One of the many indications for dental arch expansion in treating malocclusion is to achieve arch compatibility, especially in surgical cases with severe Bolton discrepancies or collapsed arches due to congenitally missing anterior teeth. These cases usually require expansion in both the sagittal and transverse plane to achieve normal arch compatibility. Arch compatibility can be achieved by either dentoalveolar or skeletal expansion or both. Orthodontically, dentoalveolar expansion can be achieved by means of expanded arch form, vertical loops, or an added assembly such as a quad helix or Ni-Ti expander from the palatal or lingual aspect of the arch. However, these modalities normally provide expansion along transverse plane. If any expansion along sagittal plane is required, then additional appliances such as TransForce or modifications in the appliance system (eg, a quad helix with extension on anterior teeth) are necessary. Vertical loops do overcome these drawbacks to a certain extent; however, at the expense of generating moments during preactivation, which may lead to tipping of segments adjacent to the loop and precludes its use for larger changes of arch dimension. This article describes a new loop design—the KD loop—that increases the arch perimeter by sagittal and transverse expansion without generating significant moments along vertical plane. ORTHODONTICS (CHIC) 2012;13:e140–e152.

Key words: arch compatibility, arch perimeter, loop