title: Wavelength and average power density dependency of the surface modification of root dentin using an MIR-FEL.
abstract: OBJECTIVE
  Surface modification of root dentin by mid-infrared (MIR) pulsed-laser irradiation is one of the candidates for a novel, non-invasive treatment to prevent root surface caries. To modify root dentin effectively and non-invasively it is essential to estimate quantitatively and qualitatively the laser parameters, such as the wavelength and power density, required for surface modification. The key aspect is to bring about effective surface modification of the root dentin while minimizing the unwanted removal of the underlying dentin.
  
  
  METHODS
  Using a tunable, MIR Free Electron Laser with lambda = 8.8-10.6 microm, we have investigated macroscopically the extent of the surface modification (morphological and chemical changes) of root dentin. We have obtained experimental results related to the ablation depth, the MIR absorption spectrum, and the elemental chemical composition.
  
  
  RESULTS
  The observations showed that the surface modification of root dentin was inclined toward well-recrystallized HAp-like material, leading to an increase in the acid resistance and dentinal tubule sealing. The laser parameters, at which efficient surface modification without enhanced ablation occurred, were estimated to be approximately in the wavelength region around lambda = approximately 9.0 or approximately 9.7 microm and in the average power density region of approximately 10-20 W/cm2 (resulting in total energy density and peak power density regions of approximately 1-2 kJ/cm2 and approximately 0.67-1.2 kW/cm2).
  
  
  CONCLUSIONS
  The surface modification of root dentin strongly depends on the laser parameters applied. We conclude that the optimum wavelengths for laser treatment of root surface caries are lambda = approximately 9.0 or approximately 9.7 microm, corresponding to the absorption peak due to P-O stretching.
authors.affiliation: Institute of Free Electron Laser, Graduate School of Engineering, Osaka University, 2-9-5 Tsuda-Yamate, Hirakata, Osaka 573-0128, Japan. heya@fel.eng.osaka-u.ac.jp
authors.forename: Manabu
authors.initials: M
authors.lastname: Heya
authors.forename: Shu
authors.initials: S
authors.lastname: Sano
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Takagi
authors.forename: Yuko
authors.initials: Y
authors.lastname: Fukami
authors.forename: Kunio
authors.initials: K
authors.lastname: Awazu
mesh_terms: D000818:Animals; D002417:Cattle; D003731:Dental Caries / Q000517:prevention & control; D003804:Dentin / Q000737:chemistry / Q000601:surgery*; D053685:Laser Therapy / Q000379:methods*; D013499:Surface Properties; D014092:Tooth Root