Effect of thymus vulgaris essential oil as an antifungal agent on the flexural strength, surface roughness, and color stability of polymethyl methacrylate acrylic resin

Polymethyl methacrylate (PMMA) denture base resins are susceptible to microbial colonization, particularly by Candida albicans, contributing to denture stomatitis. Natural bioactive compounds such as Thymus vulgaris essential oil have emerged as potential alternatives to conventional disinfectants. This study evaluated the antifungal activity of T. vulgaris essential oil and the effects of denture disinfection solutions containing different concentrations of the oil on the physicomechanical and optical properties of PMMA. The minimum inhibitory concentration (MIC) against two C. albicans strains (ATCC 14053 and NCPF 3179) was determined using the broth microdilution method. Toxicity was assessed using a Tenebrio molitor in vivo model. PMMA specimens were immersed for 7, 14, and 28 days in solutions containing MIC and 10× MIC concentrations. Distilled water and 2.5% sodium hypochlorite served as controls. Flexural strength, surface roughness (Ra), and color change (ΔE) were evaluated according to ISO 20795-1 standards. Statistical analyses were performed at a 5% significance level. The essential oil exhibited antifungal activity with an MIC of 4.5 µg/mL against both strains. No statistically significant toxicity was observed in the in vivo model (p > 0.05). At MIC concentration, no significant alterations were detected in flexural strength, surface roughness, or color stability of PMMA over 28 days. However, the 10× MIC concentration resulted in reduced flexural strength, increased surface roughness, and significant color changes over time (p < 0.05). Thymus vulgaris essential oil demonstrates antifungal activity and a favorable safety profile in the experimental model tested. When used at its minimum inhibitory concentration, it preserves the mechanical and optical properties of PMMA, suggesting its potential as an alternative disinfecting agent for removable prostheses.