What can cause a "pop off" of a porcelain veneer from the underlying gold crown?

The phenomenon of a "pop off" of a porcelain veneer from an underlying gold crown can be attributed to multiple factors that compromise the bond between the materials. Each of the causes mentioned significantly impacts the adhesion quality and integrity of the porcelain veneer.

When a pure gold surface conditioner is applied too thickly, it can prevent the proper flow and bonding of the porcelain to the underlying metal, leading to a weak bond that might ultimately fail. This thick layer may not allow for the necessary mechanical interlocking or may create areas of stress concentration, making it more susceptible to detachment.

Contamination at the porcelain-metal interface is another critical factor. Any debris, saliva, or residual oils can interfere with adhesion. Proper cleaning procedures are essential to ensure that the bonding surfaces are free from contaminants to achieve a strong bond. If contamination occurs, it disrupts the bonding process and can lead to a "pop off."

Under firing the opaque layer of porcelain can also contribute to the problem. Proper firing is crucial because it ensures that the porcelain achieves the necessary physical properties, such as strength and adhesion to the metal substrate. If the opaque layer is under fired, it may not bond effectively with the gold crown, leading to a weak link in the structure.

Therefore, all these