The dental impression is the most widely performed procedure at clinical dentistry in order to obtain an optimal final model. The aim of this study was evaluate the dimensional changes in type IV gypsum models obtained by alginate impressions; this alginate was mixed with different proportions of water (18 ml, 13.5 ml and 24 ml). The alginate used in the study was Tropicalgin by Zhermack® . A stainless steel master model was constructed, which simulated a hemi-arch and two pillars. 3 groups were assigned (group 1, the control group: 18 ml of water and 9 gr of powder which corresponds with the manufacturer’s specifications, group 2: 13.5 ml of water and 9 gr of powder and group 3: 24 ml of water and 9 gr of powder). 15 impressions were made for each corresponding group and were cast into type IV gypsum models using Elite Rock by Zhermack® . 8 measurements were taken of each of the gyp...