Internal fit and marginal adaptation of digitally fabricated interim fixed dental prostheses

STATEMENT OF PROBLEM: The clinical performance of interim fixed dental prostheses (FDPs) depends on their accuracy, which is influenced by manufacturing technique, material type, and span length. Rapid advancements in these factors warrant updated evaluation of their impact on FDPs accuracy. PURPOSE: The aim of the present study was to assess the accuracy of stereolithography (SLA) and digital light processing (DLP) 3-dimensional (3D) printing of interim FDPs of different span lengths and compare these methods with the milling technique. MATERIAL AND METHODS: A maxillary typodont cast was used to simulate 3 clinical situations of missing maxillary anterior teeth. The abutment teeth were prepared, the cast was scanned using an intraoral scanner, and the scans were exported as standard tessellation language (STL) files into a software program for designing the FDPs. The designs were exported to a milling machine, SLA 3D printer, and DLP 3D printer for production. Specimens were divided into 3 groups according to manufacturing technique (n=24) and 3 subgroups according to span length (n=8), with a total number of 72 specimens. The FDPs were seated onto their corresponding casts, and the assemblies were scanned using micro-computed tomography (µCT). The produced scans were assessed for internal and marginal gaps using the Image J software program. Gaps were evaluated at the incisal, axial, and marginal regions. The data were analyzed using 2-way ANOVA models, and modeling was followed by post hoc comparisons of estimated marginal means using F-tests and pairwise t tests with Kenward-Roger degrees-of-freedom approximation. RESULTS: Milled FDPs exhibited higher incisal, axial and marginal gaps for all span lengths than the SLA and DLP 3D printed groups. For marginal gaps, the results were as follows: 3-unit FDPs: the highest mean gap was recorded in milling (112 ±9 µm), followed by DLP (99 ±19 µm), and the lowest in SLA (45 ±9 µm) P <.001; 4-unit FDPs: milling exhibited the highest mean gap (147 ±16 µm), with DLP (102 ±14 µm) and SLA (83 ±14 µm) following P <.001; 6-unit FDPs: the highest mean gap was reported in milling (135 ±14 µm), followed by DLP (104 ±19 µm), with SLA having the lowest (78 ±15 µm) P <.001. CONCLUSIONS: 3D printed FDPs had fewer marginal and internal gaps than milled FDPs for different span lengths. All digitally fabricated FDPs exhibited marginal gap values within ranges commonly reported as clinically acceptable.