SciELO - Scientific Electronic Library Online

vol.13 issue2Effect of cleaning agents and retrofilling materials in apical microleakageEfficiency of chemical auxiliaries in the root canal instrumentation author indexsubject indexarticles search
Home Pagealphabetic serial listing  

Services on Demand




Related links


Revista de Odontologia da Universidade de São Paulo

Print version ISSN 0103-0663

Rev Odontol Univ São Paulo vol.13 n.2 São Paulo Apr./June 1999 



Evaluation of the anatomical alterations of lower molars mesial root’s apical third


Avaliação das alterações anatômicas do terço apical da raiz mesial de molares inferiores


Izabel Cristina FRÖNER*
Cristina Aparecida IMPERADOR**
Luiz Gustavo de SOUZA***



FRÖNER, I. C.; IMPERADOR, C. A.; SOUZA, L. G. Evaluation of the anatomical alterations of lower molars mesial root’s apical third. Rev Odontol Univ São Paulo, v. 13, n. 2, p. 149-152, abr./jun. 1999.

The anatomical apex of the mesial root of the lower molars presents a morphological complexity related to the number and shape of the root canals as well as of the apical foramen and isthmus  presence. The knowledge of the complexity of the endodontic system of the molar root area is essencial to select more carefully the best instrumentation and obturation technique, to obtain a more successful endodontic therapy.

UNITERMS: Molar; Tooth root; Anatomy.




For a successful endodontic treatment, the knowledge of the anatomy of the root canal is essential. During the endodontic procedures, the professional can count only on theoretical knowledge, his tactile sensitivity and radiographic images with their inherent limitations7.

In the past, endodontists worked with less information about the internal anatomy of root canals, what in most of the cases could mean therapeutical failure. Increased learning of teeth internal root canal anatomy allowed several changes in endodontic therapies, resulting in remarkable increases in the success rate10. There is not a unique technique that reaches all the endodontic system8.

Various methods were used to study root canal anatomy, such as: macroscopic evaluation9,10; microscopic evaluation4,13; macroscopic sections and in different planes10,13,17, "in vitro" and "in vivo" radiographs7,8,20; vulcanite injections12; resin injections2,17; diaphanization1,5,14,21 and magnetic ressonance3.

HESS12 (1925) and BARCKER et al.2 (1974) observed major anatomic variations in the first lower molar, while DONALD; WILLIAN6 (1984) concluded that the second lower molar shows this alterations more frequently, beforehand POMERANZ et al.16 (1981) pointed out that there were no significant anatomical differences between first and second lower molars.

Lower molars show a complex internal anatomy with major variations in the mesial root2. Morphologically, the mesial root of lower molars is considered as a fusion of two distinct roots with two root canals. The mesial roots of lower molars can be independent in the entire root length or join at different levels with variations in number, shape and localization of the apical foramen1,11.

The mesial root can show a root canal with a single apical foramen (12-58%); two canals and two apical foramens (60-13.7%); two canals and one apical foramen (73-20.6%) or yet, one canal with two apical foramens (65%)4,5,11,13,14,15,18,21,22.

Differences between the results can be related to the various methods used in the evaluation of the anatomical alterations present in lower molars, due to its complexity and different classifications of the observed alterations.

The aim of the present study is an "in vitro" evaluation of the anatomical alterations in the human lower molar mesial root apical, through stereoscopic observation.



Sixty-eight recently extracted lower permanent human molars were used, conserved in a 10% formaldehyde solution. The teeth were sectioned longitudinally with carburundum discs, achieving the separation of the mesial roots.

The roots were included in a block of self polymerizing resin, sliced by a machine which uses a 300 micrometers diamond disc with water jet and micrometric screw. In average, four cross sections were obtained from each specimen, beginning 1 mm from the root apex and going to the cervical direction, with an average thickness of 500 micrometers. These sections were then polished with sandpapers (400, 500 and 600 grit) in a Politrix Struers DP-9U2 semi-automatic 520 grams machine, with a fixture to obtain 200 micrometers thick sections.

The sections were evaluated in a Carl Zeiss-Jena stereoscopic microscope, with a 20 x final enlargement, enough for a panoramic analysis of the section.



It was observed that 99% of the cases of lower molars had a single root, with two or one canals with a single or independent apical foramen. Only one case presented 2 roots and 2 totally independent canals. During the evaluation of the apical third of the 68 lower molars, it was observed that a variation in the number of root canals occurred as the apex got closer (Table 1, Figure 1F) as well as in its anatomical shape (Tables 2 and 3, Figures 1D, E, F).

Table 1 shows the percentage of canal numbers in the apical third of the mesial root of lower molars.


TABLE 1 – Percentage of canal number in the apical third of the lower molars mesial root.
a08t1.gif (2618 bytes)



a08f1.gif (38995 bytes)
FIGURE 1- Sections of the apical third of lower molars mesial roots. (A) the presence of two independent canals; (B) two independent canals with isthmus in 1 mm from the apex; (C) two canals with a isthmus between them (arrows); (D,E) single stripe shaped canal ending round; (F) two canals joining in one.


Table 2 shows in percentages the variation of anatomical conditions of the mesial root of lower molars when there are two root canals. In the apical third these canals can be totally independent (Figure 1A) or display an isthmus between them (Figures 1B, C-arrows).


TABLE 2 –Percentage of anatomic alterations, in the apical third, of lower molars mesial roots with two canals.

a08t2.gif (2719 bytes)


Table 3 shows in percentages the anatomical variation in canal shape when the mesial root of the lower molars has a single canal. Root canals can be rounded or vestibule-lingual lengthened ("band shape"). Anatomical canal shape is altered, tending to become circular, as it reaches the root apex (Figures D, E).


TABLE 3 – Percentage of the anatomic alterations in apical third of lower molars mesial root with a single canal.

a08t3.gif (2876 bytes)



Morphological alterations in the shape of root canals evaluation, number, diameter and ramifications of the main canal have been observed, reaffirming the complexity of the endodontic system. The present study supports that the lower molars mesial root morphology is indeed complex1,2,14.

The results of Table 1 reinforce that at a distance of 4 mm from the anatomical apex the lower molars mesial root is likely to have 2 root canals (67.6%), which join or get closer to the apex (42.6%) in one apical foramen (Figure 1F). Our results are matching other authors’ results2,4,10,18. The percentile differences shown in the results can be related to the range of methods used with the evaluation, different types of classification and/or different number of teeth in the sample.

In the studied sample, in the presence of two root canals, 41.3% of the cases showed an isthmus joining the two mesial canals 4 mm from the anatomic apex. It is easy to observe in table 2 that as the apical extreme gets closer there is a decrease in an isthmus presence (20.7%) and the independent canal numbers raise (79.3%). Other researchers observed the presence of an isthmus between the canals of lower molars mesial root as well, though they used different methodology10,18,19. This anatomical alteration supports that it is very important that the professional uses abundant irrigation during the root canal preparation to remove pulp or necrotic tissue that endodontic files can’t reach.

In such cases when a single canal is present in the root (Table 3), it was observed that 50% of the cases showed a vestibule-lingual lengthened anatomical shape 4 mm from the apex, and at a 1 mm distance we could observe 79.5% circular root canals. This alteration in the root canals anatomical shape is a difficulty that this tooth presents, to its bio-mechanical preparation and final obturation.

In multirooted teeth, orthoradial radiographs do not allow the clear visualization of two canals in the same root, although a radiograph obtained in different planes, mesial or distal, will allow to distinguish two root canals and the visualization of anatomic alterations in a vestibule-lingual aspect. The radiographs present their own limitation in the recognition of the vestibule-lingual aspects of a root canal, and it is in this plane that root canals show the major number of alterations and further, the superposition of other tissues like dentin, cement and alveolar bone occurs15.

The knowledge of anatomic alterations in lower molars mesial roots is essential for an accurate choice of the best technique of instrumentation and obturation of these roots to achieve an increased rate of endodontic therapeutical success.



Supported by the methodology used in the 68 lower molars mesial roots apical 4 mm we can conclude that:

1. in 99% of the cases we found a single root, with 57,4% presenting a single canal and 42% with two canals, 1 mm distant from the anatomical apex.

2. 4 mm distant from the anatomical apex 32,4% of the cases presented a single canal and at 1 mm from the anatomical apex 57,4% presented a single apical foramen.

3. 4 mm distant from the anatomical apex 67,6% of the cases presented two canals that joined in the proximity of the apex ending (42,6%).

4. when this root presents two root canals, there is a isthmus linking these canals in 41,3% of the cases at 4 mm distance from the anatomical apex and 20,7% at 1 mm distance from the anatomical apex.

5. in such cases of a single canal, at 4 mm distance from the anatomical apex 50% are vestibule-lingual lengthened ("stripe shape") which turns to a round shape at 1 mm distance from the anatomical apex (20,5%).



FRÖNER, I. C.; IMPERADOR, C. A.; SOUZA, L. G. Avaliação das alterações anatômicas do terço apical da raiz mesial de molares inferiores. Rev Odontol Univ São Paulo, v. 13, n. 2, p. 149-152, abr./jun. 1999.

A presente pesquisa analisa in vitro as alterações anatômicas dos 4 mm apicais de 68 raízes mesiais de molares inferiores permanentes humanos, utilizando-se de microscópio esterioscópio. Cada raiz foi incluida em bloco de resina acrílica autopolimerizável, cortada transversalmente à partir de 1 mm apical obtendo-se 4 cortes em sentido cervical. Os resultados demonstraram a complexidade anatômica do terço apical da raiz mesial dos molares inferiores, com a presença de um ou dois canais radiculares. Quando da presença de dois canais radiculares estes podem apresenta-se totalmente independentes em toda extensão da raiz ou unirem-se em diferentes níveis para terminar em canal único. Verificou-se presença de istmo entre os canais mesio-vestibular e mesio-lingual. Em raízes com canal único, observou-se a alteração da forma do canal a medida que se aproxima do extremo apical.

UNITERMOS: Molar; Raiz dentária; Anatomia.




1. APRILE, E. C.; APRILE, H. Contribuições do estudo da topografia dos canais radiculares. Rev Assoc Paul Cir Dent, v. 1, n. 1, p. 13-18, set./out. 1947.        [ Links ]

2. BARCKER, B.; PARSONS, K. C.; MILLS, P. R.; WILLIAMS, G. L. Permanent mandibular molars. Aust Dent J, v. 19, n. 6, p. 408-413, dec. 1974.        [ Links ]

3. BAUMANN, M. A.; DOLL, G. M. Spatial reproduction of the root canal system by magnetic resonance microscopy. J Endod, v. 23, n. 1, p. 49-51, Jan. 1997.        [ Links ]

4. BURCH, J. G.; HULEN, S. The relationship of the apical foramen to the anatomic apex of the root. Oral Surg Oral Med Oral Pathol, v. 34, n. 2, p. 262-268, Aug. 1972.        [ Links ]

5. COSTA ROCHA, L. F.; SOUSA NETO, M. D.; FIDEL, S. R.; COSTA, W. F; PÉCORA, J. D. External and internal anatomy of mandibular molars. Braz Dent J, v. 7, n. 1, p. 33-40, jan./abr. 1996.        [ Links ]

6. DONALD, W. W.; WILLIAN. E. B. A single mesial canal and two distal canals in a mandibular second molar. J Endod, v. 10, n. 11, p. 400-403, Nov. 1984.        [ Links ]

7. FABRA-CAMPOS, H. Three canals in the mesial root of mandibular first molars: a clinical study. Int Endod J, v. 22, n. 1, p. 39-43, Jan. 1989.

8. FABRA-CAMPOS, H. Unusual root anatomy of first molars. J Endod, v. 11, n. 12, p. 568-572, Dec. 1985.        [ Links ]

9. GREEN, D. Double canals in single roots. Oral Surg Oral Med Oral Pathol, v. 35, n. 6, p. 689-696, May 1973.        [ Links ]

10. GREEN, D. A stereo-binocular microscopic study of the root apices and surrounding areas of 100 mandibular molars: a preliminary study. Oral Surg Oral Med Oral Pathol, v. 8, n. 7, p. 1298-1304, July 1955.        [ Links ]

11. GREEN, D. Stereomicroscopic study of 100 root apices maxilary and mandibular posterior teeth. Oral Surg Oral Med Oral Pathol, v. 3, n. 6, p. 728-733, June, 1960.        [ Links ]

12. HESS, W. The anatomy of the roots canals of the permanent dentition. London, John Bale, Sans and Danielsson, 1925.        [ Links ]

13. KEREKES, K; TRONSTAND, D. L. Morphometric observations on the root canals of human molars. J Endod, v. 3, n. 3, p. 114-118, Mar. 1977.        [ Links ]

14. OKUMURA, T. Anatomy of root canals. J Am Dent Assoc, v. 14, n. 4, p. 632-636, Apr. 1927.        [ Links ]

15. PINEDA, F.; KUTTLER, Y. Mesiodistal and buccolingual roentgenographic investigation of 7.275 root canals. Oral Surg Oral Med Oral Pathol, v. 33, n. 1, p. 101-109, Jan. 1972.        [ Links ]

16. POMERANZ, H. H.; EILDMAN, D. L.; GOLDBERG, M. G. Treatment considerations of the middle mesial canal of mandibular first and second molars. J Endod, v. 7, n. 12, p. 565-568, Dec. 1981.        [ Links ]

17. PUCCI, F. M.; REIG, G. R. Conductos radiculares: anatomia, patologia y terapia., Montevideo; Barreiro y Ramos, 1944.        [ Links ]

18. RIBEIRO, A. F.; ROTHIER, A.; FIDEL, R. Estudo da anatomia interna dos molares inferiores submetidos ao processo de injeção por resina plástica (vinilite). Rev Bras Odontol, v. 18, n. 6, p. 42-45, nov./dez. 1986.        [ Links ]

19. SLOWEY, P. R. Root canal anatomy road map to successful endodontics. Dent Clin Noth Am, v. 23, n. 4, p. 555-573, Oct. 1979.        [ Links ]

20. SYKARAS, P. R. Endodontic treatment of teeth with variations of the root canals. J Bristih Endod Soc, v. 5, n. 1, p. 28-31, Summer 1971.        [ Links ]

21. VERTUCCI, F. J. Root canal anatomy of human permanent teeth. Oral Surg Oral Med Oral Pathol, v. 58, n. 5, p. 589-599, Nov. 1984.        [ Links ]

22. VERTUCCI, F. J.; WILLIANS, R. Root canal anatomy of the mandibular first molar. J N J Dent Assoc, v. 45, n. 1, p. 27-28, Jan. 1974.        [ Links ]


Recebido para publicação em 06/04/98
Reformulado em 18/07/98
Aceito para publicação em 03/01/99



* Assistent professor, Endodontic, ** Dentist e *** Biologist, Morphology Science Department, Ribeirão Preto Dental School, University of São Paulo.

Creative Commons License All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License