Study On The Distance Between Root Apices And Mandibular Canal Of Mandibular Second Molars And Its Related Factors

Objective:The purpose of this study is to use CBCT technology to observe and evaluate the factors such as different age and gender of patients,especially the influence of the existence and different positions of adjacent third molars on the minimum distance between different roots of mandibular second molars and mandibular canal,in order to provide reference for avoiding damage to inferior alveolar nerve in root canal therapy,apical surgery and other related clinical operations.Methods:1.The images meeting the inclusion and exclusion criteria were collected from the wide field CBCT database of the imaging department of Stomatology Hospital of Shanxi Medical University from January 2020 to January 2022.2.They were divided into two groups according to gender and three groups according to age.The mandibular third molars were divided into presence and absence.When there were mandibular third molars,they were divided into 36 groups according to the combined classification of winter,Pell and Gregory.3.Save the image in DICOM format,and then import into the examvision software of kavo3dexam CT,locate the root tip of the mandibular second molar from the axial plane and sagittal plane,and measure the minimum distance between each root of the mandibular second molar and the inner wall of the mandibular canal on the coronal plane with the millimeter measuring scale provided by the software.The distance from the mesial root to the mandibular canal of the double mandibular second molars was recorded as M(M_L on the left and M_R on the right),and the distal root was recorded as D(D_L on the left and D_R on the right);The fusion root is marked as F(F_L on the left and F_Ron the right).The measured data were statistically analyzed with R software package(version 3.6.3).Results:1.Firstly,the CBCT images of 222 patients were included according to gender,age,left and right sides.A total of 444 mandibular second molars and 702 roots were included.There were 258 double roots,accounting for 58.11%,and 186 fused roots,accounting for41.89%.Secondly,388 mandibular second molars were selected from the above data and included according to the presence or absence of adjacent mandibular third molars and different positions.2.The minimum distance between the root tip of mandibular second molar and mandibular canal from far to near was 3.21±2.12mm,2.67±1.94mm and 2.45±2.00mm respectively(P<0.001).There was no significant difference in the distance between the root and mandibular canal between the left and right sides(P>0.05).3.Among the 702 mandibular second molar roots,the minimum distance between about 59%of the roots and the mandibular canal was≤3mm,and the minimum distance between about 20%of the roots and the mandibular canal was≤1mm(P<0.05).4.When the mandibular second molar was the fusion root,the minimum distance between the root tip and the mandibular canal changed with age(P<0.05).5.There was no significant difference in the distance between the root and mandibular canal of mandibular second molar(P>0.05),but the results showed that the distance between the root tip and mandibular canal of male mandibular second molar were greater than that of female.6.When there was mandibular third molar and they was mesial impaction&median impaction&class II,the distance between the mesial root and mandibular canal of adjacent second molars is affected;The distance between the distal root and mandibular canal of the adjacent second molar was affected when the mandibular third molar was mesial impaction&high impaction&class I;When the mandibular third molar was mesial impaction&high impaction&class II and mesial impaction&low impaction&class II,the distance between the fusion root tip and mandibular canal of adjacent second molar was also affected(all P<0.05),.However,the presence or absence of mandibular third molars had no significant effect on the distance between adjacent second molars and mandibular canal(P>0.05).Conclusion:1.Accurate determination of the working length of root canal is not only important for the result of root canal treatment,but also for avoiding the injury of inferior alveolar nerve.2.Before performing root canal treatment,apical surgery and other related operations of mandibular second molars,clinicians should treat the fused roots or distal and middle roots of mandibular second molars in young women(<40 years old),especially when the adjacent third molars are mesial impaction&median impaction&Class II,mesial impaction&high impaction&class I,mesial impaction&high impaction&Class II and mesial impaction&low impaction&Class II,CBCT can be used to accurately evaluate their relationship with mandibular canal,It is helpful to reduce the incidence of inferior alveolar nerve injury.