Soft tissue adaptability to hard tissues in facial profiles.

The purpose of this study was to investigate soft tissue adaptability to hard tissue. A canonical correlation analysis was performed in an attempt to assess the relationships between hard tissue structure and soft tissue profile in the static state. For the dynamic study, multiple-regression analysis was performed to identify the changes of soft tissue profiles associated with the retraction of upper and lower incisors. The samples comprised lateral cephalograms from 297 Japanese women for the static canonical correlation analysis and 32 sets of lateral cephalograms of pre- and posttreatment adult orthodontic patients for the dynamic multiple-regression analysis. In the static state, the vertical dimension of lower facial height and the position of the lower incisors were associated with the thickness of the upper-lip vermilion and soft tissue B, and the horizontal relationships between upper- and lower-jaw positions were associated with the thickness of upper lips and of pogonion (soft tissue chin). In the dynamic state, the results indicated that the changes of stomion and lower lip could be predicted and strongly reflected the changes of the hard tissue. On the contrary, the change of the upper lip showed a weaker association with the hard tissue changes. Predictions of chin form described by the soft tissue B and soft tissue pogonion were less accurate than estimates of upper- and lower-lip form. Chin form was influenced by the hard tissue structures such as ANB angle and lower-facial height rather than by changes in lower- and upper-incisor retraction.