oral surgeons are not going to be eager to biopsy something that they cannot differentiate in some manner from the surrounding tissue, and the brush collection system is tiny and only collects from very small spots. If you have a spot that is discolored - light or dark, is hard (indurated), is raised above the surrounding tissue (exofitic), is ulcerated, or is textured differently than the surrounding tissues.... AND has persisted for more than 14 days, biopsy is a likely path to take, to get a black and white answer.