In the UK you have to have both degrees to do the big cases (Maxillofacial surgery), if you only have a dental degree than you are limited to (Oral surgery).
In the US, they are one specialty (Oral and Maxillofacial surgery). In the US... legally there is nothing that a dual degree OMFS can do that a single degree OMFS can't do.
(In the US) you can get into most all fellowships as a single degree OMFS graduate. However, there are a (few) fellowships that "prefer" to take dual degree guys.
The current IAOMS (international association of oral and maxillofacial surgeons) guidelines state that the "gold standard" of OMFS training should include acquisition of both dental and medical degrees.
So.... basically, if you want to make sure all doors are open to you in the future such as opportunities to do fellowships and/or work overseas (UK for example) or to make sure you are eligible to apply to all subspecialty fellowships in the US, then I would suggest applying to dual degree programs.
Hope that helps.
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