The dent that you mention must be a linear skull fracture
. Simple linear skull fractures usually heal on their own. Skull fractures are usually managed conservatively in neurologically intact patients. Only certain types of depressed skull fractures and fractures in persons with neurological deficit , with underlying soft tissue injury
are the ones that require surgical intervention.
As in your case the MRI
was done and showed a normal report so the probability of underlying head injury
is ruled out. So you do not have to worry.
In case you have your doubts regarding the dent then just get a X-Ray skull ( AP and lateral view ) done.