Abstract: PURPOSE:To propose an imaging risk classification of adjacent tooth traumatisation in impacted mandibular third molar surgery for prognosis estimation and surgical design. METHODS: The impacted mandibular third molars contacting the adjacent teeth in panoramic radiographs were collected and scored using two methods. Impacting depth scoring method: position A, B, C were scored 1, 2, 3 (score A). Contacting area scoring method: the contacting area accounting for ≤1/3, >1/3~≤2/3, >2/3 of the crown were scored 1, 2, 3 (score B). Score A plus score B represented the total score. Total score 3 was classified into risk degree I (low risk), total score 4 was classified into risk degree II (moderate risk), total score ≥5 was classified into risk degree III (high risk). Cone-beam CT was used for evaluation in the same way, Kappa test and youden index were used to compare two imaging results. K-W test was used to analyze the correlations of impacting depth, contacting area and impacting direction. All statistical analyses were performed using the SAS 8.2 software package. RESULTS: 96.25% (1359/1412) of impacted teeth contacted adjacent teeth, 17.88% of them had low risks, 13.63% of them had moderate risks, 4.86% of them had high risks. The concordance of two imaging results was better after Kappa test (Kappa=0.7844). Using CBCTs as gold standard, youden index value=0.8889 when score B=1 in panoramic radiographs; youden index value=0.6781 when score B=2, youden index value=0.5560 when score B=3. The horizontally impacted teeth