There are several ways of restoring teeth, the most common being a filling or bonding. Crowns are used to repair badly decayed, broken, severely discolored, or misaligned teeth. Crowns completely cover teeth, restoring them to their natural size, shape, and function. The location of the crown in the mouth usually dictates the type of material used. The tooth under the crown is reduced in size. The crown will be permanently cemented over the reduced tooth. While you are waiting for the permanent crown to be fabricated, your dentist will provide you with a temporary one to wear. Crowns have a much longer life span than bonding, resist stains better, hold their color and resist chipping and cracking. Crowns, however, take longer to prepare than bonding and are not reversible. Your dentist can recommend which type of restoration is best for your particular situation.

If the tooth is severely decayed, or little tooth structure remains, it may be necessary to place a metal post into the tooth to support the crown. If this is the case, root canal therapy will be performed.

 Why might I need a crown?

• Aesthetic Reasons - Badly discolored and misshapen teeth 
• Restorations (Fillings) Which Just Don't Stay In - Sometimes there is too little tooth remaining for a restoration to successfully resist dislodgment
• Cracked Teeth - Teeth may have microcracks that cause sensitivity when exposed to hot and cold temperatures, pressure, and air stimulation. The full coverage afforded by crowns often relieves these symptoms while reinforcing the tooth

 Why crowns and not veneers?

Crowns require more tooth structure to be removed, hence, they cover a larger portion of the tooth than veneers. Crowns provide protection around the entire tooth and are generally indicated for teeth that have sustained significant loss of structure or have a high risk for fracture. Crowns may be placed on natural teeth or dental implants.

 How long do crowns last?

It depends on your oral hygiene and habits. On average, crowns last approximately 6-9 years. However, with good oral hygiene and supervision most crowns will far out last that time frame. Bad habits, such as grinding and clenching your teeth, chewing ice, and/or fingernail-biting may greatly reduce the life of your crowns. In addition to visiting your dentist and brushing twice a day, cleaning between your teeth is vital with crowns. Floss or interdental cleaners should be used regularly to remove plaque from the crown area where the gum meets the tooth.

Types of Crowns

All metal crowns
Porcelain fused to metal crowns
All ceramic crowns
All resin crowns

Advantages & Disadvantages

Gold crowns
Less tooth structure is needed to be removed
Adjacent tooth wear is kept to a minimum.
The main negative is color
 
Porcelain/metal crowns
Unlike gold crowns, porcelain can be matched to your adjacent teeth. The main disadvantage is that the color match to natural teeth is not quite as lifelike as with ceramic crowns. There is also a higher degree of wear to the opposing teeth than with gold or resin crowns.

All resin crowns
They're usually less expensive than other types of crowns. Unfortunately, they tend to wear over time and are less fracture resistant than porcelain/metal crowns.
 
All ceramic crowns
More natural tooth colors may be achieved than with any other type of crown. They may be more suitable for people with metal allergies. Their main disadvantage is that they're not as strong a porcelain/metal crowns. They also tend to wear opposing teeth a little more than gold or resin crowns. 

Procedure

Most crown preparation visits are reasonably long. The entire procedure usually takes two visits.

A few radiographs may be necessary to check the roots of the tooth receiving the crown and to evaluate the surrounding bone level. If the tooth is vital, the area will be anesthetized with a local anesthetic. The tooth receiving the crown will be recontoured by removing a layer of tooth structure from the chewing surface and the sides. The amount removed depends on the particular type of crown used (generally between 1 to 2mm). Once the tooth has been prepared, an impression is taken. The crown will be fabricated using this impression. A shade (or color) is then selected for the crown.

Your dentist will then fabricate a temporary crown to cover and protect the prepared tooth while the permanent crown is being made. The temporary will not be as strong as the permanent crown; it will be attached using a temporary cement so that it can be removed once the permanent crown is back from the lab. It's a good idea to avoid chewing sticky foods while the temporary crown is in place; they often become dislodged.

At the second appointment, the temporary crown is removed and the fit of the new crown is checked. If the occlusion (bite) is acceptable and the color has been matched correctly, the new crown is then cemented into place using a permanent cement.

 Procedural Steps

Possible Problems from Treatment:

Fracture
While every effort is made to evaluate teeth prior to treatment, it’s not always possible to detect cracks in the teeth through x-rays and clinical evaluation. Teeth may crack during the actual procedure or some time after. If a crack occurs during the preparation, the treatment may be modified depending on how severe the problem.

Pain or discomfort
After having a tooth prepared for a crown, it may feel tender as the anesthetic begins to wear off. If this discomfort persists for more than 24 hours, contact your dental office. Sometimes a very slight variation in 'bite' may be noticed. This may be simply relieved by making your restored tooth 'less high'.

Nerve death
Usually teeth that are crowned have had large fillings (restorations) in them. These teeth are much more likely to require root canal treatment (endodontics). If pain persists after crown preparation, contact your dental office.

Loose crown
If your crown or temporary crown feels loose, let your dental office know.  When a crown becomes loose, decay can quickly advance, undermining the remaining tooth.

Allergic reaction
Being allergic to gold or porcelain is extremely rare. Usually the metal used inside a metal/porcelain crown is a mixture of metals, including gold. Sometimes non-precious metals are used in crowns.

 Cost

Generally the cost of tooth-colored crowns is greater than the cost of gold or metal-colored crowns. Some teeth have a poor prognosis or "life expectancy" whether they are crowned or not. Whether you spend money on these teeth giving them the greatest chance of survival can often only be decided by you.