The impact of four registration strategies on the accuracy of virtual occlusal records for implant-supported prostheses in mandibular distal-extension partial edentulism: An in vitro study

Objective: To investigate how four different occlusal registration strategies influence the accuracy of the virtual occlusal record (VOR) for implant-supported prostheses in mandibular distal-extension partial edentulism. Methods: A typodont model with missing teeth (#46 and #35-37) was mounted in maximal intercuspal position on a semi-adjustable articulator. Twelve stainless steel reference spheres (0.5 mm in diameter) were fixed at predetermined maxillary-mandibular positions (16-46, 13-43, 23-33, 25-35, 26-36, and 27-37). Reference datasets were obtained using a laboratory scanner (inEox X5; Dentsply Sirona, Charlotte, NC, USA). Four occlusal registration strategies were then applied using an intraoral scanner (IOS; Medit i700; Medit Corp., Seoul, Republic of Korea): anterior registration (Group A), bilateral registration (Group B), left-side registration (Group L), and right-side registration (Group R). To reduce sequence-related bias, the order of the registration strategies was randomized. Each strategy was repeated ten times, resulting in 40 VOR datasets. Linear distances were measured using reverse-engineering software, and deviations from the reference were calculated. Because the data were not normally distributed, accuracy was analyzed using the Kruskal-Wallis test (α = 0.05). Results: VOR accuracy was significantly affected by both the registration strategy and the measurement location. In the mandibular distal-extension regions (D25-35, D26-36, and D27-37), Groups L and B showed comparable accuracy (P > 0.05) and both performed significantly better than Group R (P < 0.05). In contrast, at positions D13-43 and D16-46, Groups B and R demonstrated significantly higher accuracy than Group L (P < 0.05). Among all strategies, Group B consistently exhibited the highest trueness, with deviations not exceeding 200 μm at any measurement site. Conclusion: Within the limitations of this in vitro study, bilateral registration provided the highest overall accuracy among the four registration strategies tested using the selected intraoral scanner. VOR accuracy was greater when measurements were closer to the region of interest. In mandibular distal-extension partial edentulism, reduced VOR accuracy was observed compared with bounded edentulous situations, which may lead to underestimation of the occlusal vertical dimension.