Cervicofacial emphysema is a well-known complication associated with the use of a high-speed air turbine. However, retropharyngeal emphysema or pneumomediastinum in the absence of severe trauma is rare. Immediate recognition of this phenomenon is essential to avoid life-threatening complications such as potential airway obstruction or venous air embolism. This article reports a case of gas diffusion into the mediastinum after dental preparatory treatment for a single-tooth crown. Pneumomediastinum should be considered whenever there are anamnestic data for retrosternal chest pain accompanied by dysphagia, dysphonia, or dyspnea caused by cervicofacial emphysema after dental treatment. Int J Prosthodont 2007;20:143–144