There is no cure, unfortunately. I have periodontal disease and I have recently had the last 9 upper teeth removed and I now have dentures. (I am only 53) The 10 remaining teeth in my lower jaw are still in really good shape, fortunately. In order to effectively control it, a deep cleaning called a gum scaling/root planing is done and then quarterly cleanings is necessary to keep the disease from progressing. Brushing and flossing twice a day will also keep the progression at bay between quarterly cleanings. What is happening is, the bones in your dad s mouth keeping the teeth in place are deteriorating and developing pockets around the roots that food particles and subsequently bacteria is collecting, which is why he has a loose tooth and he is in pain. It is a viscous cycle. And, it is also inherited. My dad had a full set of upper dentures by the time he was 32, when he died at 69, he only had one tooth left. Your dad needs to see a dentist immediately. Peace.