The Root Morphology Of Mandibular Second Permanent Molars Evaluated By Cone Beam Computed Tomography

Objectives:The root morphology of mandibular second permanent molars was very complicated, and which brought great difficulties to clinical treatment of oral diseases. In the current study, we evaluated the root morphology of mandibular second permanent molars by use of cone beam computed tomography, and described the morphological characteristics of molars. Besides, we investigated the correlation between morphological characteristics and alveolar bone resorption, and provided theoretical data for clinical treatment of oral diseases.Methods:We collected cone beam computed tomography images of 378 mandibular second permanent molars from patients. The recorded data is as follows: (1) root length; (2) canal number and whether it is C-shaped; (3) root trunk length; (4) mesiodistal diameter, buccal and lingual diameter; (5) whether there were enamel pearls and root concavities; (6) the width of root furcation located in 2mm under the opening; (7) the distance from cemento-enamel junction to alveolar bone height. All of these data were measured by author and other three senior dentists, the average of these records was counted. Also, we recorded the name, gender and age of every patient.Results:1. The mean width of root furcation located in 2mm under the opening was 1.46mm, and this showed significant positive correlation with the distance from cemento-enamel junction to alveolar bone height (y=0.236, P<0.05).2. The mean root trunk length was 4.34 mm, the maximum length was 6.7mm, and the minimum length was 1.9mm. There was no correlation between root trunk length and the distance from cemento-enamel junction to alveolar bone height (Y =-0.008, P>0.05).3. The mean mesiodistal diameter in cemento-enamel junction was 10.4mm, the maximum diameter was 12.1mm, and the minimum diameter was 8.4mm. This showed significant positive correlation with the distance from cemento-enamel junction’to alveolar bone height (Y=0.286, P<0.05).4. The mean buccal and lingual diameter was 9.4mm, the maximum diameter was 11.5mm, and the minimum diameter was 7.2mm. This showed significant positive correlation with the distance from cemento-enamel junction to alveolar bone height (Y=0.323, P<0.05).5. The mean root length was 13.9mm, the maximum length was 17.2mm, and the minimum length was 8.6mm. This showed significant positive correlation with the distance from cemento-enamel junction to alveolar bone height (Y=0.230, P<0.05).6. The occurrence of root concavities showed significant positive correlation with the distance from cemento-enamel junction to alveolar bone height (Y=0.269, P <0.05). The occurrence of root concavities was 96%.7. The canal number showed significant positive correlation with the distance from cemento-enamel junction to alveolar bone height (Y=0.226, P<0.05). The occurrence of single root canal, two root canals, three root canals, four root canals and five root canals was 1%,31%,43%,24%and 1%, respectively.8. The occurrence of C-shaped canal showed no correlation with the distance from cemento-enamel junction to alveolar bone height (Y=0.114, P>0.05). The occurrence of C-shaped canal was 49%.9. The occurrence of enamel pearls showed significant positive correlation with the distance from cemento-enamel junction to alveolar bone height (Y=0.226, P <0.05). The occurrence of enamel pearls was 2.9%.Conclusions:The root morphology of mandibular second permanent molars was very complicated, and there were so many variations on root and canal. The results showed that, the width of root furcation located in 2mm under the opening, root length, mesiodistal diameter, buccal and lingual diameter, whether there were enamel pearls and root concavities were closely related to the distance from cemento-enamel junction to alveolar bone height. However, root trunk length and whether canal is C-shaped showed no correlation. Compared with other examinations, cone beam computed tomography showed obvious advantages. The results in this research offered new information for dentists, and contributed to increasing the success of periodontal therapy.