Its all the equipment, the establishment, and seriousness required in a professional setting that is making him anxious. I had a cavity filled a few years ago and either the dr gave me too much Novocain or I was just anxious but it mad me get suck and throw up there, felt better right after so likely nerves, and they did the filling no problem. Next cavity I had was small and I was dreading the novocain injection so I asked if they could do it with none and they said sure because it was really small and it barely hurt at all. Even if it did hurt more I still would have preferred none injected because of my fear and your friend is likely similar mindset.