Dental and Facial Asymmetry in Adults with Class II Subdivision Malocclusion With and Without Previous Orthodontic Treatment: A Retrospective Cross-Sectional Study

Background: Class II subdivision malocclusion is characterized by a unilateral Class II molar relationship and is frequently associated with dental midline discrepancies and facial asymmetry. It is unclear to what extent dental and facial asymmetries are present in adults who have undergone orthodontic treatment and present a Class II subdivision relationship, compared with untreated adults with the same occlusal condition. This study compared dental midline deviations and facial soft-tissue asymmetry between adults with Class II subdivision malocclusion with and without previous orthodontic treatment and investigated the association between the side of the unilateral Class II molar relationship and the direction of soft-tissue chin deviation. Methods: This retrospective cross-sectional study included 34 adults with Class II subdivision malocclusion: 21 with previous orthodontic treatment (median treatment duration 5.5 years; examined 3–4 years after completion) and 13 without previous orthodontic treatment. Maxillary and mandibular dental midline deviations were measured (mm) on standardized frontal photographs relative to the facial midline. Chin, nasal tip and Cupid’s bow deviations were classified as right, left or centered (centered = deviation < 1 mm). Two orthodontists performed the assessments independently. Inter-examiner reliability was assessed with the intraclass correlation coefficient (ICC) and Cohen’s kappa. Groups were compared with the Mann–Whitney U test and Hodges–Lehmann estimates, and the association between the Class II side and the direction of each facial landmark deviation was tested with Fisher’s exact test. Results: Inter-examiner reliability was good for mandibular (ICC(2,1) = 0.894) and maxillary (ICC(2,1) = 0.886) midline deviation, almost perfect for chin (κ = 0.900) and Cupid’s bow deviation (κ = 0.855), and moderate for nasal tip deviation (κ = 0.598). Mean mandibular midline deviation was 2.68 ± 0.89 mm in treated and 2.42 ± 1.39 mm in untreated subjects (Hodges–Lehmann difference 0.25 mm, 95% CI −0.50 to 1.00; p = 0.62); mean maxillary deviation was 0.81 ± 1.28 mm and 0.44 ± 0.87 mm (median 0 mm in both groups; p = 0.39). Neither difference was statistically significant, although differences of up to about 1 mm cannot be excluded. Soft-tissue chin deviation was directed toward the Class II side in 30 of 34 subjects (88.2%; 95% CI 72.5% to 96.7%; 16/20 right-sided and 14/14 left-sided Class II; Fisher’s exact test, p < 0.001), and the remaining 4 subjects had a centered chin. No contralateral chin deviation was recorded with Examiner 1′s classification, whereas Examiner 2 classified one subject as contralateral; the association remained significant (p < 0.001). Nasal tip and Cupid’s bow deviations were less frequent (10 of 34 subjects each), were directed to the left in 9 of 10 cases irrespective of the Class II side, and were not significantly associated with it (p = 0.18 and p = 0.050). Conclusions: In adults with Class II subdivision malocclusion, dental midline deviations did not differ significantly between those with and without previous orthodontic treatment, although differences of up to about 1 mm cannot be excluded. Because treated subjects were included only if a Class II subdivision relationship was present at examination, and their pre-treatment and end-of-treatment occlusion was unknown, the findings do not allow conclusions on the effectiveness or stability of treatment. The direction of soft-tissue chin deviation was associated with the side of the Class II molar relationship with both examiners, although Examiner 2 recorded one contralateral deviation; two-dimensional photographs cannot establish whether this reflects a skeletal mandibular asymmetry.