title: Effect of energy and pulse repetition rate of Er: YAG laser on dentin ablation ability and morphological analysis of the laser-irradiated substrate.
abstract: OBJECTIVE
  The aim of this study was to assess the effect of energy and pulse repetition rate of the Er:YAG laser (2.94 microm) on dentin ablation ability and substrate morphology.
  
  
  BACKGROUND
  Previous studies have demonstrated the ability of the Er:YAG laser for ablating dentin substrate.
  
  
  METHODS
  Fifteen crowns of molars were sectioned in four fragments, providing 60 samples, which were ground to expose dentin. Initial mass was obtained by weighing the fragments. Twelve groups were randomly formed, according to the combination of laser energies (200, 250, 300, and 350 mJ) and pulse repetition rates (2, 3, and 4 Hz), usually advised for cavity preparation. The final mass was obtained, and dentin mass loss was calculated by the difference between the final and initial mass. Afterwards, specimens were prepared for scanning electron microscopy (SEM). Data were submitted to analysis of variance (ANOVA) and Scheffé test (p < 0.05).
  
  
  RESULTS
  Pulse repetition rate of 4 Hz was statistically similar to 3 Hz, and laser energy of 350 mJ was statistically similar to 300 mJ. Increased pulse repetition rates provided higher ablation depth and slight enlargement of dentinal tubules, whereas increased energies yielded greater ablation of intertubular dentin.
  
  
  CONCLUSIONS
  The ablation ability of the Er:YAG laser on dentin raised with the increase of energy and/or pulse repetition rate, the latter exhibiting a stronger influence on mass loss rate and on morphological alterations.
authors.affiliation: School of Dentistry of Ribeirão Preto, University of São Paulo, São Paulo, Brazil.
authors.forename: Silmara Aparecida Milori
authors.initials: SA
authors.lastname: Corona
authors.forename: Aline Evangelista
authors.initials: AE
authors.lastname: de Souza
authors.forename: Michelle Alexandra
authors.initials: MA
authors.lastname: Chinelatti
authors.forename: Maria Cristina
authors.initials: MC
authors.lastname: Borsatto
authors.forename: Jesus Djalma
authors.initials: JD
authors.lastname: Pécora
authors.forename: Regina Guenka
authors.initials: RG
authors.lastname: Palma-Dibb
mesh_terms: D003804:Dentin / Q000528:radiation effects* / Q000648:ultrastructure*; D006801:Humans; D007834:Lasers; D008964:Molar, Third / Q000528:radiation effects / Q000648:ultrastructure