Mechanical Behavior of 3D-Printed Restoratives After 30-Day Water Immersion

Objectives: 3D-printed hybrids are relatively new among the dental restorative armamentaria. Therefore, little is known about how these products withstand prolonged exposure to the humid, warm conditions of the typical oral environment. We measured and compared the flexural strength and elastic modulus of four hybrid printable dental restoratives (Table 1) after 30 days water immersion in temperatures approximating the average oral cavity.
Methods: 2x2x25mm test bars (n=12/group) of each material were printed at 0° orientation following manufacturer directions. These were then placed into distilled water and randomized to be stored at 37°C/100% humidity for either 1 or 30 days. Each sample then underwent 3-point bend testing on an Instron E3000 in 37°C water circulation following ISO4049. Differences in flexural strength (MPa) and modulus (MPa) over time were compared via regression using R statistical platform (version 4.3.1). SRB at baseline (1 day) served as reference.
Results: For modulus, Day 1 values were significantly higher for SRO (p-value<0.0001, t-value=3.487) and SRC (p-value<0.0001, t-value=21.447) (Fig. 1). SRC was unique in showing a slight decrease in modulus after 30 days while all other groups showed similar increases (p-value=0.003, t-value=-2.964). The model had strong explanatory power (R²=92.2%, p-value < 0.0001, F =147.1).

For flexural strength, day 1 values were significantly higher for SRC (F-value<0.0001, T=4.128) and FLP (p-value<0.0001, T=4.899) (Fig 2). However, SRC was again unique in showing decreased flexural strength after 30 days (p-value =0.0292, t-value = -2.220) when all other groups showed variable increase. The model strength was moderate (R²=0.564, p-value<0.01, F=17.28).
Conclusions: Beyond expected differences in baseline strength and modulus, our results show these materials respond differently to water storage. This may be due to different susceptibility of the resin matrices to absorption. All products met the 80MPa threshold specified in ISO4049 excepting SRO, which is not marketed as a permanent dental restorative.