Effects of simulated gastric acid ageing on Martens hardness of denture base resins fabricated using different...

Gastro-oesophageal reflux disease exposes denture base resins to acidic conditions that may compromise their mechanical properties. This study assessed the effect of simulated gastric acid ageing on the Martens parameters of heat-polymerised, CAD/CAM milled, and 3D-printed polymethyl methacrylate (PMMA).

Three denture base resins were investigated: heat-polymerised (Lucitone 199), CAD/CAM milled (G-CAM), and 3D-printed (Denturetec). Specimens (n = 5 per group) were aged in artificial saliva (pH 5.5) or simulated gastric acid (pH 1.2) at 37°C for 24 and 96 h, corresponding to approximately 2.5 and 10 years of clinical exposure. Martens indentation testing was performed, and the following parameters were measured; Martens hardness (H_M), indentation depth (I_D), indentation modulus (E_IT), and creep indentation (C_IT). Data were analysed using two-way ANOVA and Tukey post hoc tests (α = 0.05).

Resin type significantly affected all Martens parameters (p < 0.001), with milled resin exhibiting the highest H_M and E_IT values and 3D-printed resin showing the highest I_D values. Ageing solvent significantly impacted H_M, I_D, and E_IT (p ≤ 0.049). Gastric acid exposure caused significant deterioration in Martens parameters, particularly at 96 h. Heat-polymerised and milled PMMA exhibited significant differences between solvents at specific time points, whereas 3D-printed resins remained largely unaffected by the ageing solvent.

These findings suggest that material selection based on fabrication technique may influence denture longevity in patients with chronic acid exposure, such as those with gastro-oesophageal reflux disease or eating disorders. The immersion-to-clinical time equivalence represents an approximation based on previously published accelerated ageing models and should be interpreted as a standardised testing protocol rather than an exact clinical simulation.