when a tooth has a cavity the first time a silver or tooth colored filling most likely can be used to restore the tooth to health. however, sometime too much of a tooth's structure is removed to support a filling and the tooth is over filling with filling material at this stage a crown or "cap" may be needed. a crown can be used as a dental restoration to:

restore a tooth when it is to weak to support a large filling

protect a weak tooth from fracturing or restore fractured teeth

cover badly shaped or discolored teeth

cover dental implants