There are many types of orthodontic screws, and several manufacturers.
In a variety of appliances including functional and fixed, screws play an important role.
The Midline Screw
For arch development as can be seen in the pendulum appliance.
This is the most used screw in one size or another in orthodontics for arch development.
Rapid Maxilliary Expansion Screw
This appliance is intended to split the median suture
The arms of the screw are soldered to either bands or cast silver splints, which is then cemented in situ.
To activate the screw it is turned by the patient (or often the parent) as often as possible so long as the patient is pain free.