Impactions completely covered by bone and soft tissue, do not communicate with the mouth, and have a low rate of clinically significant infection. Since the tooth never erupts, however, the dental follicle that surrounds the tooth does not degenerate during eruption, and can develop cysts or uncommon tumors over time.[1]:141 Estimates of the incidence of cysts or other neoplasms (almost all benign) around impacted teeth average at 3%, usually seen in people under the age of 40. This suggests that the chance of tumor formation decreases with age.[3]:141