| Objectives In this experiment,the shear bond strength of all of ceramagepolymeric porcelains was measured after different etching time.To discuss the best time of acid etching of polymeric porcelain under the strongest bond strength,so as to provide guidance for the strengthening of resin bonding of polymeric porcelain in clinical practice.Methods 48 teeth with no caries,no variation and no treatment were collected.Dentin layer of every toothwas completely exposed by grinding the enamel layer,and a 4mm 4mm bonding plane was prepared by using water-resistant abrasive paper.Finally,48 teethwere made into embedded specimens.Sixty polymeric porcelain specimens with diameter of 3 mm and high of 3 mm were also prepared with water-resistant abrasive paper to produce a uniform dentin bonding surface.Sixty specimens were randomly divided into group A,B,C,D,E and F according to the time of acid etching,the specific acid etchingtimewere as follows: A: no treatment;B: acid etching for 15s;C: acid etching for 30s;D: acid etching for 45s;E: acid etching for 60s;F: acid etching for 90 s.And9.0% hydrofluoric acid was used foracid etching treatment according to the corresponding etching time.Scanning electron microscopewas used to observe the micromorphology of the surface of the polymeric porcelain after different acid etching time.Then,the shear bond strength was measured between the polymerized porcelain specimen and the dental embedded specimen,which were randomly selected and bonded with resin binder.Finally,the most suitable etching time for polymeric porcelain resin bonding was summarized.The microstructure of fracture surface was observed by electron microscope.Results Scanning electron microscope showed that the surface of the polymerized porcelain after etching had obvious dissolution area,and with the increase of etching time,the cleavage and the shedding of crystal particles would occur.The surface of polymeric porcelain in group A(control group)had some roughness,but it was not obviousand grinding trace can been found.The surface of group B(acid etching in 15 s group)showed a small amount of dissolved area with irregulardistribution and low ratio.The surface dissolution area of polymeric porcelain in group C(acid etching in 30 s group)was obviously increasedwith more regular distribution and it looks like fish scales in a whole.The dissolution degree of polymeric porcelain surface in group D(acid etching in 45 s group)was further increased to cause little cleavage.The surface cleavage of polymeric porcelain in group E(acid etching in 60 s group)gradually increased and enlarged.The furrow crackof F group(acid etching in 90 s group)deepened and widened.Some crystal particles fell off and loosely accumulated on the surface.The shear bond strength of all specimens treated with acid etching was significantly higher than that of group A without acid etching(P< 0.05).The maximum shear bond surface strength(16.87 + 1.36)Mpa can be obtained in 30 s econds of the acid etching polymerized porcelain specimen when the resin binder is used to bond the dentins.SEM showed that it has difference of the fracture modes of shear specimens in different acid etching time: group A(control group)had interfacial fracture;group B(acid etching in 15 s group),group C(acid etching in 30 s group),group E(acid etching in 60 s group)and group F(acid-etching in 90 s group),they hadcohesive and adhesive fracture;group D(acid-etching 45 s group)had mixed fracture.Conclusions The adhesive strength of polymeric porcelain and dentin could be significantly enhanced with 9.0% concentration of HF,and the bonding strength between polymeric porcelain and dentin was significantly affected by different etching time.The strongest shear bond strength can be obtained by acid etching for 30 s.The adaptation of bonding plane after acid etching,be superior to the adaptation of no acid etching. |
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