Effects of scanner type and prosthesis design-luting protocol combinations on the passive fit of interim...

To evaluate the effects of scanner type and prosthesis design-luting protocol combinations on the passive fit of interim implant-supported complete-arch fixed dental prostheses (ISCFDPs) fabricated using a non-calibrated splinting grammetry system (OptiSplint). The null hypothesis was that scanner type and prosthesis design-luting protocol combinations would not affect the passive fit of interim ISCFDPs.

This in vitro 2 × 3 factorial study utilized a maxillary edentulous FP-3 master cast with 4 multiunit abutment (MUA) analogs. Extraoral scans of the OptiSplint assembly were obtained using either an intraoral scanner (IOS-OptiSplint) or a laboratory scanner (Lab-OptiSplint). Each scanning method was combined with each of the three prosthesis design-luting protocol combinations: (1) Ti-base with freehand cementation, (2) Ti-base cementation on a verification cast, and (3) Direct-to-MUA design, resulting in six experimental groups (n = 10 per group; N = 60). All prostheses were milled from pre-polymerized polymethylmethacrylate (PMMA) pucks using a five-axis milling unit. All PMMA ISCFDPs were evaluated for passive fit on the master cast using the screw-resistance test by two calibrated examiners, with discrepancies resolved by a third. Misfit was determined when incomplete seating or abnormal resistance was detected during sequential screw tightening. Inter-examiner reliability was assessed using Cohen's kappa, and misfit rates were compared via Fisher's exact tests (α = 0.05).

Inter-examiner agreement was excellent (98%; κ = 0.95). Laboratory scanning achieved complete passive fit across all three prosthesis design-luting protocol combinations. With the IOS workflow, Ti-base on Cast demonstrated 0% misfit, Ti-base Freehand exhibited 30% misfit, and Direct-to-MUA demonstrated 100% misfit. Group 3 exhibited a significantly higher misfit frequency than all other groups (p < 0.001), whereas no other pairwise comparisons were significant.

Laboratory scanning of a non-calibrated splinting grammetry system was associated with consistently complete passive fit across all groups. It may provide a predictable approach for achieving passive fit in complete-arch interim prostheses. Extraoral scanning with an intraoral scanner yielded variable results, underscoring the value of verification-cast cementation when using Ti-bases. Within the limitations of this study, the results suggest that Direct-to-MUA workflows may require laboratory-based scanning when using the evaluated systems.