THREE-DIMENSIONAL ASSESSMENT OF THE EFFECTS OF EXTRACTION ON THE SMILE IN CLASS II HIGH AND LOW MANDIBULAR PLANE ANGLE PATIENTS

Abstract

The annals of orthodontics are filled with studies aimed to understand how extraction orthodontic treatment might change the face. Although many studies have addressed profile changes due to extraction treatment, fewer studies have focused on how extractions change a patients smile. With the advent of surface imaging systems such as 3dMD, it is now possible to visualize the smile, and any changes incurred during orthodontic treatment, in three dimensions. Subjects for this study were chosen from the pool of 11-18 year old patients treated at the Podray Orthodontic Clinic at the Temple University Kornberg School of Dentistry. Subjects were Cl II patients, and must have been treated with either extraction of any combination of premolars or treated without extraction. Subjects were divided into four experimental groups based on two characteristics- mandibular angle (those with angles greater than 28o versus those with angles less than 28o) and treatment (extraction versus non-extraction). The resulting groups were separated as follows: high-angle extraction patients (n=8), low-angle extraction patients (n=6), high-angle non-extraction patients (n=7), and low-angle non-extraction patients (n=15). For each subject initial and final 3dMD images were superimposed using 3dMD Vultus software. A color histogram was constructed to visualize changes during treatment. The cheeks, commissures, upper and lower lips, chin, and nose, were also landmarked, and the changes in these landmarks were calculated. Volume changes were also calculated between pre and post treatment 3D data. Results showed that the lower lip and right commissure changes between high-angle extraction and non-extraction groups were statistically significant. A qualitative analysis of the histograms further supported these findings. In general, a greater change in soft tissue landmarks and soft tissue volumes could be seen in high-angle patients than low-angle patients. Differences in the changes that result from treatment type (extraction vs. non-extraction) were seen in the high-angle group. In contrast, similar changes result from treatment type (extraction vs. non-extraction) in the low-angle groups. Furthermore, the lip changes seen in extraction patients upon smiling are very similar to those changes seen in the same patient in repose. Most interestingly, soft tissue differences of the face due to treatment, growth, or both, seem to disappear upon smiling, with the exception of the lips. Qualitative assessment of these changes in the smile might be a more appropriate method for identifying soft tissue changes than statistical analyses. Similar studies with larger sample sizes are a promising direction for future research.