Oakville Dentist Dr Thordarson East Lake

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Black Line on Tooth:

Black Line: Sometimes a crown or cap has a “black line” along the gumline.

The Problem:

The Solution:

Black lines can be very unsightly and give a tooth an artificial appearance.  There are 4 reasons why this happens:

  1. Receding Gums: If the gums around a cap or crown recede, the root part of the tooth starts to show.  On a natural tooth this is not usually as big a problem because the root of a tooth is only a few shades darker than the tooth itself.  When a dentist places a crown on a tooth to improve its structure or appearance, the edge of the crown ends at or slightly below the gumline.  When gums start to recede, a dark line can appear where the white tooth meets the root.
  2. What the crown is made of: In the past, the most esthetic crowns available were called “porcelain fused to metal” (PFM) crowns.  These were made of a thin layer of metal (usually silver in colour) covered by a thin layer of white porcelain.  Metal was used to strengthen the tooth and an appropriate porcelain shade was chosen to match the color of the surrounding natural teeth.  When the crown is first inserted, the dentist usually tucks the edge of the crown slightly below the gum line in order to hide the seam between the crown and the root.  If the gums recede over time, this seam often appears as a dark line.
  3. A crown can cast a shadow: Natural teeth are never solidly opaque in color.  They are transleucent like a piece of coloured glass.  In fact, teeth act very much like a fiber optic cable.  When light shines on a natural tooth, some of the light is reflected, but a lot of light travels into the tooth and root, much like a fiber optic cable.  The light bounces around inside the tooth, brightening both the tooth and the gums.  When a metal-containing porcelain crown (PFM) is placed over a tooth, the metal acts as a barrier blocking the light from entering the tooth.  The result is that the tooth and gums look darker because there is no light “dancing” around inside the tooth.  The metal-containing crown casts a shadow over the gums and root making them darker.  This shadow often creates a “black line” along the gumline!
  4. Teeth with root canals: If a tooth has been treated with a root canal (root filling), the root becomes darker over time due to filling material used.  This can create a black line as well.

The Solution for black lines…

Today, crowns can be made to look prettier and more natural than ever before.  There are numerous crown materials that are extremely strong and esthetically beautiful which contain no metal.  No metal means no shadow on the root and gums.  These all-porcelain crowns act just like natural teeth allowing light to travel into the tooth and root, brightening them.  No more black lines!