Bridges for Missing Teeth

A bridge is a device that allows patients to have missing teeth replaced. The bridge that your dentist uses is similar to a bridge on the street: it’s a structure with supports on each side of a space; where both sides are connected so that it can withstand great forces. A bridge in your mouth connects a tooth on one side of a space to the tooth on the other side of the space with a false tooth or teeth in the middle. The teeth on each side are called retainers or abutments, and the tooth in the middle is called a pontic. A bridge helps to stop the adjacent teeth from tipping into the missing tooth space as well as preventing the opposing tooth from super-erupting into the space left by the missing tooth.

Bridge Types

There are eight main types of bridges:

• PFM (porcelain-fused-to-metal) bridges
• Full-gold bridges
• All-porcelain bridges
• Captek bridges
• Zirconia bridges
• Virginia/Maryland Bridges
• Encore bridge
• Implant bridges

The porcelain fused to gold bridge is where a metal substructure is covered by a porcelain substrate. It is very strong and can be designed so that no metal is visible, or some metal may be visible on the top of the bridge. The benefit is that metal is kinder to the opposing tooth and won’t accelerate wear of the natural tooth as much.

Full-gold bridges have no metal and are full-gold restorations that are virtually unbreakable. Porcelain is abrasive, but gold is very biocompatible and is the kindest of all materials to the opposing teeth.

All-porcelain bridges are bridges without metal, and they can be broken down into sub categories: pressed porcelain or feldspathic porcelain, which is built up and fired in stages.

Captek bridges have a 24K gold substructure and have porcelain baked on to the metal framework.

Zirconia bridges are made of a monolithic zirconia (a very strong ceramic material) and have almost the same strength as porcelain-fused-to-gold bridge, but without the metal substructure.

Virginia or Maryland bridges utilize a metal frame on the back of the two teeth on either side of a space, with a porcelain tooth baked on to the middle wing. This is then glued on to the teeth’s lingual, or back, so that only the porcelain tooth is visible. This technique avoids substantial shaving down of the two remaining teeth; however, the disadvantage is that the chewing and flexing of the remaining teeth can lead to the bridge debonding or coming off.

Encore bridges are used when no restorations are in the teeth adjacent to the missing space. In this case, small box-type preparations are made, and the bridge has a small wing or inlay that is cemented into each tooth. These are very conservative, but have the ability to debond on one or both wings.

Implant bridges are bridges made out of the same materials previously listed but they sit on implants instead of natural teeth.

This covers the basics, but most patients have many more questions about bridges. Here are some of the most common queries.

What is a Zirconia crown or bridge?

Zirconia is a ceramic material that is formed from pressure placed on zirconium oxide powder and Yttria, plus additional additives. It is exceptionally strong and can be milled out of blocks in a CAD CAM milling machine to fabricate crowns and bridges for dentistry.  This material is sintered for 6.5 hours at 1530 degrees Celsius and is extremely strong when finished.  It is monolithic, so it is made of one material and delamination or chipping of a porcelain superstructure won’t occur.

Which will last longer, a porcelain crown or a Zirconia bridge?

Porcelain can chip, crack, or break and is very brittle until cemented onto the host tooth. Zirconia bridges are virtually unbreakable. Due to the outstanding strength of these materials, they can be made in thinner sections so less tooth reduction is required.

Which is prettier for a bridge, porcelain or Zirconia?

All-porcelain bridges are much prettier as they are built up in layers and can have depth of color baked into them. The zirconia bridges tend to be rather opaque looking and monochromatic, so they may be a better choice when aesthetics aren’t the number-one priority.  The most aesthetically pleasing all-porcelain bridges are pressed ceramic or layered ceramic bridges. They’re used to replace front teeth where chewing forces are lower than in the back of the mouth.

Should Zirconia bridges be used for bridges that replace more than one tooth?

Long-term studies are ongoing, so there is not conclusive evidence that these bridges will last as long as porcelain-fused-to-metal bridges. That being said, current research looks very favorable for using this material for longer-span bridges.

Are cantilever bridges where a fake tooth sticks off the back of two crowned teeth?  Is this a good idea?

When a fake tooth, or pontic, hangs off the back of two splinted teeth, the forces on the back teeth are magnified. So, cantilever bridges increase the risk of fracture of the teeth, the porcelain and the bridge, and should be avoided at all costs.  A cantilever means that pushing down on a fake tooth will cause rotational forces on the front tooth of the bridge and cause the bridge to become uncemented.

How long can bridges be?

The rules about the length of bridges are based upon principles of physics. These principles say that the surface area of the missing roots (for the teeth that are gone) should be matched by the surface area of the teeth supporting the bridge. So if you are missing one tooth, then the two teeth that support the bridge will have roots with a bigger surface area than that of the missing tooth. The longer the bridge, the more it flexes under load. Consequently, longer bridges may not last as long as shorter bridges.

My dentist wants to put a bridge in for a missing eye-tooth. Is this a good idea?

Your canine teeth are located in the corner of the mouth, and the forces taken on by hooking a bridge on to a bicuspid and lateral incisor are not biomechanically favorable. The surface area of the canine root is larger than the surface area of the lateral and bicuspid, so it may fail. For these reasons, it’s not a good idea.

What should I do to clean my bridge?

Bridges should be cleaned every day.  Since bridges connect teeth, care must be taken to thread dental floss under the bridge so the remaining teeth can be thoroughly flossed.  Failure to use a floss threader under a bridge will result in periodontal disease and decay around the bridge retainers. The biggest reason bridges fail is secondary cavities from poor cleaning. Fluoride to protect the enamel and root surfaces is also highly recommended to further prevent recurrent decay.