A middle-aged woman visited a clinician with the chief complaint that her tooth hurt despite having been treated several times by an endodontist to whom she had been referred. Over the previous year, the endodontist had performed nonsurgical endodontic therapy on her maxillary right first molar and six months later performed surgical endodontic therapy (that is, an apicoectomy and a retrograde root canal filling) in an attempt to resolve her pain. However, this treatment was unsuccessful. The patient then sought a second opinion from another dentist, who advised her to have the tooth extracted and an implant placed; however, she chose not to pursue these treatment options. The patient reported that her pain intensity had not changed since she underwent the original endodontic treatment. Analgesics such as ibuprofen and acetaminophen had little or no effect on her pain. The clinical examination did not reveal any dental pathology. A periapical radiograph of the tooth and a cone-beam computed tomographic scan of the quadrant failed to identify any pathological lesion that could have contributed to her pain. What are the most likely explanations for this situation?