Microbial Contamination of Dental Unit Waterlines and Potential Risk of Infection: A Narrative Review

Abstract

Several studies have revealed that dental unit waterlines (DUWLs) are often contaminated by large numbers of various micro-organisms (bacteria, fungi, protozoa, viruses). Microbial contamination in DUWLs may originate from the mains water piped into the dental unit, the suck-back of patients’ saliva into the line due to the lack of adequate valves, and contamination from bottled water systems. Some of the main determinants of microbial contamination in DUWLs are: a very small lumen size (0.5–2 mm) of the tubing used, high surface-to-volume ratio (6:1), low throughput and the materials of which the tubing is made, water stagnation outside of working hours. The environmental conditions present inside the conduits of the dental unit may facilitate the proliferation of micro-organisms and the consequent formation of biofilm on the interior surface of the pipes of DUWLs. During the use of handpieces, particularly high-speed rotating instruments, a spray is thrown up in the form of aerosols or spatters containing biological material (saliva, blood and dental plaque) and micro-organisms. This means that the health of both dental staff and patients could be at risk of infection. The risk of cross-infections in dental settings can be tackled by implementing combined interventions to prevent the contamination of DUWLs.

Pseudomonas aeruginosa in the healthcare facility setting

“…It is estimated that most Pseudomonas water system contamination is confined to the distal 2 m of the water system [34]. P. aeruginosa is among the species frequently found in dental unit waterlines [5,[35][36][37], where it is capable of forming biofilms on the inner surface of narrow-bore plastic tubing that carries water to the high-speed handpiece, air/water syringe and ultrasonic scaler. A very small lumen size (0.5-2 mm), high surface to volume ratio (6:1), low throughput, the materials of which the tubing is made and water stagnation in DUWL, when units are not in use, further encourages biofilm growth [36].…”

Evaluation of Multidrug-Resistant P. aeruginosa in Healthcare Facility Water Systems

“…Different potential environmental reservoirs of this micro-organism have been described in healthcare settings (aerosols, taps, basin and shower drains, respiratory equipment, humidifiers, endoscopes and endoscope washers, hydrotherapy pools, dental units, etc.) [ 11 , 14 , 15 , 16 , 17 ].…”

Microbiological Contamination of the Office Environment in Dental and Medical Practice

“…A lot of human commensal bacteria of the skin such as Micrococcus spp., S. epidermidis and S. hominis were identified in the air and on the surfaces sampled. In some dental consulting rooms, bacteria such as Pseudomonas aeruginosa and Stenotrophomonas maltophilia were identified: these bacteria may originate from the water of the dental units [ 21 , 22 ]. In this study, no oral bacteria originated from the dental plaque were identified, but they may be found in dental consulting rooms [ 10 ].…”

“…Therefore, the micro-organisms indoor originated from two main sources: the outdoor air and the anthropogenic sources such as people from their skin, their clothing, and their respiratory systems [ 23 , 24 ]. They can also originate from healthcare activities or from other environmental sources such as water, notably in dental consulting rooms which are largely contaminated by aerosols or spatters containing micro-organisms originate from the dental unit [ 22 ].…”