Kulnipa Punyanirun & Chairat Charoemratrote

The objective of this study was to investigate the influence of overjet (OJ) severity and upper incisor impingement (UI-imp) on the lower lip (LL). One hundred and fifteen radiographs of skeletal Class II patients were grouped according to OJ severity: normal OJ (NOJ/n = 25), moderately excessive OJ (MEOJ/n = 45), and severely excessive OJ (SEOJ/n = 45). UI-imp was classified within subjects with excessive OJ (EOJ) according to the presence and absence of UI-imp on the LL: UI-imp (n = 50) and non-impingement (Non-imp) (n = 39). The skeletal, dental, and soft tissue characteristics were compared and analyzed for correlations. Prediction models were generated. Lower lip eversion (LLeversion), vermillion lower lip thickness (VLLT), and mentolabial sulcus depth (MSD) were significantly greater in SEOJ than NOJ. These LL variables worsened as OJ severity increased. OJ was significantly positively correlated to LLeversion and MSD and negatively correlated to upper lip strain (ULS), lip-chin-throat angle, and more backward LL position. Subjects with UI-imp exhibited similar OJ severity as the Non-imp group. The UI-imp group showed a significantly more backward sulcus inferior and deeper MSD. SNB, FMA, OJ, OB, UI, and LI contributed to the prediction models. Patients with SEOJ showed significantly greater LLeversion, VLLT, and MSD, while those with UI-imp showed increased MSD accompanied by a more backward sulcus inferior compared to those without. Improvement of lip morphology and lip-chin harmony may be expected upon EOJ and UI-imp reduction.

KEY WORDS: Lip; Incisor protrusion; Overjet; Malocclusion; Angle Class II.

PUNYANIRUN, K. & CHAROEMRATROTE, C. Influence of overjet severity and upper incisor impingement on the lower lip in skeletal Class II patients. Int. J. Morphol., 43(1):294-303, 2025.