Onlays and Crowns

In this section, we will cover:

1. What is an onlay or crown?
2. Why would I need one?
3. What are my options?
4. What does the procedure involve?
5. What if my temporary onlay/crown falls off?

Why would I need one?

Onlays and crowns are often needed if:

• you have a very broken down tooth which is not possible to restore with a dental filling 
• you have had root canal treatment on a back tooth to protect it from fracture
• you have a cracked tooth to protect it from fracture

What does the procedure involve?

Having an onlay or crown placed usually takes 2 appointments. If your tooth is very broken down, you may need an extra appointment in which your dentist will build the tooth up first to act as a "core" to support the final restoration. 

So what are the stages once the core is built? 

Appointment 1

1. Local anaesthetic 
   To make the procedure more comfortable, your dentist will numb the tooth and gum. This is usually only needed if the nerve is still alive (i.e. the tooth has not been root treated) or if the dentist will need to push the gum away from the tooth to take a mould towards the end of the procedure. 
   
   
2. Mini mould
   Before starting, your dentist will take a mould of the tooth they are working on and a couple of the teeth next to it. They can then use this to make a temporary restoration (see step 5).
    
3. Tooth preparation 
   This involves using a dental handpiece and bur to file the tooth down. This makes space for the final onlay or crown without changing your bite or overall shape of the tooth too much.
   
   The amount of tooth which needs to be filed down depends on whether you are having an onlay or crown and what material you have chosen. Some dentists will take a small mould of the tooth before starting so they can monitor how much tooth they have removed. Others will check to see if enough space has been made by asking you to bite together every so often during the appointment. 
   
   
4. Moulds
   Once your dentist is happy they have removed enough tooth to make space for the restoration, they will take a mould (or impression) of your top and bottom teeth. If the tooth preparation has extended very close to or below the gumline, your dentist will place a piece of string around the tooth to push the gum out of the way. This allows them to take a more accurate mould which will result in a better final restoration. 
   
   The moulds are are sent to the lab where the lab technician can make a replica of your teeth out of stone. They use this to see how your teeth come together and make the final restoration to harmonise with your existing bite. 
   
   
5. Temporary onlay/crown 
    Your dentist will make a temporary crown which is placed over the tooth until your next appointment. This prevents sensitivity and bacteria getting into the tooth, prevents tooth movement and overgrowth of the gum and restores aesthetics.
   
   Your dentist will spend some time adjusting this temporary restoration to ensure it is a good fit and easily cleansable before "cementing" it on your tooth. You will need to maintain meticulous oral hygiene as if the gums are unhealthy and bleeding, it will be very difficult to place the onlay/crown at the second appointment. 

Appointment 2

1. Local anaesthetic
   This is only needed if your dentist needs to push the gum out of the way (as in step 4 above) or bond the restoration to a vital tooth (i.e. a tooth in which the nerve is still alive). 
   
   
2. Removing the temporary restoration 
   In most cases, your dentist will be able to place an instrument at the margin of the temporary restoration and the tooth and lever it off with a bit of force. For particularly stubborn restorations, it is often easier and more comfortable to drill it off instead. Once it has been removed, they will remove the temporary cement from the tooth with hand instruments or a scaler. 
   
   
3. Trying on the final restoration 
   Before cementing the final restoration, your dentist will try it in the mouth to ensure there is a good fit around the margins and that it is not interfering with your bite. Minor adjustments can be made by your dentist if needed but if any major changes are needed, it is often better to retake the mould and have a new restoration made in the lab. 
   
   Your dentist will also check you are happy with how it looks, particularly if you have opted for a tooth-coloured restoration. 
   
   
4. Cementing the final restoration 
   If you are having a non-bonded crown (such as a zirconia, metal or porcelain-fused-to-metal crown), the nurse will mix up some dental cement, place it in the crown and pass it to your dentist to place on the tooth. This will take a few minutes to set and your dentist will then clean up the excess. 
   
   If you are having a bonded restoration (such as an emax, composite or gold onlay), your dentist will isolate the tooth with cotton rolls or a dental dam first. This ensures no unwanted moisture contaminates the area as this prevents successful bonding. This is a more involved process with multiple steps so it takes longer than placing a non-bonded crown. 
   
   
5. Final checks 
   Just before letting you go, your dentist will check the margins where the restoration meets the tooth, the bite and the contact points (where adjacent teeth meet) to make sure you will be able to keep it clean at home.
   
   It may take you a couple of days to grow accustomed to your new restoration.