Table 1.

Requirements for the metal alloys used with PFM restorations.

•The melting temperature of the metal alloy is greater than that of the firing temperature of the ceramic (greater than 100OC) to avoid melting and sagging of metal •The metal’s coefficient of thermal expansion (CTE) is slightly greater than that of ceramic veneer to put the ceramic in slight compression and prevent crack propagation on cooling • Metal alloy has the ability to make a strong bond with the ceramic: – through the chemical reaction between the metal surface and the ceramic (Chemically) – through metal alloy surface roughness which can be achieved after metal surface treatment such as Air-borne abrasion (Mechanically) – by the intentional mismatch in the CTEs between the metal alloy and ceramic •Metal alloy should be stiff and strong enough to withstand imposed forces and resist distortion and bending •Metal alloys should be thin enough to allow sufficient placement of the ceramic so as to mask it but still be able to resist deformation and distortion during firing and when it is used.