Physical Properties of Denture Base Resins Potentially Resistant to Candida Adhesion

The use of a dental prosthesis is indispensable for functional and esthetic rehabilitation of edentulous patients. Despite concerns about the decline in the need for prosthodontic services due to delayed edentulism, the actual unmet need for these services will rise steadily in the next two decades.1 Douglass and Watson calculated that the unmet need for prosthodontic services will increase from 488 million hours in 2005 to 560 million hours in 2020.1 It has been estimated that the need for dentures will rise to 37.9 million adults in 2020.2 Synthetic acrylics resins have a long, clinically proven history of use for dentures since they exhibit adequate physical, mechanical, and esthetic properties; however, they are susceptible to microbial adhesion, leading to denture stomatitis, which is the most common infectious disease affecting the palatal mucosa, and is highly prevalent in denture wearers.3,4 Denture stomatitis is a common clinical entity characterized by inflammation of oral tissues and colonization of the intaglio surface of prostheses by pathogenic organisms. It has a multi-factorial etiology reportedly consisting of either an ill-fitting prosthesis causing mechanical irritation or poor hygiene leading to chronic infection. Rarely, allergic response to the resin is also seen. Regardless of the initiating mechanism, denture stomatitis is characterized by the presence of a yeast biofilm on the prosthesis, primarily associated with Candida albicans.5–7 According to a report by Reichart on a group of Germans aged 65 to 74, there was an 18.3% prevalence of denture stomatitis.3 Others have shown prevalence rates near 60% in a denture-wearing institutionalized population.4 The treatment for denture stomatitis is as complex as the disease itself. Traditional treatment modalities include the use of antifungal agents and modification of the prosthesis to receive a temporary soft tissue reliner. Oral antimycotic agents seem helpful, but recurrence is rapid and assured unless the denture tissue surface is modified to eliminate candidal hyphae.8 Using either systemic fluconazole or topical amphotericin antifungal treatments for denture stomatitis, Bissell et al documented a 50% relapse in stomatitis after 12 weeks using both mycologic and clinical criteria independent of the type of therapy used.9 Additionally, compliance with antifungal regimens can be compromised by a patient’s non-perception of need for medication for a relatively painless condition. Therefore, there has been a tendency toward the incorporation of antimicrobial agents into the denture liners or the resin itself and other similar intraoral drug delivery systems.10–15 A previous study showed substantial differences in the protein compositions of the acquired enamel pellicle in comparison to denture pellicle.16 The acquired enamel pellicle contains antimicrobial peptides like histatins along with other constituents such as IgA, amylase, salivary statherins, and mucins. In contrast, the denture pellicle lacks salivary statherins and histatin. The absence of these important salivary defense molecules on the denture base has been attributed to the lack of anionic charge in polymethyl methacrylate (PMMA) polymers.16 Thus, this lack of surface charge may be responsible for the decreased protective function of the acquired pellicle on the denture. Moreover, reduction of candidal adherence has been demonstrated using a novel PMMA made with increasing amounts of methacrylic acid in place of methyl methacrylate monomer during processing. The new polymer is more hydrophilic and showed a significant correlation between the amount of methacrylic acid in the polymer and decrease in adhesion of C. albicans.17 This formed the rationale for the hypothesis that denture base resins with a phosphate-based anionic charge might also inhibit C. albicans adhesion, and should theoretically provide an enhanced biomimetic surface for the salivary cationic antimicrobials, such as the histatins. The protective role of these histatins would be a potentially viable treatment modality for denture stomatitis; however, any new denture base material must meet standards for clinical acceptability. Therefore, the purpose of this study was to evaluate the physical properties of denture resins with different concentrations of phosphate substitutions in the monomer. These resins would be compared against each other and the control resin, Lucitone 199 (Dentsply International Inc., York, PA), for suitability for denture fabrication. ISO 1567 for denture base polymers and ADA specification No. 12 for denture base polymers were followed in setting up the study design. The null hypothesis was that there would be no difference in physical properties of Lucitone 199 and the other experimental resins.