Introduction. Ocean trenches are natural tectonic plate boundaries between two crustal plates. When a continental plate converges with an oceanic plate a subduction zone forms. The heavier oceanic plate subducts beneath the lighter continental plate forming a trench.
Surgical-Medical Policy this patient has with Arkansas Blue Cross and Blue Shield provides coverage for dental. treatment only in case of accidental injury and accident-related damage to teeth, and then as a rule only to sound. natural teeth. A sound natural tooth is a tooth that is whole, free of decay, periodontal disease or other conditions, and is not in need of treatment for any reason other than accidental injury. DIAGNOSTIC X-RAYS AND THIS COMPLETED FORM ARE REQUIRED TO DETERMINE A. CONSIDERATION OF PAYMENT.
1 If a natural tooth is failing or about to fail.  If a tooth has severe periodontal disease (gum disease) that has eroded the bone that supports the teeth. Sometimes in these cases, it is preferable to extract the teeth; eliminate the disease and infection and replace the teeth with a dental implant.