It can be a hypoT symptom, but other things can cause it as well. Something as simple as biting on it during sleep, for example.
Severe hypoT, known as myxedema, will cause the tongue to markedly enlarge; therefore there isn't enough room for it in the mouth, causing the teeth to leave imprints.
Yes. I had this for awhile. I mentioned it to my doctor that my tounge felt that it was too big for my mouth. It would rub against my teeth and leave indentations on the sides! It hurt too, by the way. He brushed it off saying he did not know what would cause that and thought it was crazy. I know that I had that symptom as it can't be ignored. Eventually, it went away but guess what--it comes back when my labs get bad as my thyroid continues to fail. I don't even mention it to my family practice Dr. anymore but I will mention it to my endo the next time I get it-which I hope that I don't anymore!