Cervicofacial subcutaneous emphysema is defined as the abnormal introduction of air in the subcutaneous tissues of the head and neck. It is mainly caused by trauma, head and neck surgery, general anesthesia, and coughing or habitual performance of Valsalva maneuver. The occurrence of subcutaneous emphysema after dental treatment is rare, and diffusion of gas into the mediastinum is much rarer, especially when the procedure is a nonsurgical treatment. The most common dental cause of pneumomediastinum is the introduction of air via the air turbine handpiece during surgical extraction of an impacted tooth. Only 6 cases of pneumomediastinum after endodontic treatment have been reported between 1960 and 2008. Pneumothorax is defined clinically as an "accumulation of air or gas between the parietal and visceral pleurae," and although it is often not a medical emergency, it can result in respiratory distress, tension pneumothorax, shock, circulatory collapse, and even death. Although there are many possible causes of dyspnea during a dental procedure, 1 rare complication is pneumothorax. Although specific closed turbine systems are available for oral surgical procedures, these drills may be used in exodontia to section teeth and facilitate tooth extraction. We report a case of cervical subcutaneous emphysema and pneumomediastinum occurring after an endodontic treatment of right first molar using an air-tribune drill. We present here in a case of massive pneumomediastinum and cervicofacial subcutaneous emphysema that occurred after opening the access cavity for endodontic treatment. We describe its etiologies and guidelines for its prevention during nonsurgical endodontic treatment.