Root Terminology

The anatomic root of a tooth is that part of the dentin covered by cementum and embedded in the alveolar bone; it begins at the cementoenamel junction. The end of the root is called the root apex, and the area surrounding the apex is the periapex. At the apex is an opening, the periapical foramen, where the blood vessels and nerves enter the pulp (root) canal.

Teeth have one, two, or three roots. Teeth with two or three roots have an unbranched portion called the root trunk. The area where the root trunk branches into two roots is the furcation or furca. The opening into the furcation is the furcation entrance (Figure 26-15). The most coronal portion of the furcation is the furcation roof, which is often more coronal than the furcation entrance. The area between the roots of a two- or three-rooted tooth is the interfurcal or interradicular area.

Figure 26-15 Root terminology: root trunk and furcation entrance.

(Courtesy former Department of Dental Hygiene, Marquette University.)

When the junctional epithelium has migrated apically and there is clinical attachment loss, portions of the anatomic root are included in the definition of a clinical crown, the unattached portion of a tooth. The concept of cervical, middle, and apical thirds is one that is used when discussing root anatomy.

Cementoenamel Junction

The cementoenamel junction (CEJ) or cervical line is a structure that the dental hygienist must be able to identify subgingivally with an instrument. In health the CEJ is located within 1 mm of the free gingival margin and is slightly covered by free gingiva. The CEJ is the fixed landmark in the identification of the amount of attached gingiva. Subgingival identification of the CEJ is a competency that requires knowledge of root anatomy, development of tactile skill, and experience. Tactile, nonvisual indicators of the CEJ might include the following:

Rougher texture of the root, as cementum is not as smooth as enamel.

Location between the convex cervical third of a crown and the flatter root surface.

Facial and lingual contours of the CEJ on anterior and premolar teeth are convex (Figure 26-16); on molars, the CEJ is much straighter.

An apical dip of the CEJ, called the cervical enamel projection (CEP), may be present toward the furcation on molars.

Proximal curvature of the CEJ is more pronounced on anterior than on posterior teeth.

○ On anterior teeth the curvature is V-shaped toward the incisal surface and more prominent on the mesial surface of incisors, especially the maxillary central incisor. (These areas are particularly difficult to instrument because of limited proximal access, which may contribute to incomplete deposit removal.)

Figure 26-16 Cementoenamel junction contours. A, Anterior teeth. B, Posterior teeth.

(Courtesy former Department of Dental Hygiene, Marquette University.)

Root Surface Texture

Surface textures of crowns and roots differ owing to different degrees of mineralization of enamel and cementum and how it is altered by oral biofilm, as follows:

Enamel (anatomic crown) is analogous to glazed pottery—smooth, hard, and glassy when unaltered.

Cementum (anatomic root) is not as smooth, hard, or glassy but is more porous. Cementum can be altered by:

○ Loss of periodontal attachment, plaque by-products, and unintentional injury by client or clinician

○ Root planing using ultrasonic instruments and curets

Scaling instruments with pointed tips should not be used on root surfaces.

During root planing, varying amounts of cementum are removed and dentin may be exposed, resulting in dentinal hypersensitivity (see Chapter 38).

Root Shapes

Roots of permanent teeth vary from one individual to another. For placement of instruments on root surfaces, the following are considered:

Morphology of the individual root

Position of the teeth in the alveolar bone

Interference from crown contours

Client’s periodontal status

Instrument design

Teeth with One Root (see Table 26-1 and Figure 26-17)

All anterior teeth and maxillary second and mandibular premolars have one root. Characteristics of teeth with one root include the following:

Cone shape with facial, lingual, and proximal surfaces converging (tapering) apically with different degrees of convergence

Widest in the cervical third and tapering to a small apex

Distal inclination from a facial (lingual)view

Cervical cross-sections (i.e., crown cut off the root horizontally at CEJ) are triangular, ovid, or elliptic (see Figure 26-17, A and B):

○ Triangular: Appears to be three-sided with broad (equal) facial, mesial, and distal surfaces and a very narrow lingual surface. Proximal surfaces converge markedly to the lingual surface (e.g., maxillary central incisors). Proximal surfaces of roots that are narrower on the lingual than the facial surface (both triangular and ovoid root shapes in cervical section) are more readily instrumented from the lingual surface because there is more room.

○ Ovoid: Oval, “egg-shaped,” with facial surface broader than lingual surface; proximal surfaces are equal and broader than either facial or lingual surface (e.g., canines).

○ Elliptic: Proximal surfaces are relatively equal; facial and lingual surfaces are approximately the same size but smaller than the proximal surfaces. Root dimensions are broad from the facial and lingual view, and narrower from the mesial and distal view. Roots of mandibular incisors and maxillary premolars are elliptic in cervical cross-section.

Figure 26-17 Root shapes in cervical cross-section. A, Maxillary teeth: triangular, elliptic, and ovoid. B, Mandibular teeth: elliptic and ovoid.

(Courtesy former Department of Dental Hygiene, Marquette University.)

In midroot sections, shapes of roots are generally the same as in cervical sections, though smaller.

Roots that are triangular or ovoid in cross-section have smaller lingual than facial surfaces because of proximal surface convergence (taper) toward the lingual surface. Cervical cross-section shapes may be altered by the presence of root concavities. The cervical half of a conical-shaped root has more than 50% of the root surface area because of the convergence of surfaces apically.

Teeth with Two or Three Roots (see Table 26-1)

For periodontal assessment and instrumentation, each root of a multirooted tooth must be treated individually—that is, a two-rooted tooth is like having two single-rooted teeth. In addition, the complexity of unbranched root trunks and furcas must be considered. Posterior teeth are more difficult to reach, and the clinician’s competence influences the therapeutic outcome. Characteristics of the teeth with more than one root are as follows:

Maxillary first premolars

○ Generally have two roots (facial and lingual)

○ Furcations on the mesial and distal sides (Figure 26-18)

Maxillary molars

○ Have three roots, mesiobuccal, distobuccal, and palatal (lingual)

○ Furcations on the buccal side between the mesiobuccal and distobuccal roots, on the mesial side between the mesiobuccal and palatal roots, and on the distal side between the distobuccal and palatal roots (Figure 26-19)

○ Radiographic assessment of the roots can be compromised owing to the complex root anatomy of the mesiobuccal, distobuccal, and palatal roots (radiographs show the image only from a facial or lingual view).

Mandibular molars

○ Have two roots, mesial and distal

○ Furcations on the buccal and lingual surfaces between the mesial and distal roots (Figure 26-20)

○ Roots on second molars more likely to have longer root trunks, be closer together, and have more distal orientation.

Cervical cross-sections of maxillary and mandibular molar roots are larger and more difficult to describe (see Figure 26-17).

○ Both may show slight depressions where furcations or proximal root concavities begin.

○ The root trunk of maxillary molars has more equal sides; appears somewhat rhomboidal in shape, with the more prominent “corner” being the mesiobuccal.

○ The root trunk of the mandibular molar is more rectangular in shape, with the mesial distal width being greater than the facial lingual width.

○ Generally, roots are elliptic in cervical cross-section after the furcation.

Figure 26-18 Mesial furcation on a maxillary first premolar.

(Courtesy former Department of Dental Hygiene, Marquette University.)

Figure 26-19 Furcations on a maxillary (first) molar.

(Courtesy former Department of Dental Hygiene, Marquette University.)

Figure 26-20 Furcations on a mandibular (first) molar.

(Courtesy former Department of Dental Hygiene, Marquette University.)

Furcations

Furcations generally begin as a shallow depression on the root trunk that gradually opens into a space between the roots; this opening may be too narrow for instruments. Initially, furcations can be felt by the working end of a dental explorer and then, as the space widens, by a Nabers probe. Furcations are very difficult to access with traditional scaling and root planing instruments, as their working ends are too large. Rather, precision thin and furcation inserts for ultrasonic instruments, microbladed and minibladed curets with smaller and narrower working ends, curets with extended shanks, and furcation curets are used to debride furcation areas (see Chapters 24, 25, and 28). A very narrow furcation entrance can be surgically enlarged with burs by a periodontist. Furcation characteristics are as follows:

The more cervical the furcation, the more stable the tooth because of root divergence (separation).

Furcations are generally more cervical on first molars; root trunks of first molars are shorter than root trunks of second or third molars.

Furcations close to the CEJ are more likely to become involved with periodontal disease, though access for instrumentation is easier and therefore such disease has a more favorable post-therapy prognosis.

Furcations close to the apex are less likely to result in furcation involvement, though instrument access is more difficult and post-therapy prognosis is less favorable.

Furcation involvement occurs when there is a loss of attachment apical to the furcation and is classified according to extent (see Chapter 17, Table 17-5 for classification of furcations).

It is important to know the expected location of a furcation in both horizontal and vertical directions. Horizontally, most furcations are located midway on the root trunk. The mesial furcation of a maxillary first molar is generally located more toward the lingual surface in a horizontal direction, and therefore instrumentation of the mesial furcation of this tooth is easier from the lingual approach (see Figure 26-19). Vertically, furcations on a maxillary premolar are in the apical third to half (see Figure 26-18). Furcations on a maxillary molar are near the junction of the cervical and middle thirds of the root (see Figure 26-19). Furcations on maxillary second and third molars are more apical; furcations on a mandibular first molar are apical to the cervical one fourth of the root, making this the shortest root trunk in the permanent dentition and the most likely to experience furcation involvement (see Figure 26-20). Furcations on the mandibular second and third molars are more apical than on the first mandibular molar.

Root Concavities

Root concavities are shallow vertical depressions on the surfaces of roots. They protect the tooth from forces that could rotate it in its alveolus, and provide more root surface area and direction for periodontal fiber attachment. Root concavities complicate root instrumentation and access and make it more difficult to place the cutting edge of the instrument on the root surface. Root concavities most frequently occur on proximal root surfaces (proximal root concavities) (see Figure 26-15). Maxillary first molars have a concavity on the lingual surface of the palatal root (lingual concavity) (see Figure 26-19). Molars may have root concavities on a surface of their root toward the furcation (furcal concavities).

Tooth Alignment

Assessment of the alignment of the teeth within an arch is essential to adapting instruments subgingivally. Tooth size, prominence of its crown, contact areas, and the convergence of root surfaces determine the amount of space and interproximal bone in both health and disease. In health the mandibular anterior teeth have the narrowest amount of space and bone because they are very narrow. In disease, if loss of bone is accompanied by gingival recession, there is more access for instrumentation. When teeth have insufficient space, crowding occurs, making instrument positioning difficult. Teeth with close or altered root proximity may have minimal or no proximal space and long proximal root contact, which may significantly influence oral hygiene, periodontal health, and subgingival instrumentation.

The position of teeth within the alveoli also is a factor in root instrumentation. Axial positioning is the relationship of an imaginary vertical line representing the long axis of a tooth in relationship to a horizontal plane. This concept is diagrammed in Figure 26-21. The functions of this positioning are to bring the maxillary and mandibular teeth into an interarch relationship that facilitates incision and mastication and distributes forces throughout the bones of the skull.

Figure 26-21 Axial positioning of the maxillary and mandibular teeth in an anterior and lateral view. The slant of the roots along their long axis is shown by vertical lines that have been extended to represent the direction of the slant in both faciolingual and mesiodistal directions.

(From Dempster WT, Adams WJ, Duddles RA: Arrangement in the jaws of the roots of the teeth, J Am Dent Assoc 67:779, 1963.)

Following the vertical lines in Figure 26-21, it is clear that in a faciolingual dimension the roots of all the teeth except the mandibular posteriors have a more lingual inclination than do the crowns. Mandibular posterior crowns are more lingually inclined than roots that are more facial in orientation, making plaque biofilm removal in this area especially difficult for clients.

Again following the vertical lines in Figure 26-21, in a mesiodistal dimension the roots of the canines, premolars, and molars have a distal inclination, which is more pronounced posteriorly. Roots of the incisors do not incline distally.

Fused Roots, Fusion, and Concrescence

Molar roots may be fused together, especially second and third molar roots, and are a result of limited space during tooth development (Figure 26-22). Fused roots frequently can be observed on radiographs.

Figure 26-22 Fused roots on a mandibular and maxillary molar.

(Courtesy former Department of Dental Hygiene, Marquette University.)

Teeth may be joined together in an anomaly called fusion, in which two tooth buds fuse together during development and form one large tooth with a large crown and a single root that has two pulp canals. This needs to be confirmed by radiographs. Concrescence occurs when two adjacent teeth become joined by cementum after they have been formed.

Accessory Roots

Accessory roots are extra roots. Sometimes the mandibular permanent canines are bifurcated into facial and lingual roots in the apical third (Figure 26-23). Maxillary first premolars can have three roots—two buccal and one lingual. Buccal roots are very thin, which makes treatment difficult if periodontal disease is present. Third molars sometimes have extra roots. Accessory roots may be assessed via radiographs and are instrumented only if the attachment level is apical to their occurrence.

Figure 26-23 Accessory roots on a mandibular canine and maxillary first premolar. DB, Distobuccal; F, facial; L, lingual; MB, mesiobuccal.

(Courtesy former Department of Dental Hygiene, Marquette University.)

Palatogingival Grooves (Palatoradicular Grooves)

A palatogingival groove (Figure 26-24) extends apically from the lingual concavity of the crown of a permanent maxillary incisor, usually the lateral incisor, onto the root, often resulting in an isolated, narrow pocket. This groove provides challenges in instrumentation, is highly plaque retentive, and is susceptible to periodontal disease.

Figure 26-24 Palatogingival groove on a maxillary lateral incisor.

(Courtesy Gay Derderian, BA, DDS, MSD, Marquette University School of Dentistry.)

Hypercementosis

Hypercementosis, the excessive formation of cementum in the apical third to half of the tooth after the tooth has erupted (Figure 26-25), may be caused by trauma, chronic inflammation of the pulp, or metabolic disturbances. It is assessed radiographically. If areas of hypercementosis are exposed with apical migration of the junctional epithelium, decisions about the extent of root instrumentation will be more difficult.

Figure 26-25 Hypercementosis.

(Courtesy former Department of Dental Hygiene, Marquette University.)

Cervical Enamel Projections

Cervical enamel projections (CEPs) are apical extensions of the CEJ toward the furcation of a molar (Figure 26-26). CEPs are classified by degree of extension, as follows:

Grade I CEPs slightly extend toward the furcation and occur frequently.

Grade II CEPs approach the area of root separation.

Grade III CEPs extend into the furcation.

Grade IV CEPs are the same as Grade III CEPs, plus the furcation is visible because of recession.

Figure 26-26 Cervical enamel projection on a mandibular first molar.

(Courtesy former Department of Dental Hygiene, Marquette University.)

Periodontal attachment loss is more likely in CEP areas because periodontal fibers do not form the same type of attachment to enamel as to cementum. Most isolated furcation involvements in otherwise healthy dentitions are found to be related to CEPs. A CEP can be removed surgically to expose dentin and facilitate reattachment of periodontal fibers.

Enamel Pearls

Enamel pearls, most frequently seen on maxillary molars, are “droplets” of enamel in the furcation area (Figure 26-27). They are thought to be due to a genetic error in the developing root sheath as it reaches the area of furcation. As periodontal fibers will not attach to enamel, enamel pearls may encourage periodontal disease. Exploration of an enamel pearl can sometimes be puzzling if it is not visible on radiographs, because it may feel like subgingival calculus.

Figure 26-27 Enamel pearls near the furcation of a maxillary molar.

(Courtesy former Department of Dental Hygiene, Marquette University.)

Dilaceration

Dilaceration is a sharp bend in the root surface caused by the displacement of the root during tooth development (Figure 26-28).

Figure 26-28 Dilaceration.

(Courtesy former Department of Dental Hygiene, Marquette University.)

See Procedure 26-1 on root morphology and implications for root instrumentation.