Extraction of mandibular third molars: proposal of a new scale of difficulty.

We evaluated the accuracy of a new scale of surgical difficulty for the extraction of impacted mandibular third molars, which includes consideration of previously underestimated variables. Two hundred patients with impacted third molars were enrolled, and a preoperative clinical and radiographic assessment of difficulty was made by an oral surgeon using the new index. Five oral surgeons with similar degrees of experience then evaluated the surgical difficulty during operation. The kappa test and weighted kappa were used to evaluate the level of agreement between the preoperative and postoperative evaluations. This was 0.73, which indicated a substantial concordance between the preoperative and postoperative assessments of difficulty indicated by the new scale. The linear weight of kappa was 0.8 and the quadratic weight 0.87. We recommend this new scale of surgical difficulty for the extraction of impacted third molars for use in clinical practice.