Crowns (also known as caps) are needed when one or more of your teeth need more extensive restoration than a simple filling can provide. Crowns are indirect restorations in that they must be fabricated by a dental laboratory on a model obtained from an impression (mold) taken of your tooth after it has been prepared to accept the crown. Your tooth is protected with a provisional crown while the definitive one is being made at the laboratory. This differs from a direct restoration such as a silver or bonded filling that is completed entirely in your mouth without a provisional restoration or impression taking.
A cuspal fracture that will necessitate crown placement in this case.
A crown, which normally takes two visits to finish, encases your tooth in a protective shell that virtually eliminates the possibility of fracture during normal function. At the first visit, after you have been numbed, your tooth is shaped so that the crown can fit over it without obstructing your normal bite. Then a provisional crown is created to cover your tooth while the definitive one is being constructed. This is done using either an initial impression taken before your tooth is shaped or with a prefabricated provisional crown that is adapted to your tooth after it has been shaped. After your tooth has been shaped, a final impression is taken of your tooth that is sent to a dental laboratory and then the provisional crown has been made. The final impression is poured in stone at the laboratory to produce a model of your prepared tooth and its adjacent teeth, as they align in your bite, on which the definitive crown is completed. After the final impression is taken, the previously made provisional crown is cemented onto your tooth with provisional cement and then worn until the time when it is replaced with the definitive crown. You will be given instructions for the care of your provisional crown at this visit. The aforementioned procedures taken together are known as a crown preparation.
When the definitive crown returns from the laboratory, you will have been scheduled to come in and have it seated at the second visit. At that appointment your provisional crown is first removed which can be accomplished because the provisional cement used to seat it is not as strong as the definitive cement that is used for the final one. Then any provisional cement remaining on your prepared tooth is removed and the definitive crown is tried on to verify fit, bite and appearance (if it is in an esthetically sensitive area). When these have been approved, the definitive crown is then cemented or bonded onto your tooth. Depending on how the definitive crown is secured or how sensitive your tooth may be when the provisional crown is removed, you may or may not need to be numbed at this visit. After a half hour waiting period to ensure full setting of the cement or bonding agent, you may eat on, floss around and brush the crowned tooth like any other of your teeth. The aforementioned procedures taken together are known as a crown insert.
Crowns can be made out of several different materials depending on their location in and the conditions of your mouth. Crowns can consist of; all gold, porcelain fused to gold and all porcelain. For greatest strength, as when a patient grinds his or her teeth excessively, an all metal crown is indicated. Where additional, but not maximum, strength is needed (such as at your molar teeth) porcelain fused to metal crowns can be used. All porcelain crowns are the most esthetically pleasing and are often used for your front teeth.
When metal-free crowns are placed on molar teeth, fracture is often the result.
There are many reasons why your teeth may need to be crowned. If fracture, decay or defective fillings constitute 50% or more of any of your front teeth, they will need to be crowned. This percentage requirement is lower if any of your teeth will anchor a removable partial denture. If your teeth have large fillings and are cracked, they are at eleveated risk of breaking and should be crowned to prevent fracture that could necessitate more extensive treatment (suchas a root canal) that could otherwise be avoided. In some instances, if your back teeth have fractures, decay or defective fillings constituting 50% or more of their entirety, inlays may be appropriate when they do not anchor removable partial dentures. Any back tooth (all of the teeth behind your eye teeth are considered back teeth) that has been root canalled will need a crown after it has been built up with a post and a core. If your tooth has not been root canalled, but it lacks sufficient mass to support a crown, it will need to be built up with a core. If some of your gum tissue should grow over the fractured portion of your tooth, it may need a gingivectomy prior to being prepared for the crown. In some instances, the alignment of your teeth can be corrected with the placement of several crowns in a row. The appearance of your teeth can be improved with crowns (except for all gold ones - unless your into that), especially all porcelain ones.
Heavily filled and broken down lower back teeth... ...protected and restored to full funtion with PFM crowns.
WHEN YOU ARE CONSIDERING A CROWN VERSUS A FILLING, REMEMBER THAT FILLINGS
DEPEND ON TEETH TO HOLD THEM IN WHEREAS CROWNS HOLD TEETH TOGETHER!
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Risk Indicators for Posterior Tooth Fracture
James D. Bader, Daniel A. Shugars, Jean A. Martin
JADA 2004; 135:883-892.
|Background. Identifying posterior teeth that are at heightened risk of developing cusp fracture is an inexact science. Risk indicators based on controlled observations are not available, and dentists' assessments vary. Methods. The authors conducted a case-control study of cusp fracture in restored posterior teeth. They evaluated 39 potential risk indicators identified in previous uncontrolled studies for an association with fracture in 200 patients with fractures and 252 patients without fractures. These risk indicators delineated patients' clinical characteristics and behaviors, as well as clinical characteristics of individual teeth. The authors used logistic regression to develop models identifying risk indicators associated with fracture, both between case and control subjects and between case and comparison teeth in case subjects. Results. Two risk indicators appeared in both models. The presence of a fracture line and an increase in the proportion of the volume of the natural tooth crown occupied by the restoration substantially increased the odds of fracture (P < .001). Additional risk indicators were unique to the case subject–control subject model, including subject age and other measures related to the relative size of the restoration or to loss of dentinal support. Neither patient behaviors such as clenching, grinding and biting hard objects nor occlusal characteristics such as guidance, cusp anatomy and general wear patterns were strong predictors of fracture risk. Conclusions. Among posterior teeth with restorations, two clinical features were strongly associated with the risk of cusp fracture: presence of a fracture line in the enamel and proportional volume of the restoration. Clinical Implications. Dentists assessing the risk of fracture should consider a detectable fracture line or a high ratio of restoration-to-total-crown volume as important indicators of elevated fracture risk.|