Four in vitro studies100,164,279,282 were identified investigating the bactericidal effect of ozone compared to 2.5% NaOCl, the standard irrigation solution in endodontics. The results of these studies164,279,282 are controversial. The hazards of ozone when used in endodontics have not been investigated. Care should be taken with regard to the patient’s and the dentist’s exposure to the gas. Fig. 8-60 shows ozone equipment with a special tip for intracanal application.
Superoxidized water,152 also called electrochemically activated water241,365 or oxidative potential water,162,344 is saline that has been electrolyzed to form superoxidized water, hypochlorous acid, and free chlorine radicals. It is available as Sterilox (Sterilox Technologies, Radnor, PA). This solution is nontoxic to biologic tissues yet able to kill microorganisms. The solution is generated by electrolyzing saline solution, a process no different than that used in the commercial production of NaOCl.116 The difference, however, is that the solution accumulating at the anode is harvested as the anolyte and that at the cathode as the catholyte. These solutions display properties that are dependent upon the strength of the initial saline solution, the applied potential difference, and the rate of generation. The technology that allows harvesting of the respective solutions resides in the design of the anode and the cathode and originates either in Russia (electrochemically activated water) or Japan (oxidative potential water).240,241 Although the solutions bear different names, the principles in the manufacturing process are probably the same.
The use of superoxidized water is sparse in the endodontic literature but shows early promise. The solutions from both technologies have been tested for their ability to débride root canals,162,241 remove smear layer,344,365 and kill bacteria172 and bacterial spores.234 Results are favorable, while also showing biocompatibility with vital systems.183
Anolyte and catholyte solutions generated from one such technology (Radical Waters Halfway House 1685, S. Africa) have shown promise as antibacterial agents against laboratory-grown, single-species biofilm models.132 Such solutions have been recommended as suitable for removing biofilms in dental unit water lines240 and have even been marketed for this purpose. Cautious clinicians may prefer to wait for more studies to demonstrate safety and efficacy under ordinary clinical setting conditions before adopting newer, less tested irrigating solutions.
Photodynamic therapy (PDT) or light-activated therapy (LAT) may have endodontic applications because of its antimicrobial effectiveness.159 In principle, the strategy utilizes a selectively accumulated or endogenously produced photosensitizer (photoactive compound). The activation of photosensitizer molecules by a specific wavelength of light produces deleterious chemical entities that kill bacteria. The strong oxidizer generated during the process can act on multiple targets in a microbial cell, resulting in membrane damage, enzyme inactivation, and genomic and plasmid DNA damage, resulting in instantaneous death. In addition, the light-activated killing of bacteria has a wide spectrum of antimicrobial activity with a minimal chance of giving rise to a resistant microbial population, making it an ideal disinfectant. Fighting biofilm-mediated localized human infections is one of the potential medical applications of LAT.410 The principal agent involved in bacterial killing is the oxygen-based free radical.159 Unlike systemic therapeutic agents, LAT has the advantage of dual selectivity. Only those cells which have selectively accumulated the photosensitizer or possessing endogenously produced photosensitizers will be affected upon irradiation. Separately, the low-intensity light and the nontoxic photosensitizer generally used in LAT are harmless. In addition, the use of an optic fiber helps in directing the irradiation to the intended site of application. Studies have highlighted the possibility of killing antibiotic-resistant strains of pathogenic bacteria using LAT.409,411 Because of the wide spectrum of antimicrobial activity, instant bacterial killing, and ability to target biofilm bacteria, the application of LAT-based regimens has great promise in root canal disinfection.400 However, a thorough knowledge about the behavior of the photosensitizer and the physicochemical characteristics of the microenvironment prevailing in the root canal system is necessary for disinfection to be effectively achieved. In advanced stages of infection with mineralized biofilms, it may be necessary to do a minimal mechanical preparation of the root canal prior to LAT to achieve maximum disinfection.
Ultraviolet (UV) light is widely used for disinfection purposes. IntraLight (InterLight, Or-Yehuda, Israel) consists of an intracanal UV illuminator shaped with dimensions of an endodontic file, which allows uniform circumferential illumination of the root canal walls with 254 nm UV light. In a recent in vitro study,255 root canals were infected with E. faecalis bacteria that were allowed to grow and establish a biofilm on the root canal walls. Treatment with 5% NaOCl for 10 minutes failed to result in negative cultures in 53% of the canals. Similar results were reported by others.255,257 An additional illumination of the canal walls with 254 nm UV light (300 mJ/cm2) rendered 96% of the canals free of cultivable bacteria. A wide range of bacteria are sensitive to 254 nm UV light, including those that are resistant to Ca(OH)2.257 The device is used as a supplemental disinfection after NaOCl irrigation in the canal. Otherwise, bacteria in the inner layers of thick biofilms may be protected from the UV light, which is absorbed by bacteria in the outer layers.257
After the root canal system has been appropriately prepared, it must be obturated with a material capable of completely preventing communication between the oral cavity and the periapical tissue wound. Materials used for this purpose should be compatible with healing. This is achieved by attempting to seal the root canal system at both its coronal and apical ends, as well as throughout the canal system, to seal the openings of accessory canals. Apical and intracanal obturation blocks the exit to the periradicular tissues from organisms that have survived in the root canal after cleaning and shaping. Coronal obturation prevents reinfection of the pulp space from the oral environment. The required physical and biologic properties make the selection of obturation material critical. The materials commonly used for root canal fillings normally can be divided into a solid phase and a cementing medium (i.e., a sealer).
Gutta-percha is the most commonly used root canal filling material. It is a linear crystalline polymer that melts at a set temperature, with a random but distinct change in structure resulting. (See Chapter 10 for further discussion of the physical properties of gutta-percha.) It occurs naturally as 1,4-polyisoprene and is harder, more brittle, and less elastic than natural rubber.
The crystalline phase has two forms, the alpha phase and the beta phase. The forms differ only in the molecular repeat distance and single-bond form. The alpha form is the material that comes from the natural tree product. The processed, or beta, form is used in gutta-percha for root fillings.333 When heated, gutta-percha undergoes phase transitions. The transition from beta phase to alpha phase occurs at around 115° F (46° C). An amorphous phase develops at around 130° F to 140° F (54° C to 60° C). When cooled very slowly (i.e., 1° F per hour), gutta-percha crystallizes to the alpha phase. Normal cooling returns the gutta-percha to the beta phase. Gutta-percha cones soften at a temperature above 147° F (64° C).139,333 These cones can easily be dissolved in chloroform and halothane and dissolve less in turpentine or xylene.
Modern gutta-percha cones that are used for root canal fillings contain only about 20% gutta-percha (Box 8-4). The major component is zinc oxide (60% to 75%). The remaining 5% to 10% consists of various resins, waxes, and metal sulfates. Antiseptic gutta-percha with various antimicrobial agents has been suggested, and several studies are available concerning the effect of these additives (see Medicated Gutta-Percha).
Because gutta-percha cannot be heat sterilized, other decontamination methods must be used. The most practical method is to disinfect the gutta-percha in NaOCl before use. This can be done in 1 minute if the cone is submerged in a 5% solution of NaCOl.342 However, after this disinfection and before its use for obturation, it is imperative that the gutta-percha be rinsed in ethyl alcohol to remove crystallized NaOCl; such crystals may impair the obturation seal.349
Obturation with gutta-percha normally requires some form of compaction pressure, but real compression of gutta-percha is practically impossible.333 Pressure applied during root canal filling procedures does not compress gutta-percha, but rather compacts the gutta-percha cones to obtain a more three-dimensionally complete fill of the root canal system.
After heating, while cooling, there is a slight shrinkage of approximately 1% to 2% when the gutta-percha has solidified. Prevention of shrinkage is practically impossible in vertical warm compaction.139,334 Careful control of the temperature during warm compaction is crucial to prevent focal areas of unnecessarily high temperatures. Better temperature control is available with electrically controlled heating devices as the Touch ’n Heat, System B, Elements units (SybronEndo, Orange, CA), or the recently introduced vibrating heat carrier, DownPack67 (Hu-Frieday, Chicago, IL), or HotTip (Discus Dental, Culver City, CA), all of which are more commonly used for this purpose (see Figs. 8-41 through 8-44).
Gutta-percha oxidizes with exposure to air and light and eventually becomes brittle.198,242 It should be stored in a cool, dry place (e.g., a refrigerator) for better shelf life. Methods of “rejuvenating” aged gutta-percha have been suggested.189
Gutta-percha cannot be used as the sole filling material; it lacks the adherent properties necessary to seal the root canal space. Therefore, a sealer (cement) is always needed for the final seal. (See the following sections on sealers.)
Manufacturers now supply gutta-perch cones in tapers matching the larger tapered rotary instruments (#.02, #.04, and #.06) (Fig. 8-61). An international standard has been accepted for gutta-percha cones, based on similar size and taper standards set forth for the endodontic files (ANSI No.78) (see Table 8-1). The tolerance is much less stringent for gutta-percha compared to files. An endodontic file must be manufactured with a tolerance of +0.05 mm. Consequently, with the same size instrument and gutta-percha cone, a difference in diameter of 0.07 mm (more than one file size) is possible (see Table 8-2 for gutta-percha cone sizes).
Gutta-percha has been extensively investigated as a root canal filling material in animals and has been proven biocompatible. Compared with sealers used for root canal obturation, it clearly has the lowest tissue toxicity. When compared to Resilon, both materials were equally biocompatible.38 After subcutaneous implantation, gutta-percha normally becomes surrounded by a defined capsule rich in cells but without a significant number of inflammatory cells, although some macrophages are present.37,288,362 Results from more sensitive assays in vitro support the in vivo results, suggesting that gutta-percha used for root canal fillings has a low toxicity.295 Nevertheless, gutta-percha in the form of very small particles induces an intensive foreign body reaction, with massive accumulation of mononucleated and multinucleated macrophages.362 This is not surprising, since materials that are normally considered inert (e.g., Teflon) cause similar reactions when presented to the tissues as an irregular surface or particle.50
Resilon (Pentron Clinical Technologies, Wallingford, CT), a thermoplastic, synthetic, polymer-based root canal filling material, was developed in an attempt to create an adhesive bond between the solid-core material and the sealer. It is designed to be used with Epiphany (Pentron Clinical Technologies), a new resin sealer with a bonding capacity to dentin. Resilon can be supplied in the same ISO sizes and shapes (cones and pellets) as gutta-percha. The manufacturer has stated that it can be used with any current root canal obturation technique (lateral compaction, thermoplasticized, carrier, injection). When manufactured in cones, Resilon’s flexibility is similar to that of gutta-percha. Based on polyester polymers, Resilon contains bioactive glass and radiopaque fillers (bismuth oxychloride and barium sulfate) with a filler content of approximately 65%. It can be softened with heat or dissolved with solvents such as chloroform. This characteristic allows the use of current retreatment techniques for nonhealing cases. Because it is a resin-based system, it is compatible with current restorative techniques in which cores and posts are placed with resin bonding agents (Figs. 8-62 to 8-64).348
FIG. 8-62 A, Resilon/Epiphany cone root canal system obturation. B, Recall radiograph taken 8 months after initial treatment shows complete healing.
(Courtesy Dr. Richard Rubenstein, Farmington Hills, MI.)
Gutta-percha is now available that may achieve bonding between the solid core and a resin sealer. The uniform layer is placed on the gutta-percha cone by the manufacturer. When the material comes in contact with the resin sealer, a resin bond is formed. The manufacturer claims that this will inhibit leakage between the solid core and the sealer. The technique calls for use of EndoRez sealer (Ultradent, South Jordan, UT) with this new solid-core material (Fig. 8-65). The material with a resin sealer was compared with gutta-percha for microleakage. The results indicated a bonding between core and sealer resulting in far less microleakage than gutta-percha.348 Another study tested the apical sealer of methacrylate-coated gutta-percha, and it caused the least amount of leakage.445
FIG. 8-65 A, EndoRez environmental scanning electron microscope (ESEM) image under hydrated conditions. When a gap appears, one can be certain that it is true, not an artifact. ESEM taken at relative humidity of 95%. D, Radicular dentin from coronal third of root canal wall; G, gutta-percha; S, EndoRez sealer; asterisk, proprietary coat in EndoRez GP cones; open arrowhead, true (not artifact) gap between root filling material and sealer; pointer: true gap along sealer-dentin interface; pointer: a gap-free region along sealer-dentin interface (×350). B, EndoRez ESEM, higher magnification of (A), labels are similar. Pointer, Hybrid layer probably caused by demineralization of radicular dentin with 0.5M EDTA; open arrowhead, between sealer and gutta-percha (×1000).
(Courtesy Dr. Franklin Tay, Medical College of Georgia, Augusta, GA.)
The melding of an antibacterial substance to a gutta-percha cone or other solid-core obturation materials may have utility in preventing root canal therapy failures due to coronal or apical microleakage. In an early study, Ca(OH)2 and CHX combined with zinc oxide and eugenol were found effective against the test organisms studied.305 It is interesting to note that gutta-percha and Resilon appear to have no antibacterial or antifungal effects in and of themselves. When tested against five common organisms found in necrotic root canal systems, both materials proved not to be effective.
Several studies have attempted to examine gutta-percha cones which were formed with various antibacterial and antifungal preparations. In one study,42 gutta-percha was impregnated with either CHX or Ca(OH)2 and tested against eight organisms commonly found in infected root canal systems. CHX demonstrated inhibition against all organisms studied, while Ca(OH)2 did not inhibit any of the same organisms. The antimicrobial effect of gutta-percha cones containing a mixture of both CHX and Ca(OH)2 was found superior when compared the antimicrobial effectiveness of either substance when tested separately.291 Another study testing CHX or Ca(OH)2 with gutta-percha found CHX to be significantly more effective when tested in cultures of gingival fibroblasts.383 When epithelial tumor cells and gingival fibroblasts were used to test gutta-percha cones containing either CHX or Ca(OH)2, CHX samples showed significantly lower protein synthesis. Both tested materials induced cell growth–specific alterations.422
Early studies of medicated gutta-percha examined the use of iodoform in the solid-core material. While inhibitory against some pathogens, it was not inhibitory for all organisms.351 A later study showed no differences between iodoform and regular gutta-percha samples in delaying microleakage of E. faecalis.59 Gutta-percha discs impregnated with iodoform or other iodine combinations were tested against usual root canal system pathogens. Medicated gutta-percha inhibited all bacterial growth for 24 hours and was statistically more effective than regular gutta-percha.35
When tetracycline impregnation was compared to iodoform-medicated gutta-percha cones and Resilon and tetracycline discs, the impregnated cones inhibited growth for all species tested.251 Tetracycline integrated with gutta-percha inhibited all test organisms when compared to conventional gutta-percha.36
Although effective in the cited studies, medicated gutta-percha cones are not used on a regular basis. More testing must be done to investigate their toxicity, antibacterial and antifungal potentials, and potential for allergic reactions.
The sealer plays an important role in the root canal filling. It fills all the space the solid-core material is unable to fill because of the solid core’s physical limitations. A good sealer adheres strongly to the dentin and the core material. The sealer also must have cohesive strength to hold the obturation material together. Sealers ideally should be antimicrobial, which would be an important role in the success of root canal therapy. Sealers usually are made of a mixture that hardens through a chemical reaction. This reaction normally includes the release of toxic material, which makes the sealer less biocompatible. In general, the sealer is the critical component when the toxicity of material is assessed.
The sealer must have some degree of radiopacity to be visible on adequately exposed radiographs. Additives used to enhance radiopacity are silver, lead, iodine, barium, and bismuth. Compared with gutta-percha cones, most sealers have a slightly lower radiopacity and can be distinguished from gutta-percha alone or in combination with the sealer. A variety of sealers are available, and the clinician must be careful to evaluate all characteristics of a sealer before selecting one (Fig. 8-66, A-F).
FIG. 8-66 Scanning electron microscope replicas comparing Resilon/Epiphany and Thermafil/AH Plus in variously shaped root canal systems. Impressions of the sectioned canals were taken with an ultraflow viscosity polyvinylsiloxane (PVS), and the replicas were directly examined. They are negative impressions of gaps, with PVS impression material flowing into the gaps. When the impression material was removed, a gap would appear as a flap of PVS material sticking out of the impression. All leaflets of PVS gaps appear blunt and stick out from the regions that represent root-filling material (arrows). Two views of each canal morphology are shown. A, Thermafil/AH Plus (×269), round, narrow canal shape. B, Resilon/Epiphany (×351), round, narrow canal shape. C, Thermafil/AH Plus (×198), wider, irregular canal shape. D, Resilon/Epiphany (×241), wider, irregular canal shape. E, Thermafil/AH Plus (×198), narrow, ribbon-like (rotary instrument) shape. F, Resilon/Epiphany (×241), narrow, ribbon-like, (rotary instrument) shape.
(Courtesy Dr. Franklin Tay, Medical College of Georgia, Augusta, GA.)
Many endodontic sealers are simply zinc oxide eugenol (ZnOE) cements that have been modified for endodontic use. The mixing vehicle for these materials is mostly eugenol. The powder contains zinc oxide that has been finely sifted to enhance the flow of the cement. The setting time is adjusted to allow for adequate working time. These cements easily lend themselves to the addition of chemicals; paraformaldehyde was sometimes added for antimicrobial and mummifying effects, germicides for antiseptic action, rosin or Canada balsam for greater dentin adhesion, and occasionally corticosteroids for suppression of inflammatory reactions. However, the use of formaldehyde is completely unacceptable, given the possibility of its circulation to other body tissues and organs. Corticosteroids are generally not included in sealers in the United States; it appears that their effect is limited by the amount contained in the preparation.176
Zinc oxide is a valuable component of the sealer. It is effective as an antimicrobial agent. The incorporation of rosins containing resin acids in sealers initially may have been for the adhesive properties.148 Rosins (i.e., colophony), which are derived from a variety of conifers, are composed of approximately 90% resin acid. Resin acids are amphophilic, with the carbon group being lipophilic, affecting the lipids in cell membranes. Thus the resin acids have a strong antimicrobial effect that in mammalian cells is expressed as cytotoxicity. The resin acids work similarly to quaternary ammonium compounds by increasing the cell membrane permeability of affected cells. Although toxic, the combination of zinc oxide and resin acids overall may be beneficial. Under certain conditions, resin acids may react with zinc, forming a resin acid salt (i.e., resinate). This matrix-stabilized zinc resinate is only slightly soluble in water,249 so ZnOE cements with resin components are less soluble than regular ZnOE cements.
The antimicrobial action of zinc oxide in both gutta-percha cones and many sealers create a low-level but long-lasting antimicrobial effect. In one study, a ZnOE sealer had a statistically significant larger mean zone of inhibition than three Ca(OH)2 sealers.264 When a new preparation of ZnOE sealer (Fill Canal) was tested, it showed large zones of inhibition against all microorganisms tested.355
The setting of ZnOE cements is a chemical process combined with physical embedding of zinc oxide in a matrix of zinc eugenolate. The particle size of the zinc oxide, pH, and the presence of water regulate the setting and other additives that might be included in special formulas. The formation of eugenolate constitutes hardening of the cement, and Ca(OH)2 accelerates this action, so canal systems containing Ca(OH)2 must be well irrigated before obturation. Free eugenol always remains in the mass and acts as an irritant.
Several of the companies producing ZnOE root canal cements have been replaced by new companies, resulting in new names for older preparations such as Rickerts sealer, Procosol, and Wach’s sealer. Fill Canal (Ligas Odontologicas, Sao Paulo, Brazil), Tubli-Seal (SybronEndo), and Pulp Canal Sealer (SybronEndo) are three successors to the original ZnOE cements and have been recently investigated. E. faecalis is a highly resistant organism found in necrotic root canal systems. That organism was exposed to two ZnOE sealers, Roth’s 811 and Kerr EWT. Roth’s exhibited the largest zone of inhibition.263 Sultan, a ZnOE sealer, was one of the three most potent bacterial-growth inhibitors (E. faecalis).61,304,353 When Candida albicans was used as the test organism, a ZnOE preparation demonstrated the largest zone of inhibition.269 A direct contact test determined that the virulence of endodontic pathogens determine response to sealers.298
Historically, formaldehyde was commonly mixed into endodontic sealers, but formaldehyde is a dangerous additive to any sealer; it adds to the already toxic effect of eugenol and prevents or delays healing. Chapters 11 and 27 further discuss why potential major liabilities exist for any dentist who unwisely chooses to use formaldehyde or paraformaldehyde during endodontic therapy.
Chloropercha was another type of sealer used for many years. It is made by mixing white gutta-percha (i.e., alba) with chloroform. This allowed gutta-percha root filling to fit better in the canal. However, chloropercha has no adhesive properties and is no longer used as an obturation material in root canal therapy. The use of chloroform has been sharply curtailed for many years because of its demonstrated toxicity.436 In endodontics, the amounts normally used are insignificant and cause no detectable health hazard.39,60,338 Nevertheless, the clinician must take prudent steps to reduce vaporization during use, because chloroform is highly volatile. When used to soften gutta-percha during revision of old root fillings, the chloroform should be dispensed through a syringe and hypodermic needle and only passively expressed into the area of the pulp chamber. For other uses, the exposure time, amount used, and chloroform surface exposed should be kept to a minimum.
Some chloroform substitutes, such as halothane and turpentine, are in use. Compared to chloroform, halothane is less effective at softening gutta-percha, is similarly hepatotoxic, and has a higher local toxicity (Table 8-4). For these reasons, halothane is not a good substitute. Turpentine is not carcinogenic but is reported to cause allergic reactions.52,395 It has a high local toxicity and dissolves gutta-percha poorly. Therefore, no good substitute exists for the use of chloroform in endodontic procedures. With careful workplace hygiene, little risk is associated with the occasional use of minute amounts of chloroform in preparing customized master cones or when performing endodontic retreatments, provided no federal or state laws are violated.21,244
Several Ca(OH)2-based sealers are now commercially available, such as Sealapex (Sybron Endo), RealSeal (Sybron Endo) Apexit and Apexit Plus (Ivoclar Vivadent). These sealers are promoted as having therapeutic effects because of their Ca(OH)2 content (Box 8-5). The antimicrobial effect of Ca(OH)2 is thought to occur because of its ability to release hydroxyl ions and by having a high pH.297 Short-term direct contact tests have shown Sealapex and Apexit to be mildly effective antimicrobial agents.
BOX 8-5 Composition of Calcium Hydroxide Sealers: Sealapex, CRCS, and Apexit*
* Proportions are unavailable for CRCS and incomplete for Sealapex.
These sealers also have poor cohesive strength.325 No evidence supports the contention that a Ca(OH)2 sealer provides any advantage for root canal obturations or has any of the desirable biologic effects of Ca(OH)2 paste. In a study of diffusion of hydroxyl ions into surrounding dentin after root filling with Sealapex and Apexit, no traces were found in teeth filled with Apexit. Some hydroxyl ions could be detected in the dentin close to the root filling with Sealapex.378 In vivo studies of Sealapex and CRCS (Coltene Whaledent, Altstätten, Switzerland) have demonstrated that these sealers easily disintegrate in the tissue, and both cause chronic inflammation.
Many studies have been conducted on various classes of root canal sealers, including Ca(OH)2. The majority of these studies report that all sealers leak.85 Ca(OH)2 appears to be effective in formation of dentin bridges when used as a direct capping material,4,107 which may indicate its ability to encourage formation of root-end hard tissue. It also appears to demonstrate acceptable antimicrobial activity. Success was seen at the same levels observed for mineral trioxide aggregate.387
Despite the favorable responses seen in the cited study, the results must be considered ambivalent and variable. Adhesion of the sealer to the prepared dentin wall and the solid-core obturation material also is a consideration. There is no creditable information that states that Ca(OH)2 sealers in and of themselves provide adhesive forces. One study does state that use of an erbium-doped yttrium aluminum garnet (Er:YAG) laser does increase the adhesiveness of Ca(OH)2 sealers.27
Polymers are macromolecules composed of 10,000 or more atoms. Rubber has a polymeric structure based on a repeating isoprene (monomer). Polymeric molecules, discovered in nature (rubber), have led to synthetic analogs with a variety of properties and applications, such as adhesives (root canal sealers). While it is more convenient to discuss polymer sealers according to their classification or type, it may be more meaningful to describe them according to their ability to act in a particular manner based on what or how each group of sealers’ characteristics are when used, such as their adhesiveness, sealing ability, and similar properties.
When considering the adhesiveness of a sealer, it must have the ability to adhere to both the prepared dentin wall and the solid-core obturation material used. As such, adhesiveness becomes very important in the material’s ability to seal the prepared root canal system from coronally and apically, since the preparation procedures appear unable to sterilize the root canal space and at most may only disinfect the system.
Other significant sealer considerations include their biocompatibility, radiopacity, cytotoxicity, and bond strength.
Most of the newer sealers are polymers, including AH26 and AH Plus (DENTSPLY Caulk), Epiphany (Pentron Clinical Technologies), and EndoRez (Ultradent).
AH26 is an epoxy resin that was initially developed as a single obturation material. Because of its positive handling characteristics, it has been extensively used as a sealer. It has a good flow, seals well to dentin walls, and has sufficient working time.224 Like most sealers, AH26 is very toxic when freshly prepared.295 Earlier research indicated that AH26 toxicity was limited and principally caused by release of small traces of formaldehyde.34,176 However, recent studies using more modern methods of analysis indicate that the sealer’s mechanism for induced cytotoxicity may be due to activation of COX-2 in RNA gene expression,175 leading to decreases in iNOS protein expression,215 and the synergistic effects of root canal sealers on LPS induces COX-2 expression by macrophage cells.214 Toxicity may decline rapidly during setting, and after 24 hours the cement may have one of the lowest toxicities of endodontic sealers.187 A new formulation of AH26 is AH Plus. This is a two-paste mixing system that assures a better mixture and does not release formaldehyde upon setting.63,218 It is more radiopaque and has a shorter setting time (approximately 8 hours), lower solubility, and a better flow compared with AH26. One study demonstrated that AH Plus had a lower short- and long-term toxicity level and was less genotoxic than AH26 (Figs. 8-67 and 8-68).16,222
FIG. 8-67 AH26 implant in the mandible of a guinea pig 12 weeks after implantation. Bone has grown up and integrated with the implant. Remnants of the implant, which was lost during histologic preparation, can be seen as a black area at the top of the image. Complete healing was observed without signs of inflammation.
FIG. 8-68 Comparison of dye penetration after various obturation methods using AH26 sealer. The dye was delivered with a vacuum method, and penetration was measured as millimeters of leakage. The single cone technique and use of ThermaFil resulted in the least leakage, followed by lateral compaction, vertical compaction, and use of UltraFil. The standard deviation is high, as is common for leakage studies, reflecting the variability in the obturation method. The less complicated the obturation method, the lower the standard deviation.69
Epiphany is a dual curable dental resin composite sealer composed of BisGMA, ethoxylated BisGMA, UDMA, and hydrophilic difunctional methacrylates with fillers of Ca(OH)2, barium sulfate, barium glass, and silica. The total filler content of the sealer is approximately 70% by weight. Biocompatibility has been demonstrated both in vitro and in vivo, resulting in approval by the U.S. Food and Drug Administration. Epiphany was designed for use with Resilon instead of gutta-percha, although it can also be used with either core material. Unlike other resin sealers, this system’s sealer requires a self-etch primer before placement of the resin sealer.348 The newest iteration of the sealer utilizes a self-etching injectable paste that bonds to the prepared dentin walls and the solid-core material. Although not without controversy, used with Resilon cones, the subsequent obturated canal system may be fracture resistant.182,423
EndoRez is a UDMA resin-based root canal sealer with hydrophilic properties that allow good penetration into dentinal tubules. In addition to its biocompatibility,442,445 it offers good radiopacity. EndoRez is as radiopaque as gutta-percha, which simplifies radiographic interpretation (Fig. 8-69).444 The system includes a sealer, solid cores (resin-coated gutta-percha) and an accelerator and does not rely on heat to soften the material or pluggers to exert pressure to move the core apically. Much like Resilon/Epiphany, the bonding to both the dentin and solid core is thought to make the completed obturation resistant to fracture.160
FIG. 8-69 Transmission electron microscope image illustrates the application of EndoRez sealer to smear layer–covered dentin (created by Profile nickel-titanium instruments) following use of 6.15% NaOCl initial rinse and sterile distilled water as final rinse. (Manufacturer recommends use of EDTA as final rinse.) A, A gap (asterisk) seen between the sealer (S) and radicular dentin (D). Smear plugs (open arrowheads) retained along orifices of dentin tubules (T). The smear layer was originally loosely attached to the canal wall dentin surface. EndoRez was applied to canal walls after NaOCl and distilled water irrigation, the resin portion of EndoRez (fillers) did not penetrate the loosely arranged smear layer particles. B, During polymerization of EndoRez, shrinkage stresses pulled the smear layer (pointer) away from the dentin, resulting in the smear layer being attached to sealer (S). Gap filled with epoxy resin used for embedding.
(Courtesy Dr. Franklin Tay, Medical College of Georgia, Augusta, GA.)
Glass ionomer cements have been introduced as endodontic sealers (Ketac-Endo [ESOE]) and are known to cause little tissue irration,443 with low toxicity in vitro. Questions remain about the quality of the seal achieved with Ketac-Endo, because dentin and sealer adhesive failures have been observed.77 Some investigators have expressed concern about glass ionomers’ solubility compared with other sealers.331
RoekoSeal (Roeko, Langenau, Germany) is a polydimethylsiloxane-based root canal sealer. One in vitro study comparing it with eugenol-based Sealapex or Ca(OH)2-based Kerr’s Pulp Canal Sealer concluded that RoekoSeal was less cytotoxic.8 It has adequate solubility properties.331 When its resistance to coronal and apical leakage was compared with that of AH26, no significant difference was observed.61 With both sealers, removal of the smear layer improved the coronal and apical seal. Roeko recently introduced another version of its silicone sealer, GuttaFlow. It comes in a unidose capsule and is injected after mixing. The silicone is mixed with gutta-percha powder to form what the company calls a “two-in-one” cold filling system. GuttaFlow and RoekoSeal have recently been examined for spreadability on dentin and gutta-percha surfaces and compared to Roth 801 and AH26 sealers. Use of a sufficient load during lateral compaction is necessary for RoekoSeal and GuttaFlow to satisfactorily wet gutta-percha and dentin.200 Microleakage and sealing ability also have been tested. When RoekoSeal and GuttaFlow were compared to other sealers, leakage patterns were found to be similar to other sealers.75 GuttaFlow showed similar leakage results when used with lateral compaction or System B techniques, but it demonstrated expanding capacity over time compared to compacted gutta-percha and AH26 over a 12-month period.200 When GuttaFlow was compared to two single-cone obturation systems, it was found that the apical seal was as effective as AH Plus used with vertical compaction.274 However, in a dual-chamber leakage model with Streptococcus mutans as a biologic marker, thermoplasticized gutta-percha with AH Plus using vertical compaction was more effective in minimizing bacterial leakage.273 Evaluating the long-term sealing ability of GuttaFlow compared to Epiphany, PCS, and AH Plus, GuttaFlow and Epiphany allowed less fluid movement.41
A large group of endodontic sealers and cements had substantial paraformaldehyde additives. Some of the more common brands were Endomethasone, Riebler’s paste (Amubarut; Wera Karl, Biensingen, Germany), and N2 (Indrag-Agsa, Bologne, Italy). All of these sealers have essentially the same toxicity. N2 is also known as RC-2B or the Sargenti technique. Historically, it has been heavily commercialized. There are no creditable studies available as to establish this material’s use clinically. (Chapter 11 presents a more comprehensive discussion.) There are no clinical conditions to justify the use of these pastes.
N2 is basically a ZnOE sealer. Its composition has varied extensively over the years. The significant amount of lead oxide and smaller amount of organic mercury that were formerly major toxic components are often missing in more recent formulations. However, N2 still contains unacceptable amounts of formaldehyde.44 Because it contains 6% to 8% paraformaldehyde (and sometimes hydrocortisone and prednisolone), it loses substantial volume when exposed to fluid. It also absorbs more than 2% of fluid during the first week in situ.
N2 is extremely toxic in experiments in vitro and in animal experiments. The tissue reaction normally observed is a coagulation necrosis within a very short time. The coagulated tissue is altered to such an extent that it cannot undergo any repair for months because it is impregnated with formaldehyde. With time, the formaldehyde may be washed out of the necrotic tissue, allowing either bacteria to be established in the necrosis or, if the blood supply is adequate, repair to take place.
The Interstate Commerce Commission of the U.S. Government has banned the transport of N2 across state lines, effectively halting the sale of these types of sealers. Please read Chapters 11 and 27 to gain a fuller understanding of the legal consequences of using these unacceptable pastes in unwary patients.
Endodontic sealers are listed under ANSI/ADA specification number 57, Endodontic Sealing Material 2000 (reaffirmed 2006). This specification is for material used in endodontics within the tooth to seal the root canal space. This specification in an adoption of ISO6876:2001. ANSI/ADA Standard 57 outlines various test methods for evaluation of the physical properties of endodontic sealer-filling materials. Sealers are classified into two categories, depending on the intended use: type I materials are intended to be used with core materials; type II materials are intended for use with or without core material or sealer. Type I materials are divided into three classes. Class 1 includes materials in the form of powder and liquid that set through a nonpolymerizing process; class 2 includes materials in the form of two pastes that set through a nonpolymerizing process; class 3 includes polymer and resin systems that set through polymerization. The subclasses for type II materials are the same as for type 1 materials, except that metal amalgams are also included. ANSI/ADA No. 57 describes testing methods for working time, setting time, flow, film thickness, solubility, and disintegration; it also establishes a specific requirement for radiodensity. The tests for endodontic core materials include determinations of the material’s dimensions, brittleness, and flow. A separate ANSI/ADA standard (No. 78) examines prefabricated metallic or polymeric-based cones used in obturation procedures. Despite the standard’s often detailed requirements, significant disagreement exists on the ideal properties of endodontic sealers and fillers, so most of these expectations are guidelines that have not significantly affected the industry.
ANSI/ADA No. 41 recommends protocols for biologic evaluation of dental materials. This document covers recommended standard practices for biologic evaluation of the safety of materials used in dentistry and is not intended for use in the evaluation of pharmacologically active medicaments. This document outlines recommended test protocols for various dental materials, including certain guidelines for endodontic filling materials. These methods include general toxicity assessments (LD50), cytotoxicity assessments in vitro, sensitization assays, mutagenicity assays, implantation tests, and usage tests. It was last updated in 2006. Several test methods are presented for each of these factors, depending on the type of material.
Root canal filling materials generally are toxic, and none fulfills the expectations set forth in ANSI/ADA No. 41. However, the methods described in this specification can be used to distinguish more toxic materials. Less toxic materials produce a less intense or shorter chemical insult to the remaining apical pulp or apical periodontium. If the wound area is free of bacteria when the initial chemical necrosis occurs, as results from sealers containing paraformaldehyde, tissue repair should occur as the initial irritant declines in intensity. Some tissue irritation may occur as a result of phagocytosis of particles of the material, but an expanding lesion would not develop.362
Endodontic sealers other than those that contain paraformaldehyde should not be implicated as the cause of a periradicular bone lesion. If the tissue in the apical root area is not sterile due to infection within the root canal system, presence of sealer should not cause a chemically induced periradicular necrosis. Thus, materials that cause extensive tissue necrosis inside the root canal may become vehicles for the development of failure of endodontic treatment. This supports the idea that treatment should focus on the proper application of asepsis and antisepsis, and that materials that are as biocompatible as possible should be used.
Sealers and cements are the very toxic component of gutta-percha root filling techniques. Therefore, the clinician must take great care in selecting materials and must have an understanding of what each material contributes to a disease process. ZnOE cements have a significant drawback in their release of free eugenol and loss of volume during the hydrolysis that takes place after setting. This is somewhat mitigated by its change into a relatively inert eugenolate substance within 24 to 48 hours. Several of the polymer materials have high toxicity during the polymerization phase but may become practically inert when polymerized. Sealers with inclusions of dissolvable components, such as Ca(OH)2, lose these components in the tissue, resulting in compromise of the integrity of the obturation.
The search for a more simplified and proficient obturation technique has led to the development of many new hybrid materials. Differences focus on alternative systems for introducing the solid-core material into the root canal system while maintaining length control. The newer methods currently in use vary considerably. Most hybrid obturation methods require modification of the outline of the root canal preparation. One hybrid preparation technique involves the use of a rotating instrument that spins in the opposite direction of normal rotations and feeds the obturation material into the canal system instead of moving it out of the system. For optimal results, the clinician must consider technique variations before attempting a hybrid obturation method. A comparison of the more commonly practiced obturation methods, using an objective and sensitive vacuum dye penetration method, failed to show any major difference in the quality of the obturation.69 However, dye penetration techniques have come into question in recent years. Other evaluation methods, such as dye extraction and fluid filtration techniques, seem to produce more consistent and credible data.51
The introduction of new materials, techniques, and delivery systems is challenging basic beliefs and concepts previously thought to be standard. For example, use of a single cone of gutta-percha with sealer historically has been considered unacceptable. However, with the introduction of new technology for cleaning and shaping and the development of innovative sealer delivery systems, a paradigm shift may be occurring toward improved canal preparation to receive more flowable sealers and a single insertion of a core material. To validate the long-term success of any of the obturation techniques, clinical studies to support evidence-based practice must be one of the goals of endodontic research.
ThermaFil, ThermaFil Plus, ProTaper, and GT Obturators (DENTSPLY Tulsa Dental, Tulsa, OK) are obturation systems in which alpha-phase gutta-percha is preapplied to a flexible solid central carrier (Fig. 8-70). The gutta-percha obturator is heated in a proprietary heater (ThermaPrep Plus Oven, DENTSPLY Tulsa Dental) (Fig. 8-71) to the appropriate softness, and after the placement of canal sealer, the obturator is placed into the canal. These devices are available with a plastic, stainless steel, or titanium carrier core. In one study, ThermaFil demonstrated a greater percentage of canal obturation than either System B compaction or lateral compaction.76 If necessary, the plastic core material can be softened with chloroform or heated using a System B428 for easy removal. These obturators offer an alternative method of obturation with gutta-percha.
FIG. 8-70 ThermaFill obturators. Currently, obturators are provided to fit many of the individual types of files used in the canal. In this case: ProTaper instruments sizes F3 and F4 with their corresponding obturators.
(All rights owned by and used with permission from DENTSPLY International, Inc.)
FIG. 8-71 ThermaPrep Plus oven.
(All rights owned by and used with permission from DENTSPLY International, Inc.)
SimpliFill (Discus, Culver City, CA) (Fig. 8-72) is an obturation system designed to be used with the LightSpeed instrumentation system. The technique is based on a presized plug (5 mm long) of gutta-percha or Resilon which is attached to the end of a metal carrier. After sealer has been placed, the appropriate size SimpliFill is placed to working length, and the carrier is removed, leaving the apical segment obturated and the coronal segment open. Sealer is then injected with a syringe into the coronal segment, and a single cone (gutta-percha or Resilon) or post is inserted. In a study of coronal microbial leakage, an apical plug of SimpliFill in combination with FiberFill (Pentron Clinical Technologies, Wallingford, CT) in the coronal segment of canals was found to have significantly less leakage than lateral, vertical, and Obtura III (SybronEndo, Orange, CA) compaction techniques.348 A later study found that SimpliFill samples demonstrated the most complete coverage in both coronal and apical sections when compared to vertical compaction, Obtura III, System B and ThermaFil Plus.177
Several techniques have been described for introducing gutta-percha into the root canal system after the gutta-percha has been plasticized with heat. The Obtura system (Fig. 8-73) is currently the most commonly used injection delivery system for gutta-percha.385 It dispenses a heavy form of gutta-percha heated to a high temperature. Although the temperature of the gutta-percha in the Obtura III injection gun is as high as 302° F to 338° F (150° C to 170° C), the temperature of the extruded material may range from 140° F (60° C) to 280° F (138° C).89 When the Obtura III was compared to the System B heat source using different heat points, neither exceeded an increase of 10° C at any root level monitored.382 Intracanal temperatures after delivery, measured with intracanal thermocouples, have ranged from 107.6° F to 192.2° F (42° C to 89° C). Periodontal injuries have been reported after excessive heat during endodontic treatment of teeth in the ferret and the dog.329 Recent studies testing the Obtura III found a 10° C increase in the mandibular anterior teeth in vitro,229 less temperature rise than when a gutta-percha carrier was combined with an injectable gutta-percha.230 Shrinkage of gutta-percha in these injectable gutta-percha systems does not appear to be different from the shrinkage of normally heated gutta-percha. When plasticized by heat, gutta-percha has a volume loss of approximately 2% after cooling.145
Frictional heat also can be used to soften gutta-percha. This was first suggested with the introduction of the McSpadden Compactor device (DENTSPLY Maillefer). This technique has undergone many variations, with the development of several compaction instruments. The heat generated may exceed safe levels compared to other heat compaction techniques.329 One such device, Quickfil (J.S. Dental, Ridgefield, CT), has the ability to obturate root canals comparable to lateral compaction.62 Volumetric changes in the gutta-percha after friction heat compaction are similar to other types of gutta-percha compactions using heat. The major observed problem was the inability of the heated gutta-percha to fill the entire canal system due to the presence of sealer in the apical third of the preparation. Rotary techniques, although still used by practitioners, have become less popular in many instances with the introduction of the new solid-core resin polymer sealers.
Although not injectable systems, Touch ’n Heat and System B (SybronEndo, Orange, CA), are involved with the placement and removal of gutta-percha from root canal systems using heat. Touch ’n Heat delivers a heated, pointed probe into a mass of gutta-percha, removing the material in small increments and down packing with pluggers after each removal. The gutta-percha is warmed approximately 5 mm ahead of the heating probe, and at a distance of 5 mm from the measured end of the master cone, a final down packing is made to move the remaining mass to the apex. The System B device is an outgrowth of the Touch ’n Heat and attempts to remove the greater bulk of gutta-percha to within 5 mm of the apex in one heated mass. These techniques are often combined with an injectable technique of obturation.
If endodontic therapy cannot be completed in one visit, the pulp space must be closed with a temporary restoration. The same is true whenever a root canal procedure is completed. This restoration must provide a satisfactory seal to prevent bacteria and fluids in the oral cavity from contaminating the pulp space. The restoration must have enough structural strength to withstand the masticatory forces and retain the occlusal seal. A literature search identified 28 materials that have been tested between 2000 and 2009 (Box 8-6). The most common such materials are IRM (DENTSPLY Caulk), TERM (DENTSPLY Caulk), Cavit (3M ESPE St. Paul, MN.) and Coltosol (Coltene Whaledent). IRM is a reinforced zinc oxide cement available as a powder-liquid mix in single-dose mixing capsules. Cavit is a premixed material composed of zinc oxide, calcium sulfate, glycol, and polyvinyl acetate, polyvinyl chloride, and triethanolamine. It sets upon contact with water. TERM is a filled composite resin that is light activated. When Cavit, IRM, TERM and Fermit (Ivoclar Vivadent, Schaan, Lichtenstein) (the latter two being light-cured preparations) were compared over a 21-day period, Cavit was found to be more resistant to leakage at 7 days.19,88 Coltosol and IRM were tested against two resins, and results showed they sealed statistically better than the resins. Coltosol is a non-eugenol preparation delivered by syringe.435 In another study,442 coronal microleakage was evaluated after thermocycling, comparing Cavit, IRM, and a polycarboxylate cement (Ultratemp Firm). There was no statistically significant marginal microleakage between the three; IRM also absorbed the dye into the bulk of the material. IRM has extensive marginal leakage of fluid, whereas Cavit seems to absorb fluid into the entire body of the restoration.18,209 These findings are surprising; however, because of its eugenol content, IRM may provide a bacterial barrier but allow leakage of other liquid substances (Figs. 8-74 and 8-75). Therefore, if Cavit or other types of relatively soft temporary cements are used, they must be placed at a thickness of at least 4 to 5 mm.419 If a more robust temporary restoration is required for longer than 1 week, the soft cement must be covered with a harder cement such as IRM, glass ionomer cement, or resin.
FIG. 8-74 Temporary filling of IRM (white I). The dye has penetrated the margins and dyed the content of the pulp chamber (P). The dentin (D) has been stained by the dye penetrating the margins.
FIG. 8-75 Temporary filling with Cavit. Dye has been absorbed into the body of the restoration (C) but has not penetrated to the pulp chamber (P), which is filled with white cotton. The inner part of the Cavit is unstained.
The temporary coronal seal of endodontically treated teeth will not prevent coronal leakage if left for long time periods.19 The interval between sealing the canal system and placing the core buildup is possibly more important than the material used. In a Colleagues for Excellence newsletter, the American Association of Endodontists stated that “restoration … should commence as soon as possible after RCT.”65 Whenever possible, the bonded core buildup should be placed at the obturation appointment.
Lasers are among the alternative methods used in endodontic treatment. Various laser wavelengths have properties that may be useful when applied to access cavity preparation, cleaning and shaping of root canal systems, and three-dimensional obturation procedures. The use of lasers for endodontics is becoming more predictable with the development of different wavelengths and radially emitting probes. One of the greatest strengths in using laser irradiation is its ability to cause a change in the hard tissue of the root canal space dentin. The change occurs in the morphology and physical aspects of dentin by melting and resolidifying dentin in a manner that closes the orifices of the dentinal tubules, which may harbor microorganisms and other organic pulpal remnants. However, this strength also turns out to be laser irradiation’s greatest weakness. This occurs because of the dentin’s location, confined to a space that is curved and cylindrical that cannot be viewed in a manner where the changes can be identified or visualized, such as can occur in cavity preparation procedures. A further weakness is the amount of energy needed to effect change of internal morphology. Intertubular dentin surfaces are in the shape of calcospherites rather than the relatively flat surfaces seen in extratubular coronal dentin, which can be easily visualized and affected by the laser. The amount of energy required for intertubular procedures generates increased temperatures that may cause harm to the attachment apparatus (cementum, periodontal ligament, and alveolar bone).
Dental lasers currently in use operate in several areas of the electromagnetic spectrum, including the infrared, visible, and ultraviolet ranges.374,375 Each laser wavelength in a particular range allows the device to target various tissues and carry out different procedures. Carbon dioxide (CO2) is highly absorbed by tissues with high water content, and neodymium-doped yttrium aluminum garnet (Nd:YAG) can be absorbed by vascular tissues, having greater effect on gingiva and dental pulp tissue, respectively.
Early attempts using lasers to carry out cleaning and shaping functions were less than successful. The Nd:YAG laser used a contact probe that simulated a hand instrument, but it was composed of a fused silica (glass); it could not be precurved and could not be seen radiographically if it separated within the root canal system. In addition, the probe emitted energy at its end rather than radially over a 360-degree range. The result was a preparation that was neither fully clean nor shaped. Other lasers used noncontact probes that emitted the laser beams through a system of mirrors in an articulated arm (wave guide with CO2). Their lack of contact with the dentin walls of the root canal system precluded a sense of touch available to the operator.194,248
Several laser systems are now available that appear to be useful in root canal system preparation. Necessary to the success of these procedures is an understanding of the effects of irradiation on the morphology of the inner dentin walls. Nd:YAG lasers have been extensively studied in the past several years. A study showed that at increased power, the system produced globular formations and melting and glazing typical of earlier studies with this wavelength.326 The same group found that root canal systems treated with NaOCl and EDTA with Nd:YAG irradiation demonstrated partial obliteration of dentin tubules and removal of smear layer.106 When an Nd:YAG laser was compared to a diode laser, scanning electron microscope (SEM) images showed fusion and resolidification of the dentin surface, more evident with the Nd:YAG group, but the diode group had more uniform changes.79 The erbium/chromium-doped yttrium scandium gallium garnet (Er,Cr:YSGG) laser has also been extensively studied over the past several years since its inception, but to date, the studies have not demonstrated the same results seen with older laser systems. Improvement in the use of these systems will lead to a device that accomplishes all the requirements of a well-cleaned and shaped system and aid in three-dimensional obturation.294
More recent investigations have indicated that lasers are effective when used in infected root canal systems. When patients were treated using a step-back technique, half the teeth were treated with the Nd:YAG laser using NaOCl and H2O2 irrigants. Tenderness to percussion was less at 1 week and 3 months in the laser-treated groups compared to controls.196
Removal of filling materials and broken files in retreatment cases is often difficult but effective if temperatures are controlled.434 A recent study compared the removal of gutta-percha using two solvents with an Nd:YAG system, which raised root surface temperatures 4° C.407 Laser energy alone was found to be effective, whereas solvents did not appreciably improve removal.
Dentin exposed to the Nd:YAG laser was evaluated using five different irrigation solutions. The surfaces of the teeth were examined using a SEM, while dispersive x-ray fluorescence spectrometry assessed mineral content. Calcium levels and calcium/phosphorus ratios decreased significantly with NaOCl solutions, suggesting changes at the molecular level. Surface examination showed that the lowest scores for root cleaning occurred with the use of EDTA and the Nd:YAG laser.154 The use of the Nd:YAG laser has been suggested as a more efficient way of handling this procedure. A study using the Nd:YAG laser using a flexible quartz fiber probe which is able to be concentrated in a specific area was used to remove gutta-percha and Sealapex or AH26 and was compared to use of Gates-Glidden drills and K-files. Results showed that the use of laser ablation was significantly shorter than conventional methods.11
Together with removal of obturation materials, lasers have been used in attempts to alter the dentin surfaces of root canal systems to create greater sealer adhesion. Single-rooted teeth were tested using an Nd:YAG laser. Black ink was used in one test group as an initiator, with two groups lased without ink. Controls were not exposed to laser energy. Results demonstrated leakage in all groups at both coronal and apical test areas.82 Using an Er:YAG laser, extracted teeth were tested to determine whether increased adhesion occurred between ZnOE and resin sealers. The resin-based sealer (Sealer 26) adhered better to dentin prepared with and without laser exposure than ZnOE-based sealers.367 Increasing the frequency and use of EDTA increased adhesion when a resin sealer was used with either an Nd:YAG laser or Er:YAG laser.368 When a 980-nm diode laser was tested, bond strength again increased for the resin sealer (AH26) but did not affect adhesion of Epiphany sealer.9
When India ink was used to absorb energy to cause an effect, the Nd:YAG laser was found to remove smear layer and reduce apical leakage in extracted, obturated human teeth.144 Others found the same results, showing that this laser wavelength was useful for reducing apical leakage in obturated root canal systems.55,236 The Nd:YAG laser was also used to seal the dentin surface after apicoectomy ex vivo.143,376,377
The use of laser energy in endodontics receiving the most attention relates to cleaning and shaping (instrumentation) and laser-assisted endodontic procedures involving the use of laser irradiation within the confines of the root canal system. As noted earlier, this may cause increased temperatures extending to the outer root surface of the tooth and lead to damage to the attachment apparatus. An Er,Cr:YSGG laser used to instrument the root canal system walls for 7 seconds found average rises of temperature on the outer root surfaces were less than 8° C. An 810-nm diode laser recorded temperatures at less than 7° C when energy input was alternated with periods of no energy input. A 910-nm diode laser recorded differing temperatures depending on what area of the root canal system was being affected. Highest temperatures were found in the apical third but were judged not to be in the range harmful to the attachment apparatus. An 810-nm diode laser was able to melt dentin, which resolidified and closed tubular orifices. Temperature rise was reported to be in the range of 1.6° C to 8.6° C, below those temperatures that would adversely affect the PDL.74
The permeability of root dentin is an important consideration in endodontic therapy, and the laser has been suggested as a means of removing smear layer and melting and solidifying the walls of the preparation. Comparison of the Nd:YAG device to an Er:YAG laser showed that the former had lessened radicular dentin permeability with various irrigation regimens.45 An in vitro study using extracted teeth that were inoculated with E. coli and E. faecalis found that Nd:YAG, Ho:YAG (holmium-doped yttrium aluminum garnet), and Er:YAG lasers eliminated 99% of the organisms without causing unfavorable temperature increases at the settings used.110
Temperature rise is an important consideration in the use of any laser energy. One study used 20 extracted human teeth and an Er:YAG laser at two irradiation intensities with water spray.193 A temperature increase of less than 6° C was recorded at the apical third and less than 4° C in the midportion of the root, suggesting that the thermal effect on periodontal tissues may be minimal.
Although no widespread agreement exists on the need to remove the smear layer in root canal preparations, the Er:YAG laser has proved effective at accomplishing this task. An Er:YAG laser was compared with a CO2 laser for ability to remove the smear layer.384 A comparison was also made with NaOCl, H2O2, and EDTA irrigation regimens. The Er:YAG laser was found to be the most effective of these methods at removing the smear layer. A more recent study, using radially emitting probes with Er:YAG and Er,Cr:YSGG lasers, increased the action of EDTA in removing thick, artificially created smear layers.131 An associated study found that the use of a radial-firing tip and Er,Cr:YSGG laser was a suitable tool for the elimination of microorganisms and removal of smear layer from root canal systems. A study in modification of root canal dentin found that by varying the electromagnetic wavelength, Er:YAG energy induced different modifications to the root canal surface, which may have some utility in preparation procedures.91
Sterilization of root canal systems has continued to be an aim of successful endodontic therapy. Chemical and other liquid medicaments have been utilized alone or in combination in an attempt to sterilize these systems, with no lasting effect. The idea of removing smear layer appears to be necessary in sterilization, and lasers have been suggested for that use and altering the intracanal dentin through melting and resolidification, causing closure of dentinal tubule orifices. An Er:YAG laser was used in posterior dogs’ teeth that were necrotic with chronic periradicular lesions. Group 1 was treated by biochemical preparation, and group 2 was also bioprepared but with laser irradiation. Teeth were sampled for anaerobes, aerobes, and total colony-forming units (CFU) 7 days post treatment. Results showed increased CFU for all microorganisms and significant reduction of anaerobes in group 1 and anaerobes and total CFU in group 2.219 Using an Er:YAG laser, other investigators404 found statistically similar results between laser-treated and conventionally treated groups. One study found that treatment with an Er:YAG laser showed effective antimicrobial action against E. coli and Staphylococcus aureus.337 The results were significantly better than those achieved with NaOCl. More recently, lasers were found to be effective against Candida albicans and four other test organisms. However, 70% of specimens lased 3 mm short of the apex remained infected.299
New laser systems using diodes are now available. In the presence of methylene blue or other dyes, diode lasers activate the dyes and cause photochemical reactions that produce reactive oxygen species. The process is termed photoactivated disinfection (PAD) and has the potential to eradicate persistent endodontic infections in cases where conventional methods may be unsuccessful. When used against four common root canal microorganisms (Fusobacterium nucleatum, Peptostreptococcus micros, P. intermedia, Streptococcus intermedius), significantly higher numbers were killed. When pathogens in planktonic phase and E. coli biofilms were sensitized with methylene blue and treated with red light, all organisms were eliminated. When energy levels were raised, 97% of E. faecalis was also eliminated. Other studies resulted in the conclusion that the use of photoactivated disinfection resulted in maximum elimination of microorganisms, especially E. faecalis.*
However, when comparing teeth treated conventionally, using rotary instrument NaOCl and EDTA versus the added use of Er:YAG laser system, neither method eliminated infection.185 An in vitro study using the Er:YAG laser system found that it was effective against six of the bacterial species examined. The numbers of viable cells in the biofilms were significantly decreased with atrophic changes in bacterial cells and biofilm density.285 When an Nd:YAG laser was used to kill microorganisms seeded on dentin discs with three endodontic pathogens, bacterial eradication occurred. However, when microcolonies were found in biofilms, bacterial eradication was reduced.
The Nd:YAG system was found to be more effective than the Er,Cr:YSGG laser, with the former demonstrating a reduction of 97% and 98% of organisms.417 Researchers94 found the Er,Cr:YSGG system to be less effective than a 3% solution of NaOCl, with the latter inhibiting growth of E. faecalis in all root canal systems tested. A later study found that the same system eliminated bacteria and smear layer debris in root canals, with only moderate elevation of temperature on the outer root surfaces.336 Others have demonstrated the same results when comparing the Er,Cr:YSGG system to NaOCl, using a radically emitting laser probe for 2 minutes; 99.7% bacterial reduction occurred with the laser.142 A high-powered 810-nm diode laser was used to examine the ability to achieve disinfection in deep layers of dentin. A group of 10 extracted teeth were treated with rotary files, 0.5% NaOCl, 17% EDTA, and irradiated, with a second group treated the same but without laser exposure. A third group was treated only with saline irrigation. Results showed 100% and 98.3% disinfection when compared with the control group.86 However, few of the investigators cited were willing to call the effects sterilization as opposed to disinfection. There are also differences in results that appear to be dependent on wavelength. Therefore, the use of lasers still remains somewhat controversial for use in sterilization of root canal systems.
Laser irradiation has been used in the preparation of root-end restorations. The root-end areas prepared with burs expose dentinal tubules, which may allow leakage of microorganisms and their byproducts. When preparations using an Er:YAG laser were compared to an Nd:YAG laser and high-speed burs, the lasers demonstrated lower infiltration indices than high-speed burs.287 In a similar study, results determined that a transversely excited atmospheric pressure (TEA) CO2 laser and an Er:YAG laser showed clean, smooth root-end preparation surfaces with sealed tubules and a reduction of permeability to methylene blue dye.143 An Er:YAG laser was compared to root-end ultrasonic preparation using three filling materials (MTA, Super EBA, IRM). The laser-treated areas demonstrated lower microleakage values for all three materials.188 When comparing use of a low-speed bur and an Er,Cr:YSGG laser for reverse root-end preparations using cyanoacrylate and MTA as filling materials, MTA and laser samples presented significantly higher permeability rates.426 Alternating Er:YAG and Nd:YAG irradiation preparations with high-speed hand piece preparation showed no differences between either group exposed to lasers and no differences between bur preparations in microleakage percentages.13 Diode lasers are available at much lower costs than other systems and can also be used for root-end preparations. Groups treated with a 980-nm laser were compared to nonlaser groups, demonstrating absence of smear layer and reduced leakage when compared with nonlased teeth.418 However, when used in combination with MTA for reverse filling, the laser radiation did not improve apical sealing.87
Laser energy may prove useful for treating diseases of the root canal system and periradicular regions, but years of successful endodontic care have demonstrated the value of several already proven methods. Until independently supported, reproducible studies are published in peer-reviewed journals—wherein findings match present marketing claims—the reader is advised to exercise prudent caution before embracing these newer laser technologies.
An explosion in knowledge and technology has created an exciting time in the specialty of endodontics. New instruments and materials seem to appear faster than clinicians can learn about the preceding versions. This has created an educational challenge for practitioners, universities, and manufacturers, requiring a greater degree of cooperation among these groups than ever before. Clinicians should only use those instruments and materials that have been shown safe and effective by independent studies.
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