hello there , welcome to HCM forum,
according to the dental history provide by you it is very difficult to make a diagnosis, until i check it clinically, you have not mentioned your age, or about your personal habits, because most of the white lesions or patches that appear in the oral cavity have some or the other cause, it may be linked to
smoking, alcohol intake, dietary deficiencies, hereditary cause,infections,etc.
i would like to inform you that start using antibacterial(
betadine) mouth wash(twice/day),
it is not necessary that it(
white patch) would spread, but in order to avoid it from coming back again, kindly visit an oral pathologist, who will be able to provide you with the diagnosis as well as the treatment.
i hope i answered your query,
i wish you good health.