title: Dentin strain induced by laser irradiation.
abstract: The purpose of this study was to investigate the strain and temperature change in dentin induced by laser irradiation of human root canals with or without water cooling. Twenty-eight palatal roots of extracted human maxillary first molars were used. The strain in dentin was measured using strain gauges fixed on the apical third of the buccal root surface. The temperature change of the root dentin was monitored using thermocouples embedded into dentin near the apex. The root canal was irradiated with Er:YAG or Nd:YAG laser at an output of 1 W (100 mJ, 10 pps) for 5 s. The tip of the irradiation fibre was located 2.0 mm from the root apex. With water cooling, the mean maximum strain induced by Er:YAG laser was significantly lower than that by Nd:YAG laser (P < 0.05). However, without water cooling, no significant difference between the two lasers (P > 0.05) was found. The results suggest that the strain induced by Er:YAG laser irradiation in dentin with water cooling may be minimal, but there still might be a risk of root micro-fracture if cooling is not sufficient.
authors.affiliation: Pulp Biology and Endodontics, Department of Restorative Sciences, Graduate School, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo, Japan. s.watanabe.endo@tmd.ac.jp
authors.forename: Satoshi
authors.initials: S
authors.lastname: Watanabe
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Saegusa
authors.forename: Tomoo
authors.initials: T
authors.lastname: Anjo
authors.forename: Arata
authors.initials: A
authors.lastname: Ebihara
authors.forename: Chihiro
authors.initials: C
authors.lastname: Kobayashi
authors.forename: Hideaki
authors.initials: H
authors.lastname: Suda
mesh_terms: D001696:Biomechanical Phenomena; D002244:Carbon; D004396:Coloring Agents; D003786:Dental Pulp Cavity / Q000503:physiopathology / Q000528:radiation effects* / Q000648:ultrastructure; D003799:Dental Stress Analysis / Q000295:instrumentation; D003804:Dentin / Q000503:physiopathology / Q000528:radiation effects* / Q000648:ultrastructure; D006801:Humans; D053844:Lasers, Solid-State / Q000627:therapeutic use*; D008422:Materials Testing; D013314:Stress, Mechanical; D013696:Temperature; D013821:Thermometers; D013997:Time Factors; D019227:Tooth Apex / Q000503:physiopathology / Q000528:radiation effects; D014867:Water
chemical_list: D004396:Coloring Agents; C028433:chinese ink; D014867:Water; D002244:Carbon