A Reproducible Calibrated Dual-Pin Reference Method for Mandibular Pre- and Postoperative Scan Alignment: A Proof of Concept

In this study, a fully digital workflow enabling the alignment of pre- and postoperative mandibular intraoral scans in complete-arch implant rehabilitation using intraosseous fiducial reference markers is presented. A prosthetically driven digital workflow was implemented for mandibular complete-arch rehabilitation in which two cylindrical intraosseous pins were placed in a median or paramedian mandibular region and used as fiducial reference markers to align pre- and postoperative intraoral scans. Pin osteotomies were prepared using a calibrated drilling protocol and preserved throughout surgery to allow for the exact repositioning of the pins. Implant positions were recorded using photogrammetry, while postoperative intraoral scans were acquired after suturing with the pins reinserted. Scan alignment was performed using a best-fit algorithm based exclusively on the fiducial pin geometry. Standardized convergent scanbodies without undercuts were used for intraoral scanning. The proposed workflow allowed for the alignment of pre- and postoperative mandibular scans without additional radiographic acquisitions and was compatible with both guided and free-hand implant placement, regardless of the degree of mandibular atrophy. Within the limitations of a proof-of-concept report, the use of intraosseous fiducial reference markers represents a minimally invasive and clinically applicable solution to a critical limitation of fully digital mandibular rehabilitation workflows, without the quantitative validation of accuracy, trueness, or reproducibility.