If the person with the bad teeth has a tooth infection or bacteria in the mouth that is causing the bad teeth then yes that bacteria and infection can easily spread from person to person and can cause the other person to get sick.
Kissing someone with a tooth infection or bad teeth can potentially give you a tooth infection or cause the bacteria to spread from that persons mouth to your mouth.
So if you do kiss someone with bad teeth then use some mouth wash to kill the bacteria in your mouth.
You can also use Apple Cider Vinegar as a mouth wash to get rid of the bacteria in your mouth as well to prevent tooth infections and tooth decay.