Abstract
Introduction: Incisor protraction can cause lip changes in three dimensional planes. Biomechanical properties of the lips may affect these changes. Aims: (1) To investigate the upper lip changes induced by the simulated incisor protraction; (2) To assess the influence of biomechanical properties of the lips on the induced lip changes. Materials and Methods: Incisor protraction was simulated by placing a stent covering the maxillary incisors (4 mm thickness) and gingiva (2 mm thickness). Lip changes in 3D were measured with stereophotogrammetry utilising 3dMD scanning technology. Biomechanical properties of the lips, including muscle tone, stiffness, and elasticity, were measured by myotonometry, using a non-invasive digital palpation device (Myoton AS, Estonia). Results: An average of 2 mm displacement was observed in the upper lip with 4 mm simulated protraction in the sagittal plane. A large inter-individual variation of displacement of lip were observed. Participants of some ethnicity demonstrated less displacement of the upper lip, after adjusting for body mass index. High lip tone and low elasticity were associated with greater displacement of the upper lip in the sagittal direction. Conclusions: Lip changes induced by the simulated incisor protraction differed among the participants with different BMI, ethnicity, and lip biomechanical properties (tone and elasticity).