Porcelain is the most esthetic restorative material in dentistry. It can be used to repair broken or decayed teeth as well as to replace stained, chipped, missing or worn teeth.
Porcelain fused to metal (PFM) crowns have a proven record of success, and for many years were the only esthetic crown option available. This type of restoration has a metal substructure over which porcelain is fused. The PFM crown does not allow light to permeate through it. It blocks the light, and therefore casts a dark shadow at the edge or margin where the crown ends on the tooth. In order to hide this “dark line” margin, it is necessary to prepare/cut the tooth to a level slightly below the gum line. In this way, the edge or margin of the crown will be hidden under the gums. Over time, however, your gums can recede, thus exposing this margin.
For ultimate esthetics, it is necessary to use an all-ceramic restoration; that is, one that has no metal in it. In addition to improved esthetics, the all-ceramic restoration does not require the tooth preparation to extend below the gums just for the sake of esthetics. This preserves natural tooth structure and helps keep the gums happy, since restorations below the gums can make it hard to keep the gums healthy. Light permeates the all porcelain fillings, and therefore, the margin blends in well with your natural tooth color even if or when the gum recedes. Since this margin is more esthetic, in many instances a more conservative tooth preparation can be made. This means less cutting and destruction of your remaining healthy, natural tooth structure, which in turn means less risk of damaging the tooth’s nerve. This preservation of tooth structure helps to maintain a stronger tooth. The elimination of metal and its inherent opacity allows the underlying tooth structure to help provide more natural and lifelike esthetics by becoming the substructure for the restoration.
All-ceramic restorations must be bonded to the tooth, and this requires good isolation from saliva and other contaminants. The process of bonding is a bit trickier than the use of conventional cements and requires more finessing. Also, these restorations are more prone to chipping and/or fracturing and needing replacement than are PFM crowns. Therefore, in some cases, it may be prudent to avoid the use of an all-ceramic restoration. The farther back in the mouth the restoration is, the stronger are the forces that bite on it, thus increasing the likelihood of fracture. People who clench and/or grind their teeth also should avoid the all-ceramic material, especially in the back. The best indications for the bonded all-ceramics are veneers and anterior crowns. Many all-ceramic restorations have been successful on back teeth as well; just a little less predictable.