My dad recently had two left rear molars removed (not wisdom) he had to be put under as he has a very bad gag reflex. Since he came out of the surgery he has slurred speech. Problems pronouncing words and he drools quite a bit. It has been six months since the surgery and speech still slurs. He has been working with a speech therapist but no change. He is 78 years old. Any ideas what can be causing this?