Subcutaneous facial emphysema following dental treatment is a rare complication caused due to the invasion of high-pressure airgenerated from high-speed handpieces and air-water syringes. In serious cases, it can disseminate to the neck, mediastinum, and thorax, leading to cervical emphysema, pneumomediastinum after class V restoration.

Occurrences of subcutaneous facial emphysema after dental treatment have been reported following third molar extraction, endodontic treatment, class V restoration, crown preparation, and other treatments. The symptoms in these cases vary from mostly mild to severe swelling and crepitus on palpation of the affected area. Difficulty in swallowing and breathing has also been seen when the deep neck space was involved.

Iatrogenic subcutaneous cervicofacial emphysema with pneumomediastinum after class V restoration. The compressed air from the high-speed handpiece led the emphysema to spread from the right mandible to the facial, cervical, and anterior chest walls and the superior mediastinum.

Link:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5342974/#:~:text=Subcutaneous%20facial%20emphysema%20after%20dental,emphysema%2C%20pneumomediastinum%2C%20and%20pneumothorax.