Braz Dent J (1996) 7(1): 33-40 ISSN 0103-6440
| Introduction | Material and Methods | Results | Discussion | Conclusions | References |
The external and internal anatomy of 628 extracted, mandibular first and second molars was studied. The external anatomy was studied by measuring each tooth and by observing the direction of the root curvatures from the facial surface. The internal anatomy of the pulp cavity was studied by a method of making the teeth translucent.
Key Words: root anatomy, mandibular first molar, mandibular second molar.
The mandibular molars play a principal role in mastication and help to maintain the vertical dimension of the face, continuity of the dental arch, maintain the cheeks and tongue in position and maintain a healthy aspect by conserving the filling of the cheeks.
Pucci and Reig (1944) reported that the first mandibular molar is the only multirooted mandibular tooth that always presents two perfectly differentiated roots, one mesial and the other distal. Rarely will it present a third disto-lingual root. This third root may come from a division of the apical third of the mesial root or, less frequently, from the distal root.
Using periapical radiographs of 328 patients (105, Mongoloid origin; 106, Negro; 117, Caucasian), Ferraz and Pécora (1992) reported an incidence of three roots in 15.2% of these patients of Mongoloid origin, 7.5% of Negro origin, and 6.8% Caucasian.
Skidmore and Arne (1971) studied the internal anatomy of 45 mandibular first molars and observed that 6.7% presented two canals, 64.4% three canals and 28.8% four canals. They reported that the mesial root had three canals in 6.7% of the teeth while the presence of two canals in these roots was 93.3%. The distal root presented one canal in 71.1% of the teeth and two canals in 28.9% of the teeth.
The objective of this study was to analyze in vitro the external anatomy of mandibular molars in relation to size of tooth, number, direction, fusions and apical form of the roots, as well as the internal anatomy in relation to the number of canals in the mesial and distal roots.
The internal anatomy was studied after decalcification and clearing according to the method of Pécora et al. (1991).
Analysis of the roots of the mandibular first molars showed that 93.1% presented two roots, 1.7% fused roots and 5.2% three roots, either isolated or a result of a bifurcation of the main root (Figure 1b). In the mandibular second molars, 84.1% presented two separate roots, 15.9% fused roots and 1.5% three roots.
The distal root was single in 90.35% and 96.40% and partially bifurcated (apical third) in 9.65% and 3.60% of these first and second molars, respectively. The mesial root of the first molars had a single root in 68.42% and a partially bifurcated root in 31.58%. The second molars had a single root in 80.48% and a partially bifurcated root in 19.52%. Figure 1d shows the different forms that the distal root presented in mandibular second molars. The curvature direction of the roots of these mandibular molars is shown in Figure 1c and their respective percentages in Table 2.
The internal anatomy of the 390 mandibular molars after clearing is summarized in Tables 3 and 4. Figures 2 and 3 show the internal anatomy of a mandibular first molar and a mandibular second molar, respectively, with 3 or 4 canals.
Figure 1 - External anatomy of mandibular molars. a, Mandibular molars representing maximum and minimum lengths. b, External anatomy of teeth with 1 (fused), 2 and 3 roots. c, Types of root curvature in mandibular molars. d, Distal root forms, partially bifurcated and single.
Figure 2 - Internal anatomy of mandibular first molar with 3 and 4 canals. A and B, Mesial root presenting 2 canals and 2 foramina. C, Mesial root presenting 2 canals and 1 foramen. D, Distal and mesial roots presenting 2 canals.
Figure 3 - Internal anatomy of mandibular second molar with 3 canals (A and B). C, Note the presence of a lateral canal in the apical region and the presence of 4 canals.
This study shows that mandibular first and second molars present maximum, minimum and mean values similar to those reported by Woelfel (1990). It was also observed that the mesial side in both first and second mandibular molars presented slightly longer lengths than the distal side.
A majority of mandibular molars have two roots; however, we also found a third root in 5.2% of first molars and in 1.5% of second molars. Ferraz and Pécora (1992) observed that the incidence of three roots in human mandibular molars is greater in people of Mongolian origin than in those of Caucasian origin. This third root, when present, is located in the disto-lingual position (Pucci and Reig, 1944; Souza-Freitas et al, 1971; Cruzon, 1973; Walker and Quackenbush, 1985).
The direction of the curve of the root is fundamentally important for the choice of endodontic instrumentation. In the present study, the mesial root of the first molar was curved to the distal in 83% of the teeth and the distal root was straight in 78% of the teeth.
The data observed in this study are in accordance with that reported by Skidmore and Arne (1971); however, Fabra-Campos (1985), studying 145 mandibular molars in vivo, reported that 50.34% presented three canals, 47.59% four canals, and 2.07% five canals.
Stroner et al. (1984) published a clinical case of a mandibular first molar with five root canals distributed as follows: two in the mesial root, two in the disto-buccal root and one canal in the disto-lingual root.
Carlsen (1990) studied the morphology of extracted mandibular second molars with one root using a stereomicroscope. He observed that 42.1% presented a principal central canal in the form of a “C”, in 30.3% he found two principal canals located mesially and distally and in 23.7% there were three canals, one mesio-buccal, one mesio-lingual and one distal. The remaining 3.9% presented an extra canal in the disto-lingual position.
Thus, one can see that treatment of root canals is very complex. Researchers have shown over time that the anatomy of mandibular molars requires much attention since the number of roots and canals in these teeth is quite variable.
2. In the mandibular first molars studied, 6.5% had two canals, 32.4% had three canals and 21.1% had four canals.
3. In the mandibular second molars studied, 23.0% had two canals, 66.5% had three canals and 10.5% had four canals.
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Correspondence: Prof. Jesus Djalma Pécora, Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo, 14040-904 Ribeirão Preto, SP, Brasil. E-mail: email@example.com.
Accepted March 5, 1996
Electronic publication: September, 1996