Losing more than 1/3
Of the tooth due to decay/fracture
weakens it and needs either an inlay, onlay, or a crown
depending on the extensivity of the lost structure.
The remaining walls of the tooth usually requires a core build up with a resin material prior to preparation to receive a crown to protect and restore the normal anatomy and function of a tooth. Crowns like veneers are also used for cosmetic purposes.