Crowns, most bridges, and implants are fixed prosthetic devices. Unlike removable devices such as dentures, which you can take out and clean daily, they are cemented onto existing teeth or implants, and can only be removed by a dentist.
A crown is used to entirely cover or "cap" a damaged tooth. Besides strengthening a damaged tooth, a crown can be used to improve its appearance, shape or alignment.
A bridge may be recommended if you're missing one or more teeth. Gaps left by missing teeth eventually cause the remaining teeth to rotate or shift into the empty spaces, resulting in a bad bite.
Dental implants are metal posts or frames that are surgically positioned into the jawbone beneath your gums. Once in place, they allow your dentist to mount replacement teeth onto them.