Radiologic Assessment Of The Mandibular Third Molar And Inferior Alveolar Canal: An Comparative Study Of Panoramic Radiography And Cone-beam Computed Tomography

Injury to the inferior alveolar nerve is one of the most serious complications during third molar surgeries,which leads to numbness or disappearance of sensation in the lower lip of the affected side.The most critical risk factor leading to this complication is the relationship between the mandibular canal(MC)and the mandibular third molar(MTM),Preoperative tomography evaluation is very important to understand the relationship between the MTM and the mandibular canal,so as to avoid blind extraction of the MTM with high risk of nerve impairment.panoramic tomography(PAN)and cone beam computed tomography(CBCT)are the most commonly used imaging methods in clinic,which can show the relationship between the MTM and the mandibular canal(MC),and the integrity of the MC.Objectives: The objective of this research was to analyze the relationship between MTM and MC by PAN and CBCT,to analyze the risk factors on PAN,and to evaluate the risk of mandibular alveolar nerve injury,guiding clinical practice.Method: A total of 544 patients aged over 18 years with root development of the third molar participated in this study.The research sample included the imaging information of 953 MTMs and adjacent mandibular canals.Statistical software SPSS25.0 was used for statistical analysis,and chi-square test was used to analyze the correlation between demographic factors,type of obstruction,special imaging findings of PAN and mandibular wall defects in CBCT.The factors related to mandibular canal wall defect were evaluated by Logistic regression.Weighted kappa analysis was used to test the consistency of the distance between MTM and mandibular canal.Chi-square test was used to analyze the correlation between the type of obstruction and the spatial position of MC and MTM.The confidence interval of statistical analysis is 95%.All statistical analysis is 95%CI.Result: Among the 953 subjects included in the study,the mandibular canal wall was intact in 757 cases(79.4%)and defective in 196 cases(20.6%).Among them,there was significant difference based on age,type of impacted(Pell&Gregory classification and Winter classification)and incomplete walls of Mandibular canal.Among the special imaging findings,there were significant differences based on the four types of imaging findings: apical shadow,interruption of white line image of mandibular canal,diversion and stenosis of canal diameter.The more special imaging findings could be observed in the study subjects,the higher the rate of mandibular canal defect.In multivariate analysis,there were significant differences in P&G classification based on Mesiodistal,darkening of the root,interruption of the white line(s)and incomplete walls of mandibular canal.Compared with the panoramic radiography,the vertical distance between the mandibular canal and the third molar was observed by CBCT.There is a statistical difference in the vertical distance relationship between the PAN and CBCT,and the consistency test is general.When the MTM is high impacted,vertical impacted,or P&G I impacted,the position of MC is more likely to be located in the root of MTM.When the impacted type is P&G Ⅱ impacted,median or horizontal impacted type,the position of MC is most likely to be located on the buccal side of the MTM.When the impacted type is P&G III impacted,or low impacted type,MC was located on the lingual side of the mandibular canal or between the roots the MTM.Conclusion: Interruption of the white line(s)or darkening of the root on X-rays was the most reliable indication of a intimate relationship between roots and IAC.The other most reliable sign indicating presence of grooving was P&G Ⅱ and P&GⅢ type impacted.When the distance relationship between MTM and MC was close on PAN,there was a credible accuracy.The spatial relationship between MTM and MC can be roughly predicted by P&G classification.