A dental implant is an artificial tooth root that is placed into your jaw to hold a replacement tooth or bridge. Dental implants may be an option for people who have lost a tooth or teeth due to periodontal disease, an injury, or some other reason.
American Detal Association
When a damaged or decayed tooth is removed, both the visible part of the tooth called the crown, and the root is lost.
If nothing is done to replace the missing tooth, there is a risk of the neighboring teeth moving into the edentulous space (space where the tooth is missing), increasing the chances of those neighboring teeth also being affected. Moreover, the bone where the lost tooth was lodged begins to atrophy immediately after tooth loss, causing bone loss.