Crowns are made of three types of materials:

1. Porcelain – most like a natural tooth in color
2. Gold Alloy – strongest and most conservative in its preparation
3. Porcelain fused to an inner core of gold alloy (Porcelain Fused to Metal or “PFM”) – combines strength and aesthetics

Crowns restore a tooth to its natural size, shape and – if using porcelain – color. They improve the strength, function and appearance of a broken down tooth that may otherwise be lost. They may also be designed to decrease the risk of root decay.

In having a crown, some inherent risks exist both to the tooth and to the
crown itself. The risks to the tooth are:

• Preparation for a crown weakens tooth structure and permanently
  alters the tooth underneath the crown.
• Preparing for and placing a crown can irritate the tooth and
  cause “post-operative” sensitivity, which may last up to 3 months.
• The tooth underneath the crown may need root canal treatment
  about 6% of the time during the lifetime of the tooth.
• If the cement seal at the edge of the crown is lost, decay may
  form at the juncture of the crown and tooth.
• Porcelain may chip and metal may wear over time.
• If the tooth needs a root canal after the crown is permanently cemented,
  the procedure may fracture the crown and the crown
  may need to be replaced.

Alternatives to crowns are fillings, such as composite or silver amalgam.
These restorations remove decay and may restore teeth to
their original form, but are limited because they do not improve the
strength of broken down teeth. They also do not decrease the risk of
root decay or improve the long term function and aesthetics of broken
down teeth or crowns.

• Excessive bite forces may lead to the tooth under the crown breaking or loosening.
• Excessive bite forces may lead to the crown chipping, breaking or loosening.

• Porcelain on a crown may have a good color match with adjacent
  natural teeth when the crown is placed, but less of a match as your
  natural teeth age.
• Gum recession may lead to unsightly dark roots or crown margins
  becoming visible.
• A crown may chip or break if used for abnormal activities (e.g. biting
  fishing line, sewing thread or finger nails, opening bottles).

Sometimes a tooth breaks upon impact such as accidentally chewing a pit or being hit in the face usually a small fracture begins at the edge of the tooth then deepens over time as you clench, grind or chew.

Some people are more susceptible than others to having a cracked tooth. Factors that are more likely to lead to a cracked tooth are:

• Deep fillings that leave thin amounts of tooth structure
• Sports such as hockey, football and boxing that have a high risk of facial trauma
• People who grind their teeth or have strong chewing muscles
• People with destructive habits like chewing ice or opening things with their teeth

Your dentist will make recommendations to minimize your risk of a
cracked tooth.
Here are some things that may be recommended:

• Have crowns placed to cover weak cusps of teeth
• Have your bite adjusted by your dentist
• Have old silver fillings replaced
• Do not chew ice or use teeth to open things
• Wear a night time grinding appliance
• Wear a sports guard

It is likely that the crack will continue to deepen and eventually the tooth may become painful to chewing or pieces may break off it. Sometimes the tooth may crack completely in half, at which point it must be extracted. Other times the crack goes into the nerve and a root canal treatment may be necessary to save the tooth.