Hi.. Can understand your concern.. As per your complain if the night guard catches below your tongue and it causes pain and sensitivity of teeth the reason behind that can be that the extension of the night guard at the side of tongue must be overextended leading to hitting and injuring the soft tissues in that area and the sensitivity can be due to rubbing of the night guard along the gums causing the inflammation of the gums and thus sensitivity is elicited in gums as well as teeth. Also there can be some pointed areas on the night guard which can be traumatizing the soft tissues causing soreness sensitivity and pain.. You need not to worry about it as it is a new prosthesis and will take some time to adjust in mouth and in case of overextension and sharp pints you can get back to your dentist and get the trimming of the night guard done so that you get ease in wearing it.. Over the sore areas you can apply Mucopain gel or oragel for relief.. You can apply desensitizing paste like sensoform or thermoseal or anyother available in your location to get relieved of sensitivity in teeth.. Hope this information helps.. If you find the answer helpful kindly write a positive review and click on found this answer helpful as a token of appreciation.. Thanks and regards.. Dr.Honey Nandwani Arora..