A pilot study of mandibular expansion in combination with a fixed-appliance for increasing the effective space of the mandibular arch: Finite element analysis and three-dimensional cone-beam computed tomography

Techniques for enhancing the effective space of the mandibular arch are urgently needed. Therefore, this study aimed to perform mandibular expansion in combination with a fixed-appliance technique, with preliminary monitoring by finite element analysis and 3-dimensional cone-beam computed tomography (CBCT). Finite element models were structured according to CBCT images of a 14-year-old girl. The von Mises stress of the alveolar bone and tooth displacement were assessed in different models. The technique was also applied in an 11-year-old boy. CBCT was performed at post-expansion, post-retention, post-treatment and 2 years after treatment. Tooth movement and alveolar bone stress were assessed by the CAD software. Finite element analysis suggested that the teeth tended to stand upright in the buccal side in the expander model compared with the expander-remove model. However, minimum tooth change was observed in the normal model, indicating highest stability. The von Mises stress of the alveolar bone was decreased in the normal model compared with the expander model, suggesting that buccal-inclined teeth could more easily lead to alveolar bone stress than normal ones. Based on CBCT data and the 3D mandibular dentition model fitting, mandibular teeth tended to be upright in the buccal side after retention compared with the post-expansion condition, which somewhat differed from finite element analysis results. Furthermore, dehiscence and fenestration were not observed. This expansion technique is expected to increase the effective space after mandibular expansion and reduce buccal alveolar bone stress.