Effect of CO2 laser irradiation on hormesis induction in cultured oral cells.

BACKGROUND Many drugs (including toxicants) and radiation therapy have been reported to exert bi-phasic hormetic effects on cultured cells, but only when both the concentration and treatment time were optimal. Most previous studies have been carried out with multiple laser modalities other than CO(2) laser, and there has been no comparison of the hormetic response between normal and tumor cells. We investigated here whether CO(2) laser treatment induces hormesis in human gingival fibroblast (HGF) and oral squamous cell carcinoma (HSC-2) cells. MATERIALS AND METHODS Cells were cultured for 24, 48 or 72 hours after exposure to various irradiation powers, and the viable cell number was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. RESULTS CO(2) laser irradiation stimulated cell growth at low and inhibited it at high irradiation power. Among three dispatch modes, super pulse (SP)2 most effectively induced growth stimulation in HGF, at an irradiation dose slightly lower than that which induced cytotoxicity. Higher irradiation doses were comparably cytotoxic against both normal (HGF) and tumor (HSC-2) cells, reaching a plateau of cytotoxicity within 24 hours. CONCLUSION Since both the range and magnitude of hormetic response in HGF cells were very narrow and small, it is crucial to establish the optimal conditions for hormesis induction for clinical application in dentistry.