A dental crown is a restoration that completely encircles (caps) a tooth and cemented in place.
Benefits of crowning.
Crowns are used to protect weakened teeth (e.g. due to tooth fracture or after root canal treatment), to replace missing tooth structure (e.g. due to decay or wear), as part of a dental bridge or dental implant, to improve tooth shape and colour as well as close gaps between teeth.
What will the dentist do?
The dentist starts by examining the location, size of the defect, the way you bite and vitality of the affected tooth. If the defect is large or cannot be readily seen, he may recommend for you to take a small x-ray image to assess the situation better. Your dentist will also try to find out more regarding your expectations on the appropriate appearance and longevity of the crown.
Treatment consist of shade selection followed by careful removal of decayed and weakened areas of the tooth. Filling material may be used to fill in areas with large defects. The tooth is subsequently prepared to ensure that it has an optimal taper, well defined margins, adequate ferrule and clearance from adjacent and opposing teeth. An impression of the tooth preparation is taken and sent to the dental laboratory to facilitate crown fabrication. A temporary crown is made and fitted over the prepared tooth in between visits.
On the fitting appointment, the temporary crown is removed and the permanent crown tried in. Your dentist will check to ensure that the crown is able to seat well, have good margins and is in contact (or suitable relationship) with adjacent and opposing teeth. He will also invite you to help assess the colour and overall appearance of the permanent crown. The crown is cemented in place once it is deemed to be satisfactory.
How long will it take?
The procedure can usually be completed within 2 visits. The first visit is for tooth preparation (takes approximately 60 minutes on average) and the 2nd visit is for crown fitting (takes approximately 15 minutes on average).
What will the experience be like?
Tooth preparation is usually done under local anaesthetic with the exception of root canal treated teeth. The procedure is painless albeit a little tiring for the patient, due to prolonged mouth opening, especially for back teeth.
Crown fitting is fairly straightforward whereby the temporary crown is replaced by the permanent crown.
How do I decide on the type of crown?
Crowns can be made from stainless steel, metallic alloys, porcelain, plastic or ceramics. A combination of metal and ceramic is also possible to maximise strength and simulate the appearance of natural teeth. Commonly used varieties include:
Stainless steel crowns
These are often prefabricated for the back teeth and has to be shaped by your dentist prior to fitting. It can be fitted within one visit, making it convenient and affordable. The crown shape is however generic, resulting in a less than ideal margin and contact with adjacent as well as opposing teeth. Stainless steel crowns are seldom used for front teeth due to their appearance. It is therefore more suitable as temporary restorations in the treatment of baby teeth in children.
Metal crowns are commonly fabricated from alloys of noble (e.g. gold, palladium, platinum and silver) and base metals (e.g. tin, copper, nickel, chromium). Full gold crowns are of a better quality when they are high in noble content (at least 60% noble metal, of which at least 40% must be gold). Metal crowns require less removal of tooth structure, cause less opposing tooth wear and is able to withstand chewing forces well. The metallic colour is the main drawback, making them a good choice for out-of-sight molars, especially in patients with a strong bite or grinding habits.
Porcelain fused to metal crowns
These are hybrid crowns made of a metal core and an outer layer of porcelain. The metal core provides strength while the porcelain mimics the colour, translucence and fluorescence of natural teeth. Porcelain fused to metal crowns attempts to seek the best combination of durability and appearance. Sometimes the metal beneath the porcelain can show through as a dark line, especially at the gum margins of teeth with receded gums.
Plastic crowns are fabricated using resin based acrylic. They are tooth coloured and can be made chair-side in a single visit, making it an affordable and convenient solution. They however tend to wear down faster, are prone to fractures and tend to discolour over time when compared to other tooth coloured crowns. Plastic crowns are more suitable as a temporary restoration.
Leucite reinforced crowns
Commonly referred to as an “Empress Crown”, leucite reinforced crowns consist of a core of pressure injected reinforced ceramics and an outer layer of porcelain. Leucite reinforced crowns have excellent tooth like characteristics and are more fracture resistant compared to traditional porcelain crowns.
Alumina reinforced crowns
Alumina reinforced crowns consist of an alumina core and an outer layer of porcelain. It has been in use for more than 25 years and is at present considered to be the aesthetic standard for tooth coloured crowns. Glass infiltrated alumina cores have recently been introduced to enhanced its bond strength to porcelain.
Yttria-stabilized zirconia oxide is a very hard ceramic material that has recently been introduced in dentistry. Monolithic zirconia crowns are made entirely of zirconia oxide. It comes in a variety of tooth-like shades and is suitable for back teeth due to its hardness. Zirconia cores can be layered with porcelain to further improve its colour, translucence and fluorescents although it does not form a very strong bond with porcelain, rendering it more susceptible to chip.
Are there any risks?
Patients should always weigh the pros and cons of crowning carefully as your dentist will need to remove between 1.0mm and 1.5 mm of enamel to accommodate the crown. Crowned teeth should be maintained with a combination of good personal hygiene and professional care. Failure to do so may lead to premature failure due to decay around the tooth margins or gum disease. Another common problem is porcelain fracture due to heavy biting or grinding habits. This can be mitigated with the selection of full metal crowns or the use of a night guard when sleeping.
Modern dental crown material is biologically compatible and can last many years if properly cared for. The average lifespan is between 5 and 15 years. The decision to replace crowns often hinges on the health and appearance of the crowned tooth as well as its neighbours.