Beta-tricalcium phosphate patient-specific gap implants in bilateral sagittal split osteotomy: an innovative treatment method to enhance the mandibular border contour. Part 2: accuracy and quantitative assessment.

In the first part of this study (Part 1), the use of beta-tricalcium phosphate patient-specific gap implants (β-TCP gap-PSIs) during bilateral sagittal split osteotomy (BSSO) showed potential in preventing antegonial notching. The second part of the study was performed to evaluate the accuracy of β-TCP gap-PSIs placement within the BSSO gaps and to conduct a long-term quantitative assessment. Twelve patients who received β-TCP gap-PSIs between July 2017 and July 2018 were followed radiologically for 3-4 years (mean 45.7 ± 7.9 months). Cone beam computed tomography was used to perform 3D cephalometry, densitometry analyses and 3D voxel-based superimposition. The minimally invasive cutting guides effectively reproduced the intended positions and inclinations of the buccal corticotomies, although minor deviations were noted in advancement gaps and vertical implant positioning. Densitometry showed that β-TCP grafts underwent gradual resorption and were progressively replaced by native bone extending to the mandibular lower border. These results support the use of β-TCP gap-PSIs during BSSO as a reliable approach to prevent antegonial notching and preserve mandibular contour. Furthermore, the illusion of premature aging caused by alterations of the soft issue drape by the antegonial notch could be avoided, therefore improving the long-term aesthetic outcome.