How long has he been without teeth? What has he been eating up to now? If he has been eating dry food, you could try to add water (warm) to it. He may just not like the taste of the wet food if he has never eaten it before. Also wet food should have room temperature to allow the cat to sense the flavour.
Has he been examined by a veterinarian recently? How is his demeanor? Is he depressed? Is he drinking ? Just wondering if this is a fussy cat problem or an illness brewing. With cats, when they are sick usually the first thing you notice is lack of appetite.