What does crystal meth do to your teeth?

Methamphetamine mouth: Broken, discolored and rotting teeth likely because the drug causes the salivary glands to dry out, which allows the mouth's acids to eat away at the tooth enamel, causing cavities. Teeth are further damaged by grinding and poor diet and poor dental hygiene.

Dry mouth, soda: Meth causes dry mouth aka xerostomia (no saliva). The saliva naturally cleanses the teeth and buffers acidic plaque. Plaque acids are what eat away at enamel and causes tooth decay. Meth addicts with dry mouth tend to moisten their mouths with inexpensive sugary sodas which makes the problem even worse. Also meth addicts are largely consumed with getting more meth rather than oral hygiene.