Dental Bridges

What affects the Success of the Dental Bridge?

The success of your dental bridge depends on many things which we have touched on throughout this series. If you are considering fixed-fixed bridgework, everything affecting the success of a single crown will apply to each of the crowns that make up the bridge. It would be a good idea to go through the article in the link as it discusses the points summarised below in more detail.

The main factors that will influence the success of your bridge are:

  • The abutment teeth
(i) The quality and strength of the cores

(ii) The amount of good natural solid tooth remaining

(iii) The state of the nerves

(iv) The quality of the root canal treatments if you have them, or need them

(v) The quality of the post or posts if you have them, or need them

(vi) The periodontal condition of the teeth (amount of good bony support)

(vii) Your bite- do you have missing teeth elsewhere meaning the bridge is going to have to take extra pressure? Do you clench or grind your teeth?

  • The dentist
(i) Their experience

(ii) The quality of the preparation- how parallel the crown preparations are to one another- the height, margins, taper, shape and ability to achieve a 'ferrule'. ( A ferrule is a band of 1-2mm of natural tooth at the base of the core that helps protect the tooth against fracture from sideways-forces when chewing).

(iii) The accuracy of the impression

(iv) The quality of the bonding in procedure.

  • The bridge
(i) The type of bridge

(ii) The design of the bridge

(iii) The material for the bridge

(iv) The cement used.

  • The technician (lab)
(i) The communication with the dentist in terms of design, shape and shade

(ii) The experience of technician with this type of bridge

(iii) The fit of the bridge- its margins and contact points.

  • You
(i) Your oral hygiene

(ii) Your attention to the special cleaning of your bridge

(iii) Your diet

(iv) Regularly seeing a dentist to check everything is OK.

The success of a dental bridge relies on meeting your expectations through an appropriate diagnosis, good treatment planning and selecting the right bridge/material for your specific situation.

All of the information above will be considered by your dentist during the consultation and examination
in order to advise you of the possible solutions, outcomes and costs.

Are there any Special Investigations that are needed?

To fully assess the above factors, you can expect the dentist to perform the following special investigations:

  • Vitality testing
We want to assess the nerves in the teeth that will be supporting the bridge and we do this with an electric pulp tester or some cold spray to see if they are alive. Ideally we will have either a normal living nerve or a well performed root canal treatment for the most predictable outcome. Questionable nerves pose a bit of dilemma; should they have a root canal or should they be left? If left, it is possible, should the tooth play up later, for the dentist to perform a root canal through the bridge- though we try to avoid this situation if we can. If in doubt the dentist may choose to observe the tooth for a while or make you aware of the options and ask what you would prefer to do.

If an abutment tooth has a less than ideal root treatment, it would, in most cases be more advisable to have it re-done prior to bridge placement, rather than risk it playing up after the bridge has been has been placed. What About the State of the Nerve in Crownswill discuss this all in more detail.

These must be taken to help assess:

(i) The quality of the core; are there any deficiencies or dental caries?

(ii) The quality of the support for the abutment teeth (i.e. periodontal disease) and the amount of good quality bone available to hold the roots in position.

(iii) If there are any signs of needing a root canal, or to assess the success/failure of previous root canal treatment

X-rays are a vital part of this assessment, but pocketing and bleeding must also be examined to give a complete picture of the state of the gums.

Any active gum disease must be controlled before considering the bridge. A fixed-fixed design can help to splint loose teeth together, but may result in all the teeth in the bridge being lost at once further down the track- something you would definitely want to know!

  • Study models (+ Diagnostic wax up)
Study models are often taken but aren't always necessary. The more changes that are planned and the more crucial the aesthetics, the more likely this stage is to be needed. They also help the dentist look at your bite; how the teeth should be prepared; what design of bridge may be best and they can be used to help make a temporary bridge for you.

What are the Limitations of having a Bridge? How does the Dentist Know if a Bridge will Work?

When planning bridgework, the dentist must consider 3 important things: the retention; the support and the aesthetics of the bridge.

  • Retention
How much retention (or grip) a crown will get depends on the height and surface area of the teeth that are being prepared. Thus a molar tooth is much larger than an incisor tooth and will provide more retention and make a much better abutment for your bridge.

If your teeth are very worn down, so that only a small amount of crown is left, retention will be poor. The dentist in these circumstances should be looking at ways to increase this retention, such as crown- lengthening, opening up your bite, bonding instead of cementing your bridge or using metal-biting surfaces to keep as much tooth height as possible.

  • Support
This is very important in planning bridgework and the reason a dentist needs X-rays of the tooth.

Antes Law states that ‘the surface area of the roots holding the bridge in place should be more or equal to that of the tooth/teeth they are replacing’. This is always something that needs to be considered.

Imagine you wanted to put a rope between two trees to climb across. If you select two trees that are very tall with very little roots then the chances of these trees bending and breaking is quite high. In the mouth this is known as ‘the crown-root ratio’ and ideally the root will be longer than the crown of the tooth, thus providing a stable base for the bridge.

Now let’s say the tree only has one straight root. Will it provide the same strength and support as multiple roots that go in different directions? No...of course not. In the same way, a multi-rooted upper molar tooth, which commonly has three good solid roots is going to provide much better support for a bridge, than a spindly lower incisor which is renowned for its thin weak roots.

To complete the analogy, imagine that the soil was dug out from around the roots so that only a small amount of root remained in the ground. "Would this offer the same amount of support?" No it wouldn't... The soil is like the bone that holds your tooth in- the more of the roots that are buried in good solid bone- the better the support.

Here we are talking about the periodontal condition and if you've lost a lot of bone around the roots of a tooth, it may not make a suitable abutment to support a bridge.

The extra force placed on the already weakened teeth is likely to cause the bone around the abutment tooth to be lost more quickly. So unless the treatment is carefully planned, you may end up in a couple of years, losing another tooth and being back to where you started- just with a bigger gap.

  • Bridge Aesthetics
If a lot of bone has been lost in the area of the tooth, for example, due to extensive periodontal disease or a surgical extraction, a bridge may not look aesthetically pleasing.

The pontic (fake tooth) may have to be made rather long to cover the missing ridge and this may be noticeable when you are speaking and smiling.

Pink porcelain can be sometimes used to improve the look in such a situation. Otherwise it will be a matter of accepting it, or considering grafting some bone to the area. If you are going down this route, then an implant with ridge augmentation may be a better solution.If you were to have a removable partial denture then this can be made with a flange to replace any missing gum and restore the aesthetics.