Efficacy of super-oxidised water for disinfection

Key Points

• Dental unit water supplies become heavily contaminated with micro-organisms.

• The number can exceed the European standards for potable water.

• Super-oxidised water was used in a concentrated form to purge biofilm from dental units.

• Super-oxidised water was then used in a 5% (v/v) concentration as a maintenance dose to prevent recolonisation of the units.

• The combination of a purge and a maintenance dose of super-oxidised water reduced the micro-organisms to zero.

Abstract

Aims To determine the efficacy of super-oxidised water (Optident/Sterilox) in the decontamination of dental unit water lines.

Methods Dental units (10) were first purged with concentrated super-oxidised water. After purging, a 5% (v/v) super-oxidised water was used as a maintenance dose. Samples for microbiology were taken after 0,1,2,3,4,5,6,7 d, and each week for a further 13 weeks.

Results After purging, 5% (v/v) super-oxidised water was successful in reducing the microbial counts to zero, although in three of the units some bacteria were intermittently isolated in the first week of treatment.

Conclusions Super-oxidised water was successful in the removal of bacteria from dental unit water supplies. Complete removal required the treatment with a purge phase of concentrated disinfectant and a maintenance phase of at least two weeks.

Main

An investigation of the efficacy of super-oxidised (Optident/Sterilox) water for the disinfection of dental unit waterlines M. V. Martin and M. A. Gallagher Br Dent J 2005; 198: 353–354

Comment

A decade has passed since the American Dental Association published their recommendation that dental unit waterlines (DUWL) should contain no more than 200 cfu ml⁻¹ of aerobic bacteria. Methods introduced to improve DUWL microbiological quality have focused on four main approaches 1) physical methods - flushing, drainage and drying of the waterline and thermal controls 2) barrier methods -antiretraction valves, in-line filters 3) chemical treatments with disinfectants, super-oxidised water, UV and ozone 4) self-contained reservoirs that bypass mains water supply. The plethora of methodologies is indicative of the difficulties encountered with maintaining the water quality and in particular removing the biofilm. Physical methods when used alone are insufficient to eliminate the biofilm. Antimicrobial disinfectants have not been an unqualified success due to the intrinsic resistance of bacteria when growing within a biofilm compared to the same species in suspension. The extracellular polysaccharide biofilm matrix neutralises or impedes penetration of highly charged molecules and inhibits the action of many biocides.

There is no recognised protocol for specifically evaluating DUWL biocides. Most recent research studies have evaluated DUWL disinfectants using a combination of effluent water sampling plus removal of a portion of DUWL tubing to assess biofilm elimination using bacterial culture and microscopic-image analysis techniques. Currently, there are very few published controlled studies performed to evidence based criteria that compare the efficacy of different biocides when used in primary care. This situation makes it difficult for practitioners to compare the efficacy, cost and suitability of a product for use with their own equipment.

Laboratory evaluations of Sterilox demonstrated its ability to remove and destroy the biofilm. The present study illustrates the tenacity of the biofilm and the importance of maintaining daily dosing, as according to the authors' complete elimination of microbial count required a purge phase with concentrated disinfectant followed by a maintenance phase of at least two weeks. Sterile water is not considered mandatory in DUWL, but failure to destroy the biofilm matrix provides the necessary architecture for rapid biofilm reseeding, and subsequent deterioration of the water. To guarantee a continuing supply of high quality water the biofilm should preferentially be completely eliminated.

Manufacturer's instructions on biocide compatibility with their equipment should always be followed, as any disinfectant containing oxidising agents can potentially be corrosive. The authors reported no deleterious effects associated with Sterilox on the tubing or units over a six-month period but added the caveat that only further long-term use will establish this for certain.