What are the average IQ's for a dentist vs a physician?

It would depend on each individual dentist. Everyone has their own way of interpreting information.
If you're asking for the IQ requirement to become a dentist, there isn't one.
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Hopefully a dentist's IQ is fairly high. Dentists have to possess a lot of information not generally known by other doctors, and the skill to treat a variety of tooth ailments.