Flexural Strength of 3D-Printed Occlusal Splints at Different Print Angles

Objectives: To compare the flexural strength and modulus 3D printed occlusal splint materials at 0, 45 and 90 degree print orientation to milled and heat cured occlusal splint materials.
Methods: Bars (65 × 10 × 3.3 mm) of 3D-printed splint resins, printed in 3 different orientations 0,45 & 90 degrees, KeySplint Soft and Hard (KSS and KSH, Keystone) and Nightguard Flex and Firm (NFX and NFM, SprintRay) were printed using a DLP 3D Printer (Pro 95, SprintRay), and post-processed. Milled specimens (MILL, ProArt CAD, Ivoclar) were fabricated in a milling unit and heat-cured specimens (HC, Excel Formula, St. George Technology) were produced using a wax pattern and heat-curing technique. Specimens were polished to 600grit SiC paper. Specimens (n=14/group) were stored for 50 ±2 hours at 37C in water (wet) and half were removed from water for (dry) storage. The three-point bend test was performed for both dry and wet conditions. The specimens were placed onto a fixture in a universal testing machine (Instron 5565, Canton, MA) on 3 mm diameter supports separated by a 50 mm distance. A 2 mm diameter indenter applied force at the center of the bar at a vertical displacement rate of 5 mm/min until fracture. The test was stopped following 20 mm of vertical displacement of the indenter if the specimen did not break. The maximum failure load along with the dimensions of the specimens were used to calculate the flexural strength. Data were analyzed with 2-way ANOVA and Tukey post-hoc tests (alpha=.05).
Results: Data for flexural strength and modulus are presented in the Table. 2-way ANOVA determined that there were significant differences between materials and testing condition (wet/dry) and their interaction for flexural strength (p<0.001). Tukey post-hoc analyses found significant differences between groups as indicated by different letters in the same column in the Table.
Conclusions: Wet testing decreases flexural strength and modulus. For some materials, printing at 90 degrees produced greatest strength. 3D-printed splint materials had lower strength than milled materials.