This fixed "M" Pendex is used to increase arch width and length. The anterior anchorage needed to accomplish this movement is gained via use of occlusal bonded rests on the pre-molars( just like the Hilgers/Pendex design). The addition of the “M Pendulum Spring” makes this design unique. The spring utilizes an inverted horizontal loop -- placed in the spring half-way between the helix and the .036 lingual sheath on the molar band. The inverted loop leaves the molar roots mesially inclined after distalization, overcoming the standard spring’s tendency to cause cross-bites. A buccal and/or distal uprighting force is placed on the molar roots by simply opening the loop. The result: true bodily movement of the molars. The midline screw can be activated (as needed) to develop the lateral arch width and/or help in correcting posterior cross-bites. Note: When an increase in arch length and width are both required, many practitioners prefer to idealize the position of the molars at the same time that they expand the arch. Others prefer to initiate molar distalization several (2-4) weeks after transverse changes begin. Either way, once these movements are accomplished, the bicuspids and cuspid will have to be brought back in the arch form one at a time using fixed mechanics.