A crown is placed for a number of reasons: To support a large filling when there isn’t enough tooth remaining; to attach a bridge; to protect weak teeth from fracturing; and restore fractured teeth.
In order to determine which crown materials are suitable for an individual,the following factors are considered:
a) Tooth location;
b) position of the gum tissue;
c) the function of the tooth;
d) the amount of the tooth that shows with the smile; and
e) the colour and shade of the tooth.
Crowns are prepared and placed in the following fashions: First, the tooth is prepared by removing its outer portion to accommodate the thickness of the crown. Then an impression is made to provide an exact model of the tooth. The crown is made from this model. It is then put in place and any necessary adjustments are made. When it’s position, appearance, feel, etc. are satisfactory, the crown is then cemented into place. Once the procedure is complete, the tooth will not only be stronger, it will also look great.
The teeth are “Shade Matched” to allow the crowns to blend seamlessly into the patient’s own dentition.
There have been many attempts to make an ALL porcelain crown. In other words, a crown that would not have a metal substructure under it. The reasons for wanting to eliminate the metal are primarily to get rid of the dark line at the very edge of the crown and to let more light pass through the porcelain (to look more lifelike). There are other advantages to all porcelain as well – one such advantage is that the dentist can keep the edge of the crown just at the gumline rather than trying to “hide” it under the gumline. This becomes important in the long term health of the gum tissues as well as the appearance – even if there is slight receeding over the course of years. In the past, there have been numerous attempts to produce such an ideal crown. Unfortuately, there were always problems – they easily fractured. The porcelain is not strong enough to withstand the demands of chewing and grinding. One other problem was the less than ideal fit of the porcelain crown to the prepared tooth.
The VITA In-Ceram System consists of an extremely accurate fitting, highly stable aluminum oxide substructure that takes the place of a metal substructure. Now we can obtain a colour that is not altered by the metal underneath and that is also much more translucent (allows light to pass through it) so that is looks natural. The BIG question of course is how about its strength? Will it hold up? A study published in 1994 showed that In-Ceram crowns fractured at the same (or greater) pressure than metal-porcelain crowns did. This strength is three times greater than that of other all-porcelain systems known to date. One dental lab has now documented over 4,000 In-Ceram crowns placed over a 4 year period, the failure rate is 0.01%!!
