A mandibi splint or mandibi advancement splint is a prescription custom-made medical device worn in the mouth used to treat sleep-related breathing disorders including: obstructive sleep apnea (OSA), snoring, and TMJ disorders. These devices are also known as mandibular advancement devices, sleep apnea oral appliances, oral airway dilators, and sleep apnea mouth guards. The American Academy of Sleep Medicine (AASM) and the American Academy of Dental Sleep Medicine (AADSM) recommend that sleep physicians should prescribe sleep apnea oral appliances for the adult patients who need treatment for their primary snoring (without obstructive sleep apnea) rather than no treatment and for the patients who have obstructive sleep apnea but are intolerant to the CPAP therapy, or for those who prefer alternate therapy. Vanderveken et al (2008) researched prescription custom-made splints head-to-head with thermoplastic over-the-counter splints: "Our results suggest that the thermoplastic device cannot be recommended as a therapeutic option nor can it be used as a screening tool to find good candidates for mandibular advancement therapy." Usage The splint treats snoring and sleep apnea by moving the lower jaw forward slightly, which tightens the soft tissue and muscles of the upper airway to prevent obstruction of the airway during sleep. The tightening created by the device also prevents the tissues of the upper airway from vibrating as air passes over them—the most common cause of snoring. Mandibular advancement splints are widely used in the United States and are beginning to be used in the UK. According to the current American Academy of Sleep Medicine treatment guidelines, oral appliances should be considered for patients with snoring or minor to moderate sleep apnea, or as an alternative to CPAP in non compliant patients with severe obstructive sleep apnea. Where appropriate, they are considered a good therapy choice as they are non-invasive, easily reversible, quiet, and generally well accepted by the patient. The focus of improvement in appliance design is in reducing bulk, permitting free jaw movement (permitting yawning, speaking, and drinking), and allowing the user to breathe through the mouth (early "welded gum shield"-type devices prevented oral breathing). Evidence is accumulating to support the use of oral devices in the treatment of OSA, and studies demonstrating their efficacy have been underpinned by increasing recognition of the importance of upper airway anatomy in the pathophysiology of OSA. Oral devices have been shown to have beneficial effects relating to several areas. These include the polysomnographic