Methods: A laboratory system, simulating predoctoral dental clinic activity, was used to test rechargeable N-halamine tubing (T) compared to treated (RC) and untreated (C) dental unit manufacturer's control tubing. Pump flow cycles with source tap water were set at 1.4mL/min, 5min on and 25min off, 8 hrs/day, 5 days/week. Every three weeks, samples of effluent water, recovered adherent bacteria in solution from inside tubing surfaces, and SEM images of T, RC, and C sections were examined for bacterial and biofilm growth. After sampling, a recharging solution of chlorine bleach (1:10 dilution) was run through T and RC lines, left overnight and rinsed out next morning. Non-parametric Kruskal-Wallis and Mann-Whitney U statistical tests were used to identify group differences.
Results: Over the 8-month study period, source tap water had a mean number of bacterial CFU/mL of 6.4x102. T effluent had an average of 1.0x103, RC had 2.6x103, and C effluent had 5.0x103 CFU/mL. The mean number of adherent bacteria recovered from inside T was 1.3x102 CFU/mL; 1.4x103 from RC; and 2.0x103 CFU/mL from C. SEM imaging at periodic intervals confirmed the presence of biofilm inside RC and C, but not inside T, even after eight months. THM and TAA were within normal range.
Conclusions: This study found that bacterial counts in T were significantly lower than C (p<0.03) over eight months; N-halamine tubing completely inhibited biofilm formation without negatively affecting the physical properties of the effluent water; T effluent bacterial levels reflected the source tap water quality and proliferation of planktonic bacteria, but not biofilm activity. Further testing to investigate the effect of using a pure water source is recommended (NIH/NIDCR 5R01DE018707-02).