ABSTRACT
BACKGROUND: We have recently reported that a low level of CO2 laser irradiation induced growth stimulation (hormesis) of both human gingival fibroblast (HGF) and oral squamous cell carcinoma cell line (HSC-2), but the extent of hormetic response was much smaller than that previously reported for toxicants and radiation in other experimental systems. Here we investigated the extent of hormetic response induced by CO2 laser irradiation in human pulp cells (HPCs) and periodontal ligament fibroblast (HPLF). MATERIALS AND METHODS: HPC and HPLF cells were established from the periodontal tissues of the first premolar extracted tooth. 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: CO2 laser irradiation induced biphasic effects on the growth of both HPC and HPLF cells. The maximum hormetic response was less than 50%. The hormetic response was found within the energy density of 7.98-79.77 J/cm², and cytotoxicity emerged at powers over 132.96 J/cm². Combining with our previous report, HPCs showed the highest hormetic response, followed by HPLFs and then HGFs. Both HPLFs and HGFs showed similar time-course of hormesis response, increasing response with incubation time. CONCLUSION: The hormetic response may be the common survival mechanism by which cells escape from radiation-induced injury. Higher hormetic response of HPCs may reflect their potential for differentiation into one of the components in dentin.
Subject(s)
Dental Pulp/radiation effects , Fibroblasts/radiation effects , Lasers, Gas , Periodontal Ligament/cytology , Cell Line, Tumor , Cell Survival/radiation effects , Child , Female , Humans , Periodontal Ligament/radiation effectsABSTRACT
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.
