Study on the Objective Evaluation of Surface Friction Properties of Denture Base Materials

Purpose: A subjective evaluation has been mainly performed to determine the friction properties of denture base materials. In the present study, we used a surface friction tester in our attempts to quantify the subjective evaluation of denture base materials, such as "easiness of sliding" and "feeling of roughness" as objective data. Methods: Three kinds of materials were used: heat curing acrylic resin, cobalt-chromium alloy, and elastic thermoplastic resin. The objective evaluation by surface friction tester and the subjective evaluation using a Visual Analogue Scale test were carried out. Dry and wet conditions were evaluated, and the surface roughness of each denture material was also measured. The obtained data were analyzed by analysis of variancefollowed by Tukey's post hoc test (α = 0.05). The Pearson coefficient between the objective evaluation by surface friction tester and surface roughness was calculated. Results: The objective evaluation by surface friction tester revealed that thermoplastic resin showed a lower MIU value, indicating "easiness of sliding" and MMD value, indicating "feeling of roughness" under dry conditions. The wet conditions provided lower MIU and MMD values of all materials tested comparing dry conditions. A subjective evaluation showed similar results. From the correlation between data of the surface friction tester and surface roughness, it was suggested that the surface friction tester measured the surface friction properties by using many factors, similar to human sensitivities. Conclusion: It was suggested that subjective surface friction properties could be assessed objectively by using a surface friction tester.