Metal marks showing on crown (Photo)

This is what caused the metal to be exposed, when the bite has to be adjust in the mouth, this is what happens. Preparations for a full crown coverage either for a single crown or a bridge, need to have at least 1.5 or 2 mm of clearance from the opposing tooth, to avoid this problems, especially when porcelain-fused to metal crowns are used. Nowadays, Zirconia crowns or bridges are used, because they are stronger and because they don't show any metal, even if you need to adjust it after. Exposing metal on the occlusal surface is not a big deal, since the whole restoration is completely covering the tooth and it won't represent harm to the tooth. Unfortunately it cannot be covered with anything.