Cellular inhibition produced by dental curing lights is a heating artifact

Dental curing lights deliver energy in the 380-520 nm wavelength range. It has been reported that irradiation in these wavelengths may have a negative effect on cell function. We examined the effect of three dental curing lights on the viability of mouse (NIH3T3, Balb/c3T3) and human (HGF-1) fibroblastic cells, and epithelial (HT-29) cells grown in culture. Cell inhibition was observed using the MTT assay of mitochondrial function and measures of DNA fragmentation and DNA synthesis. Analyzing the experimental method and careful measurement of the temperature adjacent to the cell monolayer during irradiation showed that damage to the cells was not due to cumulative light exposure, but instead occurred when the temperature of the culture medium rose above 42°C. We conclude that dental curing lights do not cause cell damage as a direct result of the light irradiation. Instead it is caused by the local temperature increase in the cells.