Comparative biomechanical analysis of four different tooth- and bone-borne frog appliances for molar distalization : Athree-dimensional finite element study.

Abstract

The purpose of this study was to analyze the biomechanical effects of four different designs of frog appliances for molar distalization using finite element analysis. Athree-dimensional finite element model including complete dentition, periodontal ligament, palatine, and alveolar bone was established. Four types of frog appliances were designed to simulate maxillary molar distalization: tooth-button-borne (TypeA), bone-borne (TypeB), bone-button-borne (TypeC), and tooth-bone-borne (TypeD) frog appliances. Aforce of 10 N was applied simulating ascrew in the anteroposterior direction. To assess the von Mises stress distribution and the resultant displacements in the teeth and periodontal tissues, geometric nonlinear theory was utilized. Compared to the conventional tooth-borne frog appliance (TypeA), the bone-borne frog appliances showed increased first molar distalization with enhanced mesiolingual rotation and distal tipping, but the labial inclination and intrusion of the incisors were insignificant. When replacing the palatal acrylic button with miniscrews (TypesB andD), more anchorage forces were transmitted from the first premolar to palatine bone, which was further dispersed by the assistance of apalatal acrylic button (TypeC). Compared to tooth-borne frog appliances, the bone-borne variants demonstrated aclear advantage for enmasse molar distalization. The combined anchorage system utilizing palatal acrylic buttons and miniscrews (TypeC) offers the most efficient stress distribution, minimizing force concentration on the palatine bone.