Structure/Properties Correlation of Set Gypsum Die Material

Gypsum products have been considered among the widely used model and die materials. Modification of these materials by adding chemicals or salts would result in a changes of their structure as well as in their properties. Recently disinfection of gypsum casts got a huage concern with increasing the interest about infection control. Objectives: Several studies have evaluated the properties of gypsum after its disinfection with different techniques, but no one has concerned by examining the structure of these disinfected stones. Accordingly, This study aimed to study the internal structure of set disinfected dental stone and correlate the findings to different material’s properties by using both visual and statistical methods. Materials and Methods: This study utilized type IV stone as a representitive of the currently available gypsum products. This materials has been mixed with aqueous solutions of three chemical disinfectants as well as water as control. Both compressive and diametral tensile strengths have been evaluated. Surface roughness and hardness were also tested. Structure of the set disinfected materials was examined by the use of scanning electron microscope (SEM) and x-ray diffraction method. Statistical correlation took place between both crystal size and relative degree of crystallinity of set gypsum and the values of tested properties. Results: Results of this study shows adverse effects of disinfectants on the properties of set gypsum (ANOVA, P < 0.05) and also revealeved no clear corrlelation between these properties and the structure (For all properties Linear Fit Stone, R Square Adj > 0.05 except that of hardness when correlated to degree of crystallinity = 0.0477). Conclusions: Both properties and structure of set gypsum could be affected by using chemical disinfectants as mixing water substitutes. However, there is no clear statistical correlation between either crystal structure or relative degree of crytallinity and the properties of set gypsum.