for your problem, all the medical and dental examinations including laboratory tests such as blood test
should be done. there are many lesions which can be present in oral cavity. if the doctor feels to get the biopsy
done, then let him/her go ahead. many such focal pigmentation could be present like vascular malformations, post inflammatory pigmentation
, pigmented nevus
, etc. so its better to rule out by various tests.
thank you for your query