Biomechanical effects of fixed retainer designs under different labiolingual alveolar bone loss conditions: a finite element analysis

This study aimed to evaluate the biomechanical effects of three different fixed retainer designs in the mandibular anterior region under different labiolingual alveolar bone loss conditions using finite element analysis. Three alveolar bone models were created for the mandibular anterior region: intact alveolar bone, labial one-third–lingual two-thirds alveolar bone loss, and labial two-thirds–lingual one-third alveolar bone loss. Three different retainer designs were applied to each bone model: a multistranded stainless steel retainer, a rectangular dead-soft stainless steel retainer, and a CAD/CAM NiTi retainer, resulting in a total of nine finite element models. To simulate incisal edge loading, a total vertical force of 285.3 N was applied to the mandibular anterior teeth. Tooth displacement, maximum and minimum principal stresses in the periodontal ligament, von Mises stress in the retainer wires, and maximum principal stress distribution in the adhesive composite were evaluated. As alveolar bone support decreased, tooth displacement and stress concentrations in the periodontal ligament, retainer wire, and adhesive composite increased. The most pronounced biomechanical changes were observed in the labial two-thirds–lingual one-third alveolar bone loss models. Labiolingual displacement was the dominant movement component. Although differences were observed among the retainer designs, alveolar bone morphology had a more pronounced effect than retainer type. In patients with reduced periodontal support, fixed retainer selection should not be based solely on material or design. The degree and labiolingual distribution of alveolar bone loss should also be considered during retention planning.