The Application Of CBCT In The Risk Assessment Of Complex Mandibular Impacted Third Molar Extraction And The Design Of Preoperative Plan

Objective : To evaluate the advantages of Cone beam computer tomography(CBCT)in preoperative evaluation of lower alveolar nerve exposure and injury risk in mandibular impacted third molar extraction,and to guide the clinical operation scheme and surgical route selection.Contrast the advantages of panoramic radiography(PR)and CBCT in the risk assessment of mandibular impacted third molar extraction and preoperation protocol design.Methods: In this study,100 patients(178 teeth in total)in Qingdao municipal hospital from October 2016 to October 2017 with mandibular impacted third molars(MITM)were selected after Panoramic radiography(PR)examination for the presence of overlapping images between the roots of mandibular impacted third molars and the mandibular canal(MC).Preoperative planning according to the information provided by panoramic radiography and CBCT images.According to the information provided to extraction the mandibular wisdom tooth by CBCT.We check up the exposing situation during MITM operating.Results: There were 178 cases of overlapping images between the IMTM roots and the MC on the panoramic radiography,while 113 caps MC touch the roots by CBCT,and the contact rate was 63.48%.When MC was located between the roots of the teeth,the CBCT images were both exposed,and the contact rate of the buccal sideof the root was 47.30%.87.5% of the mandibular impacted third molars on the lingual side showed contact,and the MC was 72.82% below the root tip of the impacted third molar.Compared with the panoramic radiograph,CBCT provided a more precise and quantitative guide for bone removal,root sectioning and direction of tooth luxation(P< 0.05);There were significant differences in the two imaging examinations(P <0.001)in the risk assessment of the lower alveolar nerve injury.29 MC exposures were found during IMTM operating.The PR shows that the exposure rate is 16.29%,while the exposure rate was 25.67% after CBCT examination.The exposure rate of INA during tooth extraction were different in different buccolingual position of the mandibular canal in relation to the third molar root,the results showed that : between the roots(50%)>on the lingual side(42.86%)>below the root(26.87%)>on the buccal side(17.14%).In this study,a case of abnormal lower lip sensation was found,and the patient was treated with nutritional nerve and recovered 2 months after the operation.Conclusion : CBCT can provide more precise information compare to PR to display the three dimension relationship of impacted third molars and mandibular canal.CBCT is more sensitive andaccurate for detecting dentoalveolar structures and provide more accurate reference for clinical risk assessment.And CBCT can be used as a necessary examination to evaluate the risk of mandibular impacted tooth extraction complications.