A 45-year-old patient applied to a dental clinic for oral cavity sanation. Anamnesis data: mild case of diabetes. Objectively: mucous membrane of cheeks is unchanged, mainly in retromolar area there are symmetrically placed whitish papulae protruding over the mucous membrane and forming a lacelike pattern. On the upper jaw there are two soldered bridge dentures, the 47 tooth has an amalgam filling, the 46 tooth has a steel crown. What is the most probable diagnosis?