Abstract: Objective: To compare the effects of three powder-water ratios and four mixing times on the flowability and accuracy of alginate impression by automatic mixing. Methods: The alginate impression material was mixed by automatic alginate mixer. The fluidity and accuracy were measured by 12 combinations of 3 powder-water ratios (11.5 g:23 mL, 11.5 g:25 mL, 11.5 g:27 mL) and 4 mixing times (3 s, 6 s, 9 s, 12 s). Results: The powder-water ratio and mixing time had significant effect on the flowability of impressions (P < 0.01). The 23mL12s group had the lowest fluidity [(43.05±3.43) mm] and the 27mL3s group had the highest [(72.31±2.25) mm]. The influence of powder-water ratio and mixing time on the accuracy of impression materials was not statistically significant. Conclusion: In a certain range, the powder-water ratio and mixing time were negatively correlated with the flowability of alginate impression materials, and the effect of increasing water content on the flowability was more obvious than that of decreasing water content.

Key words: Flowability, Accuracy, Powder-water ratio, Mixing time, Automatic mixing method, Alginate impression material