Hello, At Dentistry by Design, they can put porcelain veneers over crowns and make them whiter. There is bonding technology to bond porcelain to porcelain, and also to bond porcelain to metal, so they could take the porcelain off porcelain fused to metal crown and make it whiter and newer. The reason they don’t do it is that it’s about the same amount of work as doing a new crown, so they would have to charge the same. Since a new all-porcelain crown looks so much better, it makes it impractical. To know more visit  https://www.hinsdalefamilydentist.com