Amin, a silicon crystal slice feels like a plate of steel. This device uses something like a blue Acrylic plastic bite plate coated in a clear elastomer like EVA or silicone rubber. Check your source and you will find that it is silicone not silicon and the letter e on the end makes the stiffness be reduced by about a factor of 1000.
You can't build any models if you don't know the mechanical properties of the materials. Reply when you have confirmed the materials used. When you have the two materials: the blue plate inside and the clear material molded over that, then you need geometry that has both materials. You can't use the geometry with just one material.