The crown is the upper part of the tooth, which sticks out from the gums.

But generally, it tis the artificial covering of this part of the tooth which is referred to as a „crown“.

Here you can see an extracted tooth with an „artificial“ crown.

There are vast differences in the ways this procedure is performed, and the materials used – which is why some crowns hold for 30 years and more, while some only hold for a few! This begins with the way in which the dentist prepares the tooth stumps: a tangent cut is quick and easy to perform. A part of the tooth is simply sawed off diagonally. The disadvantage to this type of cut is that the technician needs to allow some extra width for the ceramic part at the edge of the crown, as otherwise this part would break. This results in an overjet in the edges. In order to hide these, the edges of the cut are set under the gums. A dental probe or floss, as well as bits of food, can get caught on these edges. This in turn results in inflammation of the gums, which over the course of time causes the gums to recede, which reveals the edges of the crown – as seen in the picture, the risk of a root cavity is very high. Unfortunately, the tangent cut is the most common kind of cut performed!

Another type of cut is the step cut, which can also be performed relatively quickly. Here the technician has left enough room for the ceramic edges, so there is no overjet, but the glue used in cementing cannot flow away as easily, and a gap forms. The risk that the glue (usually cement) will eventually wash away and a root cavity will form is very high.
A groove cut combines all the advantages of the other types of cut and eliminates the disadvantages, but this variant is the most complicated. The glue can flow away easily, which causes a thin gap to form; the technician has enough space for the ceramic parts, the edges are tightly sealed, and food cannot get caught in them.

In order to get a good groove cut, it is necessary to use a magnifying glass and take certain criteria into account when taking an imprint. This technique requires more effort, but results in top quality work.

There are also vast differences in the way a crown is produced, in the picture you can see – or rather not see the crown – only the tooth stump shows which tooth is not real.
In this picture you can easily see that the upper 4 teeth are crowns. The difference – in the first picture the ceramic part was layered, meaning that the patient went to the technician's office, where the ceramic parts were applied layer by layer using a brush, taking the actual tooth structure into account. The crown in the picture on the right was made from a pre-fabricated shell and simply painted over. This „paint“ washes away over time, which makes the crown more visible against the background of the patient's own teeth. Even a dentist cannot tell a well-made denture from a real tooth.

However, a precise cut and optimum execution alone are not enough to ensure a good crown, many steps are necessary to maintain good results. It is thus always necessary to draw 2 threads before taking an imprint, whereby one thread is removed immediately before the imprint is taken. There are various pastes which can be used instead of threads, but they contain chemicals which react with the cast materials and cause them to warp – resulting in a crwon which is not tightly sealed.

Why are two threads necessary? On the one hand, the gums must be protected during cutting, and on the other, the edge of the cut should be placed within the so-called sulcus, underneath the fringe of the gums. The first thread is used to push the gums aside before cutting, so that they are not damaged.
Alright, but why two threads? Here you can see an imprint, which the technician fills with plaster, thus getting a good copy of your teeth on a plaster model. The denture is then prepared based on this plaster cast, so that it seals tightly around the edges. The preparatory edges for the cut should be easy to see for the technician, meaning that the cast material should be able to "flow" to the edges of the cut!

The second thread is used to expand the gums once again. When this thread is removed shortly before the imprint is taken, the cast material can harden around the edges. The animation shows a scoop filled with cast material being placed over a cut tooth stump. The threads were set on the right, the cast material flows around the preparation edges, which are clearly visible. On the left you can see what happens when no threads are used: The plaster imprint does not accurately show the stump, the cast material could not flow to the edges, and the technician prepares a faulty crown without meaning to.

There are many factors affecting the quality of a crown – the variants outlined here explain the differences in price! A good crown does not cause gums to become inflamed or to recede. It cannot be distinguished from real teeth and holds for several decades – even if the crown needs to be replaced someday, the stumps underneath are still intact.