The disclosure describes a monomer having the general formula :in whichR1 and R2 stand, independently of one another, for hydrogen, for an optionally substituted C1-C20-alkyl group or C1-C20-oxyalkyl group, optionally interrupted by 1 to 5 oxygen atoms andor sulfur atoms, or jointly for an optionally substituted C1-C20-dioxyalkylene group or C6-C20-dioxyarylene group. A receptor positioning device is provided which includes a receptor holding member and an arm including a biting surface for engaging the patient’s teeth. The channel selection logic is configured to have the wireless transceiver advertise the dedicated service on a normal operating frequency. , with selective crystallization of the -isomer.