Three-dimensional relationship between the degree of bilateral impacted mandibular third molars angulation and the mandibular dental arch parameters: a cross-sectional comparative study

Objective The purpose of this study was to three-dimensionally evaluate the relationship between the degree of bilateral impacted mandibular third molar (IM3M) angulation and the mandibular dental arch parameters in normal skeletal and dental malocclusion patients. Materials and methods In this retrospective cross-sectional comparative study, 120 adult subjects' cone-beam computed tomography (CBCT) images were three-dimensionally analyzed. The sample included 120 adults aged 20-30 years, with a gender distribution of 51 male and 69 female participants. The sample was divided into 100 adults with bilateral IM3M (study group) and 20 adults with normal bilateral erupted M3M (control group). The study group was sub-divided into three groups according to the degree of IM3M buccolingual angulation (BL degrees): group A, < 12 degrees on the center of the ridge (N = 30), group B, 12-24 degrees off-center of the ridge (N = 40), group C, > 24 degrees off-center of the ridge (N = 30). The study group was also sub-divided into two groups according to IM3M mesiodistal angulation (MD degrees): group 1 from 10 to 45 degrees (N = 36), group 2 > 45 degrees (N = 64). Comparison within and between groups was performed using one-way ANOVA followed by Tukey's post hoc test. The correlation between IM3M, BL, and MD angulation and the mandibular arch parameter was calculated using Pearson's correlation coefficient. Results Statistically significant differences (P < 0.001) were found between the IM3M BL degrees and anterior teeth inclination, arch length (AL), and inter-second molar width (inter 2(nd) MW) as well as between the IM3M MD degrees with anterior crowding and the arch length (P < 0.001). A significant positive correlation was found between IM3M BL degrees and anterior teeth inclination and between IM3M MD degrees and anterior teeth crowding and inter 2(nd) MW. A significant negative correlation was observed between IM3M BL degrees and inter 1(st) MW and 2(nd) MW. Conclusion The degree of buccolingual and mesiodistal angulation of the impacted mandibular third molars was related with mandibular dentoalveolar changes. Increased buccolingual angulation is generally associated with increased anterior teeth inclination and decreased 1(st) and 2(nd) inter-molar width. The increase in mesiodistal angulations was generally related with increased anterior teeth crowding and 2(nd) inter-molar width.