Comparative evaluation of the effect of thermocycling on the mechanical properties of conventionally polymerized, CAD-CAM milled, and 3D-printed interim materials

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Statement of problemStudies on the energy absorption characteristics by means of elastic and plastic material deformation of interim materials are lacking. PurposeThe purpose of this in vitro study was to compare the effect of different thermocycling periods on the flexural strength (σfs), resilience (Ur), and toughness (UT) of conventionally polymerized, computer-aided design and computer-aided manufacturing (CAD-CAM) milled, and 3-dimensionally (3D) printed interim materials. Material and methodsRectangular specimens (n=30 for each material) were fabricated from autopolymerized polymethyl methacrylate (PMMA), bis-acryl resin (Bis-acryl), CAD-CAM polymethyl methacrylate-based polymer (CAD-CAM/Milled), and 3D-printed composite resin (3D-Printed). Each material was divided into 3 groups (n=10) according to the applied thermocycling (5 °C to 55 °C) procedure: control (0 cycles), 2500, and 10 000 cycles. Parameters of the materials such as σfs, Ur, and UT were tested in a 3-point bend test according to International Organization for Standardization (ISO) 10477. Data were statistically analyzed with the Shapiro-Wilk test followed by Kruskal-Wallis test, the Mann-Whitney U test, the Friedman test, and Wilcoxon signed-rank test (α=.05). ResultsThe tested material and thermocycling had a statistically significant influence on the σfs, Ur, and UT values (P<.05). PMMA showed the lowest mean σfs, Ur, and UT values (P<.05), and CAD-CAM/Milled showed σfs values similar to those of 3D-Printed at all thermocycling periods. CAD-CAM/Milled showed the highest Ur values at 10 000 cycles and the highest UT values at all thermocycles. No significant differences were found in the mean change of σfs and Ur of CAD-CAM/Milled among different thermocycling periods. ConclusionsThe results suggested that digitally fabricated interim materials had better mechanical properties than conventionally polymerized materials and that milled materials had the highest stability in maintaining their initial capacity to absorb energy.