the 'meth' in crystal meth is not methalyted spirit..its short for methamphetamine..it comes in crystal form, and is smoked like cocaine so its shortened to crystal meth.
Meth mouth is caused by taking too much crystal meth. no one is totally sure why this happens, but it is probably linked to the fact you get a dry mouth, as you dont produce as much saliva, and when high you tend to grind your teeth. i suppose if you are high on drugs your last priority would be your oral health!! so its a quite quick deterioration.
all quite horrible really!