Vertical lip changes from maxillary incisor retraction

Abstract

S oft-tissue profile changes incident to growth and orthodontic tooth movement have been the subject of intense investigation for many years.ip6 Researchers7-‘i have well documented the effects of anteroposterior movement of incisors on soft tissue in the sagittal dimension. Rudee7 found that the mean ratio of upper lip movement to upper incisor movement is approximately I : 3, with the mode, however, between 1: I and 1: 2. Therefore, more cases should have upper lip retraction equal to or one half the distance of incisor movement anteroposteriorly. In developing a soft-tissue prediction method for maxillary osteotomies, Harris’” found a significant correlation of upper lip movement to maxillary incisor retraction at a ratio of 0.66: I Although variation has been noted by all investigators, a ratio of approximately 0.7 : I for upper lip movement related to upper incisor retraction has been established as a norm with a significant degree of predictability. A ratio of lower lip movement to upper incisor retraction of I : I has also been established but is less predictable than the I : 1 relationship found between lower incisor and lower lip movement.7* ’ Predictability of vertical changes in the labial soft tissue has not been established in these previous studies. Subjective evaluation has determined that as incisors are moved distally the interlabial gap decreases and the lips become thinner as viewed from the frontal aspect, but that the changes were inconsistent relative to the amount of such retraction. Most orthodontists have seen, at one time or another, normally shaped but slightly protrusive lips being reduced to a thin line of vermilion border as incisors are retracted to a functional position and/or to dentoskeletal cephalometric “norms” in the sagittal dimension. The perplexed clinician has observed that for relatively the same amount of incisor retraction, lip “thinning” varied from one patient to another. Therefore, the purpose of this study was to evaluate the vertical changes in the labial soft tissue relative to maxillary incisor retraction in an effort to correlate such retraction to closure of the interlabial gap with a significant degree of predictability.