Purpose: To describe the management of a patient with an initially unnoticed dislocated dental bur in the maxillary sinus that became symptomatic during a magnetic resonance imaging (MRI) scan. Materials and methods: A MRI scan provoked strong midfacial pain in a 31-year-old male patient, who exhibited ambiguous neurologic impairment consistent with multiple sclerosis. Conventional radiography revealed an opaque foreign body in close proximity to the orbital floor that most likely caused the painful symptoms during the MRI. Results: After additional X-ray computed tomography (X-ray CT) scans were performed, a metal dental bur was removed by a combined transconjunctival and transnasal approach under perioperative antibiotic treatment. Conclusion: The disappearance of instruments during surgical procedures requires diligent investigation and immediate retrieval. Schlagwörter: dental bur, foreign body, maxillary sinus