Comparative analysis of polishing protocols on microhardness and surface roughness of occlusal device materials fabricated using microwave-polymerized acrylic or 3D printed resins.

Statement of problem: With advancements in digital technologies, the digital workflow has revolutionized the fabrication of occlusal devices through additive methods using 3-dimensional (3D) printing. However, an established protocol for polishing 3D printed occlusal devices is lacking, despite this step being crucial for minimizing surface porosity, material fatigue and preventing bacterial plaque accumulation, thereby contributing to device longevity.

Purpose: The purpose of this in vitro study was to evaluate the impact of polishing systems on the surface roughness and Vickers microhardness of heat-polymerizing acrylic resin and 3D printing resins used for occlusal devices.

Material and methods: One hundred and twenty microwaved-polymerized acrylic resin and 3D printed resin specimens (40×40×3 mm) were divided into 12 groups (n=10) based on the type of resin and polishing protocol (Sealant, DhPro, Dhpro + Sealant, Trihawk, Trihawk + Sealant, and control). Surface roughness (Ra) and Vickers microhardness were tested. Additionally, 1 specimen per group underwent scanning electron microscopy before and after thermocycling (5000 cycles, 5 ºC and 55 ºC). Data analysis involved a 2-way ANOVA, 2-way repeated measured ANOVA, and Tukey's multiple comparison test (α=.05).

Results: The Trihawk polishing protocol yielded significantly higher microhardness and lower surface roughness values for both resins. After thermocycling, the acrylic resin maintained its surface roughness for the Trihawk, Trihawk + Sealant, and unpolished groups, but all groups showed decreased microhardness. The 3D printing resin exhibited increased surface roughness and reduced microhardness after thermocycling across all groups.

Conclusions: The polishing protocol affects the surface microhardness and roughness of 3D printing resins and microwave acrylic resins for occlusal devices. Polishing using the Trihawk polishing protocol demonstrated significantly smoother and harder surfaces for both resins tested.