A12-year-old child has a carious cavity on the surface of the 12th tooth. The cavity is localised in the mantle dentin; its floor and walls are covered with pale softened dentin. Probing the enamel-dentin border is painful. Thermal stimuli cause short-term painful reaction. Vertical percussion is painless, horisontal percussion is slightly painful. Gingival papilla between the 12th and 13th teeth is swollen, hyperemic, bleeds when touched. What is the most probable diagnosis?