I took Trouble for an old cat check up as they were doing an old cat MOT for a tenner at my vets, he had been crunching through his biscuits with gusto etc. but never let me check his mouth, when the vet opened his mouth and showed me his teeth I was horrified, all apart from three incisors were rotten, brown or missing with red inflamed gums,over £600 later he had no teeth apart from three incisors and had his 'Elvis' snarl, but still scarfed down his dry as well as his wet food. David the vet said that if it was him or me we would be climbing the walls, screaming. Cats are small predators and will not show weakness in case they become prey themselves according to David.
I would do as you said and get him checked out. Good luck.