Evaluation of marginal and internal fit of temporary crown restorations manufactured with additive and subtractive techniques after thermal aging

The aim of this in vitro study is to evaluate internal and marginal fit of temporary crown restorations in the occlusal, axial and marginal areas, manufactured with additive and subtractive techniques using the Three-Dimensional Copying and Optical Digitalization method after thermal aging. A maxillary first premolar typodont tooth was prepared according to standard principles and embedded in a round metal disc using plaster to create the master model. The master model was scanned with a high-resolution scanner and data were saved as an Standard Tessellation Language (STL) file to design a crown with a 50-micron cement gap. Temporary crowns were manufactured using subtractive and additive techniques. For additive manufacturing, SLA, DLP and LCD printer systems were used: Formlabs Form 3B+ (SLA) with Temporary CB resin (F-CB), Bego Varseo XS (DLP) with VarseoSmile Temp resin (B-VS) and Ackuretta FreeShape 120 (LCD) with GC TempPrint resin (A-TP). For the subtractive method, the Cerec MC XL milling machine with Telio CAD block was used (C-TC). Each group had 20 crowns. An isolating agent was applied inside the crown. Then a scannable light body impression material fully applied inside each crown and the crown placed on the master model. During the polymerization of the impression material equal force applied on the crown. Then the crown carefully removed from master model. The impression material remained on the master model due to the isolated crown. The impression material covered master model scanned with the same high-resolution scanner. The master model was digitally superimposed in three dimension with the silicone-covered master model to evaluate the internal and marginal fit. This process was repeated after 5000 thermocycles (5 °C to 55 °C, 20-second dwell and transfer times). The results were evaluated in the occlusal, axial, and marginal regions. The data analysis was performed using SPSS 28.0. Shapiro-Wilk and Levene tests were used to assess normality and variance homogeneity. Depending on the data distribution, Welch ANOVA, Kruskal-Wallis and Wilcoxon signed-rank tests were applied, with significance set at p<0.05. The study was evaluated in occlusal, axial and marginal fit after thermocycle aging. There was no statistically significant differences for occlusal fit among the groups both before and after thermocycle aging. There was statistically significant differences for axial fit among the groups both before and after thermocycle aging (p<0.05). After thermocycle aging, the A-TP Group showed a decrease in axial gap measurement. The C-TC Group and F-CB Group showed a increase in axial gap measurement. The B-VS Group showed a increase in axial gap measurement, but this increase was not found statistically significant. There was statistically significant difference for marginal fit among the groups before and after thermocycle aging (p<0.05). After thermocycle aging, all groups showed an increase in marginal gap measurements but increase in marginal gap measurements in A-TP Group was not statistically significant. It can be concluded that thermal aging affects the internal and marginal fit of digitally manufactured temporary crowns, leading to an increase particularly in marginal gaps. Key words: Additive Manufacturing; Subtractive Manufacturing; Temporary Crown; Internal fit; Marginal fit; Thermal Aging.