title: Influence of energy and pulse repetition rate of Er:YAG laser on enamel ablation ability and morphological analysis of the laser-irradiated surface.
abstract: OBJECTIVE
  To assess the influence of energy and pulse repetition rate of Er:YAG laser on the enamel ablation ability and substrate morphology.
  
  
  METHODS
  Fifteen crowns of molars were sectioned in four fragments, providing 60 samples, which were ground to flatten the enamel surface. The initial mass was obtained by weighing the fragments. The specimens were hydrated for 1 h, fixed, and a 3-mm-diameter area was delimited. Twelve groups were randomly formed according to the combination of laser energies (200, 250, 300, or 350 mJ) and pulse repetition rates (2, 3, or 4 Hz). The final mass was obtained and mass loss was calculated by the difference between the initial and final mass. The specimens were prepared for SEM. Data were submitted to ANOVA and Scheffé test.
  
  
  RESULTS
  The 4 Hz frequency resulted in higher mass loss and was statistically different from 2 and 3 Hz (p < 0.05). The increase of frequency produced more melted areas, cracks, and unselective and deeper ablation. The 350 mJ energy promoted greater mass loss, similar to 300 mJ.
  
  
  CONCLUSIONS
  The pulse repetition rate influenced more intensively the mass loss and morphological alteration. Among the tested parameters, 350 mJ/3 Hz improved the ability of enamel ablation with less surface morphological alterations.
authors.affiliation: Department of Restorative Dentistry, Ribeirão Preto School of Dentistry, University of São Paulo (USP), Av. do Café, S/N Monte Alegre, Ribeirão Preto, CEP 14040-904, São Paulo, Brazil.
authors.forename: Silmara Aparecida Milori
authors.initials: SA
authors.lastname: Corona
authors.forename: Aline Evangelista
authors.initials: AE
authors.lastname: Souza-Gabriel
authors.forename: Michelle Alexandra
authors.initials: MA
authors.lastname: Chinelatti
authors.forename: Jesus Djalma
authors.initials: JD
authors.lastname: Pécora
authors.forename: Maria Cristina
authors.initials: MC
authors.lastname: Borsatto
authors.forename: Regina Guenka
authors.initials: RG
authors.lastname: Palma-Dibb
mesh_terms: D003737:Dental Cavity Preparation / Q000295:instrumentation; D003743:Dental Enamel / Q000528:radiation effects*; D006801:Humans; D053685:Laser Therapy / Q000295:instrumentation; D053844:Lasers, Solid-State; D008855:Microscopy, Electron, Scanning; D008964:Molar, Third / Q000033:anatomy & histology / Q000528:radiation effects