| With the extensive development of computer assisted design/computer assisted manufacturing(CAD/CAM)technology for its high accuracy and efficiency in clinical application,the matching machinable materials are constantly updating.Machinable ceramic materials are considered as the most ideal dental material,because of their biocompatibility,chemical inertness,superior esthetics,good compressive strength and abrasion resistance.Lithium disilicate ceramics(LDCs)are widely used in dentistry because of their high strength and good esthetics.The second generation of LDC(IPS e.max,Ivoclar Vivadent)provides a substantial increase in flexural strength compared to conventional glass ceramics because of their more homogeneous and finer crystals.These ceramic materials are more brittle,easily lead to fracture and caused the failure of restoration.Recently,a new resin-matrix ceramics(Vita Enamic)was introduced to clinicians,which is filled resin material in the ceramic composition,in order to reduce the brittleness of ceramics and provides elasticity.However,the mechanical properties and bond strength of this new type of resin-matrix ceramic compared with other traditional machinable ceramics need to be further studied.Usually,the ceramic restorations are bonded to dental surface with resin adhesives,andproduced two bond interfaces between dental surface and restorations which are the tooth-resin and resin-ceramic interfaces.Many studies have shown that the bond strength between tooth and resin is relatively strong and can satisfy the needs of clinicians.However,the bond between restorations especially ceramic restorations and dental surface becomes one of the key factors influencing the success of the restorations.Several factors interact in the process of establishing a strong bond between ceramics and resin.The first factor is the surface roughness of the ceramics.The second factor is establishing a strong chemical bond between the ceramics and the resin adhesives,which is the function of the silane primer.The third factor is the mechanical properties of the ceramics.Therefore,this study adopted IPS e.max CAD(lithium silicate glass ceramic)and Vita Enamic(hybrid ceramic).By comparing the influence of different surface treatments and ceramic mechanical properties on the bond strength,evaluate the bonding effect between the ceramics and resin,and provide reference for clinical application.The study included three parts:In the first experiment,the effects of different etching treatments on the bond strength between CAD/CAM machinable ceramics and resin were studied.IPS e.max CAD and Vita Enamic were etched by 4.5% HF and 9.5% HF for different time,and coated with silane coupling agent,adhesive,bonded with composite resin.Then the bond strength was tested by Shear bond strength test.The microstructures and fracture modes of the ceramic surface were observed by SEM.The effects of different acid etching treatments on the bond strength of CAD/CAM machinable ceramics were evaluated.In the second experiment,The effects of different adhesives and silane coupling agents on the bonding strength between IPS e.max CAD and resin were studied.After etching,the IPS e.max CAD were treated with different adhesives and silane coupling agents.After bonding with the composite resin,the shear bond strength was tested by Shear bond strength test and the fracture modes were observed by SEM.The influence of different adhesives and silanes coupling agent on the bond strength of IPS e.max CAD was evaluated.In the last experiment,The mechanical properties of CAD/CAM machinable ceramics and their effects on the bond strength were studied.The specimens of three-point bending strength test were prepared according to ISO 6872 International Dental Ceramics Standard.The flexural strength and elastic modulus of IPS e.max CAD and Vita Enamic were measured by three-point bending strength test.And the microstructure of the fracturesurface was observed by SEM.The mechanical properties of CAD/CAM machinable ceramics and their effects on the bond strength were evaluated.The results of this study and conclusions are as follows:1.The best bond strength of IPS e.max CAD could be achieved by 9.5% HF etching for10 s,20s,30 s,60s and 120 s,respectively,reaching 19.09 ? 0.79 MPa,18.70 ? 0.81 MPa,20.56?2.39 MPa,20.13?2.11 MPa,20.22?1.56 MPa,and there was no significant difference between groups(P> 0.05).The results of SEM showed that IPS e.max CAD could achieve a more ideal acid etching surface after etched with 9.5% HF for 30 s,60s and 120 s.So the two aspects of the results were integrated,and it was recommended for IPS e.max CAD to etched with 9.5% HF for at least 10 s,and etched 30 s could obtain optimum and stable bond effect.Vita Enamic could achieve the maximum bond strength after etched with4.5% HF for 60 s.2.The new "Universal Adhesive" 3M Scotchbond Universal Adhesive and Kerr Optibond Versa Adhesive have a lower bonding strength to the IPS e.max CAD than the traditional two-step silane coupling agent + adhesive,And the difference was statistically significant(P <0.05).The bond strength of Kerr Optibond Versa Adhesive to IPS e.max CAD was not significantly different from the 3M Scotchbond Universal Adhesive(P>0.05).Therefore,It is recommended to use two-step silane coupling agent + adhesive for bonding IPS e.max CAD because of their superior bond strength.3.A significant difference in flexural strength(P<0.05)was found between the two groups,with IPS e.max CAD(349.06 ? 21.25MPa)>Vita Enamic(156.91 ? 12.44MPa).Significant difference in elastic modulus between the two groups(P<0.05)was found with IPS e.max CAD(75.33?2.37GPa)>Vita Enamic(75.33?2.37GPa).The elastic modulus of the resin used in this experiment is closer to the elastic modulus of Vita Enamic than the elastic modulus of IPS e.max CAD.so the stress caused by the bonding is relatively smaller which may be one of the reasons why the group of Vita Enamic exhibits a higher bond strength,and still need further study. |
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