Objective: This collaborative study was to provide longitudinal physical and chemical characterization data as well as abrasivity and cleaning power data on three dentifrice grade silica materials, Sident 8, 9, and 10, stored at normal (ISO 554: 23„aC/50% RH) and tropical (40„aC/70%RH) conditions. Method: The methods included ISO 11609 Radioactive Dentin, Profilometry with Cast Acrylic and Copper Gravimetric abrasivity methods and Indiana Cleaning Power using Bovine Teeth (JDR 61:1236,1982) to assess dentifrice functionality. Calcium pyrophosphate reference material was used for both abrasivity and cleaning power methods. Two laboratories used the radiotracer method and two used the bovine tooth stain cleaning power method. Physicochemical characterization included specific surface area, weight loss on drying, pH of 5% suspension, viscosity of CMC dispersions, particle size, tamped density (ISO 787-11) and sodium, iron and sulfate analyses. In addition to the specimens analyzed in the first report (JDR 81:233, #1776, 2002) at 4, 12, 24 and 52 weeks, specimens for this report were analyzed at 78 and 104 weeks. Results: The ISO 11609 Method radioactive dentin abrasivity data for Sident 8, 9 and 10 at 52, 78 and 104 weeks were within 95% confidence intervals with no difference between the silica stored at normal and tropical conditions. The cleaning power for Sident 8, 9 and 10 at 52, 78, 104 weeks were also within 95% confidence intervals with no difference between silica stored at normal and tropical conditions. Conclusion: Two year data from this continuing study indicate that the three silica materials are unchanged as measured by established laboratory methods to assess the abrasivity and cleaning power of toothpaste and thus the Sident materials may be suitable as an additional reference material in the future. Participants contributed their in-house costs. hefferen@ku.edu.