Why are my teeth going bad despite good oral hygiene?

See dentist: You could have a highly acidic diet that's causing your teeth to degrade. Highly acidic foods , such as mountain Dew, Red Bull, coca cola break down the enamel exposing the underlying dentin, that can develop cavities more easily. You also should avoid a lot of dried fruits - they're sticky and full of sugar that feed bacteria. See your dentist to evaluate your teeth.