Silica as a Reference for Laboratory Toothpaste Assessment Methods

While there is a multi-year supply of calcium pyrophosphate reference material for laboratory abrasivity and cleaning power methods to assess toothpaste and other oral care products, there has been a continuing desire to have a reference material more representative of current toothpaste ingredients. Objective: This longitudinal collaborative study was to characterize three commercially available toothpaste grade silica products, Sident® 8, 9 and 10. Methods: Representative samples from one lot of each silica were bagged and stored on pallets in environmentally controlled rooms at normal (ISO 554: 23ºC/50%RH) and tropical (40ºC/70%RH) conditions. Samples were analyzed at 4, 12, 24 and 52 weeks. Physicochemical characterization of the silica specimens as well as the clinically predictive abrasivity and cleaning power methods were done to compare samples taken at each time period. Analyses included specific surface area, loss on drying, pH of 5% suspension, viscosity of CMC dispersions, particle size, tamped density (ISO 787-11) and sodium, iron and sulfate. Abrasion levels of the silica samples were tested in two labs using the Radioactive Dentin Abrasivity Method (ISO 11609); in one lab using a profilometric method with acrylic substrate; and in a fourth lab using a copper gravimetric method. Two labs performed stain removal studies using the method of Stookey et. al, (JDR 61: 1236, 1984). Results: There was little difference between samples stored at normal and tropical conditions. Some physicochemical changes of the silica particles may signal possible, future changes in the predictive clinical values of abrasivity and cleaning power. Conclusion: Preliminary analysis of this continuing study indicate one or more of the three silica materials remains unchanged as measured by multiple established laboratory abrasivity and cleaning power methods for toothpaste and thus may be suitable as a reference material. hefferen@ukans.edu