Improving Class II malocclusion as a side-effect of rapid maxillary expansion: a prospective clinical study

The objective of this prospective clinical study was to evaluate the dentoalveolar and skeletal effects induced by rapid maxillary expansion (RME) therapy in mixed dentition patients with Class II Division 1 malocclusion compared with a matched untreated Class II Division 1 control group.

The treatment sample consisted of cephalometric records of 50 patients with Class II malocclusion (19 boys, 31 girls) treated with an RME protocol including an acrylic splint expander. Some patients also had a removable mandibular Schwarz appliance or maxillary incisor bracketing as part of their treatment protocol. Postexpansion, the patients were stabilized with a removable maintenance plate or a transpalatal arch. The mean age at the start of treatment of the RME group was 8.8 years (T1), with a prephase 2 treatment cephalogram (T2) taken 4.0 years later. The control sample, derived from the records of 3 longitudinal growth studies, consisted of the cephalometric records of 50 Class II subjects (28 boys, 22 girls). The mean age of initial observation for the control group was 8.9 years, and the mean interval of observation was 4.1 years. All subjects in both groups were prepubertal at T1 and showed comparable prevalence rates for prepubertal or postpubertal stages at T2. Independent-sample Student t tests were used to examine between-group differences.

Class II patients treated with the described bonded RME protocol showed statistically significant increases in mandibular length and advancement of pogonion relative to nasion perpendicular. The acrylic splint RME had significant effects on the anteroposterior relationship of the maxilla and the mandible, as shown by the improvements toward Class I in the maxillomandibular differential value, the Wits appraisal value, and the ANB angle. Patients treated with the bonded RME showed the greatest effects of therapy at the occlusal level, specifically highly significant improvement of Class II molar relationship and decrease in overjet. Treatment with the acrylic splint RME had no sustainable effects on the skeletal vertical dimension, maxillary skeletal position, or maxillary dentoalveolar dimensions.

This study suggests that the protocol described including treatment with a bonded rapid maxillary expander used in the early mixed dentition in Class II Division 1 patients can help to improve the Class II malocclusion as a side-effect, both skeletally and dentally. Evidence for this phenomenon was based previously on anecdotal data; the results of this study show that the improvements are far more pervasive than anticipated.