Let’s discuss dental crowns with dark or black lines. Have you ever seen dark or black lines around dental crowns ? Unfortunately for many people this is something that occurs around their crowns soon after having the crowns fitted or after some time in the mouth.
The dark line is usually seen at the margin of the crown and if the crown is at the front of the mouth in a very visible area it may be noticeable.
The dark line is caused more commonly by a specific type of crown called porcelain fused to metal crown. In the past this type of crown was the most common when wanting to have a tooth crowned with tooth colored porcelain.
Porcelain on its own is not very strong and for that reason it was bonded onto metal in order for the porcelain to be strengthened. This worked well functionally as the crowns are generally very strong, however the metal is usually not tooth coloured !
Several metals can be used for making the framework onto which the porcelain was bonded. Metals can vary in colour but generally most used in porcelain bonded to metal crowns are grayish in colour.
The metal structure that supports the porcelain is known as a metal coping. This coping fits accurately over the tooth prepared to receive the porcelain bonded to metal crown. The porcelain is applied carefully over the metal coping in order to create a tooth coloured porcelain crown.
The margins of the crown are where the problems usually occur. The junction where the metal finishes and meets the porcelain can pose a problem aesthetically to the dentist and to the patient. Sometimes this margin is visible in the mouth and if this should be the case a dark line may become apparent.
Sometime the junction may be tucked slightly under the gum tissue in order to hide this margin, however this may darken the gum tissue in future.
Unfortunately this means that if a dark line is present around a crown, its most probably a porcelain fused to metal crown.
What can be done?
The only remedy for this problem is to replace the porcelain fused to metal crown with a metal free crown. It’s really a simple solution. Thankfully today we have porcelains that are stronger and more resistant to chewing forces hence they are sufficiently strong without the need for a metal coping.
The advantage of using metal free crowns means that one no longer needs to accept dark crown lines.
Empress or Emax are types of porcelains used today which function very well in eliminating the dark lines around crowns.
What are the advantages of metal free crowns
1 excellent aesthetics
3 as they are metal free, some patients prefer to have no metals in their mouth as this has been known to cause general health problems
4 accurate fit,
5 if there is some gum recession then no dark lines will be seen
what are the disadvantages of metal free crowns
1 Not all metal free crowns are as strong as each other. Emax is stronger than most other metal free crowns
2 Metal free crowns are not recommended for all teeth. Back teeth which have higher than normal stresses and forces may fracture some of the weaker metal free crowns
3 If the tooth underneath is discoloured due to root canal treatment or presence of metal posts etc, the metal free crowns may transmit the darker shade through the crown. This may result in a grey or bluish shaded crown. In these cases Zirconia crowns may be an alternative solution. See previous blog regarding discoloured metal free crowns.
For more information please feel free to Contact Brighton Implant Clinic or Call us on 0800 111 6623.