title: Pulsed laser ablation of dental calculus in the near ultraviolet.
abstract: Pulsed lasers emitting wavelengths near 400 nm can selectively ablate dental calculus without damaging underlying and surrounding sound dental hard tissue. Our results indicate that calculus ablation at this wavelength relies on the absorption of porphyrins endogenous to oral bacteria commonly found in calculus. Sub- and supragingival calculus on extracted human teeth, irradiated with 400-nm, 60-ns laser pulses at ≤8  J/cm2, exhibits a photobleached surface layer. Blue-light microscopy indicates this layer highly scatters 400-nm photons, whereas fluorescence spectroscopy indicates that bacterial porphyrins are permanently photobleached. A modified blow-off model for ablation is proposed that is based upon these observations and also reproduces our calculus ablation rates measured from laser profilometry. Tissue scattering and a stratified layering of absorbers within the calculus medium explain the gradual decrease in ablation rate from successive pulses. Depending on the calculus thickness, ablation stalling may occur at <5  J/cm2 but has not been observed above this fluence.
authors.affiliation: University of Rochester, Laboratory for Laser Energetics, Rochester, New York 14623bUniversity of Rochester, The Institute of Optics, Rochester, New York 14627.
authors.forename: Joshua E
authors.initials: JE
authors.lastname: Schoenly
authors.affiliation: University of Rochester, Laboratory for Laser Energetics, Rochester, New York 14623bUniversity of Rochester, The Institute of Optics, Rochester, New York 14627.
authors.forename: Wolf
authors.initials: W
authors.lastname: Seka
authors.affiliation: University of California at San Francisco, School of Dentistry, Department of Preventive and Restorative Dental Sciences, San Francisco, California 94143.
authors.forename: Peter
authors.initials: P
authors.lastname: Rechmann
mesh_terms: D003728:Dental Calculus / Q000628:therapy*; D006801:Humans; D053685:Laser Therapy / Q000295:instrumentation / Q000379:methods*; D008954:Models, Biological; D038761:Photobleaching; D014070:Tooth / Q000601:surgery; D014466:Ultraviolet Rays