Mechanical properties of 3D-printed occlusal splints after different isopropanol washing times

Abstract

Background: The use of 3D printing for manufacturing occlusal splints is convenient; however, further studies are needed to optimize their material properties. The aim of this study was to evaluate the effect of different isopropanol (IPA) washing times on the properties of 3D-printed occlusal splints. Materials and methods: A total of 132 bar-shaped specimens printed using Formlabs Dental LT Clear V1 and V2 resins were investigated. The printed specimens from each resin were divided into three groups according to IPA washing time: 5, 20, and 60 minutes (n = 22 per group). Half of the specimens from each group were subsequently water-aged. Flexural strength, flexural modulus, water sorption, and water solubility were measured. In addition, surface characteristics were evaluated using a non-contact 3D optical profilometer. Data were statistically analyzed using ANOVA and Tukey’s HSD test. Results: The results showed that longer IPA washing times generally resulted in lower flexural strength values, except in the water-aged V2 group. Flexural modulus was lower in the non-water aged groups. Longer IPA washing times also increased water sorption. Furthermore, specimens in the water-aged V1 group were more prone to cracking and fracture after prolonged IPA washing. In contrast, short IPA washing times resulted in residual unpolymerised resin on the specimen surfaces. Based on the overall findings, a washing time of 20 minutes appeared to provide the most balanced performance among the tested groups. Conclusion: The duration of IPA washing had a significant effect on the performance of 3D-printed occlusal splint resins. Excessive washing negatively affected several material properties. Therefore, optimization of the IPA washing protocol is essential to achieve adequate cleaning while maintaining the material performance.