All About Dental Crowns in Dentistry
The tooth crown is the top part of the tooth, which protrudes out of the gums. In layman’s terms the artificial covering we put over the tooth is called a "crown".
Here you see a damaged tooth with an "artificial" crown.
There’s a difference between the functional and aesthetic characteristics of a crown. An artificial crown should always achieve the functional aspects, meaning the right fit both against the opposing teeth and in the socket and this is the main responsibility of the dentist.
The dental technician is mainly responsible for the crown’s looks. The price of an artificial crown has nothing to do with the material used as all the materials used on people have to go through a complicated acceptance process. The price is directly related to the working time required. If your dentist wants to sell you an "expensive" crown because of the material it is made of then he is not trustworthy.
What really makes a difference to the price can be seen from a few steps in the procedure here which will explain the price range to you.
Starting with the aesthetics – in the video "Dental Crown" you see, or rather, don’t see, the crown of the tooth, in the next picture you can see right away that the top 4 teeth have been crowned. The difference: In the first picture the ceramic has been coated which means that the patient sat by the dental technician who laboriously painted onto the ceramic layer after layer until it matched the original teeth. The translucent effect of the tooth can thus be recreated. It’s not every technician that can master this technique – to recreate a beautiful crown is an art.
The other crown has been made out of a prefabricated shell and has only been painted according to the colour indicated by the dentist - more about this topic in the video! The technician never saw the patient. This is quick and costs less time and ultimately less money.
There are enormous differences in the execution of a crown in the functional as well as the aesthetic characteristics and this is why some crowns last for 30 years or more and others last only a few years. The crucial factor in durability is the way the tooth is ground down, that’s to say, the way the dentist abrades the tooth:
The quick and easy way is the so-called tangential abrasion. The tooth is simply bevelled. The disadvantage with this type of abrasion is that the technician has to leave a certain residual thickness in the ceramic when preparing the crown as otherwise this would break. The result is ugly, overlapping, lumpy edges.
In order to hide these, the abrasion limits are unfortunately often set under the gums and a dental probe and dental floss get stuck on the edges of such crowns, as do food particles. These food particles cause an inflammation of the gums and you notice recurrent bleeding of the gums.
As the years go by the constant inflammations lead to a retreat of the gums and the edges of the crown become visible again and the danger of caries in the root is now very great.
Another possibility is the so-called stepped abrasion and this too is relatively quickly done. In this case the technician has hardly got place for the edges of the ceramic, so the edges hardly stick out. Unfortunately the adhesive doesn’t flow very well when it comes to cementing, so a wide joint in the glue is created. The danger that this adhesive (usually cement) gets washed away in time, by brushing, for example, and that once again caries occur in the root, is just as great.
In the round margin abrasion the advantages of the other abrasions are united and the disadvantages are eliminated. However this option is the most complex.
The adhesive can flow easily in the cementing process, which allows for a thin joint; the technician has enough room for the ceramic, the edges are tightly closed, food particles can’t get caught. To achieve a round margin abrasion, the work must be done under magnification and further, when the impression is made, particular criteria must be observed.
Although this technique requires a lot of complicated work, in return you get tight-fitting crowns.
But it’s not only a precise abrasion alone that makes for a good dental crown, a lot of other steps are necessary in between in order to obtain optimal results.
For example, before the impression is done, two ligatures should be placed, one of which should be removed just before the impression. Indeed, various pastes exist which can replace the ligatures but sometimes these chemicals react with the impression medium and cause a distortion of the mould-making compound – the result is a crown that doesn’t fit tightly.
Why ligatures, actually? Firstly because you don’t want to grind the gums away and secondly because the abrasion limit should be reached in the so-called sulcus, that is to say below the visible border with the gums.
With the first ligature therefore we pull the gums to one side in order to avoid injury whilst abrading and the limits of the abrasion can therefore reach down into the sulcus.
Fair enough, but why are there two ligatures? Now the technician pours plaster into the mould and thereby creates a model in plaster of how your teeth are situated. He fixes the crown on to this stump of a tooth; this must fit tightly all along the edges so these edges therefore must be clearly visible to the technician and that means that the impression material must also be able to ‘flow’ up to the edges of the abrasion.
By laying the second ligature the gums are pulled in the other direction. When the second ligature is removed just before the impression is made, the impression material will take the form showing the abrasion limits.
The result can be seen in the video. On the right screen the preparation limit is clearly visible. On the left screen you can see what happens if ligatures are not used: the plaster mould doesn’t correspond to the stump preparation since the impression material hasn’t moved into the limits of the ‘prepared’ area due to the gums and/or blood and/or saliva being in the way so the technician will unknowingly prepare the crown incorrectly.
There are many other details which go into making a good crown but the working methods described here clearly show why the quality and therefore the price can vary so much. A good crown doesn’t cause inflammation or retreat of the gums. It’s indistinguishable from the original and lasts for decades and even if it needs to be replaced, the underlying tooth stump is in good shape.
The alternatives to crowning a tooth depend on the reasons for its crowning or why you want it crowned. If it’s a case of looking better then veneers and/or a bleaching treatment may perhaps be a better alternative to a crown on a tooth.
The particular risks when crowning a tooth include:
The death of the nerve if, for example, the tooth is abraded too much or for too long. The consequence is a root treatment.
Injury to neighbouring teeth, mucosa, floor of the mouth, tongue or cheeks with the following possible consequences.
Problems with gums or retreating gums if certain abrasion limits are exceeded and injury is caused to the gums – what dentists refer to as injury of the biological areas.
A miss-matched bite/painful jaw-joint/headaches, if your bite is unintentionally altered by the newly crowned tooth.