Crowns can not be whitened
Unfortunately, crowns, veneers, and bonding material can not be whitened. Only the natural tooth structure is affected by whitening products. If the shade of your front crowns is really bothering you, you can have the crowns replaced. But you should whiten your teeth to achieve the shade you want before you replace your front crowns so the new crowns match your desired shade. Best, Dr. Elizabeth Jahanian.