ABSTRACT
OBJECTIVES: In part I, to derive ratios of soft to hard tissue profile changes after mandibular setback surgery and to report postoperative changes in soft tissue thickness at the lip and chin areas and, furthermore, to test the hypothesis that soft tissue thickness can act as one of the predictors of soft tissue response after surgery. In part II, to compare the predicted profile lines, using either the customized or the pre-programmed ratios, with the actual postsurgical outcomes. DESIGN: A retrospective study with the sample divided into two groups for different purposes. SETTING AND SAMPLE POPULATION: Department of Orthodontics and Department of Oral and Maxillofacial Surgery at Göteborg University, Sweden. Forty-one Caucasian subjects in need of mandibular setback surgery only. EXPERIMENTAL VARIABLE: Hard and soft tissue movements and changes in soft tissue thickness after surgery were calculated using a customized analysis. Comparisons of the predicted profile outcomes with the actual postsurgical outcomes were carried out with another customized analysis. OUTCOME MEASURE: Distance measurements of certain landmarks in relation to constructed reference lines, both in horizontal and vertical planes, were calculated. RESULTS: The upper lip thickness decreased and the lower lip thickness increased after surgery. The hypothesis that the soft tissue thickness at the lip and chin areas could act as predictors of the ratios of soft to hard tissue changes after surgery, was not supported. Ratios for the lower lip of about 83% of the horizontal and 14% of the vertical movement of the PM point on the bony chin were found in Part I. In Part II, these ratios were introduced and the predicted profile moved significantly closer to the actual postsurgical outcome than if using the pre-programmed ratios (p < 0.05). CONCLUSION: Being able to customize the ratios of soft to hard tissue changes after a particular type of orthognathic surgery will enhance the accuracy of a patient's predicted profile outcome. These ratios should be pre-programmed in future versions of the software.
