Mandibular Second Molar
Anatomically, the mandibular second molar has many similarities with the mandibular first molar (Figure 13-23). The proportions of the crown and root are very similar to those of the mandibular first molar. The roots of the second molar may be straighter with less divergence from the furcation than in the first molar. The roots may be shorter, but there is no assurance that any of these differences will be manifested in any one tooth.
Buccolingual Section
The buccolingual section of the mandibular second molar demonstrates a pulp chamber and pulp canals that tend to be more variable and complex than those found in the mandibular first molar.
The pulp horns of the mandibular second molar are usually rather prominent (Figure 13-23, A, 1, 3, 5, 6, 8, and 9; D, 10, 13, 14, 15, 17, and 18), but some pulp horns may be small to nonexistent (Figure 13-23, A, 2, 4, and 7; D, 11, 12, and 16). The pulp chamber of the mesial root (Figure 13-23, A, 1, 3, 5, 6, and 8; D, 12, 13, 14, 16, 17, and 18) is well demarcated because of the presence of two canals. The pulp chamber (excluding the pulp horns) may be somewhat square (Figure 13-23, A, 1, 3, and 8; D, 10, 12, 14, 16, 17, and 18) or rectangular (Figure 13-23, A, 5 and 6; D, 13).
Figure 13-23 Mandibular second molar. A, Buccolingual section, exposing the mesial or distal aspect of the pulp cavity. This aspect does not appear on dental radiographs. B, Mesiodistal section, exposing the buccal or lingual aspect of the pulp cavity. C, Five cross sections at cervical line and four cross sections at midroot. D, Buccolingual section, exposing the mesial or distal aspect of the pulp cavity. E, Mesiodistal section, exposing the buccal aspect of the pulp cavity.
Two root canals are usually present in the mesial root, but only one may be present. The mesial canals may be large (Figure 13-23, A, 1; D, 17 and 18), medium (Figure 13-23, A, 3, 5, 6, and 8; D, 13), or small (Figure 13-23, D, 12, 14, and 16 ). The curvature of these canals may be severe (Figure 13-23, A, 1; D, 13), moderate (Figure 13-23, A, 5 and 8; D, 12 and 16 ), virtually absent (Figure 13-23, D, 14 and 18), or a combination of the aforementioned variations (Figure 13-23, A, 3 and 6; D, 17). Most of the canals appear to exit from the mesial root separately (Figure 13-23, A, 3, 5, 6, and 8; D, 12, 13, 14, 16, and 18), but some join just before reaching the apex so that a common canal exits from the apex (Figure 13-23, A, 1; D, 17).
The apical foramen usually appears to be located at the tip of the root (Figure 13-23, A, 1, 3, and 6; D, 12, 17, and 18), but some appear to exit slightly to the buccal or lingual aspect of the apex of the root (Figure 13-23, A, 5 and 8; D, 14 and 16).
The pulp chamber of the distal root of the mandibular second molar is not as easily identified because of the extremely large pulp canal that is usually present (Figure 13-23, A, 2, 4, 7, and 9; D, 11 and 15). One canal is usually present in the distal root, but two totally or partially separate canals are possible (Figure 13-23, D, 10).
Pulp horns may be present, but they are not nearly as prominent as in the mesial root (Figure 13-23, A, 2, 4, 7, and 9; D, 11 and 15) unless two canals are present (Figure 13-23, D, 10).
The pulp canal is usually very large in the mesiobuccal sections. The pulp canal may taper gently from the pulp chamber until the apical constriction (Figure 13-23, A, 2 and 7; D, 10 and 15), or an abrupt constriction of the canal may occur in the last 2 to 3 mm of the canal (Figure 13-23, A, 4 and 9; D, 11). The apical foramen often appears to be located at the tip of the root (Figure 13-23, A, 1, 4, 7, and 9; D, 10, 11, and 15).
Mesiodistal Section
The mesiodistal sections of the mandibular second molar are very similar to those of the mandibular first molar. However, the roots of the mandibular first molar tend to be straighter and closer together (less furcation deviation).
The pulp horns are usually prominent (Figure 13-23, B, 1, 2, 3, 5, 7, 8, and 9; E, 10, 11, 13, 15, and 18), but some are small or absent (Figure 13-23, B, 4 and 6; E, 12, 14, 16, and 17 ).
The pulp chamber is rectangular (excluding the pulp horns). The size of the chamber varies from very large (Figure 13-23, B, 1, 3, 4, 5, 7, and 9; E, 13 and 16) to very small (Figure 13-23, B, 2 and 8; E, 11, 14, 17, and 18).
The curvature of the mesial canal may be severe (Figure 13-23, B, 3, 6, 8, and 9; E, 11,14,16, and 17), moderate (Figure 13-23, B, 2, 4, and 7; E, 10, 13, 15, and 18), or essentially straight (Figure 13-23, B, 1 and 5; E, 12). The canals gently taper from the pulp chamber to the apical constriction.
The apical foramen usually appears to be located at the tip of the root (Figure 13-23, B, 2, 4 through 7, and 8; E, 11, 12, 13, 15, 17, and 18), but the foramen may appear to be located mesially (Figure 13-23, B, 3; E, 10, 13, and 16) or distally (Figure 13-23, B, 9; E, 14) on the root tip.
The distal canal may be slightly curved (Figure 13-23, B, 1 through 5, and 7; E, 11, 14, and 16 ) or straight (Figure 13-23, B, 4, 6, 8, and 9; E, 10, 12, 13, 17, and 18). The distal root may be slightly shorter than (Figure 13-23, B, 1, 2, 4, and 7), equal to (Figure 13-23, B, 3, 5, and 6; E, 10, 13, 14, 16, and 17), or longer than (Figure 13-23, B, 8 and 9; E, 11, 12, 15, and 18) the mesial root.
The distal canal is usually larger than the mesial canals (Figure 13-23, B, 3, 4, and 6 through 9; E, 11, 13, 15, and 16 ) but may be equal to the mesial canals (Figure 13-23, B, 1, 2, and 5; E, 12, 14, and 18). The distal canal tapers gently to the apex.
The apical foramen usually appears to be located at the tip of the root (Figure 13-23, B, 1 through 7; E, 10 through 13, 16, and 18), but the foramen may appear to exit mesially (Figure 13-23, B, 9) or distally (Figure 13-23, B, 8; E, 14, 15, and 17) to the apex of the root.
Cervical Cross Section
The cervical cross section of the mandibular second molar is similar to that of the mandibular first molar (Figure 13-23, C, 1 through 5). The outline form of the mandibular second molar is more triangular (rather than quadrilateral like that of the mandibular first molar) because of the smaller dimensions that are usually seen in the distal aspect of this tooth. The pulp chamber also tends to be triangular. The floor of the pulp chamber may have two openings, one mesially and one distally, which are centered within the dentin. If only one canal is present in the distal root, it will be centered within the dentin.
Midroot Cross Section
Midroot cross sections of the mandibular molars demonstrate that the mesial root is very broad buccolingually and narrow mesiodistally (Figure 13-23, C, 6 through 9). The outline form is kidney-shaped (Figure 13-23, C, 6 and 7) or slightly in the form of a figure eight (Figure 13-23, C, 8 and 9).
The canals may be totally separate (Figure 13-23, C, 9) or confluent (Figure 13-23, C, 6, 7 and 8), which makes it difficult to determine the presence of two mesial canals (Figure 13-23, C, 8). The distal root may be rounder than the mesial root, because the outline form of this root is usually oval (Figure 13-23, C, 6 and 9), but broad distal roots are also seen (Figure 13-23, C, 7 and 8). One canal is usually present in the distal root, but two canals are often present.
MANDIBULAR THIRD MOLAR
The mandibular third molar pulp cavities vary greatly (Figure 13-24). The pulp cavity resembles the second mandibular molar most, but the crown looks too large for the roots, which may be shorter and curved and tend to be fused together.
Buccolingual Section
In the buccolingual section, the pulp cavities of the mandibular third molar show a great deal of variation. Two roots and three canals are often present (Figure 13-24, B, 6 and 7 ), but two canals or two roots are also possible (Figure 13-24, C, 8 and 9). The presence of one canal and one root can also be found, but usually these teeth are not of much value for restorative purposes, because they have short roots that taper quickly.
Most mandibular third molars have prominent pulp horns (Figure 13-24, A, 1, 2, and 4 through 9; D, 10, 11, 12, 14, 15, 17, and 18), although others demonstrate small to nonexistent pulp horns (Figure 13-24, A, 3; D, 13 and 16).
The mesial roots of most mandibular third molars (Figure 13-24, A, 2 and 9; D, 10, 11, 13, and 14) demonstrate a square pulp chamber (excluding the pulp horns). The mesial root usually has two canals (Figure 13-24, A, 2, 5, and 9; D, 10,11, and 14), but a single mesial root can be found (Figure 13-24, D, 14). The canals may be very curved (Figure 13-24, A, 5 and 9; D, 10) or relatively straight (Figure 13-24, A, 2; D, 11 and 13) as they taper gently toward the apical constriction.
The apical foramen usually appears to be located on the tip of the root (Figure 13-24, A, 1 and 5; D, 10, 11, and 13), but it may be located buccally (Figure 13-24, A, 9; D, 14) or lingually to the tip of the root. If two canals are present, they usually possess separate apical foramina (Figure 13-24, A, 2 and 5; D, 10, 11, and 13), but some canals join in the apical region, exiting through a common foramen (Figure 13-24, A, 9).
The distal root of mandibular third molars possesses a very large pulp chamber and canal that are difficult to delineate into separate areas (Figure 13-24, A, 1, 3, 4, 6, 7, and 8; D, 12, and 15 through 18).
The pulp canals, which are very large (Figure 13-24, A, 1, 4, 6, and 7; D, 12, 15, and 18), may taper gently to the root tip (Figure 13-24, A, 4, 6, and 7; D, 16 and 18) or may demonstrate an abrupt constriction of the canal in the last few millimeters (Figure 13-24, A, 1; D, 12, 15, and 17).
Figure 13-24 Mandibular third molar. A, Buccolingual section, exposing the mesial or distal aspect of the pulp cavity. This aspect does not appear on dental radiographs. B, Mesiodistal section, exposing the buccal or lingual aspect of the pulp cavity. C, Five cross sections at cervical line and four cross sections at midroot. D, Buccolingual section, exposing the mesial or distal aspect of the pulp cavity. E, Mesiodistal section, exposing the buccal or lingual aspect of the pulp cavity.
The pulp chambers are square or rectangular (excluding the pulp horns). The pulp chambers, which are very small (Figure 13-24, A, 3 and 8), tend to show a constriction at the junction of the pulp chamber and canal, after which they taper gently to the apical constriction.
The apical foramen usually appears to be located at the tip of the root (Figure 13-24, A, 3, 6, 7, and 8; D, 16 and 17), but it may be located buccally or lingually to the root tip (Figure 13-24, A, 1 and 4; D, 15 and 18).
Mesiodistal Section
The pulp horns of the mandibular third molar may be prominent (Figure 13-24, B, 1 and 5; E, 10, 11, 12, 14, and 15), small (Figure 13-24, A, 4, 6, and 7; D, 17), or nearly absent (Figure 13-24, B, 2, 3, 8, and 9; E, 13, 16, and 18).
The pulp chambers are usually square or rectangular (excluding pulp horns) when viewed from the buccal aspect (Figure 13-24, B, 1 through 4, 7, and 9; E, 10, 12, 13, 15, 17, and 18), but they may be somewhat square (Figure 1324, B, 5; E, 14).
The degree of curvature of the mesial root may be slight (Figure 13-24, E, 13, single-rooted), moderate (Figure 1324, B, 1, 2, 5, 8, and 9; E, 11, 15, and 17), or severe (Figure 13-24, B, 3, 4, 6, and 7; E, 10, 12, 14, 16, and 18).
The canal within the mesial root may be large (Figure 13-24, B, 2 and 4; E, 10) or very small (Figure 13-24, B, 1, 3, 5, 8, and 9; E, 11, 12, and 14 through 18). The canals usually taper gently to the apical constriction. The apical foramen may appear to be located at the apex of the root (Figure 13-24, B, 1, 2, 3, 5, 6, 8, and 9; E, 11, 12, 14, 17, 18) or mesially (Figure 13-24, B, 7) or distally to the apex of the root (Figure 13-24, B, 4; E, 10 and 15).
The length of the mesial roots may be equal to (Figure 13-24, B, 2, 3, and 8; E, 10 and 11), shorter than (Figure 13-24, B, 5 and 9; E, 18), or longer than (Figure 13-24, B, 1, 4, 6, and 7; E, 12, 14, 15, and 17) the length of the distal root.
The distal canal may be larger than the mesial canal (Figure 13-24, B, 2 through 5, and 9; E, 14 and 18), but many are equal in size (Figure 13-24, B, 1, 6, 7, and 8; E, 10, 11, 12, 15, and 17). The distal canal gently tapers to the apical constriction (Figure 13-24, B, 1 through 8; E, 10 through 18).
The apical foramen may appear to be located at the apex of the root (Figure 13-24, B, 1 through 5, 7, and 9; E, 10, 11, 12, 15, 17, and 18), or it may be mesial (Figure 13-24, B, 8) or distal (Figure 13-24, B, 6; E, 14) to the apex of the root.
Some teeth show only one root with one or two canals. If only one canal is present (Figure 13-24, E, 13), the canal will be very large. If the third molar is multirooted, the canals will be much smaller (Figure 13-24, E, 16 ).
Cervical Cross Section
The cervical cross section demonstrates a variable outline form that may be rectangular (Figure 13-24, C, 1 through 4) or triangular (Figure 13-24, C, 5).
Midroot Cross Section
The mesial root, when present, is oval to figure eight in shape (Figure 13-24, C, 6 and 7). The distal root is oval (Figure 13-24, C, 6) or kidney-shaped (Figure 13-24, C, 7). If the roots are fused (Figure 13-24, C, 8) or only one root is present (Figure 13-24, C, 9), the canals are usually larger. The canals in the roots that are kidney-shaped or are in the form of a figure eight are more ellipsoidal.
Radiographs: Pulp Chamber and Canals
Visualization of the pulp chamber and pulp canal(s) by standard radiography or digital radiography provides the clinician with evidence to augment what has been found clinically. All teeth should be examined periodically radiographically and clinically. Knowing what might be expected anatomically about the pulp chamber and pulp canal(s), which has been considered in a previous section, helps when radiographs are taken. The radiographs in Figure 13-25, A through I illustrate normal pulp chambers and pulp canals. They are what are seen generally in the dental office, not the highly selected radiographs of the various teeth.
