Why would I need an Inlay/ Onlay?

Inlays and onlays can be a useful restoration in a number of situations, the main ones are:

Let’s look at each of these in more detail and expand on why inlays and onlays can be suitable in these different circumstances:

To Restore a Large Cavity and Weakened Tooth

This could be a result of

If a tooth has a very large amount of decay, then a crown or an inlay/onlay becomes a more dependable long-term solution, compared to just having a filling.

Sometimes you may have had a large filling that has failed or another piece of that tooth that breaks away. It may be possible to repair the tooth or to replace the filling, but it is likely that at some point this will fail again and you will have to proceed to an inlay/onlay, or a crown.

Often it is more sensible and actually more economical to proceed sooner to one of these indirect long-term treatments.

  • Cracked teeth

If part of a tooth fractures under heavy biting forces (generally in people who have a grinding or clenching habit), inlays/onlays can be used to restore the part of the tooth that has broken.

Instead of a Filling

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.

White fillings 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.

Instead of a Crown

Most dentists would agree that crowns remain, in general, the best way and most predictable way to restore a heavily broken down tooth. That said, dentists can be a little quick in my opinion, to crown teeth with medium to large holes or failed fillings.

Quite commonly, they will jump from fillings to crowns missing out inlays/ onlays- when these may, in a number of circumstances, be better for the long-term strength of your tooth than having a crown. It preserves more of your natural tooth to bond-to and can avoid the need for a more extensive crown in the future.

Crowns, as we have discussed, are in the most part quite destructive to teeth and not without their consequences. Each dentist will need to weigh up the aesthetics, bite, amount of tooth remaining, state of the nerve and your finances in coming to a decision with you as to which is the better option- just something to be aware of.

There are times when filing down the core to make space for the crown will remove all the tooth holding in the filling, or weaken it considerably. The alternative is deciding to do a root canal with a post and core on which the crown can go- see below.

An onlay/inlay may be a better choice in these circumstances, as this may allow you to preserve the natural tooth and avoid that horrible situation of the crown coming off with the core inside. You can always reduce the height of the weak tooth walls and create, what we call a ‘full coverage restoration’ that ensures an even pressure across the whole tooth when you bite. This helps to protect the tooth and make sure it lasts long term.

It is important to take into consideration that different dentists will have different preferences in the treatments they provide and their recommendations to their patients will be based on their experience and the successes and failures that they have had.

What works in the hands of one, may not do so as effectively in the hands of another- but an open discussion of the options is in everybody’s interest.

To Avoid a Root Canal, Post and Crown

Bonding technology has improved so much, that even if your tooth and filling fracture and leave you with what appears to be ‘very little’ above the gum, an onlay can often be made to give you back the tooth.

When this happens it is not possible to fill the tooth. Previously, the only option, aside from taking the tooth out, was to do a root canal and place a post into the root to hold a core, on which a crown could be made.

Most people like to avoid having a root canal if at all possible (though it’s no- where nearly as bad as people make out) so when the nerve is still alive and healthy in the tooth- as far as we can tell with all our special tests– an onlay can be a good long-term way to solve the problem.

Imagine it as a crown with an inbuilt core- only the core is made of a material which can be etched and securely bonded to the tooth.

Note- If a crown breaks off with the core inside, this is completely different and it cannot be bonded back in this way because the bonding surface is not made of the correct material.

There are times where the state of the nerve is questionable. It would then be the most sensible decision to go down the root canal track as currently this still provides the most predictable outcome. See signs and symptoms of root canal treatment.