proton exchange results in the formation of a neutral and insoluble substance referred to as the precipitate.²⁶ Basrani et al.²⁶ evaluated the chemical nature of this precipitate and reported that there was an immediate reaction when 2% CHX was combined with NaOCl, even at the low concentration (0.023%). They found that the amount of PCA directly increased with the increasing concentration of NaOCl. PCA has been shown to be toxic in humans with short-term exposure, resulting in cyanosis, which is a manifestation of methemoglobin formation. In another study, the effect on root dentin and dentinal tubules was evaluated subsequent to irrigating root canals with a combination of NaOCl and CHX. They concluded that the NaOCl/CHX precipitate tends to occlude the dentinal tubules and suggested that until this precipitate is studied further, caution should be exercised when irrigating with both NaOCl and CHX. In summary, the combination of NaOCl and CHX causes color changes and formation of a neutral and possibly toxic insoluble precipitate that may interfere with the seal of the root obturation. Alternatively, the canal can be dried using paper points before the final CHX rinse.⁴³⁹

FIG. 8-48 Color change and precipitation occur when NaOCl and CHX are combined.

The combination of CHX and EDTA produces a white precipitate, so a group of investigators³¹¹ did a study to determine whether the precipitate involves the chemical degradation of CHX. The precipitate was produced and redissolved in a known amount of dilute trifluoroacetic acid. Based on the results, CHX was found to form a salt with EDTA rather than undergoing a chemical reaction.

Dentin Bonding of Chlorhexidine

During the last 2 decades, chemical and technical advances have contributed to increases in resin-dentin bond strength. However, the premature loss of bond strength is one of the problems that still affects adhesive restorations²⁷⁰ and markedly reduces their durability.^54,80,117 Researchers⁵³ evaluated the effect of CHX on resin-dentin bond stability ex vivo. They concluded that autodegradation of collagen matrices can occur in resin-infiltrated dentin, but this may be prevented by the application of a synthetic protease inhibitor such as CHX.⁵³ Because of its broad-spectrum matrix metalloproteinase (MMP)-inhibitory effect, CHX may significantly improve resin-dentin bond stability.

Allergic Reactions to Chlorhexidine

CHX, although reported to be a relatively safe solution, may induce allergic reactions. The sensitization rate has been reported in several studies to be approximately 2%.²⁰² One case of an anaphylactic shock was reported after the application of 0.6% CHX to intact skin that had signs of a rash following a minor accident.¹⁵ Further allergic reactions such as anaphylaxis, contact dermatitis, and urticaria have been reported following direct contact to mucosal tissue or open wounds.^{92,303,340,363} There are no publications reporting allergic reactions following root canal irrigation with CHX.¹⁸¹

Mode of Action

There is no detailed information on the exact mechanism of action of MTAD in the removal of the smear layer and the killing of bacteria. In most studies, its effect on the smear layer is attributed to the existence of doxycycline and citric acid. These two components in solution have been separately reported as being effective in the removal of the smear layer.¹⁶³ Its antibacterial effect is mostly attributed to the doxycycline, an isomer of tetracycline. Tetracyclines—including tetracycline HCl, minocycline, and doxycycline—are broad-spectrum antibiotics that are effective against a wide range of microorganisms. Tetracycline is a bacteriostatic antibiotic which exerts its effect through the inhibition of protein synthesis. According to Torabinejad et al.,³⁹³ this property may be advantageous because in the absence of bacterial cell lysis, antigenic byproducts (i.e., endotoxin) are not released. In high concentrations, tetracycline may also have a bactericidal effect. The role of citric acid in killing bacteria is not well known. Tween 80, the other component of MTAD, seems to have limited antibacterial activity, yet it may increase the antibacterial effect of some substances by directly affecting the bacterial cell membrane. It may also facilitate the penetration of MTAD into dentin. On the contrary, Tween 80 may also be a nutrient for some bacteria, and it may inactivate the antibacterial properties of some disinfecting agents such as CHX and povidone iodine. Doxycycline, citric acid, and Tween 80 together may have a synergistic effect on the disruption of the bacterial cell wall and on the cytoplasmic membrane.

Surface Tension

According to Grossman and Meiman,¹⁵⁰ low surface tension is one of the ideal characteristics of an irrigant. Lower surface tension may help by allowing the irrigant to penetrate better into the dentinal tubules and inaccessible areas of the root canal system.³⁸⁸

To be more effective in debris removal and to penetrate more readily into the root canal system, irrigants must be in contact with the dentin walls. The closeness of this contact is directly related to its surface tension.¹³³ Irrigants with a low surface tension are more suitable as endodontic irrigants. To decrease the surface tension, Tween 80 has been added to the MTAD solution.

Smear Layer Removal

In two studies, the efficacy of MTAD or EDTA in the removal of the smear layer was confirmed, but no significant difference between these two solutions was reported.^389,390

Antibacterial Efficacy

Reported results regarding the antibacterial properties of MTAD are conflicting. The studies measuring zones of inhibition on agar plates have shown consistently that MTAD was an effective antibacterial agent against E. faecalis.^73,201,393 Tay et al.^389,390 also found larger zones of bacterial inhibition using dentin cores irrigated with MTAD compared to NaOCl-irrigated dentin cores. When they applied MTAD to dentin that was already irrigated with 1.3% NaOCl, however, they noticed a contradictory result: the diameters of the zones of inhibition were significantly smaller than those of MTAD alone but comparable to those irrigated with 1.3% NaOCl alone. They concluded that the antimicrobial effect of MTAD was lost due to oxidation of the MTAD by NaOCl.

A study using extracted human teeth contaminated with saliva showed that MTAD was more effective than 5.25% NaOCl in disinfection of the teeth.³⁴⁷ In contrast, Krause et al.,²⁰¹ using bovine tooth sections, showed that 5.25% NaOCl was more effective than MTAD in disinfection of dentin discs inoculated with E. faecalis.

In another study performed on extracted human teeth inoculated with E. faecalis, a protocol of 1.3% NaOCl followed by 5 minutes of MTAD was more effective in the disinfection of canals than a protocol of 5.25% NaOCl followed by 1 minute of 17% EDTA and then 5 minutes of 5.25% NaOCl as a final rinse.³⁴⁷ In a series of studies, MTAD has failed to show superior antibacterial efficacy against bacterial biofilms. Bacteria collected from the teeth of patients diagnosed with apical periodontitis were grown as a biofilm on hemisections of root apices. MTAD was an effective antibacterial agent in this model, but it was unable to completely disrupt the bacterial biofilm, compared to 6% NaOCl. NaOCl (5.25%) was the most effective irrigant against a biofilm of E. faecalis generated on cellulose nitrate membrane filters, whereas the bacterial load reduction using MTAD was not significant.¹³⁴ The results of testing antibacterial efficacy of medicaments obtained from in vitro studies should be analyzed with caution. They may be influenced by factors such as the test environment, bacterial susceptibility, and the different methodologies used to evaluate the results.³⁵⁴

In vivo Clinical Trial

With the exception of one study³⁹⁴ that evaluated the effect of MTAD on postoperative discomfort, there have been no other in vivo studies to address the other characteristics of MTAD. Malkhassain et al.²³⁸ in a clinical controlled trial of 30 patients reported that the final rinse with MTAD did not reduce the bacterial counts in infected canals beyond levels achieved by chemomechanical preparation using NaOCl alone.

Protocol for Use

The clinical protocol for the use of MTAD was developed on the basis of a pilot project.³⁴⁶ The results of this project showed consistent disinfection of the infected root canals could occur after chemomechanical preparation using 1.3% NaOCl as a root canal irrigant followed by a 5-minute rinse of MTAD.

History

The compound was first described in 1935 by Ferdinand Munz, who prepared the compound from ethylenediamine and chloroacetic acid. Today, EDTA is mainly synthesized from ethylenediamine (1, 2-diaminoethane), formaldehyde (methanal), and sodium cyanide.

Mode of Action

On direct exposure for extended time, EDTA extracts bacterial surface proteins by combining with metal ions from the cell envelope, which can eventually lead to bacterial death.

Applications in Endodontics

EDTA alone normally cannot remove the smear layer effectively; a proteolytic component (e.g., NaOCl) must be added to remove the organic components of the smear layer.¹³⁶ Commercial products with such combinations are available. EndoDilator N-Ø (Union Broach, York, PA) is a combination of EDTA and a quaternary ammonium compound. Such an irrigation fluid has a slight detergent effect in addition to the chelating effect. Two newer irrigating solutions, MTAD (discussed earlier) and Smear Clear (SybronEndo), have recently been studied. Smear Clear is a clear, odorless, water-soluble solution containing water, 17% EDTA salts, a cationic surfactant (cetrimide), and anionic surfactants.

EDTA is normally used in a concentration of 17% and can remove the smear layers when in direct contact with the root canal wall for less than 1 minute. The decalcifying process is self-limiting. For root canal preparation, EDTA has limited value alone as an irrigation fluid. Since it is capable of decalcifying up to 50 µm, it can open up an occluded, very fine canal. This depth, added from two opposite canal walls, will result in a 100-µm opening, equivalent to the tip of a #010 file.

Although citric acid appears to be slightly more potent at similar concentration than EDTA, both agents show high efficiency in removing the smear layer. In addition to their cleaning ability, chelators may detach biofilms adhering to root canal walls.¹⁵¹ This may explain why an EDTA irrigant proved to be highly superior to saline in reducing intracanal microbiota despite the fact that its antiseptic capacity is relatively limited.¹⁵¹ Although never shown in a randomized clinical trial, an alternating irrigating regimen of NaOCl and EDTA may be more efficient in reducing bacterial loads in root canal systems than NaOCl alone. Antiseptics such as quaternary ammonium compounds (EDTAC) or tetracycline antibiotics (MTAD) have been added to EDTA and citric acid irrigants, respectively, to increase their antimicrobial capacity. The clinical value of this, however, is questionable. EDTAC shows similar smear-removing efficacy as EDTA, but it is more caustic.

Interaction of EDTA and NaOCl

Investigators¹⁴⁶ studied the interactions of EDTA with NaOCl. They concluded that EDTA retained its calcium-complexing ability when mixed with NaOCl, but EDTA caused NaOCl to lose its tissue-dissolving capacity, with virtually no free chlorine detected in the combinations. Clinically, this suggests that EDTA and NaOCl should be used separately. In an alternating irrigating regimen, copious amounts of NaOCl should be administered to wash out remnants of the EDTA.

Phenolic Preparations

Phenol (C₆H₅OH), or carbolic acid, is one of the oldest antimicrobial agents used in medicine. Despite the severe toxicity of phenolic preparations, derivatives of phenol, such as paramonochlorophenol (C₆H₄OHCl), thymol (C₆H₃OHCH₃C₃H₇), and cresol (C₆H₄OHCH₃), remain available. One survey noted a decrease in the use of classic phenolic intracanal medicaments with a corresponding increase in the use of Ca(OH)₂ or no medication.¹²⁸

Phenol is a nonspecific protoplasm poison that has an optimal antibacterial effect at 1% to 2%. Many dental preparations use much too high a concentration of phenol (e.g., in the range of 30%). At such a concentration, the antimicrobial effect in vivo is lower than optimal and of very short duration.²⁵⁴

Derivatives of phenol are stronger antiseptics and toxins than phenol. Phenolic compounds are often available as camphorated solutions. Camphoration results in a less toxic phenolic compound because it slows the release of toxins to the surrounding tissues.

Studies in vitro have shown that phenol and phenol derivatives are highly toxic to mammalian cells, and their antimicrobial effectiveness does not sufficiently balance their toxicity.^370,371 Phenols are ineffective antiseptics under clinical conditions.^46,96

Formaldehyde

Formaldehyde, used as formocresol, has been used extensively in endodontic therapy despite its high toxicity and mutagenic and carcinogenic potential.²²¹ The formaldehyde component of formocresol may vary substantially between 19% and 37%. Tricresol formalin, another formaldehyde preparation, contains 10% tricresol and 90% formaldehyde. All of these preparations have a formaldehyde content well above the 10% normally used for fixation of pathologic specimens. Formaldehyde is volatile and releases antimicrobial vapors when applied to a cotton pellet for pulp chamber disinfection. All formaldehyde preparations are potent toxins with an antimicrobial effectiveness much lower than their toxicity.^371,372

There is no clinical reason to use formocresol as an antimicrobial agent for endodontic treatment, based on what is known at this time. The alternatives are better antiseptics with significantly lower toxicity.

Halogens

Chlorinated solutions have been used for many years to irrigate root canals. They are also used as an intracanal dressing in the form of chloramine-T, an N-chloro tosylamide sodium salt. Iodine, in the form of IKI, is a very effective antiseptic solution with low tissue toxicity. IKI is an effective disinfectant for infected dentin and can kill bacteria in infected dentin in 5 minutes in vitro.³²⁴ IKI releases vapors with a strong antimicrobial effect. The solution can be prepared by mixing 2 g of iodine in 4 g of potassium iodide; this mixture then is dissolved in 94 ml of distilled water. Tincture of iodine (5%) has proved to be one of the few reliable agents for disinfection of rubber dam and tooth surfaces during the preparation of an aseptic endodontic workfield.²⁷²

Calcium Hydroxide

Hermann introduced^166,167 the use of Ca(OH)₂ in endodontics in 1920. Although its use was well documented for its time, the clinical applications over the next 25 years were not well known. Its use in root canal treatment as an intracanal medication has been associated with periradicular healing and few adverse reactions. Its use in root canal treatment was promoted by a series of papers^46,48 documenting the antibacterial efficacy of Ca(OH)₂ in human root canals. Subsequent studies substantiated these reports,^290,360 and the routine use of Ca(OH)₂ as an interappointment intracanal medicament became widespread.³²⁷

Ca(OH)₂ cannot be categorized as a conventional antiseptic, but it kills bacteria in the root canal space. The value of Ca(OH)₂ in endodontic treatment of necrotic, infected teeth is now well documented. Ca(OH)₂ normally is used as slurry of Ca(OH)₂ in a water base. At body temperature, less than 0.2% of the Ca(OH)₂ is dissolved into Ca⁺⁺ and OH⁻ ions. Because Ca(OH)₂ needs water to dissolve, water should be used as the vehicle for the Ca(OH)₂ paste. In contact with air, Ca(OH)₂ forms calcium carbonate (CaCO₃). However, this is an extremely slow process and of little clinical significance. Ca(OH)₂ paste, with a significant amount of calcium carbonate, feels granular because the carbonate has a very low solubility.

Ca(OH)₂ is a slow-acting antiseptic. Direct-contact experiments in vitro show that a 24-hour contact period is required for complete killing of enterococci.^324,360 Another study of 42 patients found that NaOCl canal irrigation reduced the bacteria level by only 61.9%, but use of Ca(OH)₂ in the canals for 1 week resulted in a 92.5% reduction.³⁵⁰ These researchers concluded that Ca(OH)₂ should be used in infected cases to more predictably obtain disinfection.

In addition to killing bacteria, Ca(OH)₂ has the extraordinary ability to hydrolyze the lipid moiety of bacterial lipopolysaccharides (LPS), thereby inactivating the biologic activity of the lipopolysaccharide and reducing its effect.^322,323 This is a very desirable effect because dead cell wall material remains after the bacteria have been killed and can continue to stimulate inflammatory responses in the periradicular tissue.

Ca(OH)₂ may be mixed with sterile water or saline; this formula is also available commercially from a number of manufacturers in sterile, single-dose packages (e.g., Calasept [J.S. Dental, Ridgefield, CT]; Calcijet [Centrix, Shelton, CT]; and DT Temporary Dressing, [Global Dental Products, North Bellmore, NY]) (Fig. 8-51). The mixture should be thick to carry as many Ca(OH)₂ particles as possible. This slurry is best applied with a Lentulo spiral. For maximum effectiveness, the root canal must be filled homogeneously to the working length. Saturated Ca(OH)₂ solution mixed with a detergent is an effective antimicrobial agent suitable for irrigation.

FIG. 8-51 Calciject is a calcium hydroxide prefilled, easy-to-use, single-dose syringe system. Centrix NeedleTube cartridges can be used for direct syringe injection into the root canal.

(Courtesy Centrix, Shelton, CT.)

Limitations of Calcium Hydroxide

There are some concerns regarding the use of Ca(OH)₂. The handling and proper placement of Ca(OH)₂ present a challenge to the average clinician.^233,358 Also, the removal of Ca(OH)₂ is frequently incomplete, resulting in a residue covering 20% to 45% of the canal wall surfaces, even after copious irrigation with saline, NaOCl, or EDTA.²¹¹ Residual Ca(OH)₂ can shorten the setting time of zinc oxide eugenol–based endodontic sealers.²⁴³ Most notably, it may interfere with the seal of the root filling and compromise the quality of treatment. An additional concern is that Ca(OH)₂ is not totally effective against several endodontic pathogens, including E. faecalis and Candida albicans.⁴¹⁶ Recently the ability of Ca(OH)₂ to completely eradicate bacteria from the root canal has been questioned. For example, in vitro studies have shown that dentin can inactivate the antibacterial activity of Ca(OH)₂,^155,307 and one clinical study³⁰¹ has shown that the number of bacteria-positive canals actually increased after Ca(OH)₂ medication. Other studies have also indicated that Ca(OH)₂ could not predictably eliminate bacteria or that cultures changed from negative to positive after Ca(OH)₂ placement.^301,415

When different studies report inconsistent results, a systematic review and meta-analysis technique can clarify conflicting research data and the current state of knowledge regarding specific issues. Therefore, based on the current best available evidence, Ca(OH)₂ has limited effectiveness in eliminating bacteria from human root canals when assessed by culture techniques. The quest for better antibacterial protocols and sampling techniques must continue to ensure that bacteria can be been reliably eradicated prior to obturation.

Chlorhexidine

CHX is also used as an intracanal medication and has already been discussed extensively under its own heading.

Ledermix

Ledermix (Lederle Pharmaceuticals, Wolfratshausen, Germany) is a corticosteroid-antibiotic paste. Medicaments such as Ledermix paste have been recommended as routine intracanal medicaments. Ledermix paste has been advocated as an initial dressing, particularly if the patient presents with endodontic symptoms.

Schroeder developed the material that is now commercially marketed as Ledermix paste.³³⁹ Ledermix paste contains triamcinolone acetonide as an antiinflammatory agent, at a concentration of 1%. When the Ledermix materials and other similar corticosteroid-containing formulations were commercially released, there was a considerable amount of opposition to their use.¹⁹⁵

Ledermix paste is a nonsetting, water-soluble paste material for use as root canal medicament or as a direct or indirect pulp capping agent. The release and dentin diffusion characteristics of triamcinolone from Ledermix paste when used as a root canal medicament have been investigated under different conditions.^1-3 These studies show that triamcinolone is released from Ledermix paste in the root canal and can reach the systemic circulation via diffusion through dentinal tubules, lateral canals, and the apical foramen. After the first 24 hours, 30% of the triamcinolone was released. By the end of 14 weeks, the remaining 70% had been released.

Immediate intracanal placement of Ledermix has been studied for replanted teeth, because it has been shown to inhibit root resorption after extended dry time. In a recent study done in dogs, the groups treated with Ledermix, triamcinolone and demeclocycline had significantly more favorable healing and more remaining root structure than the group filled with gutta-percha and sealer (positive control).⁵⁷

The Triple-Antibiotics Paste

The triple-antibiotics regimen, composed of metronidazole, ciprofloxacin, and minocycline, was first tested³²⁸ for its effectiveness against Escherichia coli–infected dentin in vitro. The same research group also tested its bactericidal efficacy against microbes from carious dentin and infected pulp. They found that the mixture of antibiotics is sufficiently potent to eradicate the bacteria.³⁹¹ The clinical effectiveness of the triple-antibiotic paste in the disinfection of immature teeth with apical periodontitis has been reported.⁴²⁵ One potential concern of using an intracanal antibiotic paste is that it may cause bacterial resistance. Additionally, intracanal use of minocycline can cause tooth discoloration, creating potential cosmetic complications.

Bioactive Glass

Research is underway in the use of bioactive glass as an intracanal medicament. In one study,⁴⁴⁰ the glass used was composed of 53% SiO₂ (w/w), 23% Na₂O, 20% CaO, and 4% P₂O₅ and was prepared from reagent-grade Na₂CO₃, CaHPO₄, 2H₂O, CaCO₃, and Belgian sand. When used in root canals, bioactive glass was found to kill bacteria, but the mechanism of action was not pH related, and dentin did not seem to alter its effect. Some new obturating materials (e.g., Resilon [Pentron Clinical Technologies, Wallingford, CT]) contain bioactive glass.

EndoActivator

The EndoActivator System uses safe, noncutting polymer tips in an easy-to-use subsonic handpiece to quickly and vigorously agitate irrigant solutions during endodontic therapy (Fig. 8-52).

FIG. 8-52 EndoActivator system.

(Courtesy DENTSPLY Tulsa Dental Specialties, Tulsa, OK.)

In a recent study,⁸⁴ the safety of various intracanal irrigation systems was analyzed by measuring the apical extrusion of irrigant. They concluded that EndoActivator had a minimal, although statistically insignificant, amount of irrigant extruded out of the apex when delivering the subsonic activation of the irrigant into the pulp chamber and canal. Manual, ultrasonic, and Rinsendo (Dürr Dental, Bietigheim-Bissingen, Germany) groups had significantly greater amount of extrusion compared with EndoVac and EndoActivator.

Passive Ultrasonic Activation

Ultrasonic devices were first introduced in endodontics by Richman.³¹² Ultrasonically activated files have the potential to prepare and débride root canals mechanically. The files are driven to oscillate at ultrasonic frequencies of 25 to 30 kHz. They operate in a transverse vibration, setting up a characteristic pattern of nodes and antinodes along their length.^413,414 Unfortunately, it proved difficult to control the cutting of dentin during ultrasonic preparation, which resulted in apical perforations and irregular canal shapes.^235,380

However, it has been shown that ultrasonically driven files are effective for the irrigation of root canals. Two types of ultrasonic irrigation have been described in the literature^6,420: one where irrigation is combined with simultaneous ultrasonic instrumentation (UI) and another without simultaneous instrumentation, called passive ultrasonic irrigation (PUI). During UI, the file is intentionally brought into contact with the root canal wall. UI has been shown to be less effective in removing simulated pulp tissue from the root canal system or smear layer from the root canal wall than PUI. This can be explained by a reduction of acoustic streaming and cavitation.⁶ Because the root canal anatomy is complex,³⁰² an instrument will never contact the entire root canal wall.⁴²⁹ Thus, UI could result in uncontrolled cutting of the root canal wall without effective cleaning.

Passive ultrasonic irrigation was first described by Weller et al.⁴²⁰ The term passive does not adequately describe the process, since it is in fact active. When it was first introduced, the term passive related to the noncutting action of the ultrasonically activated file. PUI relies on the transmission of acoustic energy from an oscillating file or smooth wire to an irrigant in the root canal. The energy is transmitted by means of ultrasonic waves and can induce acoustic streaming and cavitation of the irrigant.⁶ After the root canal has been shaped to the master apical file (irrespective of the preparation technique used), a small file or smooth wire (for example, size #15) is introduced in the center of the root canal, as far as the apical region. The root canal is then filled with an irrigant solution, and the ultrasonically oscillating file activates the irrigant. Since the root canal has already been shaped, the file or wire can move freely, and the irrigant can penetrate more easily into the apical part of the root canal system,²⁰⁴ with the cleaning effect being more significant.²³⁵ Using this noncutting methodology, the potential to create aberrant shapes within the root canal are reduced to a minimum. A file larger than a #15 or #20 will only oscillate freely in a wide root canal. A #25 file may in fact produce less acoustic streaming than a #15 and #20 file.⁶ Consequently, using a file larger than a #20 may be considered fundamentally different from the basic principle of PUI. The cleaning efficacy of PUI implies the effective removal of dentin debris, microorganisms (planktonic or in biofilm), and organic tissue from the root canal. Because of the active streaming of the irrigant, its potential to contact a greater surface area of the canal wall will be enhanced.

If ultrasonic activation of the hypochlorite irrigant is to be used, it appears important to apply the ultrasonic instrument after canal preparation has been completed. A freely oscillating instrument will cause more ultrasound effects in the irrigating solution than a counterpart that binds to canal walls.³¹⁸ In addition, ultrasonic files can cause uncontrolled cutting of the canal walls, especially if used during preparation.³⁸⁰ Therefore, it appears best to insert a slim, noncutting instrument in a controlled fashion after canal preparation.^402,403 As of recently, smooth wires fitting to an ultrasonic device have been commercially available. However, objective guidelines regarding their risks and benefits have not been ascertained.⁴³⁹

EndoVac

EndoVac is a combined irrigation/evacuation system. The irrigant is extruded from the system with pressure at the root canal orifice. The evacuator, a microcannula, extends to the apical region of the root canal; the dimensions of the needle are size #55 with a 2% taper. High-volume suction from the dental unit results in negative apical pressure and thus passively sucks the irrigant from the orifice to the apical part of the root canal, which is passively evacuated from the canal space. Apical extrusion of the irrigant will probably be reduced, since the canal is irrigated with negative (as opposed to positive) pressure.²⁸³ There is little research to demonstrate this device is safe and effective when there is an open (immature) apex or in cases where there is a pathologic perforating root resorption.

A similar device has been presented by Fukumoto et al.^119,120 The irrigant is delivered by a needle (outer diameter 0.41 mm, inner diameter 0.19 mm) and a tubing pump (Masterflex, Cole Palmer Instruments, Vernon Hills, IL) to the coronal or middle part of the root canal and aspirated by a second needle (outer diameter 0.55 mm, inner diameter 0.30 mm), which is introduced into the apical part of the root canal. The aspiration pressure is −20 kPa. The irrigant is flushed from the coronal to the apical part of the root canal and there finally suctioned. This technique in an in vitro experiment on teeth with resected apices resulted in significantly less overextrusion of irrigant than a conventional irrigation technique with the needle tip placed 2 mm short of the apex. When the needle was placed 3 mm from the apex, the results did not significantly differ (Figs. 8-53 to 8-56).

FIG. 8-53 EndoVac system for NaOCl delivery and vacuum evacuation. Open-ended microcannula.

(Courtesy Discus Dental LLC, Culver City, CA.)

FIG. 8-54 EndoVac system for NaOCl delivery and vacuum evacuation. Closed-ended microcannula.

(Courtesy Discus Dental LLC, Culver City, CA.)

FIG. 8-55 EndoVac system: magnification of the closed-ended microcannula.

(Courtesy Discus Dental LLC, Culver City, CA.)

FIG. 8-56 Clinical use of the EndoVac system and Safety-Irrigator.

Safety-Irrigator

The Safety-Irrigator is an irrigation/evacuation system that apically delivers the irrigant under positive pressure through a thin needle containing a lateral opening, and evacuates the solution through a large needle at the root canal orifice. As of this printing, no information on its safety or efficacy is available (Fig. 8-57). Absent clear evidence of safety and efficacy through peer-reviewed literature, the reader is advised to use caution in choosing an irrigating device.

FIG. 8-57 The Safety-Irrigator.

(Courtesy Vista Dental Products, Racine, WI.)

Self-Adjusting File

The SAF was recently introduced primarily as an endodontic file (discussed at length earlier under Instruments for Cleaning and Shaping the Root Canal Space). It should also be considered as an irrigation device since the file is hollow, which allows for continuous irrigation. The irrigant is delivered through a free-rotating hub to which a silicone tube is attached (Fig. 8-58). Either a special irrigation unit (see Fig. 8-30) (VATEA, ReDent, Raanana, Israel) or any physio-dispenser-type unit may be used to deliver a constant flow of irrigant at 5 ml/min. This maintains a continuous flow of fresh, fully active irrigant, facilitating an outflow of tissue debris and dentin powder that is generated by the file use. No positive pressure is thought to be created in the canal during this continuous irrigation procedure. The open metal lattice allows the irrigant to escape freely, minimizing the risk of irrigant transportation beyond the apical foramen.²⁶⁰ The replacement of irrigation fluid in the apical part of curved canals is demonstrated in Fig. 8-59. Further research on this device is underway.

FIG. 8-58 The self-adjusting file (SAF; ReDent-Nova, Raanana, Israel). The hollow endodontic file is used also as a continuous irrigation device throughout the cleaning and shaping of the root canal.

(Courtesy ReDent-Nova, Raanana, Israel.)

FIG. 8-59 Replacement of irrigation fluid in the apical part of curved canals. Transparent training blocks were filled with colored liquid (A-B). The canal was rinsed with either 20 ml of water using a syringe (C) or using the SAF instrument with a continuous flow of an equal amount of water (D). The short needle was unable to replace the liquid beyond the curve (E), but the SAF irrigation did it effectively (F).²⁶⁰

HealOzone

Ozone (also known as triatomic oxygen or trioxygen) is a naturally occurring compound consisting of three oxygen atoms. It is found in nature in the form of a gas in the stratosphere at a concentration of 1 to 10 ppm, being continually created from and destroyed into molecular O₂. The reliable microbiologic and metabolic properties of ozone, in either the gaseous or aqueous phases, make it a useful disinfectant with a wide range of activity. Ozone, in the gaseous or aqueous phase, has been shown to be a powerful and reliable antimicrobial agent against bacteria, fungi, protozoa, and viruses. It is generally accepted that the oxidant potential of ozone induces the destruction of cell walls and cytoplasmic membranes of bacteria and fungi. During this process, ozone attacks glycoproteins, glycolipids, and other amino acids and inhibits the enzymatic control system of the cell. This results in increased membrane permeability, the key element of cell viability, leading to immediate functional cessation. The ozone molecules then readily enter the cell and cause the microorganism to die. Ozone can also attack many biomolecules, such as the cysteine, methionine, and histidine residues of proteins. By oxidizing the biomolecules featured in dental diseases, ozone has a severely disruptive effect on cariogenic bacteria, resulting in the elimination of acidogenic bacteria. The strongest naturally occurring acid—produced by acidogenic bacteria during cariogenesis—is pyruvic acid. Ozone can decarboxylate this acid to acetic acid. It has been shown that remineralization of incipient carious lesions can be encouraged when the production of acetic acid, or other high pKa acids found in resting plaque, buffers plaque fluid.²⁴⁵

E.A. Fisch (1899–1966) was the first dentist to use ozonated water in his practice and introduced it to the German surgeon Erwin Payr (1871–1946) who used it from that time forward in surgery. He reported his results at the 59th Congress of the German Surgical Society in Berlin (1935). In dental surgery, ozonated water was used to promote hemostasis, enhance local oxygen supply, and inhibit bacterial proliferation. Theoretically, ozone can reduce the bacterial count in active carious lesions and therefore may temporarily arrest the progression of caries, resulting in preventing or delaying the need for tooth restorations.³¹³ For review on ozone use in dentistry see Azarpazhooh and Limeback.¹⁷