Four dental units which had never been treated with any chemical germicide to control water system contamination were used in this study. Two chairs were retrofitted with self-contained water systems (C1 & C2) while the remaining two were connected to municipal water supply (C3 & C4). Samples (16 mL each) from the dental unit water systems were collected at baseline post 1 minute flush, post 2 minute flush and post 3 minute flush. C1 and C2 were treated with 5000 ppm of NaOC1 for 10 minutes. The units C3 and C4 were not treated with any germicide. This process was repeated at 0 hours, 48 hours and 96 hours. Split samples of water from each unit were quantified for microbial contamination using HPC (Millipore) samplers and comparison water test kit (DT). The remaining water from each of the samples was tested for endotoxins using the BioWhittaker Quantitative Chromogenic LAL test. Descriptive statistics, paired t-test and regression analysis was conducted (a=).05) on data obtained.

Total number of water samples analyzed was 48 (n=48). About 91.5% of water samples stained gram-ve. The mean heterotrophic plate count (log₁₀) for the HPC samplers was 3.1 (SD=1.1), while the mean for the DT kits was 3.1 (SD=0.7). Mean endotoxin level was 80.7 EU/mL (SD=22.3); minimum = 29, maximum = >100 EU/mL. There was no significant difference between the two methods of heterotrophic plate counts (t=0.33 df=47, p = 0.7). Regression analysis indicated that there was no association between either methods of heterotrophic plate counts and the endotoxin levels.

In this study, data showed that the endotoxin levels in both standing and post flush water samples were extremely high. The levels of microbial contamination as determined by heterotrophic plate counts do not predict the quantity of endotoxins in the water. The concentration of endotoxins in the dental unit water systems may be significant enough to cause a febrile reaction in a normal and healthy patient. The study was supported by Diagnostic Sciences TAMUS-Baylor College of Dentistry with analytical support from Pall Life Sciences.