I wonder if this is spasms due to positioning during the dental visit??
Severe spasms can make you very uncomfortable.
I don't know that a MRI is needed yet.

Perhaps just an evaluation by a expert chiro or even a expert phys therapist although I think the chiro would be cheaper and quicker than many sessions of PT.

You've probably came across information about c1 & c2 adjustments, or upper cervical adjustments... that might be something you need since the fall on or face a yr ago.

I suggest finding a very qualified chiro or get a free evaluation as some offer those ... then see which one you feel is best before making a choice.

some chiro/c1/c2 info links for you -
Chiropractic care info- a good one can help with many symptoms:
http://www.upcspine.com/self.htm
http://www.uppercervical.org/subpag...b/about_faq.php
http://www.spineuniverse.com/index.html
http://www.coloradochiropractic.org/.../glossary.html