When applying extra
oral force to a functional appliance it is important to remember not to
use any form of cervical traction or pull that is directed horizontally.
Explain why and also indicate the most desirable direction of force to be used with a functional appliance
Muir & Reed (1979) states that most multiband appliance systems
make extensive use of extra oral forces. By comparison such forces are
much less used with removable appliances. There is no good clinical
reason why this should be so. Extra oral forces can readily be adapted
for use in removable appliance orthodontics and can extend considerably
the range of treatment which can be undertaken.
It is possible
that heavy extra oral force applied for a substantial proportion of each
day to a patient who is growing rapidly may have an orthopaedic effect.
In addition to distal movement of teeth through bone there could be a
restraint on maxillary growth. Headgear can be applied either directly
to a removable appliance or indirectly to molar bands over which the
appliance is clipped. Therefore, it is necessary to avoid patterns of
headgear that delivers cervical traction (neck strap). It is recommended
to use full headgear when applying force directly to a removable
appliance.
Ref: Muir, J.D., Reed, R.T. 1979. Tooth Movement with Removable Appliances. USA: Pitman Medical. Pg 82.
When the extra oral force is applied to a functional appliance any form of cervical traction or pull directed horizontally is inappropriate, as this is liable to dislodge the appliance.
ReplyDeleteA full headgear or high pull headgear is essential.
It is usually considered to be desirable to direct the force to a point just a above the apices of the molars, this will produce the maximum amount of inhibition.
If extra oral force is being used to enhance retention of the appliance, especially at night, then an upward component of force is clearly indicated.