This is the most common area for tartar deposits to build up because we are not aware of proper brushing technique.
It is not a sign of any other deficiency.
If your teeth are not properly aligned, then this problem would happen more often.
Cleaning by a Dentist is the only solution.
Next Steps
Visit a Dentist at the earliest for a thorough Examination and Cleaning.
Ask the proper way of brushing.
Health Tips
Start brushing at night also