| Objective:The bifid mandibular canal(BMC)is a variation formed by incomplete fusion of the mandibular canal during the embryonic period.Procedures such as the extraction of an impacted third molar,dental implantation,bone transplantation,posterior mandibular teeth with root canal treatment and sagittal split ramus osteotomy may cause complications,such as the injury of inferior alveolar nerve.And it may be easily overlooked in clinical work.In this study,cone-beam computed tomography software were used to measure and analyze the incidence and anatomical structure of BMC,providing incidence and anatomical information of BMC,which can serve as reference data for clinicians in preoperative assessments to avoid complications.MethodsA total of 400 hemi-mandibles,200 patients(102 males and 98 cases females),CBCT imaging datas were selected randomly,from Tianjin Medical University Hospital of Stomatology between June 2016 to June 2017.Images were analyzed by Ka Vo Invivo 5 software,for evaluating the incidence of the BMC,classifying the types of BMC,measuring the diameter and length of BMC,and measuring the distance of the retromolar foramen.Statistical analysis was performed by SPSS 24.0.Results1.BMCs were found in 64 of 200 patients with an incidence of 32.0 %.BMCs were observed 31(30.40%)in 102 males and 33(33.70%)in 98 females.There was no significant difference between genders(P>0.05).2.A total of 79 BMCs were found in 200 patients(400 mandibular canals),with an incidence of 19.75 %,15 cases in bilateral mandibles(accounting for 7.50 %)and 49 cases in unilateral mandibles(accounting for 24.50%).Of all the BMCs,35 are on the left side(44.30%)and 44 are on the right side(55.70 %).There was no significant difference between left and right sides(P>0.05).3.The most frequently encountered type of BMC in 64 patients was type I(retromolar canal type,n=31,accounting for 39.24 %),followed by type III(forward canal type,n=25,accounting for 31.65 %),type IV(buccolingual canal type,n=13,accounting for 16.46 %),type II(dental canal type,n=9,accounting for 11.39 %),and type V(n=1,accounting for 1.26%).it is mainly located in the mandibular ramus,molar and retromolar regions.4.The mean diameter of the main mandibular canal was 4.56mm(range: 4.56±0.70mm),and that of the BMCs was 1.83mm(range: 1.83±0.56mm).There's a weak positive correlation.And the diameter of the main mandibular canal and that of the BMC has a linear relationship.5.The mean length of BMCs was 12.99mm(range: 12.99±4.41mm);The mean length of type I was 12.61mm(range: 12.61±1.85mm);The mean length of type II was 7.20 mm(range: 7.20±1.48mm);The mean length of type III was 17.23 mm(range: 17.23±3.40mm);The mean length of type IV was 9.15 mm(range: 9.15±2.93mm).6.Type I BMC has an opening(retromolar foramen)on the retromolar region of the mandible.The mean diameter of the retromolar canal(type I)was 2.06 mm(range: 2.06±0.70mm),the mean distance between the retromolar foramen and the distal crown margin of the mandibular second molar was 12.94mm(range: 12.94±2.85mm).Type II,type III,type IV and type V BMCs have openings locating on the apical area of the first and the second mandibular molars,unexposed on the surface of the mandible.Conclusions:1.The incidence of BMC is about 32%,it is mainly located in the mandibular ramus,molar and retromolar regions,and the most common type was the type I.2.There was no significant difference in the incidence between genders and right and left side.3.CBCT is an effective method to measure BMC. |
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