title: Tensile bond strength of Er,Cr:YSGG laser-irradiated human dentin and analysis of dentin-resin interface.
abstract: OBJECTIVE
  As the bond strength of composite resin to Er,Cr:YSGG laser-irradiated dentin has not yet been evaluated, the objectives of this study were to investigate the tensile bond strength and to analyze the resin-dentin interface among bur-cut/acid-etched, Er,Cr:YSGG laser-ablated/acid-etched and Er,Cr:YSGG laser-ablated human dentin.
  
  
  METHODS
  Crown dentin disks prepared from extracted human third permanent molars were used for the observation of surface morphological changes by scanning electron microscope (SEM). The laser energy parameters were 3.5 W and 20 Hz with water spray (air pressure level, 80%; water pressure level, maximum level). Another group of crown dentin disks were prepared for composite resin restoration and observation of resin-dentin bond interface after demineralization in 6N hydrochloric acid (HCl) for 1 min and deproteinization in 1% sodium hypochlorite solution (NaOCl) for 10 min. The tensile bond strengths of the three groups were measured by a universal testing machine at a crosshead speed of 0.5 mm/min. Fracture types at the dentin-resin interface were analyzed using the digital stereoscopic microscope and fractured surfaces of the debonded specimens were examined by SEM.
  
  
  RESULTS
  All three groups showed that the treated surfaces were free of dentin debris and smear layer. The peritubular dentin protruded from the surrounding intertubular dentin after laser irradiation. The dentin-resin interface treated with Er,Cr:YSGG laser irradiation and acid etching demonstrated numerous resin tags converging into a bulge and then diverging again. The length of resin tags was greater than 100 microm. The tensile bond strengths of bur-cut/acid-etched, laser-ablated/acid-etched and laser-ablated human dentin were 5.37+/-1.51, 5.17+/-1.41 and 3.29+/-0.86 MPa, respectively. No statistical significance was found between the bur-cut/acid-etched and laser-ablated/acid-etched groups. The predominant fracture modes of bur-cut/acid-etched, laser-ablated/acid-etched and laser-ablated human dentin were Type 1 (50%), Type 2 (70%) and Type 1 (70%), respectively.
  
  
  CONCLUSIONS
  Er,Cr:YSGG laser irradiation affects adversely adhesion of resin to dentin but acid etching following laser irradiation could increase the tensile bond strength as high as that of bur-cut/acid-etched human dentin.
authors.affiliation: Graduate Institute of Clinical Dentistry, College of Medicine, National Taiwan University and National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Bor-Shiunn
authors.initials: BS
authors.lastname: Lee
authors.forename: Po-Yen
authors.initials: PY
authors.lastname: Lin
authors.forename: Min-Huey
authors.initials: MH
authors.lastname: Chen
authors.forename: Tseng-Ting
authors.initials: TT
authors.lastname: Hsieh
authors.forename: Chun-Pin
authors.initials: CP
authors.lastname: Lin
authors.forename: Juin-Yih
authors.initials: JY
authors.lastname: Lai
authors.forename: Wan-Hong
authors.initials: WH
authors.lastname: Lan
mesh_terms: D000134:Acid Etching, Dental; D000293:Adolescent; D000328:Adult; D003188:Composite Resins / Q000737:chemistry*; D001840:Dental Bonding; D003737:Dental Cavity Preparation / Q000295:instrumentation / Q000379:methods; D003804:Dentin / Q000648:ultrastructure*; D017220:Dentin-Bonding Agents / Q000737:chemistry; D006801:Humans; D007834:Lasers; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D019279:Resin Cements / Q000737:chemistry; D016369:Smear Layer; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength; D014867:Water / Q000737:chemistry
chemical_list: D003188:Composite Resins; D017220:Dentin-Bonding Agents; D008689:Methacrylates; C426984:One Coat Bond; D019279:Resin Cements; C086113:palfique estelite; D014867:Water