A 22-year-old patient complains about short-lasting spasmodic pain in the 26 tooth with long periods of pain absence. Objectively: the 26 tooth has a carious cavity in the masticatory surface, dental cavity is not opened. Probing causes pain in the pulp horn projection. Thermal stimuli cause sharp pain, percussion is painless. Regional lymph nodes are not palpable. What is the most likely diagnosis?