Comparison of the retromolar space in adults with different sagittal skeletal types and eruption patterns of the mandibular third-molar

Abstract Background: The retromolar space (RMS) has not been investigated in patients with different skeletal classes and third-molar eruption patterns. The objective of this study was to test the null hypothesis that there is no difference in the mandibular RMS among normodivergent subjects with different skeletal Classes and third-molar eruption patterns using cone-beam computed tomography (CBCT). Method: A total of 105 normodivergent patients (20-40years) were included in this study. Patients were categorized into Class Ⅰ, Ⅱ and Ⅲ groups based on ANB, and they were further categorized into third-molar impacted and erupted groups. The RMS was measured at four planes parallel to the occlusal plane along the cuspal and sagittal line. The RMS was compared among the three sagittal groups and between impacted and erupted groups. Results: The skeletal Class II group showed statistically smaller RMS (P<0.05). The RMS was larger in third-molar erupted group(P<0.05). The rates of root contact and third-molar impaction was significantly higher in Class II group. (P<0.05) Conclusions: The null hypothesis was rejected. Skeletal Class II patients have smaller RMS and higher rates of root contact and mandibular third-molars impaction. The presence of impacted mandibular third molars was observed to be associated with shorter RMS. As such, the RMS should be verified with CBCT before molar distalization, especially in patients with Skeletal Class II relation and third-molar impaction.