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The disinfection of dental impression materials has become an essential topic of universal concern, as it may be the first instance of microbial contamination during dental care. The purpose of this study is twofold: To determine the effectiveness of disinfection with 0.5% sodium hypochlorite and 2% glutaraldehyde solutions in irreversible hydrocolloid (alginate) and silicone impressions and to analyze the effect of disinfection on surface quality with a scanning electronic microscope. A total of 32 impressions (16 made of irreversible hydrocolloid and 16 made of silicone) were taken from maxillary dentate patients. Samples of 1cm2 (80 , irreversible hydrocolloid, 80 silicone) were obtained and distributed in ten groups: alginate in no disinfectant (control group 1, AL), alginate in 0.5% sodium hypochlorite (NaOCl) for 5 (AH5) and 10 minutes (AH10), alginate in 2% glutaraldehyde for 5 (AG5) and 10 minutes (AG10), silicone in no disinfectant (control group 2), silicone in 0.5% NaOCl for 5 (SH5) and 10 minutes (SH10), and silicone in 2% glutaraldehyde for 5 (SG5) and 10 minutes (SG10). Each sample was divided into two segments (one for the microbiological and one for the SEM study). Microbiological samples were planted on blood agar, Mac Conkey agar, and Sabouraud agar, and identification was made by Gram´s stain. The samples were then processed by an SEM. Immersion in the 5% NaOCl and 2% glutaraldehyde for 10 minutes completely eliminated bacteria in the impressions, compared with the control group (P=0.000004). Immersion in 0.5% NaOCl and 2% glutaraldehyde for 5 and 10 minutes significantly inhibited bacterial growth in both the irreversible hydrocolloid and silicone impressions compared with control group (P<0.05). However, in the SEM study, immersion in both disinfectant solutions for 5 and 10 minutes did not significantly affect the surface quality of the irreversible hydrocolloid and silicone impressions compared with immersion in the non-disinfectant samples. Impression materials retain bacteria. Immersion in 0.5% NaOCl solution and 2% glutaraldehyde for 5 minutes can successfully disinfect irreversible hydrocolloid and silicone impressions. The results showed that it is prudent for either the operator or the technician to treat impressions for 5 minutes by immersion in 0.5% NaOCl or 2% glutaraldehyde to reduce the level of bacterial contamination and hence the risk of cross infection.

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