Crowns and bridges
Crowns and bridges are dental restorations used to enhance tooth structure and function. A crown is typically recommended when a tooth is at risk of breaking or has undergone significant restoration, such as a large filling or a root canal. Crowns serve to protect compromised teeth and are available in various materials, including porcelain, ceramic, metal, or a combination of these. The process involves preparing the tooth, taking impressions, and creating a custom crown, often requiring multiple visits and temporary restorations during fabrication.
Bridges address the issue of missing teeth by spanning the gap with artificial teeth anchored to adjacent healthy teeth, known as abutments. They help maintain proper alignment and function for chewing and speaking. Similar to crowns, the bridge-making process includes impressions and fabrication, with the final bridge cemented in place after adjustments for fit.
The procedures for both crowns and bridges require skill and precision, with advancements in materials and technology, such as CAD/CAM systems, improving the quality and aesthetic results. Temporary crowns and bridges are provided to protect the prepared teeth until the permanent restorations are ready. Patients might experience some sensitivity post-procedure, but this typically resolves over time. Overall, crowns and bridges are vital tools in restorative dentistry, helping to restore both function and appearance to patients' smiles.
Crowns and bridges
Also known as: Restorative dentistry, indirect restorations
Anatomy or system affected: Mouth, teeth
Definition: Structures that restore the function of the mouth after teeth have been broken or lost, either covering and protecting a single tooth or replacing one or more teeth
Indications and Procedures
A crown may be needed to protect a tooth from cracking or breaking, especially one that already has a large filling. It may also be used to cover a tooth that has already broken, become infected, and required endodontic treatment (commonly called a "root canal"). A crown provides a whole new chewing surface, so it must be able to withstand tremendous jaw pressure. Crowns are indirect restorations that may be made of tooth-colored porcelain, ceramic, or resin; metal, preferably gold; or a combination of porcelain and metal. In this combination, the porcelain is fused with gold, palladium, or platinum. In all-metal crowns, gold is preferable because it can be cast accurately for a tight fit, and it will not corrode. In some cases, all that is needed is a partial crown, or onlay, which preserves more of the natural tooth beneath.
The first step in the preparation of a crown is to modify the tooth to receive a crown. Then, an impression of the tooth is made, and from this, a mold is made in which to cast the crown. Once produced, the crown is polished and contoured to approximate a natural tooth. Any porcelain is colored and glazed to match the shade of the patient’s natural teeth. Once the crown is finished, the dentist adjusts its fit in the patient’s mouth and secures the crown in place with a photosensitive resin. This process has traditionally been accomplished in two visits; the patient is given a temporary crown, usually acrylic, to wear while the permanent one is being made.
A bridge is indicated when one or several teeth in a row are missing, and there are stable teeth on either side of the gap to serve as abutments. It is important to fill the gap to maintain optimal function for chewing and speaking by preventing the remaining teeth from shifting and losing their proper alignment.
Models of the patient’s mouth are made that indicate the shapes and positions of the abutting teeth that will receive crowns to support the bridge and the gap to be filled by the artificial tooth or teeth. The components of the bridge may be made of metal, porcelain, or a combination of the two. The dentist will indicate to the bridge fabricator what shade from a standard color system to make the porcelain to best match the patient’s natural teeth. Once the bridge is made, the dentist adjusts the fit in the patient’s mouth and cements the bridge in place. The entire process may require several visits; the patient is given a temporary acrylic bridge to protect the area while the permanent one is being made.
Uses and Complications
Because the preparation of crowns and bridges involves drilling on teeth, the dentist provides local anesthetic through injection to numb the area. This numbness may last a while, and the patient must be careful not to bite the lips or tongue.
While the permanent restoration is being fabricated, the patient wears a temporary piece that is held in place with a light adhesive so it may be easily removed later. However, it may become dislodged before the next dental appointment. It is important that the temporary crown or bridge be replaced as soon as possible to keep the prepared teeth protected and stable. Should their shape or position change, the finished restoration would no longer fit properly.
Fabricating and fitting indirect restorations requires skill and patience. Any excess space inadvertently left between the tooth and the crown or bridge increases the risk of decay or infection because food may become trapped. This is especially problematic for teeth that have not had root canal treatment because a painful abscess may form under the crown. Excess space in bridgework creates the possibility of teeth shifting, which the bridge was originally designed to avoid.
When the crown or bridge is delivered, it might feel high and contact the teeth on the opposite jaw sooner than expected. The dentist will make adjustments at the time of delivery, but a return visit may be necessary if further discomfort is felt.
The teeth involved may be somewhat sensitive to cold following delivery of the restoration. This sensitivity may last for weeks, but it typically resolves on its own.
Perspective and Prospects
Indirect restorations were initially unattractive but functional metal structures. Later, fabrication with porcelain allowed for a less obvious appearance. Advances in materials science have led to the development of stronger, more fracture-resistant ceramics. These contribute to longer-lasting, more aesthetically pleasing restorations.
Technology is partnering with dentistry to generate computer-aided design and computer-aided manufacturing (CAD/CAM) for use in crown and bridge fabrication. Dentists and dental laboratory technicians are using CAD/CAM technology to increase the precision of individual restorations by capturing each tooth’s exact size, shape, and position. Digital impressions are more comfortable for the patient and less technique-dependent than customary alginate impressions. The resulting three-dimensional image appears on a computer screen, and the dentist can electronically draw the restoration design on the image instead of sculpting wax on a stone model. The details can then be transmitted digitally without distortion to the dental lab technician, who uses a CAD/CAM machine to mill a ceramic material into a detailed replica of the drawing. By looking at the same electronic image before manufacturing, the dentist and the dental laboratory technician can clearly communicate their needs and expectations for an accurate preparation that will result in a quality custom restoration. Digital impressions are also now making same-day crowns feasible.
Bibliography
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