Water Quality and Biofilm Formation in Dental Unit Waterline Systems in Mangaung, South Africa

Biofilm formation in dental unit waterlines (DUWLs) and the consequent microbial contamination of dental chair unit (DCU) water is a significant challenge. The South African government has no explicit requirements for water quality supplied to DCUs or for disinfection protocols for DUWLs.

To assess bacterial water quality and presence of biofilm-associated organisms in DUWLs of open and closed system DCUs.

Standard water sampling was followed in accordance with the South African National Standard for drinking water (SANS 241:1) and used as reference for microbial water quality to measure heterotrophic plate counts (HPC) and total coliforms for possible water contamination. Pseudomonas aeruginosa and Legionella spp. are common opportunistic pathogens found in DUWL and were also assessed using selective media.

HPC exceeded the national standard of <10 × 10³ CFU mL^-1 in water from both open and closed systems (1.48-6.94 × 10⁴ CFU mL^-1 and 1.71 × 10⁴ CFU mL^-1). P. aeruginosa was detected in fast handpieces, reservoir bottles, and distiller bottles of closed system DCUs. Legionella spp. (22 CFU mL^-1) were present in the output water from one fast handpiece of an open system DCU. Internal surfaces of taps, fast handpieces, distiller bottles and reservoir bottles also exhibited mean HPC counts which exceeded the national standard. Total coliforms were identified in the fast handpieces of open system DCUs (5.09 × 10³ CFU 100 mL^-1) and distiller bottles (6.23 × 10³ CFU 100 mL^-1) of closed systems. P. aeruginosa (3.64 × 10⁴ CFU mL^-1), was detected on the internal surfaces of the municipal tap supplying water to open system DCUs as well as, internal surfaces of reservoir bottles (5.9 × 10¹ CFU 100 mL^-1) and fast handpieces (1.5×10¹ CFU 100 mL^-1) of closed system DCUs.

Contamination levels of DUWL water and surfaces of open and closed system DCUs were high, highlighting the need for national regulations of DUWL quality and decontamination protocols in South Africa.