Whenever you pack a filling into a tooth, the filling material will put some stress or pressure on the remaining tooth. Scientists are doing their best to improve the quality of the materials we have and we are getting closer all the time to these materials behaving like a real tooth.
Inlays are a fantastic way of filling cavities
in teeth. They last longer and stay looking as good as the day they were put in. They do not deteriorate and stain in the same way that fillings can.
Currently the two main fillings in use are composite and amalgam:
These are the main type of filling used in private practice. They shrink a little on setting and this can pull on the walls of the tooth. Where a good thickness of tooth remains this isn't a problem, but where the tooth wall is very thin, this force can cause that wall of the tooth to potentially fracture.
Different composites have different amounts of shrinkage so the way in which they are placed in your tooth is important in order to reduce this shrinking effect.
The larger the filling, the more shrinkage that occurs and the more likely it is to fail in the future.
In contrast, amalgam expands when it sets and this can set up micro- cracks in the tooth, which over a long period of time (many years), with the stresses of chewing and everyday wear, can cause the wall of natural tooth to fracture off.
Again, if sufficient natural tooth remains this generally isn't a problem, but the thinner the wall of tooth and the more undercut that is placed (remember amalgam doesn't bond to the tooth like composite- it is held in the tooth by the shape of the hole), the more likely it is that a fracture could occur.
The fracturing of the tooth wall happens more commonly with amalgam than composite, but where a tooth is very weak, we would ideally put something into the tooth that doesn't put any stress on the remaining tooth- but instead strengthens it- this is achieved with the inlay/onlay.
The inlay or onlay is made by taking an impression of the missing part of the tooth and then attaching it to the tooth. Because it is made to measure, it sits passively in the tooth and does not put any stress on the remaining walls making it stronger. Check here for the full inlay procedure
Because they involve a lab stage, they are considerably more expensive than fillings, so we tend to reserve them for the cases that need them most (see above). That said, they can be used very effectively as an alternative to fillings in smaller cavities, but the advantages over fillings become even greater, when a large part of the tooth is missing.
Many people are walking around with very large silver amalgam fillings in their mouth; you may even own one or two yourself. These metal fillings
have proved to be very successful for many years, although they are not particularly attractive to look at.
bear less well in such broken down teeth and so inlays/onlays provide a very good looking, almost invisible solution, when the metal look is undesirable.
Some very high-end experienced dentists are able to achieve very good-looking and long lasting massive white fillings- the dental magazines are littered with methods and pictures about creating these beautiful 'huge' composite restorations, but few would argue that in most dentists' hands, the increased predictability of inlays and onlays are best for big restorations on back (molar and premolar) teeth.
Cerec has provided dentists with options to make inlays/onlays at the chair-side in one visit- without the need to send you away with a temporary for a week. Cerec machines work on CAD CAM technology, whereby a 3D digital picture is taken of the cavity, the restoration designed on the machine and then milled automatically from a block of porcelain in the next room- pretty cool stuff.