What affect does someone using crack cocaine have on their teeth?

It can quickly rot the teeth from the chemicals contained in the cocaine or make any tooth problem worse much quicker.

Yes, one seldom sees a long time crack addict with good teeth

Tooth damage from crack and crack cocaine use is well documented.

Chronic snorting of cocaine can result in loss of enamel surface and receding gums. This occurs through decalcification that results when cocaine mixes with saliva, creating a powerful acid. The process is aided when the user massages the oral mucosa to hasten drug absorption. Cocaine also reduces saliva, a factor
That increases the risk of decay.

Since crack cocaine is smoked, the harmful chemical compounds of the drug come in direct contact with the teeth and gums. Prolonged use can result in damage to the enamel, bone and nerve endings. There is no way to prevent this except by abstaining from use.

Use of drugs in general can affect your appetite, dietary patterns, and nutrional status, which can affect your dental health as well as your hair and nails.

The reason you don't see a crack addict with nice teeth is simply because they are junkies looking for there next hit they are not worried about going to see the dentist and also because it drys out your mouth and you need saliva in your mouth. A dry mouth will ruin anyone's teeth.