A 21 year old healthy male patient reported with a prognathic mandible, intraorally he has anterior crossbite and Class III molar relationship, cephalometrically has an SNA of 78 degrees, SNB of 89 degrees.
The presurgical orthodontic procedures involves:
In cases of severe jaw imbalances, the teeth are inclined in such a way as to partially offset the discrepancies. For eg., the lower anteriors may be upright or retroclined in a case of mandibular prognathism and proclined in mandibular retrognathism. 
This is nature’s mechanism to compensate for the jaw imbalance by proclining or retroclining the teeth i.e., as a compensation for the jaw discrepancy.
Presurgical orthodontics is aimed at removing this natural compensation i.e., decompensation. In mandibular prognathism, for eg., the retroclined incisors should be brought into the ideal axial inclination by proclining them. In mandibular retrognathism, the proclined teeth are brought back. Often, teeth are extracted for decompensation.
Decompensation makes the maxillomandibular dental relation temporarily worse. Hence, it is sometimes called “Reverse Orthodontics”.
Decompensation
Compensation
Settling elastics
Immobilization