Metal Corrosion With Commonly Used Waterline Disinfection Materials

Objectives:  There are numerous commercially available products that are currently used for dental waterline disinfection.  These include hypochlorite (bleach), peroxide based products (Sterilex Ultra®) and ethanol/chlorhexidine (Lines™).  Metals are at risk during this decontamination process from extremes of pH as well as redox characteristics of certain agents, specific corrosion of copper, aluminum, stainless steel and brass can occur.  Qualitative corrosion experiments were conducted using commercially available disinfection products and compared to a distilled water standards to determine if there is indeed corrosion of the metals used in dental unit water lines.   Methods:  Coupons of metal measuring 2.5 x 2.5 cm and 2 mm were used.  The materials included copper, aluminum and stainless steel (304).  Each was precleaned with acetic acid and rinsed thoroughly prior to the study and placed in glass beakers.  The samples included single metal tests, aluminum, copper and stainless steel.  A 4^th test was with all three coupons simulating a dissimilar metal model.  With each metal combination, materials tested were Lines™, Household bleach (5.25% , 1:10 dilution), Sterilex and distilled water for a control.  Eluent was sampled at intervals of 16, 24, 48 and 128 hours and analyzed for metallic ions of copper, aluminum and iron respectively.  Ion uptake in the eluent is an indicator of metal corrosion.  Results: The analysis demonstrated increased metal ion uptake in the eluent of the control, hypochlorite and Sterilex.  Hypochlorite and Sterilex both exceeded the control.  No uptake was observed in Lines™.  Conclusions: Distilled water and several dental waterline disinfection methodologies have a sacrificial effect on metals, types of which are found in water systems of dental units.  Lines™ does not appear to sacrifice metals within the unit and may also serve as an intermittent protective chemical during dental unit down time.