IMMERSION DISINFECTION OF IRREVERSIBLE HYDROCOLLOID IMPRESSIONS IN PH-ADJUSTED SODIUM-HYPOCHLORITE .1. MICROBIOLOGY

Sodium hypochlorite is one of the disinfectants recommended for impres sions, usually in a 1:10 dilution to minimize the negative effects on the impression material and poured gypsum cast. Dilution causes a loss of antimicrobial properties, however. Sodium hypochlorite is known to have enhanced antimicrobial properties at lower pH levels. This study evaluated the antimicrobial activity of sodium hypochlorite at progre ssively lower pH levels. A metal model of a denial arch was contaminat ed, and irreversible hydrocolloid impressions were made, cultured, dis infected (by immersion), and cultured again. Predisinfection and postd isinfection bacterial counts were compared. It was found that a 10-min ute immersion in solutions reduced to pHs 7 to 11 consistently produce d a 4-log (99.99%) or greater reduction in viable organisms. A pH of 1 0 was the only level that was consistently effective at decreased imme rsion times. It was effective in times of 3 minutes or greater.