That depends totally on your strength in your jaw. If you start with JAWLINER Beginner and have bitten through it after a while, the time is ripe to change to JAWLINER Advanced. Normally you should be able to train with it for 1-3 months.
If you already know that you have very sharp tough or very pronounced jaw muscles, we would rather recommend JAWLINER Fitness Chewing Gum. No matter how sharp your teeth are and how strong you are, you can't destroy the chewing gum.