What are methods used to prevent further bone loss due to periodontitis?

Professional care: If the teeth and roots of the teeth are kept clean you won't have any more bone loss. That means increased frequency of professional care and improved home care and diet. Talk to your dentist and hygienist for the details.

Occlusion: 3 factors causing bone loss: bacterial etiology, malocclusion, patient medical health. Maintain good oral home care and follow up with your dentist/periodontist, treat your malocclusion, maintain good health (avoiding become diabetic, etc...).

Address disease: As you already know, the non loss is a result of active periodontitis. So if you treat the disease, the bone loss will stop. A dentist or periodontist will provide you with treatment, but know that you must maintain strict daily home care to stay disease free.