Answer:
Why would that make him feel bad, I would think that's a fact of life. Good hygeine! Tell him that you want him to keep his teeth good because good teeth mean less health problems and that your worried about him. Men love it when you worry about them and fuss over him. Tell him that if he keeps good grooming habits that you will do something for him in exchange. If you care about him do it, its not about hurting someone's feelings.