A friend said he had some dental work done by a dmd not a dds. what does a dmd do?

They are the same: Different schools give different names to their degree. Both are essentially the same.

No difference: Same thing dental schools in the eastern part of the us tend to give a dmd. In the west they give a dds. There is no difference in the education. It just confuses the public.

Same: Dds (doctor of dental surgery) was the first dental degree. Later a dental school changed its degree program to dmd (doctor of dental medicine) and other schools followed suit. The degrees are interchangeable. For example my degree from temple university school of dentistry was dds in 1979. Temple changed to dmd some years later and offed earlier grads the option to convert diploma to dmd.

No difference: There is no difference between dentists with dds and dmd degrees. Different schools decide on which one they want to give.