How does artificial aging affect the mechanical properties of occlusal splint materials processed via various technologies?

Background: The mechanical reliability of occlusal splints and their long-term behavior are significant factors determining the clinical outcome of temporomandibular disorder (TMD) therapy. However, improvements are still needed in this area.

Objectives: This in vitro study aimed to (1) compare the hardness and flexural properties of materials manufactured using 3 techniques for occlusal splint fabrication (conventional heat curing, thermoforming followed by light curing, and three-dimensional (3D) printing) and (2) analyze the effect of artificial aging on the properties of the materials.

Material and methods: A total of 120 disc-shaped specimens were manufactured for the Shore D hardness evaluation, and 120 bar-shaped specimens were fabricated for the flexural properties evaluation (n = 15 for each group). Each material was tested in 2 groups of specimens, non-aged and artificially aged (stored for 90 days in water at 37°C). Statistical differences were assessed using one-way or two-way parametric analysis of variance (ANOVA) with Tukey's or Šídák's post-hoc test, or the non-parametric KruskalWallis test with Dunn's post-hoc test. A p-value of less than 0.05 was considered statistically significant.

Results: The mechanical properties of the materials varied significantly. Among the non-aged materials, the 3D-printed resin exhibited the highest Shore D hardness (85.3D), but it decreased significantly after 90 days of water storage (80.4D, p < 0.0001). The unpolished heat curing acrylic showed the highest resistance to artificial aging (p = 0.0436). However, its hardness decreased significantly after polishing (81.0D vs. 83.4D, p = 0.0015). The conventional heat curing material also exhibited superior flexural properties (σ = 89.63 MPa, E = 2616 MPa). All tested materials were susceptible to deterioration due to aging.

Conclusions: The conventional method of occlusal splint fabrication remains the optimal choice, particularly for long-term use. However, it is still necessary to develop materials that are resistant to aging in order to ensure successful clinical performance.