title: Ablation rate and morphology of superficial and deep dentin irradiated with different Er:YAG laser energy levels.
abstract: OBJECTIVE
  In this study we evaluated the ablation rate of superficial and deep dentin irradiated with different Er:YAG laser energy levels, and observed the micromorphological aspects of the lased substrates with a scanning electron microscope (SEM).
  
  
  BACKGROUND
  Little is known about the effect of Er:YAG laser irradiation on different dentin depths.
  
  
  METHODS
  Sixty molar crowns were bisected, providing 120 specimens, which were randomly assigned into two groups (superficial or deep dentin), and later into five subgroups (160, 200, 260, 300, or 360 mJ). Initial masses of the specimens were obtained. After laser irradiation, the final masses were obtained and mass losses were calculated followed by the preparation of specimens for SEM examination. Mass-loss values were subjected to two-way ANOVA and Fisher's least significant difference multiple-comparison tests (p > 0.05).
  
  
  RESULTS
  There was no difference between superficial and deep dentin. A significant and gradual increase in the mass-loss values was reached when energies were raised, regardless of the dentin depth. The energy level of 360 mJ showed the highest values and was statistically significantly different from the other energy levels. The SEM images showed that deep dentin was more selectively ablated, especially intertubular dentin, promoting tubule protrusion. At 360 mJ the micromorphological features were similar for both dentin depths.
  
  
  CONCLUSIONS
  The ablation rate did not depend on the depth of the dentin, and an energy level lower than 360 mJ is recommended to ablate both superficial and deep dentin effectively without causing tissue damage.
authors.affiliation: Department of Restorative Dentistry, School of Dentistry of Ribeirão Preto, University of São Paulo, Faculdade de Odontologia de Ribeirão Preto, São Paulo, SP, Brazil.
authors.forename: Walter
authors.initials: W
authors.lastname: Raucci-Neto
authors.forename: Michelle Alexandra
authors.initials: MA
authors.lastname: Chinelatti
authors.forename: Regina Guenka
authors.initials: RG
authors.lastname: Palma-Dibb
mesh_terms: D003804:Dentin / Q000528:radiation effects* / Q000648:ultrastructure; D006801:Humans; D066298:In Vitro Techniques; D053844:Lasers, Solid-State; D008855:Microscopy, Electron, Scanning; D008964:Molar, Third