title: Differences in bonding to acid-etched or Er:YAG-laser-treated enamel and dentin surfaces.
abstract: BACKGROUND
  Er:YAG (erbium-doped yttrium aluminium garnet) lasers have been effective in the removal of dental tissues. It has been suggested that they are also useful for preparing dental surfaces for adhesion, but results to date have been controversial.
  
  
  OBJECTIVE
  This study compared the tensile strength of bracket-tooth bonds obtained after preparation of the surface for adhesion (dentin or enamel) by conventional acid-etching or by Er:YAG laser etching and investigated microstructure of resin-tooth interfaces using the 2 procedures.
  
  
  METHODS
  Eighty healthy human premolars were used. Brackets were cemented to acid-etched enamel, laser-etched enamel, acid-etched dentin, or laser-etched dentin (20 teeth per group). Dentin was previously exposed using a high-speed handpiece. Acid-etching was with 37% orthophosphoric acid (15 seconds for enamel, 5 seconds for dentin). Laser etching was with Er:YAG laser (four 200 mJ pulses per second for enamel; four 160 mJ pulses per second for dentin). Brackets were bonded with autocuring resin paste, having first applied a primer (dentin only) and then light-cured bonding resin. Tensile strength was determined with a universal testing machine. Data were analyzed with 2-way ANOVA and subsequent t test with Bonferroni correction. Fracture patterns were compared by the Wilcoxon test with Bonferroni correction. For SEM studies of the resin-tooth interface, a total of 12 premolars were used (3 for each tissue per treatment combination).
  
  
  RESULTS
  Mean tensile bond strength for acid-etched enamel (14.05 +/- 5.03 MPa) was significantly higher (P<.05) than for laser-etched enamel (8.45 +/- 3.07 MPa), and significantly higher (P<.05) for acid-etched dentin (4.70 +/- 2.50 MPa) than laser-etched dentin (2.48 +/- 1.94 MPa). Bond failure after laser etching was due to microcohesive fracture of tooth tissue. SEM studies of both resin-enamel and resin-dentin interfaces indicated extensive subsurface fissuring after laser etching.
  
  
  CONCLUSIONS
  Adhesion to dental hard tissues after Er:YAG laser etching is inferior to that obtained after conventional acid etching. Enamel and dentin surfaces prepared by Er:YAG laser etching show extensive subsurface fissuring that is unfavorable to adhesion.
authors.affiliation: Santiago de Compostela University, Santiago de Compostela, Spain. odamain@uscmail.usc.es
authors.forename: A
authors.initials: A
authors.lastname: Martínez-Insua
authors.forename: L
authors.initials: L
authors.lastname: Da Silva Dominguez
authors.forename: F G
authors.initials: FG
authors.lastname: Rivera
authors.forename: U A
authors.initials: UA
authors.lastname: Santana-Penín
mesh_terms: D000134:Acid Etching, Dental; D000704:Analysis of Variance; D001840:Dental Bonding; D003743:Dental Enamel / Q000187:drug effects / Q000528:radiation effects*; D003804:Dentin / Q000187:drug effects / Q000528:radiation effects*; D006801:Humans; D007834:Lasers; D008855:Microscopy, Electron, Scanning; D016910:Orthodontic Brackets; D019279:Resin Cements; D018709:Statistics, Nonparametric; D013499:Surface Properties / Q000187:drug effects / Q000528:radiation effects; D013718:Tensile Strength
chemical_list: D019279:Resin Cements