Three-dimensional analysis of implant-supported fixed prosthesis in the edentulous maxilla: a retrospective study.

Background: The maxillary incisal edge position is considered the starting point for full-mouth reconstructions. This retrospective study employed three-dimensional virtually planned patient data to evaluate the positional relationship between the upper incisor and underlying alveolar bone in implant-supported fixed prostheses of the edentulous maxilla and the associated influencing factors.

Methods: Three-dimensional virtual models were constructed for 22 edentulous patients rehabilitated with implant-supported fixed prostheses using cone-beam computed tomography, facial and denture scan data. Height and prominence of the residual alveolar bone (vertical residual alveolar bone height [RHeight] and horizontal residual alveolar bone width [RWidth]), crown-to-bone profile angle (AIO, ACO), prosthetic height and width (ProsHeight and ProsWidth, respectively), and incisal position relative to the subspinale point (vertical incisal position [AHeight] and horizontal incisal position [AWidth]) were the parameters measured for the residual alveolar bone profile and the crown-to-bone positional relationship of the upper incisor. Correlation and exploratory multivariate regression analyses were used to identify the key determinants of upper incisor positioning relative to the alveolar bone.

Results: The crown-to-bone profile angles used were AIO 65.73 ± 0.92° and ACO 60.47 ± 0.99°. Multivariate regression revealed that residual bone prominence was the dominant predictor of AWidth (B = 0.694, p = 0.003, adjusted R² = 0.333). AHeight was jointly predicted by residual bone height (B = 0.374, p = 0.028) and lip length (B = 0.872, p < 0.001), collectively explaining 72.2% variance (adjusted R² = 0.722). Lip thickness and sex were found no association with prosthetic parameters (p > 0.05).

Conclusion: Horizontal and vertical positioning of the upper incisal point was predominantly influenced by the residual ridge width, residual bone height, and upper lip length. Age primarily influences incisor positioning through its effect on residual alveolar bone prominence. Upper lip thickness and sex were found no significant effect on the position of the incisors relative to the alveolar bone.

Trial registration: The study was registered at Chinese Clinical Trial Registry. (Date:2024-05-11, No. ChiCTR2400084138).