section 38 of the illustrated extendable connector 26 comprises a pair of arms 40 and 42 having free ends 44 and 46 connected to the front portion of the lower bite block 18 portion of the lower bite block close to the mouth opening when the appliance is in position in the mouth of the patient via connectors 50 and 52 respectively the interconnection between the ends 46 and 48 of the connectors 50 and 52 will be described in more detail herebelow the anterior member or section 38 further includes rearwardly projecting parallel rod portions 54 and 56 which are received within correspond parallel guide passages 58 and 60 see fig3 in the posterior section 28 these rods 54 and 46 and their cooperating passages 58 and 60 respectively guide the relative movement of the posterior and anterior sections 28 and 38 and maintains their axial alignment and thereby the alignment of the upper and lower bite blocks 16 and 18 respectively i e prevent relative rotation of the anterior and posterior sections a bridge 62 interconnects and firmly positions the arms 40 and 42 and aligns the rods 54 and 56 with their corresponding guide passages 58 and 60 the bridge 62 also includes a nut or threaded portion which receives one end 68 of a double threaded adjustor which has its other threaded end 72 threadibly received in a threaded passage 74 through the anterior portion 28 if the threaded portion 68 is a right hand thread the portion 72 is left hand threaded a or vice versa so that rotation of the adjusting member 70.