Dental Conditions
Ankylosis
Ankylosis is a dental term for a condition where a primary tooth loses its normal ligament connection to the bone, and becomes fused directly to the bone. This is a fairly common occurrence and is most often seen with lower first molars.
When a primary tooth becomes ankylosed, three problems result:
First, when the tooth root fuses to the bone, it no longer grows out at a normal rate with the other teeth. Because of this, it appears submerged when compared with the other teeth. 
Second, the upper teeth need the lower teeth for support. With a lower tooth "submerged," the opposing upper tooth grows out of the socket and also loses it normal alignment. 
The third, and more serious problem has to do with the roots of the ankylosed tooth. About 50 percent of the time, the roots of the ankylosed tooth fail to dissolve normally as the permanent tooth grows in, and the permanent tooth is blocked out of position.