Neuropathic Pain in Lower Lip after Guided Tissue Regeneration: A Case Report

Post-traumatic trigeminal neuropathic pain is mainly caused by the extraction of third molars or the placement of dental implants. This report describes the treatment of neuropathic pain arising after guided tissue regeneration (GTR). The patient was a 55-year-old woman who had to undergo GTR due to severe periodontitis in the distal aspect of the right mandibular second molar. Postoperatively, the patient had been prescribed mecobalamin for hypesthesia and allodynia in the right lower lip. No improvement was observed in these symptoms after 4 months, however, so she was referred to our Orofacial Pain Center. Preoperative and postoperative cone-beam computed tomography revealed a cyst-like lesion (radiolucent area) close to the right mandibular second molar and canal. Although the results of quantitative sensory examination were normal, rubbing the right lower lip with a cotton swab elicited mechanical allodynia. The diagnosis was post-traumatic trigeminal neuropathic pain for which the patient was given pregabalin and Neurotropin^®. The symptoms improved within approximately 32 weeks, with the medication being terminated at 64 weeks. Although hypoesthesia due to nerve injury may suddenly go into remission, allodynia is often intractable. If symptoms show no improvement after 3 months, possible nerve injury should be investigated. Additionally, the distal root of the mandibular molar may be close to the inferior alveolar nerve, necessitating appropriate diagnostic imaging of the operative field. If the lesion or distal root is close to the inferior alveolar nerve, postoperative hypesthesia or neuropathic pain may occur, even without direct trauma.