Been scratching my tounge on a sharp tooth for a few days, couldn't help it. now a white spot has formed where it has been scraping against the tooth.

Aphthous ulcer: That is a canker sore. Try putting some dental wax on the sharp tooth for a few days to let the tongue heal. See your dentist as well to have the tooth smoothed down.

Hyperkeratosis: Like a callous, thickened skin as a response to the irritation. Not problematic now, but can see some precancerous changes in the thickened tissue if the irritant is not removed.

Irritation: See your dentist to smooth or repair the sharp tooth. Try to stop the habit in the meantime and this should resolve after the tooth is treated. Your dentist can tell you if something else is going on which also needs attention. Call and make an appointment. A sharp tooth might reflect some other problem such as a bite problem or underlying decay.

Traumatic ulcer: The two most common causes of tongue ulceration is local trauma (e.g. rubbing from a sharp edge of the broken tooth on a filling). Tongue discomfort caused by a trauma is usually treated by eliminating the cause.