Effect of the mixing method on the dimensional stability of dental stones

Objective: The aim of this study was to evaluate the influence of mixing method and the empiric water/powder ratio on the dimensional change of two types of dental stones (type III and type IV) at different setting times: baseline, loss of brightness, initial and final setting (1/4 and 1pound Gilmore´s needle, respectively) and, after 48 hours at 37°C. Material and Methods: Five mixing methods were used: Gc – manufacturer´s recommendation, G1 – weighed powder/ empiric water volume and powder on water, G2-weighed powder/ empiric water volume and water on powder, G3 – empiric powder volume, graduated water and powder on water, G4-empiric powder volume, graduated water and water on powder. The linear expansion was measured according to ISO 6873. The expansion values (x10-2 mm) were analyzed by Two-way ANOVA and Tukey HSD test (α=0.05). Results: For type III, the results showed significance for both factors and for interaction; for type IV, only the time were significant (p<0.05). Limited by methodology, it could be concluded that both dental stones expanded more than the recommended by ISO. Conclusion: The expansion of type III was dependent on the mixing method, and once correct consistency is reached with type IV, there is no influence of mixing method on dimensional stability.