| [Objects]The purpose of this study was to evaluate the root and root canal anatomy morphological characteristics of mandibular second permanent molars by cone beam computed tomography (CBCT), meanwhile, to analyze orthopantomogram(OPG) radiographic features of the C-shaped root canal system in mandibular second molars, and to explore the correlation of the C-shaped root canal configuration with its panoramic X-ray features by combining orthopantomogram with CBCT.[Methods]1.593 patients received CBCT scanning in the Affiliated Stomatology Hospital of Kunming Medical University, Kunming, Yunnan, China. Within those scanning data,682 mandibular second molars with complete root formation, no root canal therapy and no post or crown restoration were selected for the study.2. One endodontist and one oral radiologist who were well trained in film reading and passed the inter-observer reliability test analyzed each mandibular second molar image. First, the classification of the molar were done according to the OPG film, then 3D analysis were performed on three planes of transverse, sagittal, coronal planes in CBCT. Based on the classification of vertucci and fan root canal morphology, respectively the root canal configurations in mandibular second molar of non C-shaped root and C-shaped root were classified. At the same time, the panoramic radiograph classification, morphology and number of root and root canal in each tooth image, and every patient’s gender, age, tooth position were recorded.3. According to the different number and morphology of root and root canal, the corresponding number of patients and teeth were counted to discuss the incidence of mandibular second molar with different root morphology, and their root canal configuration.4. According to the gender (male and female), the tooth position (left and right) and the age (young age group:14-24 years old, middle age group:25-46 years, elderly age group:47-75 years old), the statistical data were divided into different groups and counted to compare the differences of root morphology in mandibular second molar of different gender and tooth position;as well as the differences of root canal configuration in mandibular second molar among the 3 age group.5. Based on the results by analyzing panoramic radiographs and CBCT, the detection rate of C-shaped root canal in mandibular second molar with each panoramic radiograph classification were counted. In addition, the distribution of cross-sectional root canal morphology at 3 different levels (coronal, middle, and apical) of C-shaped root type mandibular second molar with different panoramic radiograph classification were discussed.[Results]1. The root anatomic morphology features of mandibular second molarIn 682 cases of mandibular second molar,59.38% was two-rooted, three-rooted and four-rooted occupied 0.88% and 0.15% respectively, the fused-rooted occupied 39.59%, in which complete fused cone single root accounted for 1.32%, and the incomplete fused C-shaped single root accounted for 38.27%. The differences of root morphology between the left side and the right side mandibular second molar had no statistical significance (P>0.05), but the difference of root morphology between male and female mandibular second molar had statistical significance (P<0.05).The symmetric incidence of C-shaped root and C-shaped root canal was 72.53%. and there was no significant difference in the symmetric incidence between male and female (P>0.05).2. Root canal configuration characteristics of mandibular second molar2.1 Non C-shaped root typeIn two-rooted mandibular second molar, the primary root canal configuration of mesial root were two root canals.35.31% of the mesial root canals were type Ⅴ (1-2), 27.06% of the mesial root canals were type Ⅳ (2).94.59% of the distal root canals were type Ⅰ (1). There was significant difference between the mesial and distal root canal configuration(P<0.05). The primary root canal configuration of cone-rooted% three-rooted and four-rooted mandibular second molars were both a single canal in single root.The difference of the root canal configuration in two-rooted mandibular second molar among different age group:There was significant difference in root canal configuration of mesial root between young age group and middle, elderly age group(P<0.05). There was no significant difference in root canal configuration of mesial root between middle age group and elderly age group(P>0.05). There was no significant difference in root canal configuration of distal root among 3 different age group(P>0.05).2.2 C-shaped root typeIn C-shaped root mandibular second molar, the primary root canal configuration at root canal coronal 1/3 level were C1 type and C2 type, at middle 1/3 level were C2 type and C3 type, at apical 1/3 level were C3 type and C4 type. There was significant difference in root canal configuration at 3 different levels (coronal, middle, and apical) (P＜0.05).There was significant difference in root canal configuration at 3 different levels (coronal, middle, and apical) of C-shaped root mandibular second molar among 3 different age group(P<0.05):There was significant difference in root canal configuration at middle and apical 1/3 level between young age group and middle age group(P<0.05). There was significant difference in root canal configuration at coronal and middle 1/3 level between young age group and elderly age group(P<0.05). There was significant difference in root canal configuration at coronal 1/3 level between middle age group and elderly age group(P＜0.05).3. OPG radiographic features of the C-shaped root canal system in mandibular second molars, and the characteristics of root canal configuration of C-shaped root type mandibular second molar with different panoramic radiograph classificationThe detection rate of C-shaped root canal in mandibular second molar with each panoramic radiograph classification were that FR I type accounted for 96%(48/50), FRⅢ type accounted for 85.11%(40/47), FRⅡtype accounted for 72.63% (138/190), NFRⅡ type accounted for 12.33%(27/219), NFR Ⅰ type accounted for 4.55%(8/176), from high to low. There was significant difference in the detection rate of C-shaped root canal with above-mentioned 5 different classification(.P<0.05).In C-shaped root type mandibular second molar with FR I type panoramic features, the primary cross-sectional root canal configuration at root canal coronal 1/3 level were C1 type, at middle 1/3 level were C3 type which was little different from incidence of C1, C2, C4, at apical 1/3 level were C4 type. In C-shaped root type mandibular second molar with FR Ⅱ and FRⅢItype panoramic features, the primary root canal configuration at root canal coronal 1/3 level were both C1 type and C2 type, at middle 1/3 and apical 1/3 level were C3 type which increased along crown-down, but compared with FRⅡtype,the incidence of C4 type in FRⅢ type at apical 1/3 level was higher. In C-shaped root type mandibular second molar with NFR I and NFRⅡtype panoramic features, C1, C2, C3 type had basically the same incidence, except C4 type did not appear at root canal coronal 1/3 level, and the primary cross-sectional root canal configuration at middle 1/3 and apical 1/3 level were C3 type. There was significant difference in cross-sectional root canal configuration at 3 different levels (coronal, middle, and apical) among the mandibular second molar with 5 different classification.(Conclusion]1.In the population that we investigated, the mandibular second molars commonly were two-rooted, less often fused-rooted(C-shaped and cone-shaped fused root), very few three-rooted and four-rooted. Besides the C-shaped root and root canal had a higher prevalence and mostly occurred symmetrically. There was no significant difference in root morphology between the left side and the right side mandibular second molar, but the fuse-rooted was more common in female, and the multirooted was more common in male.2.There was a greater difference among the root canal configuration of each root classification. The primary root canal configuration of mesial root in two-rooted mandibular second molars were typeⅤ(1-2) and typeⅣ(2). The distal root canals were commonly type Ⅰ (1). The primary root canal configuration of cone-rooted、 three-rooted and four-rooted mandibular second molars were both a single canal in single root. The root canal configuration of C-shaped canals system was complicated, C1 type mainly appear at root canal coronal 1/3 level; C2 type mainly appear at root canal coronal and middle 1/3 level; C3 type mainly appear at root canal middle and apical 1/3 level; C4 type mainly appear at root canal apical 1/3 level.The root canal configuration of two-rooted and C-shaped root mandibular second molar changed with advancing age among 3 different age group.3.The panoramic image of mandibular second molar C-shaped root canal had a series of characteristics:according to panoramic image, the closer distance and more fused tendency between root and root canal in mandibular second molar were, the higher detection of C-shaped root canal had. There are rules to follow that the cross-sectional root canal configuration of mandibular second molar with 5 different panoramic classification at 3 different levels (coronal, middle, and apical), and which had a certain reference value for clinical diagnosis and treatment. |
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