A study on soft tissue facial profile changes in orthodontic treatment with four premolar extractions

Jin, Hee Kwan; Moon, Yoon Shik

Abstract

The purpose of this study was to evaluate the differences of soft tissue profile changes between the growing patients and the adult who had passed the growth peak, in orthodontic treatment with four premolar extraction. The results which was taken by correlating the soft tissue changes with hard tissue changes, lip thickness, molar relationship and arch length discrepancy in both groups was like the followings. 1. Significant hard tissue changes were decrease of VIs, Vii, U1PP, LIMP, HE and increase of HPog' in adults and decrease of Vls, Vii and increase of VA, VPog' and all the vertical measurements in adolescents. 2. Significant soft tissue changes were decrease of VLs, VIJ, and VILS in adults and increase of VSn, VSLS, VLs, VPog' and almost all vertical measurements in adolescents, and delta LsE, delta LiE in adults and delta LsE, delta LiE, delta LiSP and delta Mlang was also significant. 3. Correlation coefficient between delta VIs and delta VLs was the greatest in adults and the next was delta Ii/delta Li, delta Ii/delta ILS, delta ID/delta Li and delta ID/delta ILS. In contrast, al the vertical and horizontal measurements of hard and soft tissue in adolescents showed statistically significant corerlation. 4. There were differences in correlation between soft tissue changes and incisor inclination and retraction at both groups, but the lower lip, nasolabial angle and mentolabial angle were commonly less influenced by the hard tissue changes in both groups. 5. The thinner the upper lip was, the more the delta LsSP was in both groups, and the thinner the lower lip was, the more the delta LiE and delta LiSP was in adolescents. 6. Molar relationship didn't influence the soft tissue profile changes. 7. Arch length discrepancy didn't influence the soft tissue profile changes.