welcome to HCM
I understand your concern. His pediatrician
is right. Young children when teething
are irritable as they have itchy gums. They tend to put their fingers into their mouths to soothe their gums. This could cause infection of the stomach in the child if it has touched something contaminated and put those fingers back it its mouth.
I suggest you listen to his pediatrician and allow the normal processes of teething to occur.