Severe marginal periodontitis often coexists with diabetes and is considered to be the sixth complication of the disease. Several factors associated with diabetes have been shown to be related to the development and deterioration of diabetic periodontitis, i.e., glycated hemoglobin (HbA(1C)), advanced glycation endproducts (AGEs), C-reactive protein (CRP), and glucose tolerance, as well as inflammatory cytokines such as tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6. A periodontal pathogen, Porphyromonas gingivalis with the type II fimbria gene, is also considered to be a related infectious factor. Among them, AGEs seem to be closely associated with the periodontitis deterioration seen in diabetic subjects. Osteoporosis and diabetes are also tightly related, and AGEs have been reported to accelerate the progression of osteoporosis. Collectively, AGEs are a critical diabetic factor to deteriorate oral osteoporosis.