A build up is used to restore a workable shape back to a badly broken down tooth prior to placing a crown over it. Not every tooth that needs a crown needs a build up. This is a case of two teeth which supported a bridge for 20 years, and the cement seal finally broke between the bridge and the tooth roots. Over time the teeth decayed under the previous crowns. Fortunately enough tooth remained after being cleaned up to support a build up on the two teeth and a new bridge. The darkness around the teeth is from the use of a dental laser, which cauterizes the tissues around the tooth and allows for a dry environment to ensure no moisture interferes with the bonding procedure. This will heal and look normal again after several days.