Forces applied to the maxillary molars are not limited to movement of the maxillary teeth alone, but to the whole maxillofacial complex. Suffice to say that for such a result to be achieved, the headgear has to be used consistently and for long periods of time. Orthopedic effects can be achieved if treatment is delivered at the appropriate age. Maxillary orthopedic treatment, then, should be initiated early. The best response is obtained during maximum growth velocity as judged by hand-wrist radiographs. This is the period 4 to 7 as described by Fishman using skeletal maturation indicators. 

kind regard

Ulrich Kritzler

Literature:

Droschl H: The effect of heavy orthopedic forces on the maxilla in the growing Saimiri sciureus (squirrel monkey). Am J Orthod 63:449-461, 1973

Kirjavainen M, Kirjavainen T, Hurmerinta K, HaavikkoK: Orthopedic cervical headgear with an expanded inner bow in class II correction. Angle Orthod 70:317-325, 2000

Kirjavainen M, Kirjavainen T: Maxillary expansion in Class II correction with orthopedic cervical headgear. A posteroanterior cephalometric study. Angle Orthod 73: 281-285, 2003

Kirjavainen M, Kirjavainen T, Haavikko K: Changes in dental arch dimensions by use of an orthopedic cervical headgear in Class II correction. Am J Orthod Dentofa- cial Orthop 111:59-66, 1997

Dr. Ulrich thank you for your answer. In your opinion, what is the best indicator for detecting skeletal response to headgear.

You will find important information concerning your question in the following paper:

http://ejo.oxfordjournals.org/content/27/5/429

Headgear defenitely has an impact on SNA, but it seems that this effect vanishes years later.

http://ejo.oxfordjournals.org/content/27/5/429

Dr. Rafael thank you for your answer. I just wish more RCTs were carried out on older children (13-15 years of age) but ethics always will prevent that.

Although in general no permanent effect remains of facial orthopedic therapy that does not mean that such a treatment does not have advantages. Essential in that respect are the temporary improvement of the sagittal maxillomandibular relationship and the increase in lower facial height through which it becomes easier to reach a neutroocclusion in a biological way. When Class II/1 malocclusions are concluded with a rigid intercuspation, the neutroocclusion will be maintained.

You will find more details here.

Thank you for your answer Dr. Ulrich. Yes, and that is why I believe so many people still work with it, despite limited skeletal effect, but it is as you said, neutrocclusion that motivates.