Purpose: To evaluate effects of a silver-citrate decontaminating agent on hetertrophs in dental treatment water and biofilms in dental unit water lines. Methods: Three dental units with self-contained reservoirs were used in this study. Units 1 & 2 were initially cleaned with 60 ppm ClO2 (4X10 minute contact) to remove/clean biofilms. Unit 3was not cleaned. For the next 8 weeks, about 750mL of municipal water mixed with one silver citrate tablet was used in Units 1 & 3 as irrigant. Fresh irrigant was made only when the reservoir became empty. Baseline, midway and end of study lines samples were harvested to study the status of biofilms using Scanning Laser Confocal Microscopy from all units after being dyed with BacLightŪ Green (Live) and Red (Dead) dye and viewed at 400X and 1600X. Baseline and weekly, water samples (10mL) were collected aseptically, neutralized with sodium thiosulphate, plated on R2A agar and incubated at room temperature for 7 days before quantification. Results: Colony counts before initial cleaning unit with ClO2 were greater than 80,000cfu/mL and all lines had a matrix of mature biofilms. After cleaning Units 1 & 2 with ClO2, biofilms were controlled/ removed but for scattered cells. Units 1 & 3 showed <10 cfu/mL after the first week, while Unit 2 showed counts >26,000 cfu/mL in 8 weeks with formation of biofilm. Unit 1 showed no biofilm while Unit 3 showed no removal of biofilm but for significantly more Red dye uptake (Dead). Conclusions: In this 8-week study, Silver Citrate by itself did not remove biofilms but clean units using Silver Citrate showed no build up of biofilms. Units using Silver Citrate as irrigant showed heterotrophic counts below 500 cfu/mL for 8 weeks. Support in part from Diagnostic Sciences, BCD TAMUS HSC. Materials provided by Confirm Monitoring System, CO.

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