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

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.

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.

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).

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).

GA adversely affected the mechanical properties of all occlusal device materials by reducing surface microhardness and increasing surface roughness.