Evaluation of the Linear Dimensional Changes and Hardness of Gypsum Product / Stone Type Ⅳ after Adding Silica Nanoparticles

Dental gypsum is routinely used as an investing and molding material for prosthodontics restoration with some acceptable linear dimensional changes in the finished restorations. This study aimed to evaluate linear dimensional stability and surface hardness of dental stone type Ⅳ when adding silica nanoparticles to it. 40 type Ⅳ stone specimens were prepared from stainless steel molds for linear dimensional stability and plastic mold for hardness, 20 of which contained silica nanoparticles (test group) while the other 20 were without any addition (control group). Each group was divided into subgroups containing 10 specimens for each one in order to compare the dimensional stability and hardness of them. The linear dimensional changes were measured using a digital caliper, while the hardness was tested with Vickers' hardness test. The data were analyzed with t-test (two-sample assuming unequal variances) and p-value. The mean value of linear dimensional changes for the control group was -0.396 and -0.386 for specimens of the test group. Mean hardness was 50.638 for the control group and 53.295 for the test group. The difference was significant for linear dimensional changes and highly significant for hardness. Adding of silica nanoparticles improved the hardness and reduced the linear dimensional changes of type Ⅳ stone.