Evaluation of bacterial contamination of dental unit waterlines and use of a newly designed measurement device to assess retraction of a dental chair unit

Abstract

Introduction: Dental unit waterline (DUWL) output water is delivered through instruments of a dental chair unit (DCU) to irrigate and cool teeth. However, these waterlines can be heavily contaminated with bacteria. Aim: The purpose of the present study was to assess retraction and investigate the contamination level and prevalence of bacteria in DUWL output water. Methods: Fifty-eight DCUs were randomly selected from 30 hospitals in 10 districts of Tianjin, one of the four special municipalities of China. A unique sampling connector was used in place of the dental handpiece to collect water samples. Evaluation of retraction was accomplished using a retraction measurement device designed in accordance with the International Standard ISO 7494-2:2015(E). Results: A total of 263 water samples were collected, and the highest concentration of bacteria [1.8 × 106 colony-forming units (CFU)/mL] was found in the handpiece group. Thirty (51.72%) water samples in the handpiece group and 21 (36.21%) in the air/water syringe groups were cultured, yielding colony counts of > 500 CFU/mL. Potential infectious agents, such as Bacillus cereus, Kocuria kristinae and Pseudomonas fluorescens, were isolated from the water samples. Thirty (51.72%) DCUs failed the retraction evaluation. There was a significant, positive correlation (P < 0.05) between the concentration of bacteria in the water sample and the retracted volume. Conclusion: It is of paramount importance to increase compliance with the standards for controlling DUWL contamination. Routine microbial monitoring and evaluation of retraction are necessary to provide high-quality water for use in dental treatment.