A 6-year-old child complains of a pain and edema in the upper right jaw, body temperature up to 37,9°C, and deterioration of general well-being. Symptom onset was 3 days ago. Objectively, the face is asymmetrical due to soft tissue edema of buccal and infraorbital regions on the right. The crown of 54 is destroyed by 1/2, percussion is painful; the tooth previously had been treated for complicated caries. On the palatine side of the affected tooth area there is a painful infiltration with fluctuation in its center; the tissues over the infiltration are hyperemic. Make the provisional diagnosis: