Bridges

Dental procedure
Overview
bridge-preparation-tooth-reduction-options-missing-teeth

Preparation of teeth for a 3-unit porcelain fused to metal bridge.

A fixed bridge is a type of denture, built to replace one or more missing teeth. Dental bridges are held in place in the mouth by slipping them over, and cementing them to, specially prepared abutment teeth, adjacent to the missing teeth. The term “fixed” means the bridge is cemented onto the abutment teeth, and is not intended to be removed by the patient. Dental bridges can be made from a variety of metals, porcelain, ceramic, tooth colored resin, or combinations of these materials. They can be made to look and function very much like natural teeth.

The process

The following describes the steps involved in a typical bridge preparation process. Your procedure can vary from the procedure described. The laboratory process involved in making the actual bridge is similar to the process for crowns.

Anesthetic

The teeth to be crowned with retainers are usually anesthetized by injecting local anesthetic around the nerve(s) that supply sensation to the teeth. Discomfort from the injection can be minimized by use of a topical numbing gel for a minute or two prior to the injection.

Pre-impression

Frequently, a preliminary impression (mold) is made of the teeth before they are altered. The material used most for crown impressions is polyvinyl siloxane, a dimensionally stable and extremely accurate elastomer (meaning it’s stretchy, but returns to the shape it takes when it cures after a minute or two). Other materials may be used. The impression can be used to produce casts, from which a temporary bridge can be made. The temporary bridge will be worn while the final bridge is being made in a laboratory, a process that can take a couple of weeks. The temporary bridge holds the abutment teeth in position and reduces sensitivity after the teeth have been prepared.

Shade Matching

If the bridge is to be tooth colored, a shade matching guide will be used to determine the shade of your natural teeth. The shade should be matched in natural lighting, also called full-spectrum lighting. Fluorescent lights can make teeth appear blue to grey; Incandescent lights can make them appear too yellow. Dental porcelains and resins available today can produce a stunningly precise match for the shade and optical properties of your natural tooth enamel, allowing a bridge to be made that matches your teeth nearly imperceptibly.

Isolation

The teeth are often isolated from mouth structures like the tongue and cheeks while they’re being prepared to prevent injuries from instrumentation used to prepare the tooth. An isolation barrier known as a rubber dam or dental dam is frequently used, but there are other retraction devices in use. Some dentists may simply use cotton rolls and cheek shields. It’s important that shade matching be completed prior to isolation of the teeth. That’s because teeth lighten somewhat (temporarily) when they’ve been isolated for more than a few minutes. Shade matching teeth that have been isolated can result in a shade match that is too light.

Core preparation

The abutment teeth are prepared by removing old restorative materials (if necessary), removing any decay, and (if necessary) filling in any deep holes or missing corners of the teeth. It may be necessary to place small metal (normally titanium) pins in the teeth to rebuild the portion of the teeth that will be crowned. The dentist may use any of a variety of filling materials to rebuild the teeth, including composite resin, glass ionomer, and silver amalgam.

Core buildups are considered a separate billable procedure from the bridge itself. Also, a distinction is made between buildups, which involve all or a substantial portion of the core of the tooth, and bases—those that require only a small amount of filling material in the core to build out a minor chip. Discuss with your dentist in advance whether a complete core build-up is going to be required or not to avoid unexpected costs.

Retainer preps

The outer surfaces of the abutment teeth are reduced in all dimensions (biting surface and sides) by 0.75mm to 3mm to make room for the retainer crowns that will be placed on the teeth. The walls of the preparation are tapered to allow the crowns to be slipped down over the teeth. A ledge (margin) is created around the circumference of the abutment teeth against which the retainer crowns will be tightly sealed.

When you have invasive dental procedures like bridges done, the dentist will review your health history. If you have replacement joints (e.g. total knee, hip, etc.), you may be pre-medicated with antibiotics for the procedure. If you have certain types of heart murmurs or replacement heart valves, you may also need to take an antibiotic pre-medication prior to the procedure.

If you are anxious about dental procedures, your dentist may recommend sedating you for the procedure. There are several methods of relaxing patients for dental treatment, including oral anti-anxiety pills like Valium®; inhaled anti-anxiety medication like nitrous oxide; and intravenous anti-anxiety medication, such as Versed®. Your dental plan may not pay benefits toward sedation.

Impression of preps

An impression of the prepared teeth is made, taking care to gently reflect the gum tissue away from the teeth so that a crisp imprint of the preparation margins will be obtained. Often, the dentist will place retraction cord in the trough between the gums and prepared teeth prior to making the impression. The cord will be removed after the impression is made.

Temporary bridge

The impression/casts that were made prior to preparing the teeth can now be used to make a temporary bridge. One technique involves the use of a denture tooth on the cast in the position of the missing tooth or teeth. From that, a vinyl tray can be made that will serve as a mold for the temporary bridge. The vinyl tray is filled with a gooey tooth-colored resin material, having the consistency of thick syrup, and placed over the prepared teeth. The resin material will gel in about a minute, and the tray can be removed from the mouth. The space between the prepared teeth and the impression of the unprepared teeth is now filled with temporary crown material, which completely hardens in about two minutes. Once hardened, the temporary bridge will be trimmed to proper fit, polished, and cemented onto the teeth with temporary cement.

Labwork and final bridge seat

The final bridge will generally be made by a technician in a dental prosthetics laboratory. When your final bridge is ready, a second visit is necessary to remove the temporary bridge and replace it with the permanent bridge. About half of the time, a patient will ask to be anesthetized for the second visit, to avoid any discomfort associated with removing the temporary bridge and cleaning the temporary cement from the prepared teeth. Teeth which have been endodontically treated (root canal) generally do not need to be anesthetized for the delivery of a permanent bridge, although many dentists prefer the patient to be numb for the bridge preparation due to the potential for discomfort associated with soft tissue management (gum retraction, etc.).

Sometimes an appointment will be scheduled to try in the reinforcing framework (ceramic bridges) before the bridge is completed. This is commonly done for long-span, and multiple-section bridges to verify passive, accurate fit on the teeth before the technician invests the time to sculpt the ceramics.

Adjust and Polish

The functional biting relationship (occlusion) of the bridge may need to be adjusted slightly, and the crowns/pontics (prosthetic replacement teeth) re-polished. This should take just a few minutes under normal circumstances.

Advantages and benefits of dental bridges
  • Replacement of missing teeth with fixed bridgework prevents the adjacent and opposing teeth from moving/drifting.
  • Replacement of missing teeth with fixed bridgework preserves the normal bite relationship between the teeth, allowing for better chewing force distribution, and preventing unnecessary tooth restoration caused by improper meshing of the teeth.
  • Prevention of tooth movement with fixed bridgework can prevent loss of vertical dimension of occlusion (bite collapse), a condition in which loss of the back teeth leads to the lower jaw rotating closer to the upper jaw than it should. Subsequent shortening of the chewing muscles causes increased chewing muscle contraction forces and frequent jaw joint problems.
  • Fixed bridgework allows near normal chewing efficiency, so that food can be properly reduced for normal digestion.
  • Fixed bridges can be made with excellent cosmetic attributes. With modern ceramics, they are nearly imperceptible in the mouth. They look and feel to the patient like their natural teeth.
  • Fixed bridges take only a couple of weeks to complete, in contrast to replacement of missing teeth with dental implants, which often take months to complete.
  • Fixed bridges do not move or shift in the mouth when chewing, like removable partial dentures can.
Disadvantages and risks of dental bridges
  • Fixed bridges require the abutment teeth to be altered through the removal of tooth structure. This introduces the possibility of inflammation and tooth abscesses for the abutment teeth. In many cases, the prospective abutment teeth are completely unrestored, and would otherwise not require any dental treatment.
  • The abutment teeth will be more heavily loaded with chewing forces when they are supporting a bridge. If the abutments have been heavily restored (and thus, substantially weakened) from previous tooth decay and other damage, they may be unable to support a bridge long term and could fail—a sort of domino effect.
  • If one of the teeth involved in a bridge fails due to decay or other reasons, the entire bridge could be lost, necessitating additional dentistry on multiple teeth due to the failure of one (domino effect again).
  • Bridges can be difficult to clean around effectively, increasing the chance that secondary (recurrent) decay might occur around one or more retainer crowns.
  • Inflammation and/or infection from the preparation procedures can occur, and may be more likely with ceramic retainer crowns, because it is necessary to remove more tooth structure than for metal crowns. This is because porcelain must be thicker than metal to have sufficient strength. Studies aiming to quantify the risk of tooth abscess following crown preparation have shown an abscess rate of about 10%.
  • If the teeth being prepared are alive (vital), they will normally be anesthetized. Local anesthetic has risks of its own, which are generally considered minor compared to the advantages of having the procedure performed comfortably.
  • Ceramic bridges can chip, requiring repair or replacement.
  • Microscopic leakage (microleakage) can occur along the interface between the retainer crowns and their abutment teeth (at the margin), leading to sensitivity and decay.
  • All dental procedures can produce lip dryness, chapping and cracking. Some patients develop cold sores following dental treatment. Some degree of post-operative discomfort frequently accompanies crown preparation, including tenderness to biting and cold which is normally temporary. Some studies have shown prolonged sensitivity of over a year in certain patients.
Other care that may be needed

If one of the abutment teeth holding the bridge in place has decay or damage that extends below the gum level, it may be necessary to expose more of the tooth, which is often accomplished in a periodontal surgical procedure known as crown lengthening. In such cases, the bridge will generally need to be replaced, and the damaged portion of the tooth will need to be repaired.

Other treatment options (for example, dental implants) may be available in such cases. The affected tooth may be removed or individually restored in such cases. Supporting a new bridge on a badly compromised tooth is generally not advisable.

Preparing a tooth for a crown (or bridge retainer) can result in inflammation of the tooth’s pulp (the blood vessels and nerve tissue that reside inside the hollow center of the tooth). Because teeth are poorly equipped to deal with inflammation, the resulting inflammation may not get better on its own without intervention in the form of root canal therapy (endodontic treatment).

Teeth that are badly broken down or extensively decayed may also become infected, requiring endodontic treatment to eliminate the infection. A tooth which has been prepared for a crown (or bridge retainer) may need endodontic treatment at any time—before, around the time of, or long after a crown is placed. Whether a tooth will need this treatment depends on many factors, including the extent of the damage/decay to the tooth and the age, health status, and patient habits (e.g. grinding the teeth, chewing ice, etc.).

If a large portion of an abutment tooth is damaged or decayed, it may be necessary to rebuild the core (core buildup) of the tooth (often with filling material), so there is enough solid tooth structure on which to set the bridge.

Sometimes it is necessary to establish an even force distribution among the teeth using a dental handpiece to adjust the surfaces of the teeth. This is done before a new bridge is made, to prevent excess chewing forces from damaging or destroying the bridge. This procedure is called an occlusal adjustment, or equilibration.

If heavy bite stresses are suspected to be a contributing factor to tooth damage, muscle or jaw pain, your dentist may recommend that you wear an occlusal guard (also called a night guard, or splint) to protect the new bridge and the remaining natural teeth.

Other treatment options

Replacement of one or more missing teeth may be accomplished in other ways:

  • Dental implants restored with single crowns, fixed bridges, or removable dentures.
  • Removable dentures may be an option if you are missing several teeth, or are expected to lose several.
  • Orthodontics can be performed to close spaces where teeth have been removed.

Your dentist might suggest other options, or combinations of the options listed.

What if I do nothing?

Teeth are held in their normal position in the dental arch by the presence of the adjacent teeth, and are kept from extruding out of the jaw by the presence of the opposing teeth. They are kept from tipping toward the cheeks by the cheek muscles, and prevented from tipping inward by the presence of the tongue. This balance of forces is upset when a tooth is lost.

The significance of tooth loss depends on many factors, but the most important is the location of the tooth that is lost. If a missing tooth is a second or third molar (also known as twelve-year molars and wisdom teeth, respectively), there may be little significance to the loss. If the remaining molar teeth are in good condition (no decay, and small fillings if any), there is generally little effect on chewing efficiency, little danger of breaking the remaining teeth, and the jaw joints remain adequately supported. The facial bones in the region of the second and third molars typically provide adequate support for the cheeks, and teeth in front of the second molars rarely tip backwards if a second molar is lost.

However, if a tooth is lost forward of the second molars, the remaining teeth in the vicinity of the missing tooth definitely tend to move. If a tooth opposing a missing tooth has no positive stop when the teeth are closed, the opposing tooth will generally move into the space left by the missing tooth. When that happens, the extruding tooth’s neighbors will drift into the space made by the erupting tooth. As a result, the entire bite relationship between the upper and lower teeth on the affected side changes, producing an improper force distribution on the teeth. Loss of multiple teeth can have significant consequences including the following:

Bite collapse

Bite collapse (loss of vertical dimension of occlusion) is a condition in which the lower jaw rotates further closed than normal. This is significant, because it causes the chewing muscles to shorten on the affected side. Shorter muscles can produce greater than normal contraction forces that can cause damage to the remaining teeth (creating a potential domino effect) and the temporomandibular joints (TMJs), which may not be adequately supported if back teeth are missing.

Inability to chew efficiently

Which can cause problems with the proper digestion of food. This can lead to weight loss or gain, depending on how the patient’s diet is affected.

Change in appearance of the face

Change in appearance of the face as the facial muscles change shape and lose their underlying support. The lower face becomes shorter, and the cheeks collapse inward.

Chapping of the lips and chronic cracking at the corners of the mouth

Chapping of the lips and chronic cracking at the corners of the mouth (angular cheilitis) as the lips and cheeks are compressed secondary to the bite collapse.

Other factors

Other factors also determine whether there will be significant tooth movement when a tooth is lost. Age is one of them. Younger patients generally experience greater shifting, possibly due to the greater pliability of the bone in younger people. How the patient uses their teeth also plays a role. Those who clench, grind, chew ice or popcorn kernels; or otherwise apply heavy forces to their teeth are more likely to experience problems after the loss of a tooth. Also, if the teeth adjacent to, and opposing the missing tooth have stable contacts with the teeth around them, the patient may not experience much movement in their remaining teeth. Your dentist is the most qualified to evaluate the potential complications of missing teeth in your mouth.

Author: Thomas J. Greany, D.D.S. / Editor: Ken Lambrecht

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This page was last updated on July 8, 2015.

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Links to dental and medical journals

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