Crowns

What are Dental Crowns?

Both crowns are fixed prosthetic devices. Crowns are cemented onto existing teeth or implants, and can only be removed by a dentist.

How Do Crowns Work?

A crown is used to entirely cover or "cap" a damaged tooth. Besides strengthening a damaged tooth, a crown can be used to improve its appearance, shape or alignment. A crown can also be placed on top of an implant to provide a tooth-like shape and structure for function. Porcelain or ceramic crowns can be matched to the colour of your natural teeth. Other materials include gold and metal alloys, resin and ceramic. These alloys are generally stronger than porcelain and may be recommended for back teeth, however their appearance makes them least favoured by the patients. Porcelain bonded to a metal shell is used because it is both strong and attractive.

Crowns may be indicated to

  • Replace a large filling when there isn't enough tooth remaining
  • Protect a weak tooth from fracturing • Restore a fractured tooth
  • Cover a dental implant
  • Cover a discoloured or poorly shaped tooth
  • Cover a tooth that has had root canal treatment

How Are Crowns Made?

Before a crown is made, the tooth (or teeth) must be reduced in size so that the crown will fit over it properly. After reducing the tooth/teeth, your dentist will take an impression to provide an exact mould for the crown. If porcelain is to be used, your dentist will determine the correct shade for the crown or bridge to match the colour of your existing teeth. Using this impression, a dental lab then makes your crown, in the material your dentist specifies. If possible, a temporary crown will be put in place to cover the prepared tooth while the permanent crown or bridge is being made. When the permanent crown is ready, the temporary crown is removed, and the new crown is cemented over your prepared tooth.

Q: How is a tooth prepared for a crown?

A: The dentist will prepare the tooth to the ideal shape for the crown. This will mean removing most of the outer surface, and leaving an inner ‘core’. The amount of the tooth removed will be the same as the thickness of the crown to be fitted. Once the tooth is shaped, the dentist will take an impression of the prepared tooth, one of the opposite jaw and possibly another to mark the way you bite together. The impressions will be given to the technician, along with any other information they need to make the crown.

Q: Who makes the crown?

A: The impressions and information about the shade of your teeth will be given to a dental technician who will be skilled in making crowns. They will make models of your mouth and make the crown on these to be sure that the crown fits perfectly.

Q: How does the crown look like?

A: The crown will be made to match your other teeth exactly. The shade of the neighbouring teeth will be recorded, to make sure that the colour looks natural and matches the surrounding teeth. A temporary crown, usually made in plastic, will be fitted at the end of the first appointment to last until the permanent one is ready. These temporary crowns may be more noticeable, but they are only in place for about two weeks.

Q: How long does the treatment take?

A: You will need to have at least two visits: the first for the preparation, impression, shade taking and fitting the temporary crown, and the second to fit the permanent crown.

Q: Does it hurt to have a tooth prepared for a crown?

A: No. A local anaesthetic is used and the preparation should feel no different from a filling. If the tooth does not have a nerve, and a post crown is being prepared, then local anaesthetic may not be needed.

Q: Are post crowns different?

A: Post crowns may be used when the tooth has been root filled. The weakened crown of the tooth is drilled off at the level of the gum. The dentist makes a ‘post’ to fit into the root canal. This can be either prefabricated stainless steel or custom made. The post is cemented into the root canal, and the other end holds the crown firmly in place. Q: Are there any alternatives to post crowns for root-filled teeth? A: If a root-filled tooth is not completely broken down, it may be possible to build it up again using filling material. This ‘core’ is then prepared in the same way as a natural tooth and the impressions are taken.

Q: How long will a crown last?

A: The life of a crown will depend on how well it is looked after. The crown itself cannot decay, but decay can start where the edge of the crown joins the tooth. It is very important to keep this area as clean as your other teeth, or decay could endanger the crown. Also gums should be well maintained, the teeth and crowns are lost to gum disease as they lose the bone support. Also sometimes if the capped tooth breaks due to trauma or accidents, the crown will be lost too. Properly cared for crowns will last for years however no absolute guarantee can ever be given and they may need to be replaced in time.

Q: How are crowns fixed to teeth?

A: Once the fit and appearance of the crown has been checked – and approved by you – it will be cemented in place with special dental cement. The cement also forms a seal to help hold it firmly in place.

Q: Will the crown feel different?

A: Because the shape of the crown will be slightly different from the shape of you tooth before it was crowned, you may be aware of it. It may feel too tight at the beginning .Within a few days it should feel fine, and you will not notice it. The crown may need some adjustment if it feels higher than the surrounding teeth. If it is at all uncomfortable ask your dentist to check and adjust it.

Q: How do I look after my crown?

A: Exactly the same way you would care for your natural teeth:

  • Make sure you brush at least twice a day with a fluoride tooth paste,
  • Restrict or avoid sugary food
  • floss all the teeth including the capped ones daily
  • Use interdental brushes daily
  • Use a mouth wash once or twice a day.
  • Avoid consumption of sticky food like toffees and jelly babies as they may make the crown loose.
  • Keep regular check-ups
  • If you play contact sports, wear a mouth guard to avoid trauma to your teeth or crown.
  • If you have a grinding/clenching habit, wear a night guard to make sure the habit does not damage your teeth or the crown.

Crown complications: The unexpected need for root canal treatment.

When a dentist places a dental crown on a tooth, it's no doubt their hope that doing so will be the last procedure that that tooth will require for a very long time. Unfortunately, since crowns are not placed on pristine teeth but instead those that have been seriously compromised by fracture, breakage or the presence of tooth decay, complications can and do occur. In some cases, it's possible that the same traumatic event that has caused the need for crown placement has also damaged or compromised the tooth's nerve tissue (pulp). If so, root canal treatment will ultimately be required.

. Dental research has identified a statistical relationship between those teeth that have had a dental crown placed and those that subsequently require root canal treatment.

Relative to the time of crown placement, this need for root canal may become apparent either immediately, or else in the near or even very distant future.  Whitworth et al. (2002) performed a review of available dental literature. They estimated that 4 to 8% of teeth that have had a dental crown placed will require root canal treatment within ten years.

Why is it so? Various scenarios can take place that ultimately lead to a tooth's need for root canal treatment.

They include:

A) Inflammation triggered by trauma. Any type of incident that causes tooth trauma (such as a blow that has fractured a tooth) can have a detrimental effect on the health of a tooth's nerve tissue (dental pulp). The reason for this is as follows.

• When a tooth receives mechanical insult, its nerve tissue (just like any other type of soft body tissue) responds with what is called an inflammation reaction. A part of this reaction includes tissue swelling.

• In the case of teeth, when this swelling occurs the pulp tissue is compressed (the nerve tissue expands due to swelling but is limited by the hard confines of the tooth). As the compressive forces build up, they restrict the flow of blood through those vessels that service and supply the nerve tissue. Blood vessels perform vital functions that help a tooth's nerve recover from the trauma it's received. This includes the delivery of oxygen and nutrients, as well as carrying away the fluids that have caused the swelling. The net effect is that the events that should take place to help the tooth's nerve tissue to recover are instead stifled.

What are the consequences? In severe cases, the dental pulp will fail to recover and ultimately die. As a result, root canal treatment will be required. In lesser cases, the nerve may survive but linger on in a debilitated state. Root canal treatment may not be required for weeks, months or even years.

B) Bacterial invaion. Once bacteria and oral contaminates have reached a tooth's nerve tissue, it's quite likely that its degeneration will begin and root canal treatment will ultimately be required. Events that can lead up to this scenario include the presence of advanced tooth decay or possibly tooth fracture. In many cases, the dentist has no way of knowing how much damage has occurred and can only make a repair and hope for the best. If required, the tooth's need for root canal treatment may become apparent immediately, in the near future, or possibly not for years to come.

How do these scenarios relate to crowned teeth? Tooth breakage, fracture or the presence of a large amount of tooth decay can also be events that cause enough damage to a tooth that dental crown placement is required.

So, there is a correlation between crown placement and the need for root canal therapy. But it's not that one has caused the other but instead that the precipitating event has caused a need for both (although the need for root canal treatment may not be diagnosed for months or years to come).

Can your dentist anticipated the ned for the root canal treatment in the future? You might wonder why your dentist has warned you that your tooth may need root canal treatment beforehand. Dentists have tests that can help to evaluate the health of a tooth's nerve tissue. And it's most likely that these were performed (and you simply did not realize it) at that visit when your tooth's need for a crown was first evaluated. Unfortunately, the results of these tests are often vague and difficult to interpret. And in those cases where collectively their conclusions are ambiguous, your dentist will most likely refrain from recommending root canal treatment for fear of performing an unnecessary procedure. However they will warn you in advance that it can become necessary in the future.

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