Bond strength of porcelain to dental alloys – an evaluation of two test methods

Abstract

– Two methods for measuring shear strengh of the porcelain‐metal interface, a rod/disk‐push test and a cube/cube‐push test, were compared using the same metals and porcelain material. Both types of specimen showed evidence of complex stress distribution at the interface during loading and fracture line located mainly in the opaque porcelain layer. Both methods were thusmainly a test of the “strength” of the porcelain at the interface. The “Bond strength values” obtained with the rod/disk specimen seemed to depend on the geometry of specimen and the values obtained with the cube/cube specimen scemed to depend on the quality of the porcelain work. It seem questionable whether “bone strenghth values” as obtained with these two methods can be the basis for requirenments in a standard for porcelain‐metal systems.

The Zirconia Ceramic: Strengths and Weaknesses

“…Upon fracture, similar to porcelain-alloys [162], a thin porcelain layer remained attached to the zirconia surface, showing that cohesive strength was lower than adhesive bond strength [27]. Even scientific evidence was lacking, Fischer assumed that bond between zirconia and ceramic was chemical [86].…”

Comparison of Adhesion of a Novel Pre-sintered Cobalt-Chromium to Pre-sintered Zirconia and Cast Nickel–Chromium

“…Previous studies reported fractures mostly adjacent to core veneer interface, 38,39 while others reported mostly cohesive failure mode in metal ceramic group. 40 10% of the specimens showed cohesive fractures within the porcelain in groups Zi and Wi. Cohesive fracture happens when ceramic strength is less than that of ceramic core interfacial bond strength.…”

Correlation between metal-ceramic bond strength and coefficient of linear thermal expansion difference

“…Various tests have been designed and selected by researchers to evaluate metal-ceramic bond strength and the minimal value recommended by the ISO standard 9693 15 for metal-ceramic dental restorative systems is 25 MPa for 3-point bending test. However, it can be affirmed that this value is related more to the flexure strength of the metallic substrate than to the metal-ceramic bond strength 12 , 13 , 18 , causing difficulty when comparing different metallic substrates.…”

“…High palladium alloys were introduced in the early 1980s and are currently widely used in metal-ceramic restorations, even though they have not yet been scientifically investigated to the extent that their widespread use requires 10 , 13 , 14 , 17 , 18 . This type of alloy presents characteristics that, in spite of not interfering with the porcelain-to-metal bond, must be observed.…”

“…Another characteristic of the palladium alloy is its high sensitivity to the presence of carbon during casting procedures. This could generate problems such as ceramic porosities and carbon contamination in the alloy 6 , 15 , 17 , 18 . The carbon promotes a formation of carbon monoxide during the ceramic baking, creating bubbles and porosities, which could be partly responsible for undesirable outcomes, such as cracks or fractures.…”