Irradiation Degradation of Curing Lights in a Clinical Hospital Setting

Objectives: To assess the intensity output degradation data collected for the QTH LCUs in a clinical hospital setting every month using a standardised protocol to determine the mean output intensity degradation rate and the mean bulb lifetime. The hypothesis proposed was that the QTH LCUs would degrade linearly with time. Methods: A single operator reviewed the output intensity from the QTH LCUs in a clinical hospital setting every month from January 2004 to December 2007 using a standardised protocol with a radiometer and a brand new standard 8 mm diameter light tip. The output intensity was measured for 20 s after the LCU had been heated for three 20 s cycles. Data for the QTH LCUs was used when it had at least six consecutive readings and was continuous over time. Halogen bulbs were replaced when the output intensity was reduced below 400 mW/cm².A regression analysis was performed on the data to determine if significant reductions in output intensity were evident over the lifetime of the QTH bulb. Results: The mean QTH LCU lifetime (operating above 400 mW/cm²) was less than one year in the clinical hospital setting where the study was undertaken. The output intensity degradation rate of 18 (12) mW/cm² per month for the 137 QTH LCUs investigated could be clinically significant. Conclusions: The results suggest that the linear deterioration of the output intensity with time could result in QTH LCUs with less than the recommended output intensity being routinely employed clinically when not assessed regularly. The poor performance of RBCs placed in the general dental services in England and Wales could in part be due to GDPs not maintaining their QTH LCUs.