[Purpose] We have developed a system for integrating three-dimensional facial and dental data obtained by optical laser scanner. The purpose of this study was to three-dimensionally analyze changes in soft tissue with those in hard tissue after mandibular setback surgery by a multiple linear regression analysis, and to improve the accuracy of explaining soft tissue changes.
[Materials and methods] The subjects consisted of 18 skeletal Class III patients, who had been surgically treated by BSSRO at the Department of Oral Surgery, Niigata University Medical and Dental Hospital. Ten subjects had over 3mm midline deviation of the lower dentition compared with the upper one.
Materials included three-dimensional surface data of the face with the anterior teeth, dental casts and lateral cephalograms taken before and after orthognathic surgery. Three-dimensional facial and dental data were integrated according to the method previously reported, and then the coordinate system, measurement regions and measurement items were established.
A multiple linear regression analysis was performed, with the variation of soft tissue as the dependent variable, and the change in hard tissue, variation of soft tissue thickness, soft tissue thickness before orthognathic surgery, overjet, and midline deviation in each area as explanatory variables, by the stepwise method (y = b₁x₁ + b₂x₂ + ··· + b_ix_i + c, p = 0.2). Adjusted R-squares were worked out as an index of the regression equation.
[Results] Obtained values of adjusted R-squares were 0.716-0.862 in the lower buccal region of the deviation side, lower lip region and chin region, and 0.284-0.687 in the upper buccal region of the deviation side, subnasal region, upper lip region, upper buccal region and lower buccal region of the non-deviation side. Although the latter values were less than 0.7, they were better than the values obtained by a simple linear regression analysis in our previous study.
[Conclusions] The results suggest that multiple linear regression analysis can be used to precisely explain soft tissue changes after mandibular setback surgery.