CBCT Study Of The Relationship Between The Mesial Impacted Mandibular Third Molar And The Mandibular Second Molar With Distal Alveolar Bone Loss

Objective: To measure and analyze multiple CBCT parameters of mesial impacted mandibular third molar(MTM)on distal alveolar bone loss(DBL)of mandibular second molar(MSM).To provide clinicians with experimental data to judge the impact of MTM on MSM and to provide a reference for clinical treatment plan.Methods: Collected 274 cases' CBCT of MTM from December 2018 to December 2019 in the Second Hospital of Hebei Medical University,the age ranged from 17 to 61 years old.Observe and measure the angle of long axis between the mesial impacted MTM and MSM,the distance between mesial CEJ of MTM with distal CEJ of MSM(MTMMCEJ-MSMDCEJ),MSMDBL,and count the age,gender,and MTMPG typing.SPSS Statistics 25.0 software was used for satistical analysis.Results:1.The influence of the angle of long axis between the MTM and MSM on MSMDBL was significantly different(P<0.05);the angle of long axis between the MTM and MSM was positively correlated(P<0.05),and the Pearson correlation index was 0.502,which was a weak correlation.When the angle was less than 22.5°,The MSMDBL was only 2.77±1.61 mm.As the angle increases,the MSMDBL gradually increases,and when the angle exceeds 45°,the growth trend of MSMDBL slows down.The angle of long axis between the MTM and MSM was correlated with MSMDBL,which was an independent risk factor.2.The effect of MTMMCEJ-MSMDCEJ on MSMDBL was significantly different(P<0.05);the effect of MTMMCEJ-MSMDCEJ on MSMDBL was positively correlated(P<0.05),and the Pearson correlation index was 0.627,which was a strong correlation.Among them,the OR value of the degree of MSMDBL was 45.388 times higher in the group with 9mm? MTMMCEJMSMDCEJ <12mm than in the group with?12mm,while there was no significant difference in the other groups.It can be concluded that the degree of MSMDBL was the most severe in the group with 9mm? MTMMCEJMSMDCEJ<12mm.The MTMMCEJ-MSMDCEJ was correlated with MSMDBL,which was an independent risk factor.3.There was a significant difference in the influence of age on MSMDBL(P< 0.05);there was a positive correlation between age and MSMDBL(P< 0.05),and the Pearson correlation index was only 0.217,which was a weak correlation.Under 41 years old,MSMDBL aggravated with age,but there was no significant statistical difference in the degree of MSMDBL among the patients aged 41 years and over.Age was correlated with MSMDBL,which was an independent risk factor.4.There was a significant difference in the effect of MTMPG typing on MSMDBL(P < 0.05),among which MSMDBL was the heaviest in the case of low impacted MTM,while no significant difference was found in the case of high or median impacted MTM(P > 0.05).MTMPG typing was correlated with MSMDBL,which was an independent risk factor.5.There was no significant difference in the effect of gender on MSMDBL(P > 0.05).Conclusions:1.The angle of long axis between mesial impacted MTM and MSM was positively correlated with MSMDBL.When the angle ? 22.5°,MSMDBL was significantly increased.2.MTMMCEJ-MSMDCEJ was a strong positive correlation factor affecting MSMDBL.When 9mm?MTMMCEJ-MSMDCEJ<12mm,MSM DBL was the most severe.3.The angle of long axis between the MTM and MSM exceeding 22.5 degrees or the MTMMCEJ-MSMDCEJ exceeding 9 mm could be regarded as the guiding principle for the preventive removal of MTM.4.Age was positively correlated with MSMDBL,which was a weak correlation.When the age exceeds 41 years old,MSMDBL was in a relatively stable state.5.When the patient was over 41 years old,MTM could be appropriately and conservatively managed if there was no significant indication for tooth extraction.6.Low impacted MTM led to more MSMDBL than high and middle impacted MTM.7.Low and mesial impacted MTMs should be removed early.