A Crown is needed when a tooth decay or fracture involves more than 3 surfaces of the tooth in question. There simply are not a sufficient number of remaining walls to give the direct composite restoration/filling the retention it needs. Before the days of bonding technology, dental crowns nearly always needed to be made with a metal foundation. Today, we can make them out of pure porcelain or other ceramics. There are still occasions on the back teeth when the durability of a metal underlay in the crown makes it the restoration of choice, but even those cases now with the arrival of Zirconia (synthetic diamond) crowns, can be managed in a metal-free fashion. But when it shows prominently in your smile, wouldn't you rather have one that looks as natural as possible?
Carefully chosen porcelain crowns selected by an expert cosmetic dentist look exactly like a natural tooth; it will be very difficult for people to tell that it isn’t real.
Dentists need special training in cosmetic dentistry in order to place these restorations.