title: Characterization of enamel and dentin response to Nd:YAG picosecond laser ablation.
abstract: OBJECTIVE
  We investigated the main characteristics of human dental tissue under Nd:YAG picosecond laser ablation.
  
  
  BACKGROUND
  The use of ultrashort laser pulses for teeth ablation prevents overheating and is an alternative for mechanical material removal; it also minimizes the volume of damaged material.
  
  
  METHODS
  Laser pulses of picosecond at 15 Hz repetition rates from a Q-switched and mode-locked Nd:YAG laser were focused on sound human molars for 30 seconds. Variation of light intensity in the pulse train allowed us to obtain drilled holes with different characteristics. Enamel and dentin surfaces were examined by optical and scanning electron microscope (SEM). The samples consisted of three sound human molars. The ablation rate was determined after taking an average of all samples.
  
  
  RESULTS
  Images from the SEM showed an interesting contrast between the morphology of the ablated enamel and dentin regions. In enamel, the ablated region appears to be more superficial than in dentin. The dentin fragility normally causes cracks that originate in the ablated region. The ablation rates in both enamel and dentin demonstrate a saturation behavior as the laser intensity increases. Furthermore, the ablation rate in dentin is about eight times greater than in enamel for the same laser fluence.
  
  
  CONCLUSIONS
  Our results show an important correlation between the surface morphology and the pulsed laser fluence, which is compatible to the ablation mechanisms presented when ultrashort laser pulses are used.
authors.affiliation: Instituto de Física de São Carlos, USP, São Carlos, SP, Brasil. lizarelli@hotmail.com
authors.forename: R F
authors.initials: RF
authors.lastname: Lizarelli
authors.forename: C
authors.initials: C
authors.lastname: Kurachi
authors.forename: L
authors.initials: L
authors.lastname: Misoguti
authors.forename: V S
authors.initials: VS
authors.lastname: Bagnato
mesh_terms: D003743:Dental Enamel / Q000528:radiation effects* / Q000648:ultrastructure; D003804:Dentin / Q000528:radiation effects* / Q000648:ultrastructure; D006801:Humans; D066298:In Vitro Techniques; D007834:Lasers