Chemical, mechanical, and biological effects of repeated chlorhexidine disinfection on acrylic and polyamide denture base materials: A six-month in vitro study

Abstract

Objective: This study aimed to evaluate the chemical stability, leachate release, surface properties, mechanical properties, water sorption, solubility and cytocompatibility of polymethyl methacrylate (PMMA) and polyamide denture base materials after 6 months of repeated disinfection with chlorhexidine.

Methods: Heat-polymerised PMMA specimens and injection-moulded polyamide specimens were subjected to distilled water, 0.12% chlorhexidine and 2% chlorhexidine. The immersion time for each day was simulated as 10 minutes, and the rinsing time for each day was simulated as 60 seconds for six months.

Results: Chlorhexidine caused concentration-dependent changes in both materials. Following this simulated 6-month period, 0.12% chlorhexidine produced an increase in surface roughness (0.31±0.05 µm in PMMA and 0.34±0.06 µm in polyamide), and a decrease in flexural strength (83.8±6.4 MPa in PMMA and 69.8±5.5 MPa in polyamide). For PMMA, 1.74±0.28 µg/mL of methyl methacrylate was released, while for polyamide, 0.91±0.19 µg/mL of caprolactam-related compounds was released. The viability of the fibroblasts decreased to 78.6±6.2% and 84.9±5.8%, respectively. Exposure to 2% chlorhexidine resulted in higher deterioration, with the PMMA cell viability reduced to 66.9±6.4%.

Conclusion: Repeated chlorhexidine disinfection produced concentration-dependent changes in both PMMA and polyamide denture base materials. The 2% chlorhexidine group showed the greatest chemical, mechanical, surface, and biological deterioration. PMMA released more methyl methacrylate and caused greater fibroblast viability reduction, whereas polyamide showed higher water sorption and surface roughness. Routine daily immersion in 2% chlorhexidine should therefore be avoided or used with caution.