Dental crowns are used for treatment of defects and damages of teeth. They cover the tooth completely and reach the dental neck. They protect the tooth from future damage. Crowns are made of different materials – plastic (temporary crowns), metal (nickel-chromium alloy), gold, metal and plastic, metal-ceramic, or all-ceramic (zirconium) crowns. Different types of crowns are described in detail in the “Crowns and bridges“ section.
Crowns are made for dental defects, resulting from abrasion (loss of tooth structure), fractures, wedge-shaped defects, Discolouration of the teeth and inability for teeth whitening, root canal treated teeth with thin walls, etc.
Crowns can be made for both alive and endodontically treated teeth.
Choosing the right crown depends on many factors – location of the tooth, the aesthetics of the crown, price. The cost of the crowns depends on the type of material and method of making.
Having selected the appropriate type of crown, the teeth are prepared and an anesthetic is used in healthy teeth.
There are two main types of preparation – grinding with threshold and without threshold.
Threshold grinding is done to ensure adequate thickness of the crown edge and proper transition between the crown and the hard dental tissues. It is used in metal-ceramic, plastic and metal, and all-ceramic crowns. Special burrs with specifically determined form on the top are used for threshold preparation, in order to achieve an appropriate threshold. The advantages of threshold preparation are that the crown edge fits tightly the threshold of the tooth neck and the crown cannot sink and irritate the gums.
In grinding without threshold, there is no threshold and the burr is used between the gum and tooth, thus achieving the necessary level of grinding. It is used in all types of jacket crowns and it is the oldest method of grinding of teeth. The disadvantage is that the crown edge can enter freely and unevenly in the gum, and thus causing irritation. This type of preparation is easier and does not require a special burr. An advantage of this method is that the deep-reaching edge of the crowns provides a better splinting effect and greater stability in deeply damaged roots.
The fabrication of a crown requires three to four visits depending on the type.
First visit – The tooth is prepared either with threshold or without. A temporary crown can be placed at the discretion of the dentist or if desired by the patient. It is not recommended to take an impression at the same visit as preparation of the tooth, because the grinding usually hurts the gum. The irritated gum should be left 4-6 days to recover, and only then an impression is taken. If this is done the same day, the crown can be made shorter and it does not cover entirely the neck of the tooth, which requires corrections.
Second visit – an impression of the tooth stump is taken using special spoons with silicone and alginate. The colour of the crown is then determined (depending on whether the crown will be from plastic or ceramics). Then, the impression is sent to a dental laboratory where a gypsum model of the tooth stump is moulded. Then, the crown is modelled of wax, and moulded from metal, and then cleaned and polished.
Third visit – Conventional crowns (of metal or metal and plastic) are fitted and cemented during this visit. A sample of the metal base of the crown is done with metal-ceramic crowns, and in some cases, with unpolished ceramic crowns. After the shape, colour and occlusion are determined, the crown is completed (polished).
Fourth visit – metal-ceramic crowns are cemented using a suitable cement, depending on whether the tooth is alive or not. At the discretion of the dentist, the crown can be glued with temporary cement and the patient can eat with it for about a week in order to check how it feels before it is cemented permanently.
What follows is giving guidance to the patient on good oral hygiene and nutrition. If a crown has been properly made and well-fixed, patients get used to it for a couple of days. Crown endurance is about 6-7 years, but they remain in the mouth for a longer period of time, thanks to the strength of the teeth and periodontium and maintenance of good oral hygiene. This is the most commonly used way to restore defects of the tooth crown.
Detailed information about the various types of crowns (metal and plastic, metal-ceramic, all-ceramic), as well as the advantages and disadvantages of different materials, can be found in the “Crowns and bridges” section.