title: A comparative study of nanosecond and picosecond laser ablation in enamel: morphological aspects.
abstract: OBJECTIVE
  We have investigated and compared the main morphological features of human enamel tissue under Nd:YAG nanosecond and picosecond laser ablation.
  
  
  BACKGROUND
  The use of ultrashort laser pulses on teeth ablation is an alternative to avoid overheating and presents the advantage of minimizing the volume of damaged material during laser ablation. Comparison of the morphology obtained in laser ablation using nanosecond and picosecond laser pulses is a way to investigate the advantages of ultrashort laser pulses for ablation.
  
  
  METHODS
  Trains of pulses with picosecond duration from a Q-switched and mode-locked Nd:YAG laser and pulses with nanosecond duration from a Q-switched Nd:YAG laser, both operating at 15 Hz kept at the same average power, were focused in human sound molars for 30 sec. Drilled holes with different morphological characteristics were observed using several laser intensity regimes. Enamel surfaces were examined using a scanning electron microscope (SEM) and their morphological characteristics compared.
  
  
  RESULTS
  An interesting contrast between the morphology of the enamel when treated with different level of laser power and pulse duration was observed. Picosecond pulses promote a better-defined material removal with a minimum intermediate region, whereas nanosecond pulses at the equivalent average power level cause a large intermediate modified region between ablated and normal tissue, as well as a complete superficial modification of the existent original structure.
  
  
  CONCLUSIONS
  Our results show an important correlation between the surface morphology and the pulse width of the lasers, suggesting advantages toward the use of ultrashort laser pulses in dentistry.
authors.affiliation: Instituto de Física de São Carlos-USP, SP, Brazil. 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: D003731:Dental Caries / Q000209:etiology*; D003743:Dental Enamel / Q000528:radiation effects* / Q000648:ultrastructure*; D006801:Humans; D066298:In Vitro Techniques; D028022:Low-Level Light Therapy / Q000009:adverse effects*; D013997:Time Factors