A mouth guard is a device that is worn over your teeth to protect them during sports or other activities where teeth may become injured. It may also be recommended to protect teeth from persistent grinding or clenching, so teeth don't become unevenly worn or loose. Patients with the temporomandibular joint (TMJ) disorder may also be prescribed guards to help cushion the jaw joints, especially when sleeping. Customized mouth guards are fitted specifically to your mouth so they provide the most beneficial protection for your teeth and jaw.