Cheryl,
I use a digital caliper to measure the width from the inside surface of the left first molar tooth to the inside surface of the right first molar. Otherwise use a ruler and do your best to get the most accurate reading. The ideal width should be 38mm.

Thank you Catherine for your suggestion re Dr Brad Neville, i've just started reading his excellent articles.
It's interesting about the Bell's Palsy. Nobody could know for sure, but it seems logical to think that the linea alba on the same side of the paralysis, was due to chronic irritation on that side, ie, cheek biting. In the absence of pain sensation due to biting, there is no protective mechanism for withdrawal. Re scalloped tongue on the other side, it means that the upper arch is too narrow to accommodate the tongue, ie it's 'squashed' against the teeth.

Jack