Objectives: The purpose of this study was to evaluate the shear bond strength between CoCrMo dental alloy and porcelain restorations by application of different metal-ceramic transitional interfaces aiming at improvement of the bond strength and fracture tolerances.
Methods: Several metal-ceramic specimens with different composite interlayers were produced. The interlayers consisted of metal/ceramic composites with different metal volume fractions (20 M; 40 M; 60 M; 80 M). The metal-ceramic bond strength as well as the fracture strength of the composites and monolithic base materials were assessed by the means of a shear test performed in a universal test machine. The interfaces of fractured and untested specimens were examined by the means of optical microscopy. The microstructures of monolithic base materials were analyzed using SEM/EDS. The elastic and inelastic properties of the homogeneous compositions were additionally evaluated using dynamic mechanical analysis.
Results: The bond strength results obtained for metal-ceramic gradated specimens were the highest (261±38 MPa) for 40 vol% metal in the interlayer [40 M] vs. 109±27 MPa for a direct metal-ceramic joint. The Young's moduli and the fracture resistance of the composites revealed an increasing trend for increasing metal contents.
Significance: This study shows that a graded transition between metal and ceramic, provided by a metal/ceramic composite interlayer, is regarded for an increase by 2.5 times in the bond strength between the two materials relative to conventional sharp transitions. The elastic modulus of the composites used as interlayers might be very reasonably approximated by a micromechanical model.
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