It seems that your dentist
is right and there is nothing to worry. Local oral infections can lead to such lesions and the lesions take some time to disappear. I am assuming that it is neither an ulcer nor a patch (white or red) in which case it is dangerous and maybe cancer or precancerous. But the lesion of your description just needs observation for two weeks. Also start yourself on a multivitamin
. If the lesion doesnt subside in 2 weeks or changes character, then consult a cancer surgeon.