Hello I've Been Reading About Meth And Different Teeth Conditions.

Hello I've been reading about meth and different teeth conditions. I have a friend that claims her saliva is to acidic so that is why her teeth are rotting. But her husband has the same issue with his teeth. Is this contagious? Especially If my friend were to kiss me? I've been just reading about cavities and that they are contagious. Most of her teeth look black and her hubby has nerves exposed.