Background Only a few studies have used 3D cone-beam computed tomography (CBCT) analysis to evaluate the positional and morphological characteristics of the temporomandibular joint (TMJ) in adults with skeletal Class II. No studies have focused on the case of skeletal Class II with mandibular retrognathism in different vertical skeletal patterns. As a result, this study aimed to evaluate and compare the position and morphology of TMJ in adults with skeletal Class II with mandibular retrognathism in different vertical skeletal patterns to the position and morphology of TMJ in the normal Chinese adult population in three dimensions. Methods This retrospective study analyzed CBCT images of 80 adult patients. Subjects with skeletal Class II with a normal sagittal position of the maxilla and mandibular retrognathism were classified according to the mandibular angle and facial height ratio into three groups of 20 subjects each: hypodivergent, normodivergent, and hyperdivergent groups, as well as a control group of 20 subjects. The following 3D measurements of TMJ were evaluated: (1) position, parameters, and inclination of the mandibular fossa; (2) position, parameters, and inclination of the mandibular condyle; (3) condyle centralization in their respective mandibular fossae; (4) anterior, posterior, superior, and medial joint spaces; and (5) 3D volumetric measurements of the TMJ spaces. Measurements were statistically analyzed by one-way ANOVA test, followed by Tukey’s post hoc test. Results Significant differences were found in the hyperdivergent and hypodivergent groups compared with the normal group in the vertical and anteroposterior mandibular fossa position, vertical condylar inclination, and condylar width and length. The hyperdivergent group showed the significantly highest condylar inclination with the midsagittal plane; anterior and superior positioning of the condyle; smallest anterior, superior, and medial joint spaces; and largest volumetric total joint space relative to the two other groups. Conclusions The condyle-fossa position and morphology differ with various vertical facial patterns in individuals with skeletal Class II mandibular retrognathism. These differences could be considered during TMD diagnosis and orthodontic treatment.

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Objectives: The purpose of this study was to three-dimensionally evaluate the relationship between the degree of bilateral impacted mandibular third molars (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 was divided into four groups according to degree of M3M buccolingual angulation (BL°); Group A <12° on the center of the ridge (N=30), Group B 12-24° off-center of the ridge (N=40), Group C >24° off center of the ridge (N=30), and Group D (control group with normal erupted bilateral M3M).The study subjects were further also divided into three groups according to IM3M mesiodistal angulation (MD°); Group 1 from10° to 45°, Group 2> 45° and Group 3 (control group with normal erupted bilateral M3M, 0 -10°). Comparison within and between groups were performed using One-way ANOVA followed by Tukey's post hoc test, respectively. Correlation between IM3M, BL and MD angulation and mandibular arch parameter was calculated using Pearson's correlation coefficient. Results: Statistically significant differences (P < .001) were founded between the IM3M BL° and anterior teeth inclination, arch length (AL) and inter second molar width (inter 2nd MW) as well as between the IM3M MD° with anterior crowding and the arch length (P < .001). Significant positive correlation was founded between IM3M BL° and anterior teeth inclination, and between IM3M MD° and anterior teeth crowding and inter 2nd MW. Significant negative correlation was observed between IM3M BL° and inter 1st MW and 2nd MW. Conclusion: The degree of buccolingual and mesiodistal angulation of the impacted mandibular third molars was associated with mandibular dentoalveolar changes. The increase in buccolingual angulation is associated with increase of anterior teeth inclination, and the decrease of 1st and 2nd inter-molars width. The increase in mesiodistal angulations was associated with increase in anterior teeth crowding and 2nd inter-molars width. Clinical relevance: Assessment of the relationship between the impacted mandibular third molars and the degree of arch discrepancy, and the position of mandibular incisors in the three planes of space might help in the decision-making process for extraction of the impacted third molars in adult patients.

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