Masaki Kobayashi

Background There is little evidence regarding risk prediction for surgical site infection (SSI) after lower third molar (L3M) surgery. Methods We conducted a nested case–control study to develop a multivariable logistic model for predicting the risk of SSI after L3M surgery. Data were obtained from Hokkaido University Hospital from April 2013 to March 2020. Multiple imputation was applied for the missing values. We conducted decision tree (DT) analysis to evaluate the combinations of factors affecting SSI risk. Results We identified 648 patients. The final model retained the available distal space (Pell & Gregory II [ p = 0.05], Pell & Gregory III [ p < 0.01]), depth (Pell & Gregory B [ p < 0.01], Pell & Gregory C [ p < 0.01]), surgeon's experience (3–10 years [ p = 0.25], <3 years [ p < 0.01]), and simultaneous extraction of both L3M [ p < 0.01]; the concordance‐statistic was 0.72. The DT analysis demonstrated that patients with Pell and Gregory B or C and simultaneous extraction of both L3M had the highest risk of SSI. Conclusions We developed a model for predicting SSI after L3M surgery with adequate predictive metrics in a single center. This model will make the SSI risk prediction more accessible.