Diabetic Mellitus have multiple impacts on dental care. To provide competent care to patients with diabetes mellitus, dentists play a major role in health care team. It is important for dentists to be familiar with the pathogenesis, medical managements, and medical history of patients with DM. Dentists are required to have the ability to recognize the complications and oral manifestations indicating poorly controlled or undiagnosed diabetes mellitus and give adequate managements in time. There are multiple oral manifestations. Among them, periodontal disease is the most common manifestations and considered to be the sixth complication of diabetes mellitus. Other manifestations such as xerostomia, dental caries, oral infection, and delay wound healing all play a role in dental treatments and should be take into consideration when making a treatment plane.