The accidental displacement of foreign bodies into the maxillary sinus is not an unusual complication in dental clinical practice. However, dental materials, and, in particular, dental impression materials, introduced into the sinus several weeks to months after a maxillary tooth extraction or dentoalveolar surgery through either a small, long-standing oroantral fistula or an insufficiently healed extraction wound is uncommon. In the case reported, 3 months after a maxillary molar extraction, the material used for maxillary impression was pushed into the antrum through a small, almost invisible, oroantral fistula that was unseen by the specialists the patient had been visiting, worsening the patient's existing sinusitis. Keywords: foreign body, impression material, maxillary sinus