My question would be is it a baby tooth or an adult tooth? If it is an adult tooth, it could have been most likely periodontally involved. Basically, your gums and bones have pulled away from your teeth due to bacteria left behind from non-effective brushing and flossing. I recommend a visit to the dentist. Thats a serious disease that can have great effects to your general health. Perio disease is directly linked to heart disease and diabetes. and if you've lost one to this disease, you will loose more. Getting in touch with the right dentist can stop the disease from getting worse and save your teeth.