One more thing to save your teeth when you are receiving a men strike is not just to keep mouth shut but also make some distance between the teeth of upper and lower jaw.
So when you are receiving a strike your jaw will probably move a little but that distance will allow your teeth not to crash into each other, because there is an empty space between them.
But your lips are still closed ? that gives you elasticity and actually a possibility for your teeth not to clatter. When my teeth are clenched they clatter when I receive a men strike. That solution helps me at least.
Kendo-Guide.Com: Thank you for sharing your experience. I am learning a lot too. Thanks!