All you need to know about dental crowns
This article is aimed at anyone who is thinking about dental crowns or for someone who has just been told that they need a crown. So, let’s first start with why a crown may be needed.
- To protect your tooth from cracking.
Teeth can become weak if they are heavily filled or if you have a large decaying lesion in them. By the time you have taken away the decay, you are sometimes left with thin parts of the tooth and the studies show that these are likely to fracture at some stage. Every time you’re eating it’s like someone’s putting a hammer to the tooth and this can cause the thin bits to crack. If you’re a grinder then it’s way more likely to fracture. The job of a crown is to act like a helmet, it protects the tooth from cracking. Now you may think that it’s worth leaving it and when it does crack, to crown it then. The problem is that you never know how much of it will crack. If it’s a large crack then the tooth may not be salvageable, and you may need to have it taken out. That’s why it’s better to crown them right from the start so you can increase the longevity of the tooth.
- To improve the appearance of your teeth
Crowns cover the whole surface of your teeth so if done right, they can improve the colour, size/shape and orientation (i.e. straighten your teeth).
- Treat worn teeth
If you have moderate to severe tooth wear, crowns may be the ideal solution for you. They can be used to restore the lost tooth tissue you have and improve your bite.
The longevity of dental crowns depends on many factors, but a decent lifespan should be 10-15years.
What affects the longevity?
- Clinicians ability – the better knowledge and skill the dentist has, the longer they will last. I have seen a large mix of skill levels of dentists working at many different practices and I can say sometimes the quality is poor. Be sure to pick a good dentist
- The material – some materials are better than others. Gold, although it doesn’t look nice (in my honest opinion), has been shown to last the longest and that’s because of the strength and castability of it. I will go into more detail about this later.
- How much tooth structure you have. This is probably the single most important factor, if you have a good amount of tooth structure to begin with the crown should last a long time. Conversely, if you have a very broken-down tooth, and there is not much of the tooth to bond to, then the crown may de-bond in the future. If the tooth is very weak after the crown preparation, the tooth may fracture and hence the crown de-bonds.
- How well you look after your teeth. If you consume a high amount of refined sugars, you can get decay in the tooth and once this happens, it’s best to replace the crown to seal the tooth once again. This is the same if the tooth gets infected.
Although 15 years is a decent amount of time, there have been plenty of instances where crowns have lasted 40 years plus so when we do them, we are expecting them to last a long time.
For cosmetics, the colour of the crown is the most important factor. It must blend in with the adjacent teeth nicely so that any observer is oblivious to the fact is it a false tooth. How do we get this right?
First of all, there are around 20 different shade tabs on a standard vita shade guide, and this will help us to choose the colour of your teeth and you must remember that each tooth does not just have one colour but a variety. See the shade guide below.
The picture below illustrates the different colours (hue), value (brightness) and chroma (intensity of colour) a tooth can have. Mimicking nature can be a very hard thing to do and that’s why you need to be sure you have picked a good dentist and also a good dental technician.
How crowns stay on teeth
Crowns are bonded onto your teeth with special biomaterials. There are a variety of different types that have different characteristics. The most common ones nowadays are resin cements or glass Ionomer cements. There are still some traditional dentists who use older materials such as zinc phosphate.
Can you whiten crowns on your teeth?
No, unfortunately, once they have been cemented, it’s not possible to whiten them. The best thing to do is to have them replaced. Tooth whitening will whiten your teeth, but it will not whiten the fillings you have or crowns or veneers.
What is the best crown for teeth?
There is no best crown as they all have their pros and cons. The most common ones used today are:
Emax – This is an all ceramic material and it looks fantastic. It is a lot stronger than the traditional ceramic, but you wouldn’t want to use it some circumstances like on back teeth for someone who has a heavy bite or for a long span bridge.
Zirconia – This is a super strong all ceramic material. Although it is white, the aesthetics are not very good as the material is really opaque. If you look at a natural tooth, there is some element of translucency which is how the light shines through it. Zirconia doesn’t have this so it can look artificial. It’s generally very good for back teeth but not so good if you are using it for a front tooth. However, what you can do is make the core (inside surface) of the crown out of Zirconia and then layer it with emax and it works very well. You gain the strength of Zirconia and the aesthetics of emax.
PFM (Porcelain Fused to Metal) – This is the traditional type of crown. The inside core is made from metal and the outside is built from porcelain. This type of crown is not the best one to use nowadays as Zirconia and emax produce better results, however you will find some dentists still using it.
Gold – Although it doesn’t look great due to the colour, gold is a good material to use for back teeth. It combines good strength with good castability, so the fit is always good. It has been shown to have one of the longest survival rates of crowns.
Can bottom teeth be crowned?
Yes, bottom teeth can be crowned however it is generally not a good idea. Each material has its own minimum thickness it needs in order for it to be strong. If you make it really thin then it will crack. Let’s say if this is 1mm, that means you have the grind the tooth down by 1mm around the whole tooth. After it’s been done, the tooth itself looks very thin, meaning that it is weak. Often alternatives are more appropriate like veneers or bonded cosmetic white fillings.
Crowns on baby teeth
There has been some research which shows that putting stainless steel crowns on baby teeth that have decay in them, is a good idea. The survival rate is higher than then alternatives (i.e. normal fillings). Although the research shows they are good, in general practice it is often not done. This is because it’s harder to ensure young children cooperate fully – it’s a lot easier to do a simple filling. Also, the crowns are not bespoke, like they are with adults, and some are premanufactured. You have to pick the correct size out of a box and therefore they will never fit 100%, which can have its disadvantages.
Article written by Dr Suril Amin
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