Faq FAQ Most frequent questions and answers How long do i have to leave them for? You can wear them at night to prevent tooth grinding. This is 8 to 10 hours. How long does the mouthguard last? Mouth guard can be last one mouth Can this be helpful for clenching teeth? Yes, it is perfect for clenching teeth when you apply with the right size guard Can this be Used on children Yes! This product have a large and small mouth size.