How does the gastric acid environment influence the mechanical behavior of occlusal device materials?

STATEMENT OF PROBLEM: Bruxism and gastroesophageal reflux disease (GERD) frequently coexist, and GERD-related gastric acid (GA) exposure reduces oral pH; however, its effects on the mechanical properties of different occlusal device materials remain unclear. PURPOSE: The purpose of this in vitro study was to compare the surface microhardness and surface roughness of occlusal device materials manufactured by autopolymerizing acrylic resin (AP), 3-dimensionally (3D) printed acrylic resin (3DP), and heat-polymerized acrylic resin (HP) after GA exposure simulating GERD conditions. MATERIAL AND METHODS: Sixty disk-shaped specimens (Ø16×3 mm) were fabricated from AP, 3DP, and HP materials. After baseline measurements of surface microhardness (Vickers hardness number [VHN]) and surface roughness (Ra), specimens were randomly divided into 2 subgroups according to immersion solutions (n=10): GERD subgroups immersed in GA solution with pH 4 for 87.6 hours to simulate 1 year of GERD exposure and control subgroups immersed in artificial saliva (AS) solution with pH 7 for the same duration. Final VHN and Ra values were measured, and changes from baseline were calculated as ΔVHN and ΔRa. Data were analyzed by 2-way ANOVA, 1-way ANOVA, the post hoc Tukey HSD, and Student's t and paired samples t tests (α=.05). RESULTS: GA exposure significantly decreased surface microhardness and increased surface roughness in all tested materials (P<.05), whereas AS exposure increased surface microhardness and decreased surface roughness (P<.05). The reduction in surface microhardness (ΔVHN) of HP was significantly greater than that of AP and 3DP following GA exposure (P=.001). CONCLUSIONS: GA adversely affected the mechanical properties of all occlusal device materials by reducing surface microhardness and increasing surface roughness.