Implementation and Preliminary Evaluation of a Low-Cost Sodium Hypochlorite Shock Disinfection Protocol for Dental Unit Waterlines.

Background/

Objectives

This exploratory study aimed to characterize the microbiological contamination of dental unit waterlines (DUWLs) and to conduct a preliminary evaluation of a 0.5% sodium hypochlorite shock treatment.

Methods

Water samples from five dental units in a single teaching institution were collected from the air/water syringe and high-speed handpiece lines at four time points: baseline, immediately after a shock treatment, and 7 and 14 days post-treatment. The water supply source was also analyzed. The intervention consisted of a 15-min exposure to 0.5% sodium hypochlorite. Bacterial and fungal contamination was assessed using validated semi-quantitative microbial samplers, and key bacterial isolates were identified.

Results

Baseline assessments revealed substantial bacterial contamination in most units (≥301 CFU/mL), despite minimal contamination in the water supply source (<10 CFU/mL). An immediate reduction in microbial counts was observed following the shock treatment for both bacteria and fungi counts; however, resilient species such as P. aeruginosa and the spore-forming B. cereus persisted, while K. pneumoniae was no longer detected. Bacterial levels increased again within 7 days in several units, while fungal contamination remained low at the follow-up. At 14 days, bacterial results were variable and inconsistent. In contrast, fungal contamination remained suppressed in most units throughout the follow-up period.

Conclusions

The sodium hypochlorite shock treatment produced an immediate decrease in microbial load in DUWLs, but the findings suggest that its sustained effect on bacterial control may be limited. Given the small sample size and single-center design, these results should be interpreted cautiously. The study demonstrates the feasibility of implementing a structured DUWL monitoring and maintenance program using a simple, low-cost sodium hypochlorite protocol, providing a practical model for improving water quality and patient safety in dental clinics.