1993 Head Drop Study Test:
This ground-breaking, first-of-its-king Sensor laden Head-Form Study was the first that considered/hypothesized that energy can enter the skull from the Salient(free-floating/movable).  A confirming Study was then run in 2005 which returned very similar results.

Brain-Pad – TMJ Jaw Joint Protector  vs.
Custom Dental Appliance  vs.
over-the-counter-’boil and bite’ appliances.
NOCSAE Head DropTestiNOCSAE Head Drop Testing JAW IMPACTS and MOUTH GUARD TYPES Summary Printing 1993 .PDF
[ Partially Funded by NFL Charities ]