Changes in vermilion lip morphology following orthodontic treatment with premolar extraction for Angle Class II maxillary protrusion

Abstract

Objectives: The objective of the study was to clarify the changes in vermilion lip morphology following orthodontic treatment in Japanese patients with Class II maxillary protrusion. Materials and Methods: The subjects were 15 adult women diagnosed as having Angle Class II maxillary protrusion who had undergone orthodontic treatment with premolar extraction. For analysis, profile photographs taken at the first examination and at completion of active treatment were used for linear and angular measurements. For linear measurements on the lateral facial photographs, an X–Y coordinate system was established using a lateral cephalogram superimposed along the line of the profile. Measurement points relating to the vermilion lip morphology were measured on the facial photographs by digital processing, with the Frankfort horizontal (FH) plane as the X-axis, and the line perpendicular to the X-axis passing through the alar curvature point (Ac) as the Y-axis. Results: The results of linear measurements showed significant retraction of approximately 3.0 mm in the upper vermilion lip, and mean retraction of the upper incisors after treatment was approximately 6.0 mm. However, whereas mean retraction of the lower incisors was approximately 1.0 mm, there was significant retraction of the lower vermilion lip of over 3.0 mm. Significant reduction in vermilion height was also found in the upper vermilion lip. With regard to angular measurements, the upper lip and total vermilion showed significant reductions that indicated inversion. Conclusion: Adequate retraction of the upper incisors in the maxillary protrusion with excessive overjet may retract not only the upper vermilion lip but also the lower one, suggesting that morphological changes in the lower lip are affected by the positioning of the upper incisors. In addition, the patterns of morphological changes differed between the upper and lower vermilion lips, with a large proportion of rotational change toward the mucous membrane in the upper vermilion lip and with a pattern of change resembling horizontal displacement in the lower vermilion lip. Total vermilion showed a significant reduction in vermilion height due to the reduction in height of the upper vermilion lip.