I have never taken the USMLE Step 1, but from what I hear from my medical friends and many OMFS residents, the NBDE Part 1 is nothing compared to the USMLE Step 1 exam, the USMLE Step 1 being the more challenging one. I guess we can compare them to our DAT to the MCAT, DAT is a joke when compared to the MCAT.
Now, I personally thought the NBDE Part 1 is the most difficult standardized exam I've encountered thus far in my academic journey. I've taken the ACT, SAT, DAT, and the NBDE Part 1. I anticipate the USMLE will be much more difficult in the sense of materials tested and the details involved.
Even if you passed NBDE Part 1 with 90s, often dental graduates can't even pass the USMLE Step 1 the first try. Keep in mind, only dental related people I know that attempt the USMLE Step 1 are OMFS residents in MD-integrated or MD-Option residencies.
Long story short, meds got it tougher, that's for sure.
MCAT is harder than DAT
USMLE is harder than NBDE
BY FAR!!!!
All the MD OMFS residents on here should be able to share with us their view and experiences with the two exams.