I have done some research ie. hypothyroidism and have found no correlation between the disease and increased decay rate in teeth.I would have to consider something in your diet or the possibility of zerostomia(dry mouth).
Dental care was of primary importance growing up, so I was happy to go the first 40 years of my life with no dental problems. My routine check-up at the dentist three years ago rocked my world - 10 cavaties! Up to @ 30 total now. Diagnosed with unspecified acquired hypothyroidism in August of 2006. My dentist "office", not dentist as of yet (I have an apointment next week), feels the cavaties are a result of medications. Do not know what your history is, but I am becoming fairly confident that inappropriate medication therapy caused the majority of my ailments. Some side effects from medication may cause dry mouth (which I had), leading to decay; unfortunately hypothyroidism also causes extreme fatigue (in bed for months, my case) with my mouth closed etc. which could also impact teeth. I do not know the answer for you, but these are things I am discovering about myself.
God Bless
I have had a form of thyroid auto immune disease for many years. It is called Hashimotos thyroiditis, a chronic inflammation of the thyroid. There is another auto immune condition called Sjogren's which causes dry mucous membranes, including the mouth, These two conditions can cause tooth problems.Find a good rheumatologist. who deals in rheumatoid illnesses, but above all find a good endocrinologist who can tell you about problems with auto immune illness in relation to the thyroid. There is a line of products at the drugstore called Biotene---tooth gel and mouthwash which is lubricating to add moisture to the mouth. Also ask your dentist for a toothgel prescription for Prevident which has fluoride to protect against decay. Drink lots of water and stay away from sugar.With auto immune thyroid your thyroid can change off and on from hyper to hypo. The low or hypothyroidism is most likely to cause tooth decay due to dry mouth. You will need to take a thyroid supplement when it is low. Bloodwork at least every three months until stablized has helped me.