Effect of Disinfection of Alginate on Gypsum

Statement of the problem: Disinfection of impressions is considered essential, however there is contradictory evidence on its effect on the accuracy and hardness of subsequent casts. Purpose: The purpose of this study was to analyse the effect of disinfecting irreversible hydrocolloid impression material (alginate) on the surface reproduction and hardness of resultant type III gypsum casts. Materials and methods: Under standardised conditions, 80 impressions were made of a ruled test block (ISO Specification 1563) using alginate and 3 commercially available disinfectants, Perform-ID, ImpressiV and Dimenol. Once treated, the impressions were poured with type III gypsum. ISO specifications for alginate state that it must reproduce a 50µm line. For evaluation of surface detail reproduction, two independent examiners, under a light microscope at 12x magnification examined the 50µm line. For evaluation of surface hardness, a Wallace hardness tester was used. Statistical analysis for line reproducibility was performed using a chi-squared test. For hardness, a one-way ANOVA and a Post-Hoc test were used. Results: None of casts poured from alginate disinfected with Perform ID were able to reproduce the 50µm line. The control group was statistically harder than the Perform ID and Dimenol groups. Conclusions: (1) Perform ID significantly affects the surface detail reproduction of subsequent type III gypsum casts. (2) Perform ID and Dimenol, both significantly affect the hardness of poured gypsum casts. Clinical implications: Careful consideration needs to be given to the disinfecting medium and procedure used in order to not compromise the surface reproduction and hardness of casts.