Flexural Strength, Monomer Release, and Wear of Occlusal Splint Materials Fabricated Through Conventional, Milled, or 3D-Printed Methods

Abstract

Objective: To evaluate the flexural strength, monomer release, and wear resistance between conventional, milled polymethylmethacrylate (PMMA), and 3D-printed resins built at 90° and 60° printing angles for occlusal splints. Materials and Methods: 60-rectangular and 100-disc specimens were fabricated from heat-cured PMMA (Oracryl [HP], Bracon Dental, United Kingdom), milled PMMA (Kerox Premia [KP], Kerox Dental, Hungary), and 3D-printed resins (FreePrint Splint2.0 [FS], Detax, Ettlingen, Germany, and KeySplint Hard [KS], Keystone Industries, Myerstown, USA) at 90° and 60° printing angles. Specimens for flexural strength and wear tests were immersed immediately in 37°C water for 50 h and thermally aged for 20,000 cycles. Flexural strength was evaluated using a three-point bend test. Wear was tested using a chewing simulator for 140,000 cycles, and volume loss was calculated using Autodesk MeshMixer software. Monomer release was analyzed via UV spectrophotometry over 7 days. Statistical analysis was performed using the Shapiro–Wilk test and one-way ANOVA with Tukey's multiple comparison tests. Results: KP showed the highest mean flexural strength (115.5 ± 5.3 MPa, p < 0.0001), followed by HP (86.6 ± 10.8 MPa, p < 0.0001), with 3D-printed resin showed the lowest. Meanwhile 90° FS showed greater flexural strength (60.5 ± 3.8 MPa) compared to 60° FS (p < 0.001) and KS (p < 0.01). The difference between 90° and 60° KS were not statistically significant (p > 0.05). Monomer release peaked on Day 3 for all groups, with KS consistently showing the highest concentration (29.7 ± 3.6 ppm), followed by FS (28.8 ± 3.8 ppm), HP (27.9 ± 4.9 ppm), and lastly, KP showed the lowest concentration (24.9 ± 3.8 ppm). KP demonstrated the lowest mean volume loss (2.5 ± 1.3 mm3, p < 0.01), followed by HP (4.4 ± 1.7 MPa), whereas 3D-printed resin showed the highest. No significant wear differences were observed between 90° and 60° printing angles. Conclusion: Milled PMMA outperformed other materials, followed by conventional PMMA, while 3D-printed resin showed inferior performance in flexural strength, wear resistance, and monomer release. Printing angles significantly influenced flexural strength but not wear properties in 3D-printed resins.