The inactivation of certain bacteria found in the oral cavity occurs through a photothermal rather than photochemical process, according to a study in the Journal of Biophotonics (June 2010, Vol. 3:5-6, pp. 296-303).
Lasers are used in dentistry for various indications, including the disinfection of root canals or the sterilization of residual caries. While many studies have demonstrated the ability of lasers to kill bacteria, the fundamental mechanism of the laser effect remains unclear, according to researchers from the Institute for Laser Technologies in Medicine and Metrology at the University of Ulm.
They heated bacteria suspensions of a nonpathogenic strain of E. coli by a water bath and by a diode laser (940 nm) with the same temporal temperature course. They also irradiated bacteria suspensions while the temperature was fixed by ice water. The killing of bacteria was measured via fluorescence labeling.
The killing rates between laser and water-based heating showed no significant differences, the researchers noted. The most important parameter was the temperature, they added; laser irradiation of bacteria at low temperatures did not kill bacteria.
"Our experiments show that, at least for E. coli bacteria, inactivation by high-power laser irradiation is solely based on a thermal process," they concluded.
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