Tensile bond strength of Er,Cr:YSGG laser-irradiated human dentin and analysis of dentin-resin interface.
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.
Lee
Bor-Shiunn
BS
Graduate Institute of Clinical Dentistry, College of Medicine, National Taiwan University and National Taiwan University Hospital, Taipei, Taiwan.
Lin
Po-Yen
PY
Chen
Min-Huey
MH
Hsieh
Tseng-Ting
TT
Lin
Chun-Pin
CP
Lai
Juin-Yih
JY
Lan
Wan-Hong
WH
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
D003188:Composite Resins; D017220:Dentin-Bonding Agents; D008689:Methacrylates; C426984:One Coat Bond; D019279:Resin Cements; C086113:palfique estelite; D014867:Water