Physical properties of the upper lip measured during simulated tooth movement

Abstract

Differences in the physical characteristics of the lips of different individuals could account for differences in the lip response to tooth movement between individuals. This study was designed to address this possibility. The hypothesis tested was that lip profile changes in response to orthodontic tooth movement are not predictably associated with the physical properties of the upper lip measured during simulated tooth movement. This laboratory and cephalometric study involved seven adult subjects whose maxillary incisors were retracted during previous treatment at the University of Manitoba. An experimental apparatus was constructed to record the forces associated with the displacement of the relaxed upper lip. The physical properties of the upper lip were quantified by the slope of the stress:strain and horizontal flange displacement:horizontal lip displacement (flange$\sp{\rm H}$:lip$\sp{\rm H})$ linear regression relationships, as determined using the video data. The area of tooth retraction (ATR) was determined by superimposing pre- and post-treatment occlusograms. Regression analysis showed a high level of statistical significance for both the stress:strain and flange$\sp{\rm H}$:lip$\sp{\rm H}$ relationships (p $<$ 0.001), but these relationships were not found to be related. Both prediction models had a strong correlation to the cephalometric results (r = 0.95), with the most important variable being the ATR. (Abstract shortened by UMI.)