Comparison and Evaluation of Various Drying Methods on Surface Hardness of Type IV Dental Stones: An In vitro Study

Accurate dental restorations require die materials with optimal surface hardness. This study evaluated drying method effects on three Type IV dental stones: Elite Rock (ZERMACK), Fuji Rock (GC), and Kal Rock (KALROCK). One hundred twenty samples of ZERMACK, GC, and KALROCK were prepared using manufacturer-recommended water/powder ratios. Samples were divided into four subgroups based on drying method: 1-hour air drying, 24-hour air drying, 1-hour air drying followed by 10 min of microwave drying at low power, and 24-hour air drying followed by die hardener application. Knoop hardness testing was conducted according to ADA specification #25. One-way ANOVA and pairwise comparisons were used for statistical analysis. GC showed the highest mean hardness (84.58), followed by ZERMACK (74.82), and KALROCK (67.07). Significant differences existed (F [2, 27] =190.463, <i>P</i> < .001). GC had significantly higher hardness than KALROCK (17.52 difference) and ZERMACK (9.76 difference) after 24 hours. GC exhibited superior surface hardness. Material selection and drying methods significantly impact Type IV gypsum hardness for dental dies.