Effect of Three Commercially Available Die Hardening Agents on the Compressive Strength and Surface Hardness of Type IV Dental Stone: An In Vitro Study.

INTRODUCTION: Type IV dental stone is the material of choice for fabricating working dies in fixed prosthodontics because of its high strength and dimensional accuracy. However, repeated laboratory manipulation may reduce its surface integrity through abrasion and marginal deterioration. Limited evidence exists regarding the combined effect of various die hardeners and drying methods on the mechanical properties of Type IV dental stone. Therefore, the present in vitro study aimed to evaluate the effects of three commercially available die hardeners, used with two different drying protocols, on the compressive strength and surface hardness of Type IV dental stone.

MATERIALS AND METHODS: This in vitro experimental study was conducted on 80 standardized Type IV dental stone specimens that were prepared and divided into four experimental groups according to the die hardener used: cyanoacrylate, resin-based, colloidal silica-based, and untreated control. Each group was further subdivided into two drying protocols: 24-hour air drying and one-hour air drying followed by microwave drying. Compressive strength and surface hardness were evaluated using standardized laboratory testing procedures. Data were analyzed using two-way analysis of variance, Tukey's post hoc test, and an independent-samples t-test, with statistical significance set at p < 0.05.

RESULTS: The cyanoacrylate die hardener combined with microwave drying demonstrated the highest mean surface hardness (87.6 ± 3.8 Vickers hardness number (VHN)) and compressive strength (73.2 ± 4.1 megapascals (MPa)), whereas the untreated control with 24-hour air drying showed the lowest values (60.5 ± 4.9 VHN and 52.4 ± 5.0 MPa, respectively). Both the type of die hardener and the drying protocol significantly influenced surface hardness (F = 78.45 and 32.78, respectively; p < 0.001) and compressive strength (F = 68.42 and 33.10, respectively; p < 0.001). Microwave drying increased surface hardness by 4.3-5.3 VHN across the die hardener groups and increased compressive strength by 4.5-4.7 MPa in the cyanoacrylate- and resin-treated groups; these increases were statistically significant for the cyanoacrylate and resin groups compared with conventional air drying. Cyanoacrylate produced significantly greater improvements than the colloidal silica-based hardener for both surface hardness (mean difference = 13.75 VHN, p < 0.001) and compressive strength (mean difference = 10.45 MPa, p < 0.001).

CONCLUSIONS: The application of die hardener significantly improved the mechanical properties of Type IV dental stone. Among the tested materials, the cyanoacrylate-based die hardener produced the greatest enhancement, particularly when combined with microwave drying. This combination may enhance the mechanical properties of Type IV dental stone used for working dies in fixed prosthodontic procedures.