Residual Bioload of Disinfected Curing-Lights in a Dental School Clinic

Objective: Identify areas of potential contamination of dental curing lights in a dental school clinical environment in order to optimize disinfection protocols.

Method: Specific curing lights (LE Demetron, Kerr) used in dental student clinics were disinfected prior to clinical use. Specific locations of each curing light were swabbed using a sterile cotton tip, and immediately streaked onto blood agar plates.  Samples were taken from seven areas on 20 light units: tip, light guide shank, blue-blocker shield, air vents, activation button, unit body, and the battery sides and end. The eighth was the negative control (sterile swab). Biologic growth in these areas represented control values for comparison to samples taken after the lights were used clinically. Students were not informed of the testing. Proper clinical procedure dictated that the student cleaned all surfaces of the curing light with a liquid, cold disinfectant (Dispatch, Clorox) between patients.  At the end of the day, the same locations of the curing lights were swabbed as described previously. Swabbed plates were incubated for 48 h at 37^oC and were evaluated for colony and bacterial morphology studies.

Result: Thirty-one colonies grew from the 140 samples taken pre-clinical use while 27 colonies grew after use in the clinic.  A wide variety of bacterial and fungal organisms were found.  Most of the colonies had one of three morphologies:1) yellow, raised, well-defined colonies 2) milky, raised colonies 3) black, fuzzy, non-defined colonies. Of particular interest was a b-hemolytic Staphylococci that was found on five different units.  Most bacteria were found in the samples from the vents and buttons of the light.

Conclusion: The number of colonies detected after clinical use were less than those found prior, suggesting good infection control compliance by the students.  Areas identified that could be better disinfected included the curing light vents and activation buttons