Stability of unilateral posterior crossbite treatment with the Function Generating Bite appliance : Association with reduction of mandibular clockwise rotation and increased maxillary transversal width measurements.

Purpose: This observational study aimed to evaluate the stability of unilateral posterior crossbite (UPXB) correction with the functional appliance function generating bite (FGB appliance) during follow-up and its effects on craniofacial growth.

Materials and method: A total of 102 age- and gender-matched patients were included: 51 with UPXB (male [M] = 19; female [F] = 32; mean age ± standard deviation [SD] = 7.6 ± 1.4 [years.months]) and 51 controls (C; M = 19; F = 32; mean age ± SD = 7.9 ± 1.3). UPXB was corrected with the FGB appliance. Study casts were collected before treatment (T0), after correction (T1), after a follow-up of 3.7 ± 1.6 [years.months] (T2) and different transversal measurements were performed with calipers: intermolar (IMD), intermolar gingival (IMGD), intercanine (ICD), and intercanine gingival distances (ICGD). In treated patients, in addition, lateral cephalometric tracings were analyzed at T0 and T2.

Results: At T0, all maxillary measurements were significantly smaller in the UPXB group compared to the controls (p < 0.001). Between T0 and T1, all maxillary variables increased significantly in the UPXB group (p < 0.001; IMD +4.3 ± 2.1 mm; ICD +3.1 ± 2 mm). Between T1 and T2, maxillary IMD increased further (p < 0.05; +2.2 ± 2 mm). The mean T0-T2 increases were 6.6 ± 2.6 mm (IMD) and 4.3 ± 2.6 mm (ICD). At T0, the cephalometric analysis showed significantly stronger mandibular clockwise rotation (p < 0.01) in the UPXB group compared to the control group. Between T0 and T2, the UPXB group showed a significant reduction of mandibular (p < 0.001; SpP-CoOr T0 = -3.47°± 4.38, T2 = -1.14°± 4.01) and occlusal plane (p < 0.01; SpP-Oc T0 = 11.37°± 3.91, T2 = 9.86°± 3.83) clockwise rotation, and of intermaxillary divergence (p < 0.01; SpP-GoGn T0 = 27.8°± 5.39, T2 = 26.65°± 5.49).

Conclusions: Treatment of UPXB with the FGB appliance effectively increased maxillary transversal width measurements, especially in the posterior region, even after follow-up, indicating stable results. Concurrently, mandibular clockwise rotation was reduced, indicating control of the vertical dimension.