late effects with teeth

We have been told that children who undergo chemo often do not form adequate enamel on their teeth.  This may be the case with my son, who is a survivor of 11 years.  He is feeling quite self conscious of the yellow color of his teeth.  I notice he tries to smile without showing his teeth.  We feel concerned about using a bleaching kit and introducing toxins into the cancer area.  Has anyone tried anything or heard of anything more natural, less toxic, that may help whiten teeth.  I know there can be many worse side effects.  But it's starting to effect his confidence level, so I'd like to find something that would help him feel better about his smile.  Thanks for any responses.