The evaluation of Rosemary Oil as an anti-candidal agent and its effect on the flexural properties of a thermoplastic denture base resin – An In Vitro Study

Abstract Background: Chemical denture cleansers play a vital role in maintaining the hygiene and serviceability of the dentures. They are of utmost importance in patients with compromised dexterity, who cannot use the physical methods of denture cleansing. Bacterial resistance to these chemical agents paved way to plant-extracts as novel denture cleansing agents. Several in vitro studies have verified the antifungal activity of oils against Candida albicans, with 8% Rosemary oil (Rosemarinus officinalis) being one such oil tested on acrylic resin. Candida biofilms had a greater growth upon polyamide resin compared to conventional PMMA and a more stringent disinfection protocol is required. However, the effect of rosemary oil as a denture cleanser on the physical properties of the thermoplastic denture base resin has not been evaluated. Objectives: Evaluate the anti-candidal activity of 8% rosemary oil on thermoplastic denture base material (Valplast) and its effect on flexural strength of the material on immersion and to compare it with 1% sodium hypochlorite solution. Methodology: In vitro, 18 acrylic resins were exposed to C. albicans and after a process of 30 minutes in immersion in the three groups, the specimens were washed and incubated for 24 hours in 37°C. The growth was determined by colony counting. Flexural strength assays were evaluated in 30 thermoplastic denture resin specimens distributed into three groups (1 test group and 2 control groups - distilled water and hypochlorite 1%), totaling ten specimens per group for each solution. Immersion was done for 30 days changing the cleanser solution every 8hrs simulating an 8 hour/day immersion for 90 days. The analyses were performed at the end of 30 days immersion. For comparisons between the groups in the disinfection test, ANOVA with post hoc Bonferroni were performed by the SPSS program. Results: 8% Rosemary oil did not show similar anti-candidal activity as compared to 1% sodium hypochlorite on thermoplastic denture base resin – Valplast. At higher concentration of Candida albicans similar growth was seen in distilled water and rosemary oil whereas there was no growth seen when sodium hypochlorite was used. At lower concentrations rosemary oil showed mild anti-candidal activity but it was not comparable to sodium hypochlorite which showed complete inhibition of the yeast at all concentrations tested. Mean flexural strength was higher for sodium hypochlorite group (32.942 ± 2.467) followed by Rosemary oil (32.228 ± 3.548) and Distilled water (28.757 ± 2.403). After immersion in the respective solutions there was an increase in the flexural strength of the samples immersed in sodium hypochlorite and rosemary oil compared to that in distilled water. There was no statistically significant difference in flexural strength between the samples immersed in sodium hypochlorite and rosemary oil. Conclusion: 8% rosemary oil influenced the flexural strength of thermoplastic denture base resin Valplast in the same manner as 1% sodium hypochlorite although the anti-candidal property of the essential oil was found to be inferior and non-comparable to 1% sodium hypochlorite which was proven to be successful in completely inhibiting the growth of yeast in all concentrations tested. The outcomes of the investigations have implications on the viability of 8% rosemary oil as a disinfectant solution for denture cleansers, more importantly for thermoplastic denture base resins.