This document provides an overview of diabetes mellitus and periodontal diseases. It begins with classifications of diabetes, including type 1 caused by autoimmune destruction of insulin-producing cells, and type 2 related to insulin resistance and impaired insulin secretion. Complications of diabetes are discussed, involving pathways like advanced glycation end products, protein kinase C activation, and the polyol pathway. Oral manifestations of diabetes include increased periodontal disease risk. Proper dental management can help diabetic patients reduce risks.