A 43-year-old patient complains of increased tooth sensitivity to thermal and chemical stimuli, gum itch. Objectively: the roots of the teeth are exposed to 1/3 of their length, the gums are dense, pale pink. Thre is a small amount of dental plaque. In the region of the 15, 14, 24, 25, 44, 34 teeth there are wedgeshaped defects within the dentin. Probing of exposed cervices and wedge-shaped defects causes pain reaction. What is the most likely diagnosis?