A Plaster Cast Contact Scan Method to Assess the Accuracy of Full-Arch Computer-Aided Implant Surgery

Purpose: The aim of this study was accuracy assessment of placed implants in full-arch cases using specific software and hardware to perform static computer-assisted implantology and immediately loaded prostheses. The degree of deviation existing between planned and achieved implants was carried out by a new noninvasive measurement procedure of the implant position performed on stone casts.
Materials and methods: Fourteen stone casts retrieved from 14 full-arch fully guided implant treatments were selected to perform the study. Each cast, manufactured for the surgical treatment by using a specific laboratory kit, was obtained from the respective surgical guide. A sleeve for each implant was embedded into the guide, which helped the examiners to manufacture a stone cast per guide containing the implant analogs, which was used to recover the final position of the planned implants. A total sample of 60 implants were assessed. The postoperative casts, poured to produce the immediate prostheses, were then processed by a contact (or tactile) scanner, and the generated standard tessellation language (STL) files were overlapped (best-fit alignment) using engineering software that revealed all the measured discrepancies. In terms of accuracy, differences relating to arch, assessed bone quality, implant length, and drill length (prolongation short or long) were reported.
Results: The use of a noninvasive tactile scanner revealed mean entry point horizontal deviations of 0.30 mm (SD: 0.39 mm), mean entry point vertical deviations of 0.20 mm (SD: 0.25 mm), mean apical horizontal deviations of 0.50 mm (SD: 0.73 mm), and mean apical vertical deviations of 0.24 mm (SD: 0.28 mm). The frontal and lateral angular deviations were investigated, and corresponding mean values of 1.99 degrees (SD: 2.30 degrees) and 1.80 degrees (SD: 2.44 degrees) were detected.
Conclusion: The reported results demonstrate that the contact tactile scan is a viable and biologic way to assess implant deviations.