I have a client whose frenulum looks very deep in her tongue and her tongue may be restricted, but I am not sure if it is a big deal. I used the QTT range of motion scale, and she could open her mouth wide open 50 (cm?); when her tongue was to the spot she could open it 25; when she suctioned her tongue to the roof of her mouth she could open to 20. I know it should be at least half as open when the tongue is suctioned, which is what she got for the tongue to the spot measurement. Would you refer to a pedodontist for this?
The reading you described was borderline and usually would require deeper testing. I use the TAP, Tongue-tie Assessment Protocol by Carmen Fernandez. These are the things you should examine: Where does the frenum attach into the floor of the mouth? Well behind the lower alveolar ridge? Right behind it? On the ridge? High high on ridge? Where does the frenum attach to the tongue? Midway? More anterior than midway? Close to the tip? Is it “embedded” into the anterior area of the tongue even if it is superficially attached midway? Is it short? Is it flexible? Hard and inflexible? What problems are you seeing the patient for? Artic? Swallowing? orofacial myology? These are the questions you have to answer as you proceed to make the determination.