An in vitro model for evaluating denture cleaning toothpaste regimes

Objectives: Persistence of microorganisms in the form of biofilms on the non-shedding surfaces of acrylic dentures occurs in cases of poor denture-cleansing. The biofilms may then be responsible for oral infection such as Candida-associated denture stomatitis (DS). As a result, both the development and evaluation of denture cleaning products is important. The objective of this study was to identify appropriate methodology for the in vitro evaluation of denture-cleansing using physical brushing and an experimental denture cleansing paste.
Methods: A 200-μl volume of human saliva, artificially contaminated with Candida albicans was overlaid on the surface of acrylic squares which had previously been immersed in an artificial saliva for 24 h at 37°C. The acrylic was incubated at 37°C for 72 h, with addition of artificial saliva at 24 h intervals. The acrylic was immersed in sterile water for 5 min and selected samples were also air dried at 37°C for a further 72 h. Brushing with cleansing paste or water for 2 min, used a powered toothbrush positioned so the bristles just made contact with the acrylic surface. Cleansing agent was removed by immersion and gentle agitation of the acrylic in sterile water for 1 min. Microorganisms on acrylic were fixed in 4% (v/v) formalin for 24 h, stained with propidium iodide and imaged using confocal laser scanning microscopy or scanning electron microscopy (SEM). CLSM images were converted to binary black and white to determine the percentage area colonised using ImageJ software.
Results: An extensive biofilm (mean percentage area colonised=3.9%) was generated on non-brushed control acrylic. Compared with unbrushed controls, significantly reduced colonisation (mean percentage area colonised=0.6%) occurred following brushing with cleansing paste (P<0.001). Brushing with water (mean percentage area colonised=3.9%) did not reduce colonisation compared with unbrushed controls.
Conclusions: An in vitro method of evaluating the efficacy of denture cleaning approaches has been developed. Using this model system, it was evident that when coupled with toothbrushing, use of a cleansing paste provided added value to removal of a microbial biofilm on acrylic surfaces.

The study was funded by GlaxoSmithKline Consumer Healthcare, Weybridge.