An 11 year old male patient complains that his upper front teeth appear to be sticking out. Intra-oral examination reveals a Class II incisor and molar relation. Fixed orthodontic therapy along with a high pull headgear was initiated. What type of anchorage does this appliance provide?
Anchorage can be reinforced by having the patient wear an extraoral appliance (headgear) placing backward force against the upper arch. The reaction force from the headgear is dissipated against the bones of the cranial vault, thus adding the resistance of these structures to the anchorage unit. 
Cortical anchorage: Rickets introduced the concept of cortical anchorage, which uses the denser alveolar cortical bone for anchorage. 
Simple anchorage: Resistance of the anchorage unit to tipping. 
Compound anchorage: Resistance provided by more than one tooth with greater support to move teeth with less support.
Contemporary orthodontics, William Proffit, 4th edition page 346, 380
Cortical
Simple
Compound
Reinforced