Crowns and Bridges
By Joseph Preziosi Jr., DMD
Crowns are a long term treatment for replacing missing tooth structure when there is no longer sufficient tooth structure remaining to support a filling. This can be caused by caries (tooth decay), tooth fractures, lost fillings, traumatic injuries, or a combination of these and other factors.
A crown is placed on an individual tooth, somewhat like a thimble over a finger, so the tooth has to first be prepared prior to the crown being fabricated to insure there is sufficient space for the different materials the crowns are made out of.
Crown preparation always begins by removing any diseased tooth structure and any old fillings to ensure there is no disease processes occurring under them. Often times a pulp cap will be done to protect the nerve of the tooth and decrease the risk of the tooth needing a root canal later. This is followed by a core build up to replace some of the missing tooth structure so that there is adequate tooth structure for the crown preparation to have the proper shape and size for accommodating the final crown. There will be times when crown lengthening will be necessary due to caries (tooth decay) that goes below the gum line, an old filling that goes below the gum line or a fracture that extends below the gum line. This procedure removes some of the bone that's around the tooth and allows the crown to be finished on healthy tooth structure while also allowing enough room between the end of the crown and the bone for healthy gums.
After all the necessary crown preparations are competed an impression will be taken of the crown preparation, the adjacent teeth and the opposing teeth all vital information for the laboratory to custom design and fit your specific crown to your mouth. This impression will be sent to a dental laboratory that will fabricate the crown as per the doctors prescription. Then a temporary crown will be placed on the crown preparation so that the nerve of the tooth will be protected, the patient will be able to chew food and the esthetics of the area can be reestablished.
The materials the doctor's prescription will direct the laboratory to make the crown out of will depend on the circumstances of each individual case and the doctor's personal judgment from years of experience. For most back teeth durability and strength are paramount, therefore crowns are usually porcelain fused to gold. The gold provides strength and all but eliminates the possibility of the remaining tooth preparation from fracturing while the porcelain establishes the bite and satisfies the esthetic needs of the case. When strength is utmost and esthetics are not a concern then an all gold crown may be the restoration of choice. This restoration is extremely strong and durable and has no porcelain that can fracture off. For front teeth where esthetic concerns are paramount there are a number of types of crowns available, such as porcelain fused to ceramics, pressible porcelain and milled ceramics. These types of crowns give the highest esthetic qualities possible to the restorations and are becoming stronger and more durable all the time.
Bridges have all the qualities and characteristics of crowns and are employed to replace missing teeth. The remaining teeth on either side of the space are prepared just like crowns are and the laboratory will suspend pontics (replacements for the missing teeth) from the abutment crowns restoring these teeth. Just as with the crowns the doctor has the choice of several types of materials and combinations of materials to have the bridges fabricated out of depending on the clinical situation.
Once the crowns and bridges are finished they are cemented into place and become a fixed restoration. This means the patient is not able to remove the crown or bridge from their mouth. Only a doctor can take fixed crowns and bridges out of a patient's mouth and when they are removed the crowns and bridges usually need to be redone. This is because the safest way to remove a crown or bridge without seriously damaging the tooth structure underneath them is to cut them off, thus destroying the crown or bridge that is being removed.