Orthodontic Overjet Correction Effects on Lip Prominences and Form

The relationship between tooth and facial esthetics is an important consideration in successful orthodontic diagnosis and treatment. Objectives: Determination of the effects that overjet correction has on lip prominences. Methods: Lateral cephalometric analysis of 29 Caucasian subjects (16F, 13M; 8-18y/o) was performed to determine the correlation between overjet correction and lip prominences and form. All subjects presented with Class II malocclusions. Pre- and post-orthodontic cephalometric x-rays were traced and analyzed to include millimetric measurements of upper lip-E line, lower lip-E line, lower lip-H line, subnasale-H line, supramentale-H line, and incisor overjet. Results: Mean overjet correction of 2.62mm correlated to a mean 2.17mm increase in upper lip-E line distance (p<0.05), and a mean increase of 2.07mm between lower lip-E line (p<0.06). Although the same mean overjet correction was associated with lip form changes as the lower lip-H line distance increased 0.65mm, subnasale-H line decreased by 0.24mm, and supramentale-H line distance deepened by 1.48mm, these changes were not statistically significant (p>0.05). Reproducibility of all measurements was determined as accurate to Pc>0.93. Conclusion: Overjet correction is associated with changes in upper and lower lip form and position. In contrast to other studies, overjet correction was correlated with greater change in upper lip than lower lip position. H line movement with upper lip position changes makes this reference line unsuitable for lip analysis. Further studies on changes in lip form are recommended utilizing other parameters of curvilinear measurements.