Why should one not eat or drink before going to see a dentist?

Eating is Fine: You can eat and rink before any routine dental procedure. Of course, it would be common courtesy to brush and floss afterwards, before your dentist starts working in your mouth. The only time you should not eat is if you are going to be sedated, such as for oral surgery. Your dentist or oral surgeon can tell you specifically what is appropriate for each visit. Normal visits are fine either way.

Please eat...: Actually if you are having a dental procedure, and will be receiving a local anesthetic, (injection), it is advisable to eat prior to your appointment. If you are using IV type sedation eating is not recommended. Ask your dentist for instructions prior to oral surgery with sedation.

You can: Unless you are having general anesthetic, there is no reason you can't eat or drink. General anesthetic is usually used by oral surgeons for extractions.