Microbial deposits in dental unit water lines (DUWL) are a potential h
ealth problem. Flushing with sodium hypochlorite is one possible proce
dure for controlling biofilm in DUWL; however, strong oxidizing agents
, such as 5000 ppm sodium hypochlorite or 5000 ppm sodium hypochlorite
in 1% acetic acid, may attack metal components in a dental unit. Dent
al units in five clinics equipped with separate water reservoir system
s (SWS) were analyzed for metal content in the water. Source water for
these units was either municipal water (MW), distilled water (dH2O),
or sterile deionized water (sdH2O). Except for calcium, there were no
major differences in the metal content of source water drawn from any
of the units. The units using dH2O and sdH2O had been treated with eit
her 500 or 5000 ppm bleach from several weeks to several years. A meta
l profile of the effluent obtained during treatment with hypochlorite
showed no major dissolution of metal components (average Cu=0.56, Ni=0
.17, Zn=0.91 mg/L). The final water sample flushed from the units afte
r hypochlorite treatment with SWS contained less metal than the water
from the units connected to the local municipal water system. The meta
l ions in the effluent from units being treated with hypochlorite in 1
.0% acetic acid were approximately 10 times greater than those from un
its treated with sodium hypochlorite alone (Cu=20, Ni= 1.5, Zn=22 mg/L
). Flushing DUWL with 5000 ppm bleach and using sdH(2)O in the SWS cau
sed less corrosion and resulted in lower metal concentration in the wa
ter than the use of municipal water. (C) 1997 Academic Press.