Sometimes if while eating something sharp gets lodged in gums or palate
hurting/injuring that area it causes blanching of the tissues resulting in a white bump. The area you have mentioned already has a small bump anatomicaly called incisive papilla from where nerves and vessels pass.so an injury
may have drawn your attention to it. this condition is reversible and is not dangerous at all. As your dentist
has ruled out cancer, abcess and a blocked duct then you should just wait and watch the area for any changes. If you do smoke then please stop till you are sure that the area has reverted to normal. If any changes occur i strongly recommend you to re visit your dentist.