There are essentially 3 alternatives for treating any skeletal malocclusion

Growth Modification
Dental Camouflage
Orthognathic Surgery

Growth modification should be opted wherever applicable because this precludes the need for both Tooth Extraction and Surgery.

Goal of growth modification is to alter the unacceptable skeletal relationships by modifying the patients remaining facial growth to favorably change the size or position of the jaws.

There are 3 types of Orthodontic appliances that can be used for modifying the growth of maxilla/mandible-

Orthopedic appliances
Functional appliances
Inter arch elastic traction

Orthopedic appliances.

2 types of forces used in orthodontics-
a) Orthodontic force- when applied brings about dental change. They are light forces ( 50- 100 gm) bringing about tooth movement.
b) Orthopedic force- when applied brings about the skeletal changes. They are heavy forces ( 300-500gm) that bring about changes in the magnitude & direction of bone growth.

The appliances that produce skeletal changes by applying orthopedic forces are known as orthopedic appliances.

Since they employ heavy forces, adequate anchorage required is gained by extra oral means using occipital, parietal, frontal cranial bones and cervical vertebrae.
The most widely used orthopedic appliances are- a) Headgear b) Protraction Face Mask (reverse pull headgear) c) Chin Cup

Orthopedic appliances generally use teeth as “handles” to transmit forces to the underlying skeletal structures. Basis of Orthopedic appliance therapy resides in the use of intermittent forces of very high magnitude. It is advisable to begin Orthopedic appliance therapy while patient is still in the mixed dentition period, to make most of the active growth occurring prepubertal growth spurt.

Treatment may have to be continued until the completion of adolescent growth, so as to prevent relapse caused by the re-expression of patients fundamental growth pattern after cessation of orthopedic therapy

Timing of force application

Optimum timing of extra oral force application is considered to be during evening & night.
This is because, an increase release of growth hormone and other growth promoting endocrine factors has been observed to occur during the evening & night rather than during the day.

Functional appliances

These appliances are used both to move the teeth and to modify the growth of the jaws . The most common objective is to correct a small lower jaw.
Occasionally a functional appliance, is the only orthodontic treatment that is required for a patient . However more commonly fixed appliances are also required and are either worn at the same time or after the functional appliance.
Functional appliances when indicated are worn when the patient is going through their pubertal growth spurt . To help take advantage of the normal facial growth which is already occurring. Functional appliances are either removable or fixed.

Removable functional appliances

These are removable appliances which use the muscles of the face and jaws to improve the way that the teeth bite together.
They are usually advised in those patients who have very prominent teeth (known as an increased overjet) and with good patient co-operation they can produce dramatic improvements in the way that the teeth bite together.
Functional appliances tend to work most effectively in growing patients so are not used in adult patients
Although they are removable, they usually need to be worn throughout the day and in bed each night in order to work effectively. They are usually only removed when you brush your teeth and when taking part in contact sports or swimming.
The treatment time with functional appliances can vary according to how prominent the front teeth are at the beginning of treatment but typically most treatment is completed in 9 to 12 months. It is possible to wear functional appliances even if there are still deciduous (baby) teeth present.
Most functional appliance treatment patients then progress onto fixed appliance orthodontic treatment to fully correct their orthodontic problem.

Activator

It is a passive tooth-borne appliance designed to move the mandible forward for correction of Class II malocclusions and open the bite.
It could also direct erupting posterior teeth meaning it could change dental relationships in all three planes of space.

Twin block

The twin block appliance is a functional appliance that is used to push the lower jaw forward in order to align it with the upper jaw. It is called a “twin block” appliance because there are two parts to the appliance - the upper part and the lower part - that work in tandem.
The two parts have the appearances of plastic blocks. When you bite, the blocks fit together in such a way as to position the lower jaw forward. Over time, the lower jaw will permanently stay in this position.
Functional regulators are removable orthodontic appliances belonging to the large group of functional orthodontic devices because of their growth-inhibiting or growth-promoting effects.
This appliance significantly changed muscles activity and whole physiological state of orofacial complex

Fixed functional appliances

Fixed functional appliances are effective in the management of Class II malocclusion. This is the only successful bite-jumping treatment for noncompliant, postpubertal patients that does not require orthognathic surgery at a later stage.
As compared to removable functional appliances, fixed functional appliances do not require patient compliance and can be used with brackets