title: [Effects of fluence and scanning velocity on the ablation efficiency of dentin and enamel by femtosecond laser].
abstract: OBJECTIVE
  To measure the effect of laser fluence and scanning velocity on ablation efficiency of enamel and dentin.
  
  
  METHODS
  Two extracted human incisors and two molars were cut transversely along the axial plane with a diamond saw to obtain dentin and enamel slices with thickness of about 1 mm. Samples were fixed on a motorized translation stage, the linear reciprocating movement in the plane perpendicular to the direction of laser incident was programmed by the controller, and the laser focused on the tooth surface, then 36 ablation lines on enamel and 48 ablation lines on dentin were produced. A femtosecond laser system with wavelength of 800 nm, pulse width 30 fs, repetition frequency 1000 Hz was used, and the diameter of the focused spot was approximately 25 µm. A group of different fluence (1.33, 1.77, 2.21, 4.42, 8.85, 17.69 J/cm(2) for enamel and 0.44, 0.66, 0.88, 1.33, 1.77, 2.21, 4.42, 6.63 J/cm(2) for dentin) and two scanning velocity (10 mm/s and 20 mm/s) were tested. Confocal laser scanning microscope was used to measure the ablation volume.Ablation efficiency for enamel and dentin was then calculated.
  
  
  RESULTS
  Under the fluence of 8.85 J/cm(2) there was the highest ablation efficiency for enamel, 18.703×10(-3) mm(3)/J (20 mm/s), and the highest ablation efficiency for dentin was found under the fluence of 2.21 J/cm(2), ie.223.458×10(-3) mm(3)/J (20 mm/s).
  
  
  CONCLUSIONS
  Fluence and scanning speed of this femtosecond laser can affect ablation efficiency for both enamel and dentin, and this suggests that with appropriate choice of fluence and scanning speed we can improve the ablation efficiency for enamel and dentin.
authors.affiliation: Center of Digital Dentistry, Peking University School and Hospital of Stomatology, Beijing, China.
authors.forename: Hu
authors.initials: H
authors.lastname: Chen
authors.forename: Jing
authors.initials: J
authors.lastname: Liu
authors.forename: Wen-qi
authors.initials: WQ
authors.lastname: Ge
authors.forename: Yu-chun
authors.initials: YC
authors.lastname: Sun
authors.forename: Yong
authors.initials: Y
authors.lastname: Wang
authors.forename: Pei-jun
authors.initials: PJ
authors.lastname: Lü
mesh_terms: D003743:Dental Enamel / Q000528:radiation effects*; D003804:Dentin / Q000528:radiation effects*; D006801:Humans; D007180:Incisor / Q000033:anatomy & histology; D007834:Lasers; D008963:Molar / Q000033:anatomy & histology