A 4-year-old child has developed acute spontaneous pain in the tooth on the lower right jaw, which aggravates on biting. Objectively: in the 85 tooth there is a deep carious cavity non-communicating with the dental cavity. Probing is sharply painful at all points of the cavity ?oor. Painful reaction to cold water stimulus and percussion is observed; mucosa surrounding the 85 is hyperemic. Submandibular lymphadenitis is detected. Make the provisional diagnosis: