This document discusses growth and development of the maxilla, mandible, and face. It explains that the maxilla grows downward and forward with new bone added at sutural attachments. The mandible grows upward and backward to maintain contact with the skull as it is translated downward and forward. Facial growth continues into adulthood but at a lower rate. Growth modification treatments work best during growth spurts while surgical correction is done after growth cessation. It also provides information on hand-wrist x-rays, terminal planes, growth modification treatment, biomechanics of tooth movement including tipping, torque, and uprighting, and sliding mechanics.

1. Growth and Development
Maxilla growth
As growth of surround soft tissues translate the
maxilla downward and forward, opening up space at
its superior and posterior sutural attachments, new
bone is added on both sides of the sutures.
Mandible growth
Mandible is translated downward and forward.
Mandible grows upward and backward in response to
this translation to maintain contact with the skull.
Facial growth
Facial growth continues throughout adult life; it
varies among individuals and is considerable in some
cases. It has less rate and magnitude than that
observed during childhood. (Vertical growth more
prominent than antero-posterior growth)
Growth Spurts & Growth Modification Treatment
Growth modifications by functional and orthopedic
appliances elicit better response during growth
spurts. Surgical correction involving the maxilla and
mandible can be carried out only after cessation of
the growth spurts.
Compiled by Dr Nay Aung, BDS, PhD

2. Hand-wrist x-rays
Please be careful with chronological age.
Two girls at age 12
Terminal plane
Mesio-distal relation between the distal
surfaces of the upper and lower second
deciduous molars.
Terminal plane determines the Angle’s
Molar relation in permanent dentition.
Growth modification treatment
Orthodontic treatment in growing child
includes supervision, guidance and
correction of the growing and mature
dentofacial structure (growth modification
treatment) through the stimulation and
redirection of the functional forces within
the craniofacial complex.
Compiled by Dr Nay Aung, BDS, PhD

3. Biomechanics
Optimal force
The current concept of optimal force is based on the
hypothesis that a force of a certain magnitude and
temporal characteristics (continuous vs intermittent,
constant vs declining, etc.) would be capable of
producing a maximum rate of tooth movement
without tissue damage and with maximum patient
comfort. The optimal force for tooth movement may
differ for each tooth and for each individual patient.
Tipping
A single force is applied to the crown.
The crown moves in direction of force.
Bodily movement
Periodontal Ligament (PDL) loaded uniformly from
alveolar crest to apex.
Bodily movement needs twice the force of tipping.
Force passes through the center of resistance in
bodily movement.
Torque
Torquing moves the tooth facially or lingually.
Torque is a force system produced by the torsion in
an archwire which creates a couple when interacted
with a bracket slot – interaction between wire
corners (best with rectangular wires) and slot.
Torque spins the tooth around its center of
resistance.
Compiled by Dr Nay Aung, BDS, PhD

4. Uprighting: Tipping the root mesially or distally
3 order of force
First order – in out bends made in plane of archwire to compensate for difference in tooth width
and buccolingual position
Second order – bends in vertical plane of archwire – mesiodistal movement
Third order – torque
Compiled by Dr Nay Aung, BDS, PhD

5. Biomechanics
Second order bend / angulation / tip
Torque the incisor
Upright canine and premolar
Differential tooth movement
The bodily movement of posterior teeth is pitted
against the distal tipping of anterior teeth, using
round wires and light forces – Begg’s
Uprighting and Torquing of roots after space closure
[see incisor root position]
Compiled by Dr Nay Aung, BDS, PhD

6. Sliding Mechanics (Straight Wire)
When canine is retracted with sliding mechanics, archwire exerts moments to prevent tipping.
These moments or couples produce vertical forces responsible for friction.
A. With play between wire and bracket, tooth tips without friction.
B. After archwire engages, friction begins and less tipping occurs.
C. Greater moment is produced as tooth goes through translatory phase, when friction is
highest.
Compiled by Dr Nay Aung, BDS, PhD