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the side protections guide the drill on the whole length of the arch protecting the tongue and the smouth parts. - 309 to 311 & 409 to 411 : the protection at the bottom of the drill protects the smouth part in the back of the mouth.
309 bis 311 & 409 bis 411: die schutzkappe wurde speziell entwickelt, um die hinteren backenzähne zu erreichen, ohne die schleimhäute zu verletzen.