OBJECTIVE  To investigate the disinfection efficacy of ozonated water in dental unit waterlines （DUWLs） and its inhibitory and destructive effects on biofilms.

METHODS  A laboratory model of DUWL disinfection with ozonated water was established. Ozonated water （concentration: 0.1–0.5 mg/L） was used for disinfection. Bacterial colony counts for the biofilms on the surface of tubing membrane were performed before disinfection and on Day 7 after disinfection. Biofilm structures were observed via scanning electron microscope （SEM） on Day 7 and Day 14 after disinfection. The efficacy of periodic disinfection with chlorine-containing disinfectants was compared with continuous disinfection with ozonated water. This study spanned 186 days. For the first 14 days, water samples from three outlets （mouth rinse water, three-way syringe outlet water and ultrasonic scaler connection water） were collected before and after each shift daily for total bacterial colony counts. On Day 60, Day 121 and Day 186, post-shift water samples from the three outlets were collected for total bacterial colony counts. Before ozonated water disinfection and on Day 21 and Day 60, sections of the waterline tubing were excised for observation of biofilm structural changes under confocal laser scanning microscope （CLSM） and SEM.

RESULTS  Regardless of whether the tubing membrane contained Ag⁺, the total bacterial colony counts on Day 7 after ozonated water disinfection were lower than those in the distilled water control group. On Day 7 and Day 14, no significant bacterial aggregation was observed on the membrane surfaces in the experimental group, whereas bacilli were found growing aggregatedly on the surfaces in the control group. Among 420 periodically disinfected water samples collected from Day 1 to Day 7, the median total bacterial colony counts for mouth rinse water, three-way syringe outlet water and ultrasonic scaler connection water were 92.50, 265.00 and 470.00 CFU/ml, respectively （P ＜0.05）. Among 420 continuously disinfected water samples collected from Day 8 to Day 14, the median total bacterial colony counts for the three sites were 145.00, 37.50 and 130.00 CFU/ml, respectively, with no statistically significant differences. Daily water quality compliance rates ranged from 15.00% to 66.67% during periodic disinfection and from 36.67% to 100.00% during continuous disinfection. On Day 21 of continuous ozonated water disinfection, the live/dead bacteria ratio observed under CLSM significantly decreased compared to periodic disinfection, with a marked increase in dead bacteria proportion of the biofilm on the water flow surface. SEM revealed biofilm peeling. On Day 60, the proportion of dead bacteria in the biofilm increased, typical structures were disrupted, and only scattered residual bacteria remained.

CONCLUSIONS  Continuous disinfection with ozonated water can effectively control microbial contamination in DUWLs, improve the compliance rate based on GB 5749 standards, and disrupt pre-existing biofilms in waterlines over long-term use.