Strength/Stiffness Analysis of Aged Resin in 3D-Printed Occlusal Guards

Objectives: This study aimed to investigate the effect of resin age on the ultimate flexural strength and Young’s modulus of 3D-printed occlusal guard materials.
Methods: Two 3D-printed materials (SprintRay Nightguard Firm and SprintRay Nightguard Flex) at two different time points (new resin vs. shelf-aged (6 months after expiration date)) were examined, creating 4 subgroups (n=9). The specimens were printed at 90° (3.5x12x64mm) at a layer height of 100mm and polished to 3.3x10x64mm. All samples were stored in distilled water for 50±2 hours at 37±1°C. After storage, ultimate flexural strength and Young’s modulus were determined by a three-point bending test, according to ISO 20795-2:2013. Data were statistically analyzed with the independent-samples t-test and Mann-Whitney U test to compare the two different material ages in terms of ultimate flexural strength and Young’s modulus (p<0.05) for each material.
Results: As seen in Table 1, all comparisons were statistically significant. For SprintRay Nightguard Firm, ultimate flexural strength and Young’s modulus significantly decreased with a shelf-aged resin. However, for SprintRay Nightguard Flex, ultimate flexural strength and Young’s modulus significantly increased with a shelf-aged resin. (Table 1).
Conclusions: Within the confines of this study, shelf-age of occlusal guard resin after expiration date may affect the mechanical properties (ultimate flexural strength and modulus) of 3D-printed occlusal guard materials. This study demonstrates that it is important to assess the material storage and expiration date of the 3D-printed occlusal guard resin, as age of the resin may result in inconsistent mechanical properties with time.