Accuracy of additive and subtractive methods for interim tooth-supported restorations: An in vitro comparison of occlusal, axial, and intaglio surfaces

Statement of problem: Subtractive and additive manufacturing methods have been commonly used for interim tooth-supported restorations. However, the accuracy of the occlusal, axial, and intaglio surfaces remains unclear. Purpose: The purpose of this in vitro study was to compare the accuracy of 1 subtractive and 2 additive manufacturing methods among occlusal, axial, and intaglio surfaces in the production of interim tooth-supported restorations. Material and methods: Interim crowns simulating a maxillary first molar were designed and manufactured using the following 3 methods: milling from polymethylmethacrylate (PMMA), stereolithography (SLA), and digital light projection (DLP), with 13 specimens per group. The manufacturing processes were standardized, and all specimens were scanned under consistent conditions with an intraoral scanner. The standard tessellation language (STL) files of the specimens were exported, and analyzed using a metrology software program. The analysis was performed for the overall crown and for the axial surfaces, nonfunctional and functional cusps, central fossa, margin, and intaglio. The root mean square (RMS) deviations were calculated, and color maps were generated. Statistical analyses including the Welch 1-way analysis of variance (ANOVA) with the Games-Howell post hoc tests (α=.05) and the 2-way ANOVA with the Bonferroni correction tests (α=.05), were performed to assess the impact of technology and crown surface on accuracy. Results: The milled PMMA method demonstrated significantly greater precision than the SLA or DLP methods (P<.001), with no significant difference in trueness between milled PMMA and SLA (P=.239). Milled PMMA and SLA methods exhibited the highest accuracy for the marginal area, whereas DLP showed the lowest. The intaglio surface accuracy was similar among all methods (P>.05). Conclusions: Subtractive and additive manufacturing methods demonstrated comparable accuracy on the intaglio surface, remaining within clinically acceptable limits. Milled PMMA exhibited better occlusal accuracy.