title: Dentin microhardness and subsurface morphology after Er:YAG laser cavity preparation using different parameters.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the influence of the Er:YAG laser, using different parameters, on dentin microhardness and subsurface morphology.
  
  
  METHODS
  One hundred thirty dentin fragments were randomly assigned to 13 groups: 12 received laser irradiation with different energies (200, 250, 300, or 350 mJ) and pulse repetition rates (2, 3, or 4 Hz); and 1 (control) was prepared using a carbide bur. Specimens were bisected. One hemisection was fixed with the subsurface face up and polished. The other one was prepared for scanning electron microscopy. The microhardness test was performed at 5 depths (30, 60, 90, 120, and 150 microm) and 7 points (6 in the cavity edges and 1 in a nonirradiated area). Data were tested by analysis of variance and Tukey test.
  
  
  RESULTS
  The highest microhardness values were recorded for lased-irradiated groups with 250 mJ/4 Hz and 350 mJ/4 Hz, only in the deep region of the cavity and until 60 microm. The parameters 300 mJ/3 Hz, 350 mJ/3 Hz, and 200 mJ/4 Hz changed the morphology until 10 microm; and 250 mJ/4 Hz, 300 mJ/4 Hz, and 350 mJ/4 Hz until 30 microm (P=0.0328). The bur-prepared group displayed the lowest microhardness values, being statistically similar to 200 mJ/2 Hz (P=0.1824), and the subsurface did not exhibit morphological alterations.
  
  
  CONCLUSIONS
  The Er:YAG laser with 250 mJ/4 Hz and 350 mJ/4 Hz increased dentin microhardness in the deepest area of the cavity until 60 microm. Use of the lower parameters (200 mJ/2 Hz, 250 mJ/2 Hz, or 300 mJ/2 Hz) to prepare dentin with the Er:YAG laser produced results similar to those for bur-prepared cavities.
authors.affiliation: Department of Restorative Dentistry, Ribeirão Preto School of Dentistry, University of São Paulo, São Paulo, Brazil.
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: Pecora
authors.forename: Regina Guenka
authors.initials: RG
authors.lastname: Palma-Dibb
authors.forename: Silmara Aparecida Milori
authors.initials: SA
authors.lastname: Corona