Effect of 2% glutaraldehyde disinfectant on dimensional stability and mechanical properties of gypsum model

Objective To evaluate the effect of 2% glutaraldehyde disinfectant on properties of Ⅳ type gypsum model, and the morphological characteristics of the fractured surfaces of gypsum samples were observed by scanning electronic microscope (SEM) , which provided the basis for the clinical application of disinfectant blending method. Methods Type Ⅳ gypsum models were made by type Ⅳ gypsum mixed with distilled water and 2% glutaraldehyde, respectively. At 24 hours after the mixture of type Ⅳ gypsum, samples were measured to calculate their dimensional change, and the Knoop hardness of the sample surface was tested. The compressive strength and bending strength of models at one and two hours were evaluated. Data were statistically analyzed with t-test of two independent samples (SPSS 20.0) . The morphology of the fractured surfaces was observed by SEM. Results The minimum and the maximum values of model size change were OH 0.0006% and OO′ 0.1290% in the 2% glutaraldehyde group, respectively. The maximum surface hardness of gypsum samples was 68.30 N/mm2 in the distilled water group, and the minimum value was 58.20 N/mm2 in the 2% glutaraldehyde group. There was no significant difference in dimensional changes and surface hardness between the group of distilled water and 2% glutaraldehyde (P>0.05) . The minimum compressive strength (32.00 MPa) and bending strength (7.42 N/mm2) were found in the group of 2% glutaraldehyde at1 h. There was significant difference in compression strength between the group of distilled water and 2% glutaraldehyde at 1 h (P 0.05) . There was significant difference in bending strength between the group of distilled water and 2% glutaraldehyde at 1 h (P 0.05) . SEM of the group of 2% glutaraldehyde at 1 h showed a relatively neat aggregation of short crystals. Crystals of the distilled water group and the 2% glutaraldehyde group at 2 h showed the same plate-like crystals which were staggered similarly. Conclusions There are no effects of 2% glutaraldehyde on the 24 h dimensional stability and surface hardness of type Ⅳ gypsum. The Ⅳ gypsum mixed with 2% glutaraldehyde had reduced compressive strength and bending strength at 1 h, while its bending strength and compressive strength at 2 h increased to meet the mechanical requirements of dental model. It is recommended that the demoulding time should be two hours after gypsum mixed with 2% glutaraldehyde. Key words: Glutaral; Calcium sulfate, dental models; Hardness, surface; Compressive strength; Bending strength; Dimensional change