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What is The anchorage utilized by quad helix is: and explain in detail?
Anchorage in which the resistance of one or more dental units is utilized to move one or more opposing dental units is reciprocal anchorage. 
Reciprocal anchorage is also employed in the correction of Class II malocclusion where intermaxillary elastics are used from the maxillary to the mandibular arch, the 
Another simple form of reciprocal anchorage is the correction of posterior crossbite by the use of palatal expansion screw or Quad helix. 

​Textbook of ORTHODONTICS Sridhar Premkumar