The best anti-snoring mouthpiece (also known as a mouthguard) depends on your personal preferences. Most mouthguards fall into one of two categories. Mandibular advancement devices (MADs) have upper and lower trays designed to fit around your teeth and physically move the jaw forward, which expands the breathing passage and allows more air to pass through. MADs are often “boil-and-bite” mouthguards made of thermoplastic. Owners boil them in water, then bite into the thermoplastic to create a customized impression. After the material cools and hardens, the MAD will be ready to use. Other MADs are specifically created using a customer's dental impressions, and some can later be adjusted for advancement level. The customized nature of MADs makes them very effective. They also allow sleepers to breathe through their mouths, and a lack of protruding parts means these mouthguards are compatible with any sleep position. However, MADs are associated with more jaw pain and stiffness, drooling, and other negative side effects. Many people – including those with braces or dentures – won't be able to use them, and a prescription is normally required. The other type of anti-snoring mouthguard is the tongue-retaining device (TRD), which are designed with flanges that rest against your lips and a small compartment for the tongue. The compartment essentially suctions the tongue in place, preventing it from falling back into the throat – a common source of heavy snoring. TRDs are lighter and easier to wear than MADs, and not associated with as many adverse effects. They also won't interfere with dentures or braces, and most don't require a prescription. However, TRDs usually can't be customized, and instead have a “one-size-fits-all” design that will serve some sleepers better than others. They can also restrict breathing by forming a seal around the mouth.