How do dentists determine that there is decay under a crown?

EXplorer and x-ray.: The dentist will take an explorer and test the tooth structure around the crown at the margin of the crown. If there is decay, it will start here. An x-ray may also show the existence of decay around the margin of the crown and deeper into the tooth itself.

Not always obvious: Meticulous regular exams and x-rays will likely show decay under crowns before they become serious issues, however, since most crowns block the x-rays from showing the tooth structure beneath, it is possible to miss the recurrent cavity. Please note that once found, it is important to take care of any decay under a crown as it definitely jeopardizes the crowns prognosis.

Diagnosis.: Decay can be felt with special instruments, x-rays can identify decay under crowns as well as using decay detecting lasers and stains.