Impact of Overjet Severity and Skeletal Divergence on the Perioral Soft Tissue Area

Abstract

Overjet (OJ) and skeletal divergence affect the perioral soft tissue. However, no previous study has investigated the combined effects on perioral soft tissue, which includes the upper lip (UL), lower lip (LL), and chin projection. We explored the impact of OJ severity and skeletal divergence on the perioral soft tissue. Lateral cephalograms of 133 untreated skeletal Class II adult patients were allocated into three categories according to the degree of skeletal divergence: hypodivergence (Hypo), normodivergence (Normo), and hyperdivergence (Hyper). Furthermore, OJ was classified as normal OJ (NOJ), moderately excessive OJ (MEOJ), and severely excessive OJ (SEOJ). A matrix of skeletal divergence and OJ variables produced the following groups: NOJ-Hypo, MEOJ-Hypo, SEOJ-Hypo, NOJ-Normo, MEOJ-Normo, SEOJ-Normo, NOJ-Hyper, MEOJ-Hyper, and SEOJ-Hyper. The skeletal, dental, and soft tissue parameters were measured. Statistical analyses showed that increased hyperdivergence and OJ severity corresponded with a more retruded mandibular perioral soft tissue (MPST), except for the Pog’ in the SEOJ-Hypo group, which was insignificantly more prominent than the MEOJ-Hypo group. Unlike the LL, the UL was similar among the groups. Multiple regression indicated that greater OJ and skeletal divergence significantly influenced MPST retrusion and increased vermilion lower lip thickness (VLLT) while independently affecting deeper mentolabial sulcus depth (MSD) and a more obtuse lip-chin-throat angle (P < 0.05). The effect of OJ was most significant at the LL and gradually decreased down to the chin; conversely, divergence increased downwards. The SEOJ-Hyper group displayed the greatest retruded MPST, thickest VLLT, and deepest MSD, which highlighted the combined effect of OJ and divergence.