title: Effect of CO2 laser irradiation on hormesis induction in cultured oral cells.
abstract: 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.
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Division of Operative Dentistry, Department of Restorative and Biomaterials Sciences, Meikai University School of Dentistry, Sakado, Saitama 350-0283, Japan. iwasaka@dent.meikai.ac.jp
authors.forename: Kensuke
authors.initials: K
authors.lastname: Iwasaka
authors.forename: Kayoko
authors.initials: K
authors.lastname: Tomita
authors.forename: Yumi
authors.initials: Y
authors.lastname: Ozawa
authors.forename: Tadashi
authors.initials: T
authors.lastname: Katayama
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sakagami
mesh_terms: D048708:Cell Growth Processes / Q000528:radiation effects*; D002478:Cells, Cultured; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000166:cytology / Q000528:radiation effects; D005562:Formazans; D005881:Gingiva / Q000166:cytology / Q000528:radiation effects*; D006801:Humans; D054020:Lasers, Gas / Q000009:adverse effects*; D009061:Mouth Mucosa / Q000166:cytology / Q000528:radiation effects*; D013778:Tetrazolium Salts
chemical_list: D005562:Formazans; D013778:Tetrazolium Salts; C079782:MTT formazan