Elasticity: It is the property of a material to return to its original form. ELASTIC MATERIAL: Presents usually 3 properties: 1 - a distorsion not going beyond its limit of elasticity 2 - physically homogeneous 3 - isotrop, giving the same force in any direction LIMIT OF ELASTICITY: It is the amount of forced distorsion without deterioration and loss of elasticity . CLAPEYRON’S THEOREM OF RECIPROCITY When an elastic force is applied to two identical ELASTOMERS General term encompassing materials returning to their original dimensions immediately after substantial distorsion. Under this term are: - natural rubber or latex - synthetic rubber polymers Presentation of Orthodontic Elastics Rubber elastics have been offered in: - different sizes - different shape forces giving a precise applied force. They are presented in a plastic bag decorated with various symbols to help patients recognize which elastic was received for the last prescription.

1. Orthodontic Elastics
ACHIEVED BY: Dr.Maen Dawodi

2. Definition
• Elasticity:
• It is the property of a material to return to its original form.
• ELASTIC MATERIAL:
Presents usually 3 properties:
1 - a distorsion not going beyond its
limit of elasticity
2 - physically homogeneous
3 - isotrop, giving the same force in any
direction

3. • LIMIT OF ELASTICITY:
• It is the amount of forced distorsion without deterioration and loss of
elasticity .
• CLAPEYRON’S THEOREM OF RECIPROCITY
• When an elastic force is applied to two identical

4. • ELASTOMERS
• General term encompassing materials returning to their original dimensions
immediately after substantial distorsion. Under this term are:
- natural rubber or latex
- synthetic rubber polymers

5. Presentation of Orthodontic
Elastics

6. • Rubber elastics have been offered in:
- different sizes
- different shape forces giving a precise applied force.
• They are presented in a plastic bag decorated with various symbols to
help patients recognize which elastic was received for the last
prescription.

7. • All elastics are sold in packages of 100 with a rapid zip and forces are
indicated with:
Colour
coding
countries fruit
first name animals toys
plants sports objects

8. • Use:
• Intraoral • Use:
– Extraoral

9. Usually,the prescribed force is obtained
when the elastic is stretched out three
times its diameter.

10. ***CORREX or DONTRIX gauges
- use to check the elastic forces

11. ADVANTAGE OF ELASTICS:
• placed and removed by the
patient
• discarded after worn out
• no activation required by the
orthodontist
• effect increased by mandibular
movements ( mastication,
phonation )
• can be changed upon
prescription one, two, three
times a day or even worn at
night.
DISADVANTAGE OF ELASTICS:
• deterioration and loss of
elasticity
• moisture absorption makes
the elastic swollen and
odoriferous.
• non odor free when worn
after 24 hours.
• unpredictably variable forces
exerted if the prescription is
not well explained and
controlled.
• the exerted force is not
constant and depends on
patient compliance
• elastics can be placed
incorrectly

12. After 2 hours in the mouth, the module elastic force
decreases about 30%, and after 3 hours about 40%.

13. Classification of Forces

14. • Force application plays a strategic influence on orthodontic
movement by means of wires and elastic rubber bands
• An optimum force should not exceed the capillary blood pressure (
20 to 25 gm/cm2 ).
• Z. DAVIDOVITCH had proposed intermittent forces as more suitable
because their duration would not be sufficient to produce anoxic
destruction of the ligament.

16. BASIS FOR PRESCRIBED PRESSURES
• Brian LEE theory
• 200g/sq. cm
• R.M. RICKETTS
• 150g/ sq. cm

17. Root rating scale in transversal movements:

18. • On average, a force of:
➩ 635 g. in maxilla
➩ 550 g. in mandible
to move all of the teeth.

20. Class 1 Elastics
The Class I elastic can be a chain, a rubber band, a
ring or a thread placed on a single arch and having a
vertical or a horizontal force movement.
The Class I elastic has a reciprocical biomechanic
action in a straight line

21. Biomechanics
• Whatever it is a chain, a ring or a thread, the Class I elastic has
reciprocal action in straight line.
• The force exerted depends on clinical objectives, considering the
STABLE force or anchorage used and the MOBILE force to move the
teeth, we must always have:
STABLE force > MOBILE force

22. Be careful!!
Elastics not well hang on or worn by the patient can complicate
treatment objectives.

23. Class I elastics effects with continuous
archwires
The effects may include:
• space closure
• distal movement ( retraction )
• mesial movement ( advancement )
• tipping
• extrusion
• intrusion

24. Class I Elastics Indications
➨ to rotate of a single tooth or reciprocal teeth
➨ to achieve space closure
➨ to use force couple maintaining the centroïd axis of a tooth during
rotation control
➨ to move a tooth which is difficult to tie in the archwire
➨ to intrude a tooth or a group of teeth ( cuspid intrusion )
➨ to extrude a tooth which is impacted or in ectopic position.

25. Clinical applications of Class I Elastics
Clinical applications are numerous:
1 - SPACE CLOSING
2 - DENTAL MOVEMENT
3 - EXTRUSION
4 - INTRUSION
5 - TIPPING CORRECTION
6 - ROTATION
7 - STRENGTHENING FORCE
• the loosening anchorage
• the maximum anchorage
• the midline shift correction.

26. Elastomeric chains
•Polyurethane chain elastics
- long filament chain
- short filament chain
- closed loop chain.
•Mainly used for intra arch tooth movement and for
spaces closing,
**The longer the chain’s filament, the lower the
initial force

27. O Shape Occlusal Elastic
• To correct dental transverse malposition, which is most of the
time unitarian.
• This elastic is placed occlusally on the maxillary or mandibular
arch in order to correct:
• a buccal tooth position which is in buccal cross bite degree 1 or 2
• an arch asymmetry
• spaces or diastemas
• a lack of canine contact in maxillary arch

28. Biomechanics
• The “ O ” shape elastic moves one tooth or a limited group
of teeth transversaly.
• Usually, it can be worn on a simple way or in criss cross
according the clinical objectives
• The “ O ” shape occlusal elastic:
➨ must be worn during night only
➨ must be worn during a short time because of its
efficiency
➨ must be controlled every week.

29. Class II Elastics Forces
Intermaxillary elastics placed on the maxilla anteriorly, and on the
mandible posteriorly.
They are primarily used to cause Antero-posterior tooth changes that aid
in obtaining CL I cuspid relationship from a CL II relationship

30. Disposition
➨ the mandibular arch
posteriorly buccally,
lingually or simultaneously
from:
• different teeth M2, M1, Pm2, Pm1
• distal to a molar tube
• a hook
• a loop
• a JARABAK or KAYABASHI ligature tie
• a buccal hook coming from a lingual
arch
• a bite plate with a distal hook.
➨ the maxillary arch anteriorly
from:
 a sectional archwire
 a Class II utility arch
 a continuous archwire
with anterior loop
 a sliding hook
 a JARABAK or KAYABASHI
ligature tie
 a bracket hook
 a Jig
 a Class II headgear
 a reciprocal archwire 0.45
with hooks
 a reciprocal Mini Chin
Cup.

31. Class II elastics indications
Class II elastics may be used for main or secondary objectives
according to the individual clinical case such as:
• skeletal and/or dental Class II malocclusions
• anchorage reinforcement
• backward movement of the upper incisors
• mandibular arch advancement
• bite opening
• buccal tipping of retruded lower incisors
• midline deviation correction
• dual bite correction.

32. In CL II elastics we can observe some
following important features:
• 1. Light but direct force applied to both mandible and maxilla to
stimulate maxillary retardation and mandibular growth.
**Negative side effects such as loss of maxillary anterior torque can take place
if elastic are used early in treatment.
• 2. Mandibular incisor advancement, especially with arch wire of low
stiffness and lingual tipping of maxillary anteriors.
• 3. Extrusion of mandibular molars.
• 4. Occlusal plane tipping.
• 5. It may exaggerate the increased lower anterior facial height.

33. In occlusion, if this elastic makes a 20 degree angle with the upper
continuous archwire and a 100 g force, the elastic effect has:
• ➩ a horizontal component force of: 100 X cos 20° = 93.90 g.
• ➩ a vertical component force of: 100 X sin 20° = 34.20 g.
In centric occlusion

34. In 10mm opening
• • With a mouth open 10 m/m at the incisors level, the force varies with
different angulation of the Class II elastic and has different effects upon:
MAXILLARY ARCH (29° angulation)
➩ The vertical component of extrusion is: 160 X sin 29° = 77.60 g.
because the elastic has now a 29° angulation with the upper arch
.➩ The horizontal component of distalization is: 160 X cos 29° = 139.90 g.
MANDIBULAR ARCH (35° angulatioin)
➩ A forward component force of: 160 X cos 35° = 131 g.
➩ A vertical component of extrusion force which is: 160 X sin 35° = 91.8 g.

35. In 25mm opening
• With a mouth open 25 m/m, which can happen when the patient is
speaking, smiling or yawning, the elastic force can be again increased to
190 grams. But this force cannot be constant and is going to decrease with
time, in the saliva. This maximum force occasionally exerted has again
different effects upon:
MAXILLARY ARCH
➩ The vertical component of extrusion force is: 190 X sin 38.5° = 118.3 g.
➩ The horizontal distalizing force is: 190 X cos 38.5° = 148.7 g.
MANDIBULAR ARCH
➩ The horizontal forward force is: 190 X cos 52.5° = 115.7 g.
➩ The vertical component of extrusion force is: 190 X sin 52.5° = 150.7 g.

36. • The clinician must understand that the use of Class II intermaxillary
elastics has to take into account the facial type in order to avoid a
facial pattern aggravation.
• During day: Intermaxillary elastics have a vertical component of
extrusion that is much more significant than the horizontal
component.
• During night Intermaxillary elastics have an equivalent vertical and
horizontal component.

38. CLASS II ELASTICS EFFECTS WITH CONTINUOUS ARCHWIRES
➨ EFFECTS UPON THE MAXILLARY
ARCH
• backward movement of the
upper arch
• extrusion and downward
movement of anterior occlusal
plane
• upper incisors are more vertical
• all teeth are distallized.
➨ EFFECTS UPON THE
MANDIBULAR ARCH
•entire mandibular arch is
brought forward
•the lower molar can be
extruded
•buccal tipping of lower
➨ EFFECTS UPON OCCLUSAL
PLANE
•sagittal correction of Class II
relationship
•downward tilting of the
anterior occlusal plane.
➨ EFFECTS UPON FACIAL PATTERN
•the mandible is brought
forward with a posterior
rotation
•chin goes forward
•the lower facial height is
increased according to the
amount of elastic force used and

39. Clinical applications of Class II elastics
➨ In dental Class II malocclusions
• Any kind of elastics can be used whatever they are Class I
postero anterior, regular Class II or combined with different
ones. In case of dental open bite, closing Class II elastics are
recommended to close the bite
➨ In skeletal Class II patterns
• We must differentiate:
• vertically normal: where the Class II elastic has a light effect of
posterior mandibular rotation.
• deep bite: the extrusion component of Class II can be used with the
combination of triangular Class II.
• open bite: in those cases the use of Class II elastics must be avoided
because their effects increase the mandibular rotation even when
using closing Class II. It’s better to use Class I elastics associated with
judicious extraction strategies and/or surgery

40. Remember!!!!
➩correct the overbite before the overjet
➩ level the curve of Spee before using the Class II
elastic
➩ segment the maxillary arch.

41. Clinical problems with Class II elastics
Many clinical problems may be observed even with careful clinical
watching on:
• insufficient wearing
• excessive wearing
• parodontal problems such as: - lower incisors dehyscence -
abnormal rotation and fenestration
• biomechanic complication such as:
- space opening
- space closing
- anchorage lost
- abnormal tipping
- exaggerated rotation
- exaggerated extrusion.