Definition: The term "Meth Mouth" describes the state of tooth decay that is caused from using methamphetamines. Frequent use of methamphetamines can cause one to neglect their mouth for long periods of time. It often leaves a person's teeth looking black, rotten or brittle which puts them at high risk of losing all their teeth.
From the ADHA (American Dental Hygiene Association) website: Symptoms of diabetes disease often appear in the mouth, while almost one-third of people with diabetes have severe periodontal disease. This is believed to be a result of the diabetic patient's greater susceptibility to developing infections. Conversely, severe periodontal disease may increase the risk of developing diabetes, and may make it more difficult to manage blood sugar levels. However, studies have found that patients who receive treatment for periodontal disease may be able to control the condition with less insulin.
For more information on how Diabetes affects the mouth see www.adha.org/downloads/factsheets/diabetes.pdf