External and Internal Anatomy of Mandibular Molars

 
Luciane F. da COSTA ROCHA1
Manoel D. SOUSA NETO1
Sandra Rivera FIDEL2
Wanderley F. da COSTA1
Jesus Djalma PÉCORA1
 
1Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brasil
2Faculdade de Odontologia, Universidade Estadual do Rio de Janeiro, Rio de Janeiro, RJ, Brasil

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.

Introduction

The development of various areas of odontology requires precise study of the morphology of human teeth with the objective of providing better oral health restoring stomatognathic function.

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.

Material and Methods

A total of 232 intact mandibular first molars and 396 mandibular second molars were studied. Observation of the number of roots, direction of curvature, fusion and apical root form were carried out by direct inspection and with the help of a 10X magnifying glass (Wild M7A). The length of these teeth was measured with a digital pakimeter (Tesa, Switzerland) using the apex of each root and its respective cusp as reference.

The internal anatomy was studied after decalcification and clearing according to the method of Pécora et al. (1991).

Results

Table 1 shows the total length of the roots of the mandibular first and second molars. Two mandibular first molars which represent the maximum and minimum values obtained in this study are shown in Figure 1a.

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.

Discussion

Studies of the internal and external anatomy of teeth have shown that anatomical variations can occur in each group of teeth, in each person and in general in each racial group. There is that which can be called normal, in other words, that which is present in most cases, but anatomical alterations ought to be expected as a frequent possibility. Thus, the endodontist must be fully aware of dental morphology in order to better serve his client.

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.

Conclusions

1. We found that 93.1% of the mandibular first molars had two roots, 1.7% had fused roots and 5.2% three roots. In the second molars, we found that 84.1% had two roots, 15.9% fused roots and 1.5% three roots.

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.

References

Carlsen O: Root complex and root canal system: a correlation analysis using one-rooted mandibular second molars. Scan J Dent Res 98: 273-285, 1990

Cruzon MEJ: Three-rooted mandibular permanent molars in the Keewatin Eskimo. Can Dent Assoc 37: 71-73, 1971

Fabra-Campos H: Unusual root anatomy of mandibular first molars. J Endodon 11: 568-572, 1985

Ferraz JAB, Pécora JD: Three-rooted mandibular molars in patients of Mongolian, Caucasian and Negro origin. Braz Dent J 3: 113-117, 1992

Pécora JD, Saquy PC, Sousa Neto MD, Woelfel JB: Root form and canal anatomy of maxillary first premolars. Braz Dent J 2: 87-94, 1991

Pucci FM, Reig R: Conductos Radiculares. Barreiro y Ramos, Montevideo, Vol. I, 1994

Skidmore AE, Arne M: Root canal morphology of the human mandibular first molar. Oral Surg 32: 778-784, 1971

Sousa-Freitas JA, Lopes ES, Casati-Alvares L: Anatomic variations of lower first permanent molar roots in two ethnic groups. Oral Surg 31: 274-278, 1971

Stroner WF, Remeikis NA, Carr GB: Mandibular first molar with three dental canals. Oral Surg 57: 554-557, 1984

Walker RT, Quackenbush LE: Three-rooted lower first permanent molars in Hong-Kong Chinese. Br Dent J 159: 298-299, 1985

Woelfel JB: Dental anatomy: its relevance to dentistry. 4th ed. Lea and Febiger, Philadelphia, 1990

Correspondence: Prof. Jesus Djalma Pécora, Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo, 14040-904 Ribeirão Preto, SP, Brasil. E-mail: pecora@usp.br.

Accepted March 5, 1996
Electronic publication: September, 1996

BACK TO CONTENTS