Cervical Cross Section
The cross section at the cervical level shows the kidney-shaped outline form characteristic of the maxillary first premolar (Figure 13-11, C). A mesial developmental groove is usually present, giving this tooth its classic indentation. The pulp cavity may demonstrate a constriction adjacent to the developmental groove (Figure 13-11, C, 2, 3, 5, 6, and 9), or it may follow the general outline of the root surface (Figure 13-11, C, 1, 4, 7, and 8). Some roots demonstrate two separate root canals (Figure 13-11, C, 7 ), whereas a cross section of a three-rooted maxillary first premolar will show three separate canals (Figure 13-11, C, 3).
Figure 13-11 Maxillary first premolar. 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, Cervical cross section at the cementoenamel junction exposing the pulp chamber. These are the openings to root canals that will be seen in the floor of the pulp chamber. 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.
MAXILLARY SECOND PREMOLAR
Buccolingual Section
Most maxillary second premolars have only one root and canal. Two roots are possible, although two canals within a single root may also be found.
The pulp cavity may demonstrate well-developed pulp horns (Figure 13-12, A, 1, 2, 6, 7, and 8; D, 10, 11, 12, 14, 16, and 17 ); others may have blunted or nonexistent pulp horns (Figure 13-12, A, 3, 4, 5, and 9; D, 13, 15, and 18). The pulp chamber and root canal are very broad in the buc-colingual aspect of teeth with single canals. The pulp cavity does not show a well-defined demarcation between the root cavity and the pulp cavity because of the large buccolingual extent of the pulp cavity in the upper half of the tooth. In the apical half or third of the tooth, the pulp cavity often narrows abruptly (Figure 13-12, A, 1, 2, 4, 6, and 8; D, 11, 12, 13, and 18) and then tapers gently toward the apex. Some teeth possess dentinal islands in the apical third of the root; this situation essentially forces the clinician to treat these as teeth with two canals (Figure 13-22, A, 5; D, 15 and 17). Other maxillary second premolars have a canal that bifurcates at the apical third of the root (Figure 13-12, D, 10, 15, and 16). It should also be noted that buccal and lingual pulpal projections or fins are present at the level of the CEJ (Figure 13-12, A, 2; D, 12 and 18). Some teeth show a constriction at this same level (Figure 13-12, D, 10).
The apical foramen often appears to exit at the tip of the root (Figure 13-12, A, 1, 2, 5, 6, and 8; D, 11, 12, and 14 through 18). Some apical foramina appear to exit on the buccal aspect of the root (Figure 13-12, A, 4; D, 13), on the lingual aspect of the root (Figure 13-12, A, 7 and 9), or on both sides of the root tip (Figure 13-12, A, 3; D, 10 and 15).
Figure 13-12 Maxillary second premolar. 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, Cervical cross section at the cementoenamel junction exposing the pulp chamber. These are the openings to root canals that will be seen in the floor of the pulp chamber. 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.
Mesiodistal Section
The view of the pulp cavity in the mesiodistal section of the second maxillary premolar does not vary from that found in the maxillary first premolar. The pulp horns are blunted, and the pulp cavity tapers slightly from the occlusal aspect to the apex. The apical foramen may appear to be located off center of the root tip (Figure 13-12, A, 2, 6, and 9; D, 10 and 13) or appear to exit at the root tip (Figure 13-12, B, 1, 3, 4, 5, 7, and 8; E, 11, 12, and 14 through 18).
Cervical Cross Section
The cervical cross section of the maxillary second premolar is usually oval (Figure 13-12, C, 2 and 4 through 9), with some teeth having a kidney-shaped cross section (Figure 13-12, C, 1 and 3). The pulp cavity is centered in the root and may have a constriction in the middle of the canal space (Figure 13-12, C, 1, 4, 6, and 9), an entire separation (Figure 13-12, C, 2), or an elliptical pulp cavity (Figure 13-12, C, 3, 5, 7, and 8).
MAXILLARY FIRST MOLAR
Buccolingual Section
The buccolingual section of the maxillary first molar in Figure 13-13 shows the pulp cavities of the mesiobuccal and palatal root. These roots were chosen to demonstrate the pulp cavity anatomy because of the complexity of the mesiobuccal root. The distobuccal root is straighter and smaller and presents fewer variations in shape. The entire removal of the pulp is an impossibility in many maxillary first molar teeth because of the complexities of the root canal system (see Figure 13-7).
The maxillary first molar usually has three roots and three canals. The palatal root usually has the largest dimensions, followed by the mesiobuccal and distobuccal roots, respectively. The mesiobuccal root is often very wide buc-colingually and usually possesses an accessory canal commonly called MB2, which usually is the smallest of all the canals in this tooth.
Figure 13-13 Maxillary first 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.
The pulp horns are usually prominent in this tooth (Figure 13-13, A, 1, and 4 through 8; D, 10 through 13, and 15 through 18). The pulp chamber is somewhat rectangular (excluding the pulp horns) when viewed from the mesial aspect of the tooth. The palatal root usually has the largest canal (Figure 13-13, A, 1, 2, 3, 5, and 6; D, 10, 15, 17, and 18). The mesiobuccal canal is often very small (Figure 1313, A, 2 and 6; D, 10, 14, and 17), but some mesiobuccal canals may be very wide within a very wide root (Figure 13-13, A, 9; D, 12 and 13).
The presence of an unmarked MB2 is strongly suggested when the root canal appears to be off to one side (Figure 13-13, A, 2, 6, and 8; D, 10, 11, 13, 14, 15, 17, and 18).
The root canals of the wide mesiobuccal roots are widest at the midroot level and taper to a very fine diameter at the apical foramen. The palatal root canal and the mesiobuccal root canal of most teeth taper gently to the apical region, where they terminate at or near the apex. The apical foramen of the palatal canal may appear to exit at the apex (Figure 13-13, A, 1, and 4 through 9; D, 11 through 17), slightly lingually (Figure 13-13, A, 2; D, 10) or buccally to the root tip (Figure 13-13, A, 3; D, 18).
The apical foramen of the mesiobuccal canal may appear to exit on the tip of the root (Figure 13-13, A, 2 through 5, 7,, 8, and 9; D, 10, 12, 13, 17, and 18) or on the buccal (Figure 13-13, A, 1 and 6; D, 14 and 15) or lingual (Figure 13-13, D, 16 ) aspect of the root.
Mesiodistal Section
The mesiodistal section of the maxillary first molar includes the distobuccal root, which was not visible on the previously mentioned buccolingual section. The mesiobuccal root has a great tendency to possess a more curved root and canal than the distobuccal root (Figure 13-13, B, 1 through 8; E, 12, 14, and 15). Some of the buccal canals are relatively straight (Figure 13-13, E, 10, 11, and 13).
The pulp horns are very distinct from this view, with the mesiobuccal pulp horn usually appearing a little larger than the distobuccal pulp horn (Figure 13-13, B, 1 and 3 through 9; E, 10 through 13 and 15 through 18). In some teeth, the pulp horns are of equal size (Figure 13-13, B, 2; E, 14). The pulp chamber is somewhat square (if the pulp horns are excluded) when viewed from the buccal aspect. The demarcation of the root canal is much more distinct in the mesio-distal section. The root canals appear much smaller when viewed from the buccal or lingual aspect. The canals taper slightly as they approach the apical foramen. The apical foramen often appears to be located at the tip of the root (Figure 13-13, B, 1 through 7 and 9; E, 11, 14, 16, and 18), but the apical foramen may appear to be located on the mesial (Figure 13-13, E,10 and 17, mesial root only) or on the distal aspect of the root (Figure 13-13, B, 8; E, 12 and 13, distal root only).
Cervical Cross Section
The cervical outline form of the maxillary first molar is rhomboidal with rounded corners (Figure 13-13, C, 1 through 5 ). The mesiobuccal angle has an acute angle, the distobuccal angle is obtuse, and the lingual angles are essentially right angles. The orifices of the root canals have the following relation to the floor of the pulp chamber.
The palatal canal is centered lingually; the distobuccal canal is near the obtuse angle of the pulp chamber; the mesiobuccal root canal is buccal and mesial to the distobuc-cal canal, in what seems to be the extreme corner, positioned within the acute angle of the pulp chamber. If an accessory mesiobuccal canal (MB2) is present, it will be located lingual to the mesiobuccal canal. The canals of this tooth form a triangular pattern; a line drawn between the mesiobuccal canal and the palatal canal makes the base of the triangle, and the distobuccal canal, which is slightly closer to the palatal canal, makes the third point of the triangle. If a mesiobuccal accessory canal is present, it will be between the mesiobuccal and palatal canal just off an imaginary line between the two canals (Figure 13-13, C, 7, 8, and 9). The MB2 may even be mesial to a line connecting the mesiobuc-cal and the palatal canals (Figure 13-13, C, 8).
Midroot Cross Section
The midroot sections were added to the molar descriptions because some molars possess more than one canal within the root (Figure 13-13, C, 6 through 9). The palatal root is usually the largest root having a round outline form. The distobuccal canal is oval to round but much smaller than the palatal root. The mesiobuccal root is an elongated oval to kidney-shaped root with the indentation located toward the furcation. The root canals of the palatal and distobuccal root are oval to round, whereas the mesiobuccal canals are elongated (Figure 13-13, C, 6 and 9), elliptical (Figure 13-13, C, 7), or round (Figure 13-13, C, 8 and 9). The pulp canals may be extremely difficult to locate and instrument if secondary or irritation-induced dentin is abundant (Figure 13-13, C, 9). A thorough knowledge of the anatomy of the pulp chambers and canals is necessary if endodontic procedures are to be accomplished.
MAXILLARY SECOND MOLAR
Buccolingual Section
The buccal roots of the maxillary second molar are straighter and closer together than those of the maxillary first molar. The tendency for root fusion is greater in the second maxillary molar than in the first maxillary molar, but the palatal root is usually separate. Most often maxillary second molars possess three roots and three canals.
The mesiobuccal root of the maxillary second molar is not as complex as that formed in the maxillary first molar. The tendency for a very wide mesiobuccal canal is not present in the maxillary second molar. The presence of two canals in the mesiobuccal root is not as common in the maxillary second molar as in the maxillary first molar; however, it does occur (Figure 13-14, A, 5 and 7).
The pulp horns may be well developed (Figure 13-14, A, 1 through 3, 5, 8, and 9; D, 10 through 18) or virtually absent (Figure 13-14, A, 4, 6, and 7). The pulp chamber appears somewhat rectangular (excluding the pulp horns). The pulp canals gradually taper toward the apex until reaching the apical constriction, which occurs just before the apical foramen.
The mesiobuccal root canal of the maxillary second molar does not have the tendency to be extremely large, as is demonstrated in the mesiobuccal canal of the maxillary first molar. The apical foramen of the palatal root often appears to exit at the tip of the root (Figure 13-14, A, 1, 2, 3, and 5 through 8; D, 11, 13, 14, 16, 17, and 18), but it may exist on the lingual (Figure 13-14, A, 4 and 9; D, 15) or buccal aspect of the root (Figure 13-14, D, 10 and 12).
Mesiodistal Section
The mesiodistal section of the maxillary second molar is similar to that of the maxillary first molar. The buccal roots of the second molar are not as far apart as they are in the maxillary first molar, and their buccal roots have a greater tendency to be fused.
The pulp horns are usually well developed (Figure 13-14, B, 1 through 5, 8, and 9; E, 10 through 15 and 17). Some teeth demonstrate an obvious blunting or absence of the pulp horns (Figure 13-14, B, 6 and 7; E, 18). The mesiobuc-cal pulp horn is often larger than the distobuccal pulp horn (Figure 13-14, B, 1, 4, 5, 8, and 9; E, 10, 12, 13, 15, 17, and 18).
The pulp chamber appears much smaller in the mesio-distal section than in the buccolingual section. The pulp chamber is square (excluding the pulp horns) when viewed from the buccal aspect. The pulp canals gently taper from the pulp chamber to the apical constriction. The mesiobuc-cal pulp canal has a greater tendency to be curved than the distobuccal canal. The majority of the apical foramen appears to exit at the tip of the root (Figure 13-14, B, 1, 2, and 4 through 9; E, 10 through 16 and 18).
Cervical Cross Section
The cervical cross section of the maxillary second molar demonstrates angulations of the outline form that are more extreme than those found in the maxillary first molar. The mesiobuccal angle is more acute and the distobuccal angle is more obtuse than that found in the maxillary first molar, and the outline form of the pulp chamber reflects these differences.
Figure 13-14 Maxillary 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 or lingual aspect of the pulp cavity.
The mesiobuccal canal orifice is located farther to the buccal and mesial aspect of the pulp chamber (Figure 13-14, C, 4 and 5). The distobuccal canal more nearly approaches the midpoint between the mesiobuccal and palatal canal (Figure 13-14, C, 4). The palatal canal is located at the most lingual aspect of the root.
Because of the tendency for the roots to be fused or at least closer together, the orifices of the root canals are much closer together in the maxillary second molar than in the maxillary first molar (Figure 13-14, C, 4). In the cervical cross section, the triangularity of the floor of the pulp chamber is clearly demonstrated.
