Three-dimensional analysis of the relationship between mandibular retromolar space and impacted third molars types in non-hyperdivergent adults

Abstract

Background The anatomical position of the mandibular third molars(M3)is located in the posterior space of the molars, and many two-dimensional studies on them in the previous literature. This study evaluated the relationship between retromolar space(RS) and different impacted classifications of M3 in three‑dimensional(3D) cone‑beam computed tomography(CBCT). Methods 206 mandibular third molars from 103 patients were included and separately separated into three classifications concurring to four classification criteria which included PG-A/B/C, PG-I/II/III, mesiodistal angle and buccolingual angle. 3D hard tissue models were reconstructed by CBCT digital imaging. RS was measured respectively by utilizing the fitting WALA ridge plane (WP)which was fitted by the least square method and the occlusal plane(OP) as reference planes. The SPSS (version 26) was used to analyze the data. Results In all classifications of classification criteria, RS diminished steadily from the crown to the root (p < 0.05), the minimum was at the root tip. From PG-A classification, PG-B classification to PG-C classification and from PG-I classification, PG-II classification to PG-III classification, RS both appeared a diminishing tendency (p < 0.05). As the degree of mesioangula impaction diminished, RS appeared an expanding trend (p < 0.05). RS in classification criteria of buccolingual angle had no statistical difference(p > 0.05). Conclusions RS were related to the impacted classifications of M3. With the increment of the impacted degree of M3 ,the retromolar space gradually diminished. In clinic, RS can be evaluated by watching the PG classification and mesial angle of M3.