Aspiration of foreign bodies is a serious complication that may occur during the course of dental treatment. A case report of a 60-year-old man with recurrent pneumonia is presented. One year after the onset of his initial symptoms, a hard substance that made a complete mold of the bronchial tree at the inferior right lobe was extracted with a rigid bronchoscopy. This green material of elastic consistency was dental impression material (polyvinylsiloxane). On careful questioning, the patient indicated that he had dental impressions taken 2 months before the onset of the symptoms. Surgery was indicated and lobectomy of the inferior right lobe was performed without incident. To avoid this complication, some preventive precautions such as identifying high-risk patients; using rubber dam; tethering any small instrument with a ligature; placing a gauze screen to protect the oropharynx in sedated patients; and using custom impression trays to minimize the amount of impression material required have been suggested. In case of a suspected aspiration, the patient must be referred to appropriate medical care.