A biopsy is simply, the removal of a tissue sample to determine if it is diseased. In dentistry, both teeth and tissue may be sent for biopsy. A biopsy can be used to diagnose oral cancer.
If you have lesions in your mouth for which there is no explanation, or about which you have concern, those lesions need to be examined by a dentist. Such lesions may, or may not be, cancerous but they do require medical observation.