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