I Have An Underbite And I Am Missing Three Upper

I have an underbite and I am missing three upper teeth where the molars were, and now my bottom middle teeth are hitting the back of my gingiva behind my right from teeth and causing an ulceration. My dentist indicated that I needed a mouth guard at night and a partial put in where the missing teeth are to prevent my bottom teeth from hitting the upper gingiva. What does this sound like to you?