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Troubleshooting Dental Water Quality Problems 

Bacterial growth is logarithmic in nature, and generation times for some waterborne organisms are measured in minutes. As such, untreated or improperly treated units can be quickly re-colonized from small numbers of "survivor" organisms.

When clinical testing shows rebound contamination in a treated dental unit, the USAF Dental Investigation Service found that the higher levels of bacteria could be attributed to one of the following human errors. 

These troubleshooting tips have been adapted from the USAF Dental Investigation Service's document "Troubleshooting Dental Water Quality Problems".

1. Non-compliance. Dental units must be treated according to the established and recommended schedule. Failure to treat when indicated will result in rapid regrowth of the biofilm.

Untreated units left idle for various reasons usually exhibit re-growth of biofilms. If a unit is to be out of service for an extended period of time, follow the manufacturer’s instructions of the dental unit manufacturer and the compatible water treatment system for extended downtime protocols.

For short periods of disuse, continue weekly treatment. All units left unused for more than the standard retreatment period should be re-treated before clinical use.

2. Incomplete treatment. All lines (including ultrasonic scaler and air/water syringe lines) capable of carrying water have the potential to grow biofilm, whether they are routinely used or not. Untreated lines provide a refuge for bacteria and other organisms that can quickly re-contaminate the entire system.

In newer dental units with separate water reservoirs, use the purge mechanism to facilitate simultaneous treatment of multiple waterlines.

3. Failure to air purge. Many intermittent chemical treatment protocols are more effective when water is removed from the lines both before and after introduction of chemical solutions.

The first air purge assures minimal dilution of chemical agent. The second purge following disinfectant treatment enhances the effectiveness of the water flush to remove residual chemicals. A final air purge, to leave the unit dry when not in use, discourages regrowth of biofilm bacteria.

Always follow the manufacturer’s directions for use for the intermittent chemical treatment system and assure it is compatible with the dental unit manufacturer’s recommendations.

4. Inadequate contact time. For most chemical treatments, the effects of shorter than recommended treatment times are unknown but unlikely to be beneficial.

5. Improper dilution. Dilution can influence treatment efficacy. As an example, studies have shown 5.25% bleach diluted 1:10 (that is, 1 part bleach to 9 parts water) to be more effective than a 1:100 dilution in controlling bacteria in treatment water.

However, just as dilution that is too weak is likely to be ineffective, dilution that is too strong is likely to cause deterioration of dental equipment that contains metal components.

Note: The recommended 1:10 dilution is based on using commercial bleach packaged by the gallon at 5.25% (52,500 ppm) sodium hypochlorite, which dilutes to a 5,250 ppm bleach solution. The recommended 1:10 dilution is based on using commercial bleach packaged by the gallon at 5.25% (52,500 ppm) sodium hypochlorite, which dilutes to a 5,250 ppm bleach solution. To correct for the higher concentrations, the proper dilution for waterline treatment should result in approximately 5000ppm. As an example, a 7% solution should be diluted to approximately 1:13 (1 part bleach and 12 parts water), which yields a 5,385 ppm sodium hypochlorite solution.

"Note" on NaOCl concentration in Item 5 provided by Richard Karpay, DDS, MPH.