What are Dental Crowns made out of and which material is best?
Dental crowns can be made from a variety of materials, but which one is best? Your dentist may use a certain material, but most of the time, they won’t discuss it with you first. Here is a guide to dental crowns, so you can have a full conversation with your dentist and feel happy with your decision.
What factors are considered when choosing a material for dental crowns?
The three main factors to consider are:
The strength of the crown
This is an important factor if you want your crowns to last – ideally, they should last a minimum of 10 years. The other thing you must consider is that the stronger the material is, the thinner the crown can be. Why is this important? Well, before we fit the crown we must prepare the tooth – we do this by gently grinding the tooth away so it has space for the crown to fit over it.
Before crown preparation
After crown preparation
The tooth on the left has been prepared for a zirconia crown.
The tooth on the right has been prepared for a traditional PFM crown.
Notice how much tooth is saved by having a zirconia crown.
Compressive strength is measured using megapascal units (MPa), which tells us how much pressure can be applied to the material before it cracks or fails.
Our aim is always to make the crown look as good as possible and the different materials will have different optical properties.
Accurate fitting of the crown
Most materials will have a great fit, however some are better than others. We use digital scanners at all our practices which means that the fit is always extremely accurate.
The different crown materials
These are the different materials available for crowns:
Zirconia is a relatively new material and it’s made a massive impact on dentistry. It’s a white ceramic material that is super strong. It has a strength rating of about 1200MPa which means that it’s considerably stronger than traditional crowns. It can be made thinner, which saves more tooth structure. The major disadvantage of zirconia is that it can sometimes look opaque. It is fine for back teeth, however for front teeth you want a higher level of aesthetics. Natural teeth are slightly translucent which means light will shine through them to some degree. To overcome this disadvantage, we sometimes make the inside fitting surface of the crown (the core) out of zirconia and then layer it with emax ceramic. This allows us to combine the superior aesthetics of emax ceramic with the strength of zirconia.
The other disadvantage of zirconia is that the bond strength is not that good and you need a conventional crown preparation to secure it. Zirconia is generally the go-to material for back teeth and it is used a lot for cores of front teeth. It is also popular if you are having a crown replaced.
Emax ceramic crowns
The problem with traditional ceramic is that it looks great, but is very weak. In order to make the material strong it would have to be thick, and it couldn’t be used on surfaces that would take a lot of stress, ie the biting surfaces of the back teeth. Emax changed that when it came out – the material is a blend of good strength and great aesthetics. This means you can use it for back teeth and also use it in very thin sections when making veneers. The thinnest you can make it is 0.3mm. If you compare this to the amount of space required for an old-school PFM, which is 1.5-2mm, the amount of tooth structure you save is incredible. It really is a wonder why dentists still use old-school methods and most of the time they simply don’t have the advanced knowledge our dentists do.
The other great thing about emax is that it bonds to tooth structure incredibly well, so you can make onlays/veneers with it. This means we can perform minimally invasive dentistry which is a lot kinder to your teeth.
Another advantage is that pretty much everything can be made from emax, including veneers, crowns, implant restorations etc, which means that if you are doing very high-end work and restoring the whole smile, you can keep the material the same. Keeping the material the same will mean that all the teeth have the same optical properties, so the end result is stunning. When you place two different materials next to each other, they always look slightly different.
Emax has a strength rating of 500 MPa
PFM (traditional crowns)
As mentioned previously, old school ceramic was not that strong. If you wanted a white crown, you would have had to make the inner core out of metal and then cover it up with porcelain. This meant that each material needed a minimum thickness for it to be strong, which in turn meant the total minimum thickness of the crown was 1.5-2mm. This invariable leads to excessive tooth structure being lost.
Although the crowns are tooth coloured, the aesthetics are never as good as they could be. This is because light shines through it and as soon as it hits the metal surface it bounces back. The teeth are often very dull and opaque. With natural teeth, the light shines through nicely which creates depth and beauty.
The strength rating is 150 MPa
These can be made from a variety of metals. Gold is generally the best, or alternatively a semi-precious metal. The major, most obvious problem with metal crowns is that they don’t look nice due to their colour! That’s why it’s rare nowadays for dentists to use them.
As you can see, there are a lot of different types of crowns you can choose and it’s important to pick a dentist that understands the pros and cons. If you are interested in discussing this further then please call our friendly team on 020 8655 1118.