Temporarily. Mouthguards worn during sleep also known as Nightguards are often fitted differently from sports mouthguards as they incorporate a definite imprint of the teeth on the opposite jaw. Nightguards may have different composition of materials with several layers and some have a very hard exterior. Generally sports mouthguards are soft on the outside. As a temporary nightguard however, the mouthguard may be used to determine if relief can be obtained for clenching or TMJ problem.