Crowns are used most commonly to entirely cover or "cap" a damaged tooth. They are made by a technician and bonded by the dentist in the surgery. They can be made of porcelain, porcelain fused to metal, zirconia and even gold. Your dentist may recommend a crown to:

Replace a large filling when there isn't enough tooth remaining
Protect a weak tooth from fracturing
Restore a fractured tooth
Attach a bridge
Cover a dental implant
Cover a discoloured or poorly shaped tooth
Cover a tooth that has had root canal treatment

Bridges cover the space where the teeth are missing and are cemented to natural teeth or implants surrounding the space.