Microstomia, an abnormally small oral orifice, is a complication of perioral facial burns. In this case, contraction of the circumoral tissues and hypotonia of the musculature is responsible for this microstomia, which can produce aesthetic and functional impairment with eating, swallowing, communication (speech and facial expressions), compromised dental care and maintenance due to limited oral access, social interactions, and psychological well-being. Conservative management involves providing physical resistance to scar contracture, with opposing horizontal and vertical circumoral forces by means of appliances that aim to stretch the commissures and fibrotic muscles. Numerous appliances, either intraoral or extraoral, have been described to prevent or treat microstomia by delivering a static or dynamic stretch horizontally or vertically, with most designed to stretch the mouth horizontally. Finding a comfortable effective way to stretch the mouth vertically has proved to be a challenge. This article describes the fabrication of a dynamic commissural appliance, constructed using acrylic resin and expansion screws, which provide simultaneous horizontal and vertical circumoral forces. This appliance is constructed easily and inexpensively without the need for taking impressions, can be adjusted so that it is almost painlessly inserted, and is progressively activated. It is convenient for use because the patient controls the pressure that is applied by the appliance. Its use in a case is described where the appliance has improved mouth opening and consequently functional outcomes.