Dental Bridges
 

What Types of Bridge are there?

As we have clarified, a bridge is a way of replacing one or more of your missing teeth. When discussing the different types of bridges it is important that we understand a bit of 'dentist lingo'. So here is an explanation of the main words used in relation to bridges:

In the mouth:

  • Abutment: This is a tooth (or implant) that provides support for the bridge.

On the bridge:

  • Retainer. This is the part of the bridge which is cemented to the abutments. It is most commonly a full crown, but can also be a ¾ crown, an inlay/onlay, the wing of a resin-retained bridge, a post crown or an implant.
  • Pontic. This is the fake tooth that replaces the gap and is attached to the retainers. There are two main types, the first is used in the vast majority of cases:

    • Ridge lap- This contacts your gum on the visible side of the fake tooth to look like a natural tooth, but on the back, it is cut away from the gum to help with cleaning.

    • Hygienic- This doesn’t contact the gum and makes cleaning underneath much easier. Obviously this doesn’t look so good, thus can only be used in areas at the back of the mouth where it won’t be seen.
  • Precision attachment. This is a movable joint that provides a bit of suspension to the bridge. It consists of a female part generally on the retainer into which a male part on the pontic sits. Different teeth move different amounts and in different directions under the pressure of your bite. When fixed rigidly together, this can stress the teeth and bond of the bridge. Precision attachments can sometimes be used to help buffer these forces.

General:

  • Units. This is the number of teeth involved in the bridge. This equals the number of pontics + the number of retainers. For example, two fake teeth supported by three retainers would be called a ‘5 unit bridge’. The most common design is 3-unit bridge that has one pontic, supported by two retainers (crowns).

Most websites on dentistry will tell you about three types of bridge and focus on the fixed-fixed bridge. This type of bridge provides the most support, is by far the most common and has the best-proven track record.

Others can be useful in certain situations, and if applicable to your situation, the dentist will discuss them with you.

  • Fixed-fixed bridge. This is the staple approach and involves two single crowns either side of the space holding a pontic in the middle. The abutment teeth (those that hold the fake tooth) can be natural teeth or implants.They tend to be one or the other, not a combination of teeth and implants. The reason for this is that teeth can move around a bit in their ligament, but implants are rigidly fixed to the bone and this difference can be problematic.
  • Cantelever bridges. Here the pontic is attached only on the one side of the space. Depending on the tooth that is being replaced, on rare occasions two abutments can be used on the one side to provide extra support. Imagine the fixed-fixed bridge but forgetting the crown on one side. .
  • Resin-retained bridge. This may also be called a' Maryland Bridge' or a 'Sticky Bridge'. It has metal or porcelain wings that are bonded to the teeth either side of the gap, suspending the fake tooth in the middle. Sometimes this type of bridge may have a cantelever design- meaning it is only attached by a wing on the one side..

The other less commonly mentioned options for a bridge are:

  • Fixed– movable. Here the pontic is fixed solidly to an abutment on one side of the space and via a moving joint to the other. Both abutments provide support, but only the one to which the fake tooth is attached, holds it in place. The movable joint is commonly a precision attachment which may be incorporated into a crown. Sometimes an inlay is placed into a tooth and the bridge simply has a rest that sits on top of the inlay. The reason, the rest cannot sit straight onto your tooth, is decay could occur underneath it- where it would be very difficult to clean.
  • Inlay bridges. It is sometimes possible to incorporate an existing cavity into the design instead of crowning the whole tooth. The more surface area involved for bonding-in, the better. Of course it is a compromise, you do not want to unnecessarily remove tooth structure or it defeats the main purpose of this conservative type of bridge.
  • Glass fibre re-inforced composite bridges. Essentially a tooth made of white filling is built up in the space. It is bonded to the teeth either side and supported with some glass fibres running through the middle. It is a very effective and conservative way to replace a space where the teeth to support the bridge are relatively untouched or have just small fillings. It is not routinely taught in dental school and is quite technically sensitive, requiring a bit of practice to perfect.

As you can see, the dentist has quite a few options to tailor make the best bridge for your situation.

All that being said and done, the fixed-fixed bridge with a ridge lap tooth and full crowns either side is by far the most common, so much so that the design to most patients has almost become synonymous with the word bridge.

What Materials can Bridges be made from?

Your bridge can be made from any of the methods andmaterials used for a single crown- Clicking the link will take you to a more detailed discussion.

Your dentist will make the decision on the most suitable type of material, taking into account- the bridge design, your teeth, your bite, their past experiences, the technician/ceramist, your finances etc.

Here is a brief summary:

  • Porcelain–fused to metal
As with crowns, this is the most common type because of its predictability, strength and great aesthetics. If a precision attachment or rest is required then to incorporate this feature, the bridge must be of this type.

  • All porcelain
Dental porcelains are improving all the time, though long- term data regarding the success of these newer porcelains is not yet readily available. Cad-Cam technology (CEREC) has also advanced to being able to offer multiple porcelain units i.e. bridges, not just single crowns. There are many different types of porcelain available, some are stronger, some are more aesthetic- the main types are discussed in dental crowns options.

  • All metal
These have the advantage of requiring less tooth to be removed, but the issue of aesthetics means they are rarely used. With the price of gold sky rocketing, the cost of a gold bridge could be prohibitively high, given that the cost of a single gold crown is expensive enough.

Other metals, though less superior to gold in their physical properties can be used. Porcelain-fused to metal gives the dentist the added bonus of being able to choose the amount of metal/porcelain, so where maximum tooth needs to be kept for strength, a metal surface can be used whilst still having the tooth coloured porcelain on the side for aesthetics- a bit of a compromise.

What Type of Bridge is Best for Me?

Assuming that a bridge is the right alternative for restoring your missing tooth, how do you decide which type of bridge is best?

Well luckily, when it comes to treatment planning, the dentist is a professional used to making these decisions, so don’t feel overwhelmed; they will present you with the different options.

Fixed bridgework is essentially crowns holding a fake tooth or teeth. As such the dentist must take into account all of the information we discussed when 'choosing a crown'.

There are some additional considerations to appreciate that are specific to bridges. These factors are weighted differently and your dentist will put them in the context of your desired outcome, timing, expectations and finances in helping you to make the right decision.

Factor to consider include:

  • The state of the abutment teeth
These are the teeth to be used to support the bridge. Are they healthy and untouched by dentist hands, or are they heavily restored and filled, or even crowned?

If they are untouched, the more conservative a bridge the better- an all-porcelain fixed-fixed bridge would involve a lot of drilling down of your tooth and would be better avoided in favour of an implant.

The more heavily filled teeth are, the more having crowns on them, as part of the bridge will have a protective role rather than a destructive one. Small fillings can sometimes be replaced and incorporated into an inlay bridge or used to gain extra surface area for bonding-in a 'sticky type' bridge.

Glass fibre re-inforced composite bridges are not very widely performed, but if your dentist does them, they can be a good option when you have largely healthy teeth that you want to protect.

  • The position of the tooth

(i) For front teeth, these are suitable options:

-Fixed-fixed bridges

-Cantelever bridges

-Resin retained or bonded bridges.

(ii) For back teeth, all bridge designs are possible- it just depends on the situation as to whether they are appropriate. The vast majority of the time- the extra forces that need to be absorbed at the back of the mouth from chewing make the resin-retained bridge unsuitable.

  • The look of the bridge
The best aesthetic bridges are unarguably the fixed-fixed type bridge or single fixed cantelever. The metal wings of a resin-retained bridge (RRB) which bond it to the teeth next door, can cause some greying of the holding teeth. Porcelain bonded bridges can now be made which act on the same principle (still minimal drilling), but they do away with any metal and its associated problems.

A single cantelever is commonly used to replace a lateral incisor using the canine as the abutment. Canine teeth have very long strong roots, so it is not always necessary to prepare the central incisor as well- unless there is a problem with it avoiding the need and extra expense of a fixed-fixed design. The lateral incisor, (one of the most common teeth to be lost) is also replaced fairly well with a RRB if the conditions in your mouth (bite etc.) are favourable.

The further back in your mouth that you go, the less a small amount of metal work matters- that said you may insist, for aesthetic reasons, you would like an all porcelain bridge to be made.

  • If an abutment tooth has had root canal treatment
If one of the supporting teeth has had a root canal filling, protecting it with a crown is a good idea anyway. So a fixed-fixed or fixed movable design would be ideal. However, if it also has a post into the root canal, this tends not to be regarded as the most ideal situation for supporting a bridge. Pressures on the bridge can risk the post fracturing the root- this would cause the tooth to be lost and a major rethink would be needed.

When I say it is not ideal, I mean, we (dentists) still have to do it in many situations when our options are limited, but it is a risk you need to be aware of. A post crown as part of a bridge, in say a bruxist with a heavy grinding habit, would not be the best idea.

  • How long you want it to last
There are many factors that will determine the success of each individual bridge. Generally speaking, resin-retained bridges are regarded as the least reliable because they involve the least tooth preparation and rely entirely on the strength of the cement.

If this was to fail, it can probably be stuck back in, though the length of time it would be expected to last generally wouldn't be as long as before. The other types of bridge and alternatives do however still remain open if it fails and can be progressed to if need be.

Fixed-fixed and fixed-movable are both very reliable bridges and have excellent long- term outcomes. They are both most consistent and predictable.

  • The dentist’s preference
Dentists will have treated cases similar to yours before, (although not exactly the same). They will therefore have a good idea as to what is most likely to work in your given situation and they can share their experiences to help you make a decision.

If a patient asked for a particular type of bridge and I felt it wouldn’t work, or was not in their best interests, then I would politely say- "No!" If I felt that it might work, I would just need to make sure they understood the limitations of that option, even if it was not the choice I would have made!

  • Your bite
Whatever work you have done at the dentist, your bite is a key factor in its success. You can bite on a fixed- fixed bridge as you would normally, but a resin-retained bridge-bridge would need to be kept out of the bite, if it was to stand any real chance of lasting. You would also need to be careful when biting and chewing hard foods.

  • Cost
The cost of the bridge may also narrow down or dictate your options, including reconsidering a partial denture, until you have saved enough money for a bridge or implant if that's what you decide to do.