What would you advise a new dentist if their practice name domain is taken?

There would be a couple of considerations to be made here. Personally me as designer and SEO guy.. would stay away from the matchy matchy dentist anything EMD. Is the practice name and with the added "DDS" or whatever other acronym the dentist may have available?

Google looks as "DDS" in almost the same way it does "Dental" and "Dentist" there is a slight variance in local pack listings but to have DDS in the URL and then "Dentist" in the business name section would more than likely put you ahead of your competition by a long shot.

First name last name DDS would be the direction I would shoot for. or go way off into left field and look for "nothingbutteeth.com" - yeah the word butt in there... but you get the idea.

have you looked at the " .dentist " extension? kinda goes against my principles of EMD but in this case that may very well be an option.

I agree with this. You can always add a DDS, Best, Top, east, west, north, south, central or even something like "TheJoeSmithDentistry.com", etc.

Personally, I think using an EMD is just fine and always will be because EMD's are relevent to a search. They may not always be ranked high just because they're an EMD, which used to be a given, but with a few pages of quality content, decent on and off page SEO and a little elbow grease, they should do just fine.

I just started doing this (again) recently and it's working out well so far.

Something else, what does Google Instant tell you as you're typing a local term for your client? What phrases begin to appear after the first few letters? There may be a hidden gem that's already being searched for often that you can grab.