A 65-year-old patient complains of pain in the area of mucous membrane of hard palate on the left that is getting worse during eating with use of a complete removable denture. He has been suffering from this for 1,5 month. Objectively: leftsided hyperemia and edema of mucous membrane of hard palate; at the border of distal denture edge there is an ulcer with dense walls and fundus, surrounding tissues are infiltrated. The ulcer floor is tuberous, covered with fibrinous deposit; ulcer palpation is painful. What examination method is to be applied in the first place?