A 34-year-old man reports that cold drinks cause pain in the lower left first molar that lingers for about 40 seconds, and the tooth has woken him twice this week. The tooth is tender to percussion and to biting. A periapical radiograph shows a deep distal composite close to the pulp and a widened periodontal ligament space at the mesial root apex. Which pulpal and periapical diagnosis is most appropriate?