Asymmetric Maxillary Arch in Unilateral Posterior Crossbite: Implications for Interceptive Treatment

Objectives: The symmetrical transverse maxillary expansion in subjects with unilateral functional posterior crossbite in the mixed dentition does not always lead to a full correction of the midlines discrepancy and of the asymmetric inter-occlusal sagittal molar relationship. The aims of this investigation were to study the maxillary arch asymmetry in these patients during the mixed dentition and to evaluate the association of the maxillary arch asymmetry with the midlines discrepancy and the inter-occlusal sagittal molar relationship.
Methods: Digital dental cast measurements were performed in a sample of 48 subjects with unilateral posterior crossbite (14 males and 35 females, mean age 9.6 ± 1.2 years) and in a control group of 35 subjects with normal Class I occlusion (17 males and 18 females, mean age 9.9 ± 1.3 years). The Fisher’s exact test, the independent sample t-test, and the Pearson correlation were used for statistical comparison.

Results: A clinically significant “Upper Molar Rotation Asymmetry” was present in 60% of the subjects with unilateral posterior crossbite versus 5.7% of the control group. The “Upper Molar Rotation Asymmetry” group presented also a significant difference of the mesio-distal and bucco-palatal position between upper molars and canines in the right and left side when compared with the control group. A correlation has been found between upper molars and canines mesio-distal position, the upper midline deviation and the inter-occlusal sagittal molar relationship.

Conclusions: The findings of this study show an asymmetric maxillary arch in unilateral functional posterior crossbite and the correlation with the Class II subdivisions present in these patients. The maxillary arch asymmetry might play a role in the aetiology of the posterior crossbite and requires a correction as part of the interceptive treatment of this malocclusion in the mixed dentition to obtain a symmetric inter-occlusal sagittal molar relationship.