3D evaluation of condylar changes after rapid maxillary expansion
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INTRODUCTION: Orthopedic maxillary expansion, also commonly referred to as Rapid Maxillary Expansion (RME) is a widely used orthodontic technique for early treatment of skeletal transverse deficiencies1. Condylar changes in response to RME have been observed using a variety of imaging techniques such as tomograms2, magnetic resonance imaging3-4 and cone beam computerized tomography5. To this day, most of the studies have focused on changes in condylar position after RME but to best our knowledge, no study has examined the changes in condylar shape and volume in addition to position. OBJECTIVES: The aim of this retrospective cohort study is to determine the long term effect of Rapid Maxillary Expansion (RME) on condylar shape, volume and orientation as well as on mandibular rotation. METHOD: Pre- and post-expansion cone beam computerized tomography (CBCT) images of forty-four healthy subjects (mean age=11.8±2.06) who previously had undergone banded RME were selected from a CBCT repository. Due to extensive time range existing between the pre- and post-CBCTs (0.7-4.7y, average time = 2.4y ± 0.97), a stratified analysis was run to account for the subject’s growth. Two subgroups were created according to the Baccetti Cervical Maturation stage : a “growing” group (n=37, mean age=11.86y, diff CVM>1) and a “non-growing” group (n=7, mean age=11.73y, diff CVM<1). Linear, angular and volumetric changes as well as condylar surface area differences and changes in mandibular rotation were assessed on isolated 3D condyles using Mimics version 20.0 software (Materialise, Leuven, Belgium). The condyles were segmented by a plane passing through the sigmoid notch (Snp) and parallel to a Frankfort Horizontal derivative plane (FHD). Changes in mandibular rotation were evaluated by analyzing the alterations in the angle between mandibular plane and FHD plane before and after RME. Paired T test was performed to compare pre- and post- expansion for all variables stated above. Statistical significance was set at <0.05. RESULTS: In the “growing” group, the right and left condylar heights and widths significantly increased by 0.61mm±1.19mm (p=0.0035), 0.80±1.26 (p=0.0005) and 1.01mm±0.95mm (p<0.0001), 0.89±0.93 (p<0.0001) respectively. The right and left condylar volumes significantly increased by 117.7mm3±149.3mm3 (p<0.0001) and 106.7mm3±133.5mm3 (p<0.0001), respectively. In the “non growing” group, the right condylar height and the right condylar width statistically increased by 1.56mm±1.65 and 0.42mm±0.42 respectively. The right and left condylar volumes also increased by 114.1mm3±104.3 and 141.5mm3±89.1 respectively. No statistically significant changes were found in condylar orientation and mandibular plane angle for either of the two sub-groups. CONCLUSION: Right condylar height, width, and right and left volumes were significantly increased after rapid maxillary expansion. No statistically significant effect on condylar orientation and mandibular plane was found. Condylar growth still remains to be an important co-founding factor which potentially affected the results of our study. A control group will be required to assess the effects of growth in our current findings to limit the effects of growth on our results.