Good points about the illicit ingredients in street meth.
However, I can testify - via my own use (prior to Oct 1995) and the shared experiences of many meth abusers during my years working with recovery groups - that the principle reasons street meth users are tore up are dehydration and malnutrition
Meth removes the normal body urges to eat or drink. Additionally, use of strong stimulants pulls most of the body's Vitamin Bs and those are a key component to healthy oral hygiene.
"meth mouth" is not a byproduct of meth per se. Rather it is a byproduct of the mouth being chronically dry and deprived of Vitamin B.