Finite element analysis of the nonlinear response of oral mucosa in labial tissue induced by spherical versus square self-ligating brackets

OBJECTIVES: This study employs finite element analysis (FEA) to compare the biomechanical effects of spherical versus square self-ligating brackets on the labial mucosa. METHODS: Two distinct tooth-bracket-lip models, featuring spherical and square brackets, were developed to simulate labial tissue mechanical responses under various incisor spatial configurations. Each model incorporated five clinical scenarios and employed a hyperelastic Ogden model, a two-stage simulation process (bracket placement followed by orthodontic sliding), and a hierarchical computational framework for localized stress analysis. Nonlinear interactions-including contact, material, and geometric couplings-were rigorously resolved. RESULTS: The stress concentration areas on the labial mucosa are primarily attributed to the clip groove of the spherical bracket and the edge angle of the square bracket, respectively. Under various loading conditions, the maximum stress exerted on the labial mucosa by the spherical bracket consistently remains lower than that induced by the square bracket. Furthermore, compared to the square bracket, the spherical bracket features a smoother surface profile, which significantly reduces mechanical stress on the labial mucosa and achieves a more uniform pressure distribution. CONCLUSIONS: Spherical brackets significantly reduce biomechanical stress on the labial mucosa by optimizing surface topography. This advantage may result in a lower incidence of mucosal lesions and improved clinical comfort, supporting their preferential application in orthodontic practice.