At the dentist office today, i was laying down in the chair with my mouth open while the dentist was talking and looking at my teeth. mid-sentence a drop of his spit flew in my mouth! what are my chances of contracting oral herpes? he didn't have any sore

Low risk: You have a low risk of herpes.

Very low: Unless the dentist had an active infection at the time your chances of getting any kind of illness from this incident is very, very low. That being said, I would switch dentists. Any time a dentist is talking "over" a patient they should be wearing a mask. This simple procedure protects both the patient and the dentist from unwanted exposure to germs when they are in each others personal space.