Impact of curing temperature on accuracy and physical properties of additively manufactured FDPs and bar specimens

Additive manufacturing based on photopolymer resins requires additional light curing during postprocessing to achieve the final mechanical properties. The present in-vitro study aimed to evaluate the impact of the curing temperature during postprocessing on the fracture resistance and accuracy of both additively manufactured four-unit fixed dental prostheses (FDPs) and bar-shaped, ISO-conform specimens. All samples were fabricated by either additive manufacturing using two different light-curing resins or subtractive manufacturing using polymethyl methacrylate. Three different curing temperatures were evaluated (40 °C, 60 °C, 80 °C). All bars (n = 136) were subjected to a three-point bending test after 68 of them had been stored in water for 24 h. All bridges (n = 90) were analyzed for dimensional accuracy and afterwards subjected to static loading until fracture. Additively manufactured bar-shaped specimens exhibited significantly higher flexural strength compared to the subtractively manufactured counterparts. In contrast, all but one group (p = 0.082) of the additively manufactured four-unit FDPs demonstrated significantly lower fracture strength than the subtractively manufactured bridges (p < 0.024). Post-curing temperature had no significant effect on accuracy for the temporary resin (p > 0.469), whereas the permanent resin showed significant differences for some regions of interest and temperature combinations. For the recommended curing duration of 40 min, the lowest tested curing temperature of 40 °C already resulted in a sufficient degree of cure and mechanical properties with no general benefit to higher curing temperatures, indicating their use to be unnecessary.