Bonding to dentin with a self-etching primer: the effect of smear layers.
OBJECTIVE
The purpose of this study was to investigate the effect of smear layers on the tensile bond strength to human dentin. Bond strength was determined on dumbbell-shaped specimens to determine the feasibility for clinical use of a self-etching primer.


METHODS
The dentin of extracted human teeth was exposed by grinding with either #180 or #600 abrasive paper. A self-etching primer was then applied to the prepared dentinal surfaces and left undisturbed for 30s. It was then air-dried and a photocured bonding agent applied and irradiated for 20s. A composite resin was then added to the primed dentin and light-cured for 60s to complete the bonded assemblies. Mini-dumbbell specimens (3.0 x 2.0 mm2) were prepared from the bonded samples. These specimens were stored in 37 degrees C water for 24h before tensile loading to failure at a crosshead speed of 1.0 mm/min. Surfaces of fractured specimens, both resin and dentin, were examined under a scanning electron microscope (SEM).


RESULTS
Significantly different tensile bond strengths (TBS) of 10.0+/-7.2 and 28.5+/-5.2MPa were found for #180- and #600-prepared dentin, respectively (p<0.01). The former specimens fractured within the hybridized, relatively coarse smear layer, while the latter demonstrated adhesive failure between the composite resin and an attached PMMA rod, not between the dentin and applied adhesive agent.


CONCLUSIONS
The presence and quality of a smear layer yields significantly different bond strengths to prepared human dentin, in vitro. However, a TBS of 10+/-7MPa is evidently adequate, since self-etching primers have been well accepted in dental clinics.
Koibuchi
H
H
Department of Organic Biomaterials, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, Tokyo, Japan.
Yasuda
N
N
Nakabayashi
N
N
D000134:Acid Etching, Dental; D000268:Adhesiveness; D003188:Composite Resins / Q000737:chemistry; D001840:Dental Bonding; D003804:Dentin / Q000648:ultrastructure*; D017220:Dentin-Bonding Agents / Q000737:chemistry*; D005240:Feasibility Studies; D006801:Humans; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D019904:Polymethyl Methacrylate / Q000737:chemistry; D016369:Smear Layer; D013223:Statistics as Topic; D013499:Surface Properties; D013696:Temperature; D013718:Tensile Strength; D013997:Time Factors; D014867:Water / Q000737:chemistry
C112274:Clearfil Liner Bond 2; D003188:Composite Resins; D017220:Dentin-Bonding Agents; D008689:Methacrylates; D014867:Water; C092420:Clearfil Photo Posterior; D019904:Polymethyl Methacrylate