I have a painless lump at centre of roof of mouth-- what it could be?

Palatal Tori: Palatal tori is a slow growing hard lump in the roof of the mouth that is usually painless. These growths run in the family. It is not cancerous but can become sore from eating hard or sharp foods such as chips. It needs to be removed if you want to wear an upper denture. As with any changes in your mouth it is a good idea to have a dentist examine the lump to rule out cancer or tumor.

Bony overgrowth: If this lump is hard and has been very slowly growing, it most likely is a palatal tori. This is an overgrowth of bone and is quite common. It usually does not require any treatment but can become irritated or scratched at times. However, if the lump has developed very rapidly or is soft and spongy, you should see your dentist asap for evaluation to rule out an abscess, cyst, or other pathology.