Establishment Of Difficulty Prediction Model Of Impacted Third Molar Extraction:A Retrospective Cohort Study

Objective: The aim of this study is to build a prediction model by means of the regression analysis with potential factors that might affect the difficulty of the extraction of impacted lower third molars(LM3),so as to help to design a individualized operation plan before the mandibular third molar surgery,which can shorten the operation time,minimize the surgical trauma as well as reduce intraoperative and postoperative complications.Materials and methods: This study is a retrospective cohort study based on the classification of surgical difficulty.60 impacted lower third molar extraction cases from September to December in 2018 were enrolled into our study.Potential factors(independent variables)included in the correlation analysis were divided into three groups: anamnesis factors(gender and age),radiographic factors(Angle of LM3,the depth of impacted Retro Molar Space,the width of LM3,the length of LM3 and the root anatomy)and operational factors(the incision of the surgery and the location of LM3).All patients were required to take a panoramic radiograph before the surgery and we used Vceph 6.0 to measure the LM3 radiographic factors on panoramic radiograph.The operative method and the location of the lower third molars extraction were defined as binary variables.The operation time is defined as the time required from the beginning of the incision to the end of suturing.According to the median of the operation time from all cases,the difficulty of LM3 removal was divided into 2 levels(the simple and the difficult).Then,data was processed by Statistical Package for the Social Sciences(SPSS)and R software.Those factors that had less influence on the difficulty of LM3 extraction were eliminated by LASSO analysis(Least absolute shrinkage and selection operator),while factors that had greater impact on the difficulty of LM3 extraction were regarded as predictive variables.Finally,the difficulty of tooth extraction was seen as the result variable being used to establish the logistic regression model.Result: The range of the operation time of all cases was 16.7±7.4 minutes and the median of the operation time was 16 minutes.Patients' gender,the incision of the surgery,the angle of LM3,the retro molar space,the width of LM3 and the length ofLM3 were eliminated through LASSO regression.Finally,the age of patients,the location of LM3,the depth of LM3 and the root anatomy were included in the prediction model.Conclusion: Anamnesis factors,radiographic factors and operative factors are all associated with the difficulty of impacted LM3.But oral surgeons should pay more attention to the age of patients,the depth of impacted LM3 and the root anatomy before the mandibular third molar surgery.In the meanwhile,a more suitable operative method should be taken into consideration as well.