My cat stopped eating his dry food a few days ago...

He’s been on “Natural Choice” for at least 5 of his 10 year life without any issues, so the change came suddenly. Today, I observed him as he tried to chew his food without success – whole pieces of his food practically fell to the floor un-chewed. Panicked, I went out and bought him the same brand of food in packets and he made short work of two packs in one sitting. It’s almost obvious that he’s having issues with his teeth or jaws, but any suggestions before I take him to the vet tomorrow are greatly appreciated. I also noticed someone mentioning on this site that the brand “NUTRO, Natural Choice” caused his/her cat kidney problems, so I would welcome your feedback on this brand. I hate to give the little guy sub-standard food and would gladly spend any amount on the appropriate food.
Thank you!!