title: Effect of dentin hardness on ablation rate with Er:YAG laser.
abstract: OBJECTIVE
  This study used artificially demineralized bovine dentin to ascertain the effect of hardness of demineralized dentin on ablation rate with the Er:YAG laser.
  
  
  BACKGROUND
  Before restoration of carious teeth, it is necessary to ablate any infected dentin that cannot be remineralized due to softening by the invading caries. A correlation has been suggested between the ablation efficiency of the Er:YAG laser and the progression of caries in dentin. To the best of our knowledge, no studies have investigated the relationship between degree of demineralization by dentinal caries and ablation rate with the Er:YAG laser.
  
  
  METHODS
  Bovine mandibular anterior tooth roots were used as dentin samples. Each sample was soaked in a demineralizing solution (2 M lactic acid, pH 4.0) for 3 d to obtain demineralized dentin (DD) samples. Another group of samples were prepared without demineralization as a sound dentin (SD) group for comparison. After determining the Knoop hardness number (KHN) of each sample, the dentin surface was ablated with an Er:YAG laser. Tip output and pulse rate were set at 50 mJ and 20 pulses per second (pps), respectively, and the water spray was set at 3.5 mL/min. Ablation width, depth, and volume were measured following irradiation.
  
  
  RESULTS
  In the DD group, dentin hardness was 10.4 +/- 1.6 KHN at 100 microm from the surface. In the sound dentin group, Knoop hardness was 51.0 +/- 1.6 KHN cross-sectionally throughout. No differences were observed from the surface to a depth of 2000 microm. In the DD group, dentin ablation volume at the superficial demineralized layer was 2888 +/- 272 x 10(4) microm. In the SD group, dentin ablation volume was 1298 +/- 219 microm(3). The relationship between ablation volume and Knoop hardness was defined as Y = -40.699x + 3350, revealing a marked negative correlation.
  
  
  CONCLUSIONS
  The results demonstrate that the ablation volume for demineralized dentin was greater than that for sound dentin. The results suggest that the Er:YAG laser is capable of ablating infected dentin without damaging sound dentin by adjustment of tip output and pulse rate.
authors.affiliation: Department of Operative Dentistry Tokyo Dental College, Chiba, Japan. osuka@tdc.ac.jp
authors.forename: Keigo
authors.initials: K
authors.lastname: Osuka
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Amagai
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Kukidome
authors.forename: Yasuaki
authors.initials: Y
authors.lastname: Takase
authors.forename: Shigeo
authors.initials: S
authors.lastname: Aida
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Hirai
mesh_terms: D000818:Animals; D002417:Cattle; D003804:Dentin / Q000528:radiation effects*; D006244:Hardness; D053685:Laser Therapy / Q000295:instrumentation / Q000379:methods*; D053844:Lasers, Solid-State / Q000627:therapeutic use*; D023421:Models, Animal