He probably served in Vietnam for the era he went in. Michael Baum is a common name and you need a lot more info if you have it.
You need to go to first check the Military Board and from there go and check Vietnam and then check General Board. There might have been someone who was stationed with him. If you had more info on him. You could do a general search and then a military search on him.
I said vietnam; because he was a dentist and they had need for Dentist and he was probably sent there.
If he was born around 1937 and finished Dental School. He would have entered the military aound 1960 or 61. His term would have been up around 1964 or 1965 and he could have re-enlisted for Europe; but eventually he might have wound up in Vietnam. He would have been an officer and he doesn't have much say about it.
If he was born in and around 19140/41 and Finised Dental School he would have been around twenty three or four and I doubt anyone goes right into the service after college unless he wants to get it over before he started his career; because they were drafting then. He might have had to go in; because he got a deferment; because he was in school when they call him to the Draft Board.
If he went in after school to get it out of the way or he went in on a higher calling. It would hve been about 1964 or 1965. He would most likely wound up in Vietnam in the Medical corps in the Navy.
I did a military search and there was quite a few Michael Baums. and his name sounds European and he probably if he were christian or Jewish. He probably had more than one name. You need some more info on him to do a decent search; but I would go to the Military Board. You might run into someone who served with him or knew of him.
You should try getting in touch with the Navy and see if they can help you out at all. If he was not killed or incapacitated from the war. Where he could not perform as a Dentist. You might check with the American Dental Association and see if they have anything on him.
I hope I have helped you in some small way.