UCSF

Objectives: The aim of this study was to evaluate the effect of maxillary rapid palatal expansion on the eruption vector of the canines and premolars in the early mixed dentition using CBCT.

Methods: The study population consisted of 42 individuals 7-11 years of age in the early mixed dentition, with all Ds and Es present, and all permanent first molars, maxillary central incisors and lower incisors erupted. No subjects had posterior crossbites or severe sagittal discrepancies. The treatment group of this study consisted of 21 children who had rapid palatal expansion using a Hyrax maxillary expander and active lower lingual arch in the early mixed dentition, as well as phase II comprehensive treatment records. The control group of this study consisted of 21 subjects who did not undergo rapid palatal expansion following their phase I records but returned in the full permanent dentition for comprehensive treatment records. All subjects were imaged using cone beam computed tomography (CBCT) as a part of their initial records, and again prior to beginning comprehensive Phase II treatment in the full permanent dentition.

Results: A canonical variate analysis revealed significant differences between control and treatment groups (p=0.03). There were no significant differences between groups in a principal component analysis, however mild differences between principal component 2 and principal component 8 were observed. Principal component 2 was responsible for 14% of shape variation and was the only principal component in this study to demonstrate shape differences between the treatment and control groups. Canines and premolars erupted with a slightly more upright angulation in patients treated with phase I expansion than those who were untreated.

Conclusions: Canines and premolars were slightly more upright in patients who had phase I expansion than patients who did not. These differences were very minor and were statistically significant in a canonical variate analysis (p=0.03).