Evaluation of the Antimicrobial Functions of N-halamine Dental Unit Waterline Tubing for One Year

Abstract

Objectives: The objective of this study was to test the biofilm-controlling properties of N-halamine antimicrobial dental unit waterline (DUWL) tubing (T) tubing, without recharging over one year, compared to a control line (C).

Methods: A simulated clinical model was used to pump ultrapure water through T and C lines at a rate of 1.4 mL/min, five minutes on, 15 minutes off, eight hours/day, five days a week. Samples of source water, effluent from T and C, and from the stagnant water in the carboy (liquid container) after bench work was completed (S2), were collected aseptically, serially diluted, and cultured on R2A agar for seven days every six weeks. SEM images of the inside surfaces of detached tubing sections were also taken. The carboy was rinsed with a 1:10 dilution of sodium hypochlorite after six months. Means of log transformed CFU values obtained in triplicate were paired by T and C lines across months for comparison by paired Student's t-tests.

Results: An increase in effluent and carboy bacterial counts were noted after six months, but decreased after bleach rinse of the carboy. No significant difference (p > 0.25) between T and C lines were observed; similarly, T and carboy were not significantly different (p > 0.30). SEM images showed biofilm attachment on the inside surface of C after two months, but not on T. Organisms identified in the effluent reflected those in the source carboy.

Conclusions: No biofilm attachment was detected on the N-halamine test line after 12 months, indicating its antimicrobial properties were retained. Further evaluation is recommended to determine the optimal recharge interval for N-halamine DUWL tubing when ultrapure source water is used.

Keywords: N-halamine; biofilm; dental unit waterline contamination; dental unit waterlines.

Figure 1

Graph of means of triplicate CFU values for each effluent sample across six-week intervals obtained from carboy (S2), test (T), and control (C) sources. The dependent (CFU) axis is log transformed to adjust for the exponential distribution of the CFU count values. Note that the three source lines connecting the means in chronological order are mostly parallel.

Figure 2

SEM Images (5,000 magnification) showing inside surfaces of N-halamine tubing at baseline, six, and twelve months with no biofilm attachment (A, B, and C); biofilm attachment on the Control Tubing with an increase in density over time (D, E, and F).