By Giorgio Fiorelli
(Co-author, together with Birte Melsen, of the "Biomechanics
in Orthodontics" CD-ROM)
Cantilevers are a very powerful tool that can be used in order to achieve
a great variety of dental displacements.
Advantages of the use of cantilevers are:
The orthodontist can easily estimate the force system on both units,
just measuring the length of the appliance and its force by means of a
dynamometer and thereby predict the clinical result.
A high degree of constancy of the M/F (with respect to
the bracket). This means also an homogeneous dental movement. The force
system being always directed towards the treatment goal, this is rapidly
achievable, with a minimum of round tripping and iatrogenic damage.
In this article you will find:
General principles of the use of cantilevers
Clinical guidelines (configuration and wire selection)
Some clinical examples 
Dental movement analysis software (a useful tool to design your mechanics).