What Type of Crown is Best for Me?
Your dentist will advise you about the most appropriate dental crown material after assessing and discussing the following things:
Note. With all things being equal, they will simply give you a choice of material options- porcelain, porcelain fused to metal or gold.
- The amount of tooth remaining.
If you only have a small amount of natural tooth holding the core together and the core is filed down, removing this can weaken the whole foundation of the crown and compromise it’s prognosis. Porcelain fused to metal crowns (PFM or VMK) and standard porcelains crowns generally require more tooth to be removed than metal alone or the high strength porcelain, Zirconia. Metal margins and gold crowns would be a good choice for thin walls where aesthetics are not essential, such as at the back of the mouth or where the thin wall is on the inside. Full Zirconia is good more aesthetic alternative. Sometimes it is possible to keep the outside wall and produce what is known as ¾ crown that leaves the wall untouched.
- If the tooth has been root filled or had a post.
If the tooth has had a metal post it may be preferable to place a PFM crown with a metal substructure, as this type of crown totally masks the colour of the metal post. A full porcelain crown without adequate masking of the metal may appear slightly grey. If a carbon fibre post is used this is not a problem. And various opaquing cements that you paint on the metal post to hide the colour are also available.
- The importance of the tooth in your smile.
A common complaint made by patients who have had a porcelain fused to metal crown for many year, is that the dark margins have now become visible in their smile. Your gum shrinks up at about 0.1- 0.2mm per year, that’s 2mm over 10 years and can often mean that a crown that has been in place for 10-20 years starts to show its margins and this may or may not be acceptable to you. The crown itself is likely to be just fine (i.e. functionality wise) but if the way it looks is a problem, then the crown can be replaced and the margins taken up once again to meet the gum. For this reason, all porcelain crowns may be preferred when highly visible in the smile. That said, a VMK prepared slightly sub gingivally i.e. just under the gum by a quality dentist and a good technician, will only become visible after many years. We have the most reliable long-term data on this type of crown (and gold crowns) since they have been used for the longest.
- The position of the tooth.
Teeth that are being crowned at the back of the mouth are more difficult to clean than those near the front and the look of the crown is not quite so critical. In these circumstances, where suitable it is best to place the margins of the crown at or just above the gum level to help with your tooth brushing and cleaning.
- Is there enough space?
If the tooth is already very short then removing 2mm of the biting surface will make the height of the core so small that the crown is more likely to come off. If you compromise by removing less tooth, then standard porcelain will not have sufficient thickness on the biting surface to be strong and is more likely to fracture. In this circumstance, it may be better to have a metal biting surface, gold crown or choose zirconia as the material. We can also increase the height by a crown lengthening procedure- taking the gum down a little so we have some extra height to play with. New cements are making bonding crowns to teeth easier than ever before- this is meaning that short preparations (cores) can still have a good restoration that is going to stay there as long as there is sufficient strength/thickness of porcelain.
We know that grinding, places any restoration under significant pressure. Crowns are no exception, but since they cover the tooth fully and ensure an even pressure as the teeth move across it, they are pretty good at resisting these forces. We must also consider the wear and damage that the crown may have on the opposing teeth if someone is grinding.
Certain porcelains such as those made from pure zirconia are very hard. This has the advantage of resisting stresses from grinding but it can sometimes increase the wear on the teeth that they bite on to. This only occurs if the teeth opposite are natural, a similar crown, tooth of a partial denture or implant would have little effect.
Gold is fantastic once again in these circumstances, but gets more and more expensive as the price of gold increases. I have seen porcelain fused to metal crowns, where the porcelain has been chipped off by people who grind excessively, particularly if they do not wear a night splintlwhich they should! A replacement will then be needed if it is an aesthetic problem. Occasionally lab errors or insufficient porcelain thickness, due to not enough preparation have a part to play.
Unfortunately, all porcelain crowns are also not free from this problem and chips can occur sometimes compromising the whole restoration. As you can appreciate a solid core of sound tooth and filling is even more important in bruxists and a suitable dental splint must be worn afterwards.
What are Your Expectations?
What are your expectations?
- How important is the look to you?.
There is no doubt that certain crowns are superior in looks to others and this comes down to not just the material but the way the shade is taken and communicated with the lab and also the technician responsible for creating the crown.
All porcelain crowns have the advantage that even if the gum shrinks you don’t see the dark line of the metal core of a PFM crown. Sometimes if the tooth underneath is very dark (more likely to be the case with root treated teeth) this shrinking of the gum may still pose a cometic problem.
Some crowns are milled out of a single block of coloured porcelain, often zirconia. Whilst being very strong they do not match the multiple shades and flow of colour seen in most natural teeth very well. Various different shades of porcelain blocks exist but because teeth themselves are rarely one colour, they tend to be reserved for the back of the mouth.The cost of dental crowns like these, tends to be a little cheaper.
We often see a progression from a slightly darker base near the gum to an almost translucent edge at the tip. So having a crown that allows for this artistic interpretation and the ability to add in stains and colour will provide the most natural appearance. This is even more important if you are matching a crown to existing teeth.
Some crowns will have a milled core and a different type of porcelain built up on the outside, which can be modified by the technician before being glazed and fired (e.g. LAVA crowns). This has the advantage of the strength of the strongest porcelain for the core and the flexibility for the technician to get artistic with the overall shade.
There is a balancing act between the aesthetics required and protection of the underlying tooth and the amount of tooth removed. The more of your tooth that is removed by the dentist and the more space the technician has to play with- the more layers they can build up and the better looking the final result tends to be. However, the more tooth that is removed, the greater the likelihood of |damage to the nerve and the weaker the core becomes.
The dentist must make a judgment call and every situation is different- do they potentially compromise the long-term health for the best-looking result?
- Are your expectations realistic?
It is important particularly when considering multiple crowns and veneers that you and the dentist are on the same page when it comes to the look of the treatment. What the dentist considers to be a nice natural result may be quite different from what you had in mind. This problem is most obvious with full denture patients, who often insist on the whitest of white teeth, which in my opinion makes it quite clear they are fake. However they may object profusely to the suggestion of a moderately dark tooth, which would be suitable and natural to a patient of their age and complexion.
Ultimately the choice is yours but a good chat about it is important so there is no confusion.
There are many different factors that make up getting the aesthetics right.
Matching other teeth is always a bit tricky since no two teeth are the same. Only when a number of crowns or veneers are made all at the same time from the same batch of porcelain do you get a perfect result. This can involve the preparation of multiple teeth and can be quite destructive, so at least consider more minimal cosmetic treatments before deciding this is right for you.
Sometimes your dentist may advise that you crown or veneer the other central incisor, if this is the tooth in question, as the eye notices asymmetry more than anything else. This can provide a more predictable aesthetic outcome but may involve drilling on a healthy tooth. If the other front tooth is also damaged then it would perhaps make more sense.
- How long will it last?
Most long-term data as we have mentioned exists for gold crowns and VMK’s which have proved very successful over many years. The newer materials obviously have less data to prove how long they will last and they tend to be heavily marketed by the dental laboratories and companies that develop them. The proof is always in the pudding as they say- how these new crowns perform ,only time will tell.
- Your finances?
When it comes to the cost of crowns unfortunately they are all quite expensive. Generally there is only a difference of a couple of hundred dollars between all porcelain crowns and VMKs. Often this reflects the extra money the dentist has to pay the lab technician for the more expensive crown. The actual procedure and time taken for the dentist is the same regardless.
Don’t be afraid to ask questions! As dentists, we want to do what is right for you and for you to be happy… this involves a two-way conversation! It is our job to answer your questions and concerns and educate you on the reasons why something is or is not advisable or indeed possible.
Some of my favourite questions you can ask your dentist are; ‘What would you do if it was your tooth?’ or better still, ‘What would you do if it was your daughter’s tooth or smile?’ or ‘What would you do if money was not a factor?’, ‘What is the worst case scenario?’, ‘What will give me the best long term result?’, ‘What is the most predictable treatment?’.