Dental Crowns
 

So what are the Actual Choices for a Crown?

As far as crown costs go, there tends to be three differnet prices- one for all porcelain crowns, one for metal fused to porcelain crowns and one for full metal crowns, of which gold is the most common.

The reality is that within this choice the dentist still has a number of options and different types of crown available to them. Each crown is slightly different and it is not possible to go into the details of each without overwhelming you and it all getting rather confusing.

Suffice to say there are more expensive crowns and cheaper crowns.

The difference comes down to the material used, the skill level of the technician, the location of the technician (In Australia or overseas), the amount of time required to make the crown and apply the necessary artistic touches.

Some prosthodontists and high-end cosmetic dentists will work with technicians that charge double the normal lab bill and unfortunately that cost has to go somewhere and so will be factored into the price you pay. The restoration that results will be excellent, predictable and last as long as a crown could with excellent marginal fit meaning few problems are likely to result in the future.

As to whether you personally will ever notice the difference from just a really good crown, that’s highly debatable particularly if your having a back tooth worked on. All dentists are capable of achieving these sorts of results; the more experience in doing these types of restoration the better.

Different types of crown are being developed and marketed to dentists all the time. Newer, stronger, better-looking, more economical materials maybe an improvement on the tried and tested crowns of years gone by but we must rely on the available clinical data to confirm this.

You may think that we want a crown to be as strong and hard as possible right? Well sort of, strength is very important for sure, but the hardness, if it exceeds that of a natural tooth can mean a lot of wear for the opposing tooth, or teeth that bite on to it. The mouth is a very hostile environment and whether we are replacing lost tooth with a filling or with a crown, the aim is to get the mouth back to looking and functioning as close to a normal tooth as possible.

Here is a summary (not an exhaustive list) of the main types of crown available :

  • All metal crowns . These require only a very minimum amount of the tooth to be prepared preserving the core for maximum strength and retention. They very rarely chip or fracture, don’t wear opposing teeth and look as good as the day they were put in. One disadvantage is color unless you like your gold. They can be made of precious metal (i.e. gold) semi-precious (a combination of gold and other metals) or non-precious (a mix of lower cost metals). A good choice where space is minimal on molars you cannot see and if you have severe habits of clenching or grinding teeth.
  • Gold crowns. The higher the percentage of gold the better (over 75%)- this is often mixed with other metals such as, silver or copper and palladium. As the price of gold sky rockets so obviously does the price of the gold crown. The larger the crown, the more gold will be needed and the more you will pay. Gold is the most durable, predictable and best tolerated of all the crown materials- it's just the issue of the colour.
  • Base metal alloys such as nickel – chromium (sometimes with beryllium), titanium. These have been developed as a cheaper alternative to the gold crown. They do not have the same fit and wear characteristics, as gold.
  • All ceramics crowns. All ceramic crowns now have far superior properties to those of the porcelain jacket crowns of a decade ago which were so prone to fracture. They look very good and natural. Without the metal substructure (underneath) of a Porcelain fused to metal (VMK) crown, most have improved optical qualities- the way light passes through the tooth. They keep their aesthetics better in the long term and are also good for patients who have allergies to particular metals used in other types of crowns. The major risk with porcelain is fracture which will lead to failure and the slightly deeper preparations that are required for sufficient thickness of porcelain for the crown to have strength (not zirconia crowns which are super strong in thin section).
  • Zirconia crowns. Zirconia is a very popular material currently, some crowns are made purely of zirconia making them very hard (even abrasive if not polished properly. The whole crown can be milled from a single block and in this case it is harder to get a really excellent shade match (as the block is a more uniform colour). The advantage here is that you don't need to remove much tooth at all since the material is very strong in thin sections. Zirconia can also be used for the first part of the crown (that sits over the teeth) and standard porcelain built up on top to mimic the natural tooth more closely, not just in its looks but in its characteristics too. Because zirconia is so hard it is not possible to etch the porcelain and so, a good long lasting crown relies on the retention of the preparation and the cement. See successful crowns for more information.
  • Other porcelain crowns (aluminous). E.g. Empress and emax. A big advantage of these types of crowns is that the porcelain is a little more porous than zirconia so it can actually be etched with acid (in the same way as a composite filling). This makes it possible to create a chemical bond between the crown and the tooth making it very strong. This is the property that makes this type of crown ideal for use in inlays and onlays. These crowns are also the most aesthetic crown and so are used in areas of the mouth where the appearance is very important.
  • Porcelain fused to metal crowns. These have been the staple of the crown world for many years and with good reason. They look good and are very strong. They have a proven track record for success for both front and back teeth. They are sometimes called PFM’s which means porcelain fused to metal or VMK which stands for Veneered metal crowns – don’t ask why it is not VMC! The front and top part of the teeth require a similar amount of tooth filing to a porcelain crown to make way both the metal substructure and porcelain on top. The inside area of the tooth can have the margin left in metal and can be thin, thus preserving the strength of the core. They are great for use in bridges and incorporating features such as ‘rest seats’ if you wear a partial denture. The porcelain can sometimes fracture off, exposing the metal core. This is pretty rare and often only an aesthetic problem, but it can cause concern for some patients. It is usually found in patients with a grinding habit. Another more common problem to do with ‘the look’ is that over many years the dark line of the metal underneath can begin to show as the gum shrinks down. The metal surface can also be treated underneath to help enhance the bond of the cement with the tooth. Sometimes it may be appropriate to place an all porcelain collar on the crown which may help avoid this cosmetic problem.

In terms of the fit of the crown, I have not found any studies currently that recommend conclusively one crown over another. All too often the dentist relies on the laboratory and advertising rather than clinical evidence. Ultimately, it is a compromise between the crown material, the structure of the core, your bite, other teeth, personal factors and expectations that will determine the final choice.