Investigation of the effect of bonding factors on strength of porcelain bond to soft metal alloys after application of thermal cycle

The chemical bond between the metal and the porcelain component is likely to fail in metal‑porcelain restorations. This is due to the thick oxide layer that Cr–Co alloys create. This study aimed to investigate the effect of metal conditioner on controlling the oxide layer formed on the surface of the Sintron alloy and the strength of the metal–porcelain bond.

In this in vitro study, 33 samples were divided into three groups based on surface treatment (n = 11). In all three groups, an oxide layer was created. In the first group, Shofu metal conditioner, in the second group, metal conditioner of Creation, and in the third group, no metal conditioner was applied. All samples were then subjected to 3000 heat cycles between 5° and 55°C with a stop time of 5 s. The specimens were then placed in a universal testing machine for shear bond testing. A force was applied between the alloy and the porcelain by a 5 kN load cell at the speed of 1 mm/min until a fraction occurred. Intergroup comparison was made by the one‑way analysis of variance followed by the Tukey’s multiple comparisons test (α = 0.05).

The mean shear bond strength of the first group was 34.93 MPa and the mean shear bond strength of the second group was 31.37 MPa.The mean shear bond strength of the first and the second group was significantly higher than the third group (23.37 MPa) (PV < 0.001).

The use of metal conditioners between ceramill Sintron alloy and porcelain (Vita VMK MASTER) led to increasing the bond strength.