Force and its use in orthodontics

FORCE AND USE OF
FORCE IN
ORTHODONTICS
Reporter: Dr. Turgut NOVRUZLU
Scientific Supervisor: Asst. Prof. Hale GÜNER

Outline
Introduction
and history of
Force
01
Force
Newtonian laws
02
Characteristics
of Force
03
Constancy of
Force
04
Optimal Force
05
Friction
06
Conclusion
07
Discussion
08

01 Introduction
◦ Force is the main tool of an Orthodontist. The only element which gives us ability to
manipulate over direction, speed and degree of tooth movement is the Force. [2]
◦ Orthodontics is also actively engaged with Mechanics, hence mechanics is the field of
physics which is related to forces.

01 Introduction
◦ Since we utilize physics and mechanics upon living cells, we must name these branches as
Biophysics and Biomechanics.
◦ For an orthodontist it is important to clinically imply insertion of appliances, however
we should also train our brains to understand “hows” and “whys” of biomechanical
aspect orthodontic treatment.

01 Introduction
◦ Importance of proper understanding of force and its effect on tooth, periodontium and
aesthetic appearance of patients is crucial in order to avoid unexpected surprises.
◦ We must stick to classical physics which was founded by giants such as Hooke, Galileo
and Newton.
Robert Hooke 1635-1703 Galileo Galilei1564-1642

01 Introduction
◦ For sake of simplicity we will avoid talking about Pre-Newtonian concepts of
force such as Theory of Impetus* or Aristotelian physics.
◦ Special attention will be given to Newtonian mechanics that was introduced by Sir Isaac
Newton in his thesis “Philosophiæ Naturalis Principia Mathematica” in 1687
* Precursor of concepts of inertia, momentum, acceleration in classical mechanics, it was later modified by in the 12th century by Nur ad-Din al-Bitruji
Aristotélēs 384 BC-322 BC

02 Force
◦ Force is any interaction that, when unopposed, will change the motion of an object.
◦ To explain the relationship between an object and force we will refer to laws defined by
Sir Isaac Newton
Sir Isaac Newton1643-1727

02 Force
◦ Newton’s 1st law: Law of intertia.
◦ An object will not move and will not change its velocity and direction (if it is in motion)
unless acted upon by an unbalanced force.
(Image: Fouad A. Saad/Shutterstock)

02 Force
◦ Newton’s 1st law: Law of intertia. Usage in Orthodontics
◦ This is the most important law for orthodontic practice, because it is the basis for
majority of appliances.
◦ Activated appliances and restrained teeth within the bone are proper examples for first
law.
Usage in orthodontics

02 Force
◦ Newton’s 1st law: Law of intertia. Usage in Orthodontics
◦ A coil spring is in deactivated state (rest) and there are no
forces applied on it. After we activate it, there
will be 100g equal forces will be applied and
the spring will remain in equilibrium since it
is not attached to a tooth.

02 Force
◦ Newton’s 2nd law: Law of acceleration
◦ Rate of change of momentum of a body over time is directly proportional to the force
applied, and occurs in the same direction as the applied force.
Image: Fouad A. Saad/Shutterstock

02 Force
◦ Newton’s 2nd law: Law of acceleration.
◦ This law of the Newton is less related to orthodontics , since a tooth does not gain a
momentum* during orthodontic treatment. [1]
◦ The teeth are moving, but we should not forget that they are restrained objects hence
their bodies are in equilibrium and at rest.
* Not to confuse with Moment

02 Force
◦ Newton’s 3rd law: Law of action and reaction.
◦ Every action always have an equal and opposite reaction.
◦ Action and reaction forces do NOT cancel each other, because they act on
different objects
◦ Think of it like wings of bird. When bird pushes air downwards with their wing, the air
reacts by pushing the bird upwards
Usage in orthodontics

02 Force
◦ Newton’s 3rd law: Law of action and reaction. Usage in orthodontics
◦ The coil spring is activated by mesial force
to allow it’s placement on canine hook.
◦ After applying this activation force on
hook of canine we can observe two equal
forces Newton’s 3rd law .

02 Force
◦ The blue line(FA) is the activation force
◦ The red line(FD) is the opposite force
◦ The hook pulls the coil and the coil pushes
the hook.

02 Force
◦ Action and Reaction law is important in orthodontic practice.
◦ It is extraordinarily difficult to move only the tooth or teeth that we want to move
without moving the other teeth that you we don’t want to move. [3]

02 Force

03 Characteristics of Force
◦ Attributes of Force:
Degree
Direction
Sense
Point of application
Line of action
Duration
Distribution

◦ Direction of force is defined by its line of action and it is referred as sense.
◦ On the diagram it is shown:
Hook: Red dot
The Line: Direction
Arrowhead: Sense

◦ On illustration we see 3 forces acting on the Red dot (hook on maxillary arch)
◦ Forces are vector quantities that cannot be added algebraically
we can only add them geometrically.
◦ Elastics that are used in orthodontics have
different angles to each otherand they all have
difference lines of force application/vectors

◦ Force magnitude is given in grams (g)
◦ Magnitudes are shown as arrows, the length of
arrow is proportional to magnitude of force
◦ Lets pay special attention to inter and intra arch
elastics
◦ 150g is for inter-arch elastic arrow is
3x as long as vertical elastic and half of intra-arch
elastic arrow

◦ Cartesian coordinates are used to specify direction of a force vector.
◦ Proper understanding of axis coordination is important
for evaluating the molar movement.
René Descartes 1596-1650

◦ To evaluate the movement of molar we
use coordinate system which shows
mesiodistal(buccolingual) axes of tooth.
◦ Red: elastic force has both lingual and
mesial components of force: Yellow.
René Descartes 1596-1650

04 Constancy of force
◦ Before starting to talk about types of force, we must understand how the continuity of
force is measured.
◦ The most common way to determine the continuity of force is to relate the change of
force to appliance deflection (or change in tooth position) g/mm

◦ Continuous force. This type of force depreciates slowly, but never diminishes to zero
within two activation periods.
◦ Mostly used in levelling phases.
◦ Open coil is an example

◦ Interrupted forces are reduced to zero shortly after they have been applied.
◦ RME is an
example

◦ Intermittent force is reduced to zero when patient removes the appliance, it continuous
from its previous level when inserted back and reduces slowly.
◦ This type of force usually achieved with
help of extra oral appliance.
04 Constancy of Force

04 Constancy of Force
◦ Cuoghi OA, Tondelli PM, Mendonça MR, Aiello CA, Costa SC, Tanaka OM. Effect of different types of force on the amount of tooth movement, hyaline areas, and root
resorption in rats. Eur J Gen Dent 2018;7:66-71.
RIP to rats which were
sacrificed during this study

05 Optimum Force
◦ The optimal orthodontic force produces a maximum rate of tooth movement. Forces above optimal lead to the
formation of hyaline areas and prevent frontal resorption of the alveolar bone, thus leading to reduction in the rate of
tooth movement.[5]
◦ Features of Optimal Force according to Ze’ev Davidovich D.M.D*
1. It should strain Para dental tissues;
2. It should cause minimal tissue damage ;
3. It’s distribution in PDL and Alveolar bone is uniform;
4. It’s distribution depends on anatomical constraints and type of tooth movement;
5. It’s magnitutde must not exceed levels where cell death may occur.
*Professor in Harvard School of Dental Medicine

05 Optimum Force
◦ Factors such as magnitude, duration and direction must be determined individually for
each patient, taking into consideration their pain threshold and condition of
periodontium.
◦ When potentially damaging movements of dental roots such as uncontrolled tipping,
moving roots labially, buccally or palatally into the palatal compact bone plates are
avoided, we can consider force biologically and clinically optimal

05 Optimum Force
Correlation between pain and hyalinization during tooth movement induced by different types of force, 2019 The Angle
Orthodontist Marcos Rogério de Mendonça

05 Optimum Force
Correlation between pain and hyalinization during tooth
movement induced by different types of force, 2019
The Angle Orthodontist Marcos Rogério de Mendonça

06 Friction
◦ What is Friction? : Friction is the force that resists against the movement of one surface
in relation to another and that acts on the opposite direction of the desired movement[6]
◦ When one surface slides over another, two new forces will generated: Frictional Force
(f) and Normal Force (N)
Guillaume Amontons 1663-1705 Charles-Augustin de Coulomb 1736-1894

06 Friction
◦ Experimental verification of Friction was initially done by Amomtons and Coulomb in
17th and 18th centruies.
◦ Amomton’s 1st Law: Frictional force (f) is directly proportional to applied load (N)
◦ Amomton’s 2nd Law: The force is friction is independent of the apparent area of
contact
◦ Coulomb’s Law of Friction: Kinetic friction is independent of
the sliding velocity

06 Friction
◦ What is the importance of Friction in Orthodontics?
◦ Orthodontic sliding mechanics represents a clinical challenge to orthodontists as friction
reduces effectiveness of mechanics and complicate anchorage control.

06 Friction
Pacheco MR, Jansen WC, Oliveira DD. The role of friction in orthodontics. Dental Press J
Orthod. 2012 Mar-Apr;17(2):170-7.

07 Conclusion
◦ Simplifying all the given information, Force must be used efficiently and wisely by
the clinician. If used correctly in a way that it will be considered as “optimal” it
will give us the fastest and most effective outcomes in short amount with
minimum resorption.
◦ To understand basics of force, we must stick up to the classics and develop our
outlook on this thread starting from scratch.

References
[1] The Biomechanical Foundation of Clinical Orthodontics p25
[2] Biology of Orthodontic Tooth Movement ISBN 978-3-319-26609-1
[3] https://www.jco-online.com/media/22362/jco_2008-05-261.pdf The Biomechanics of TADs, Robert G. Keim, DDS, EdD, PhD
◦ [4] Burstone CJ. The biomechanics of tooth movement. In: Kraus B, Riedel R (eds). Vistas in Orthodontics. Philadelphia: Lea and Febiger,
1962:197–213.
◦ [5] . Krishnan V, Davidovitch Z. Cellular, molecular, and tissue level reactions to orthodontic force. Am J Orthod Dentofacial Orthop.
2006;129:469.e1–32
◦ [6] Rossouw EP. Friction: an overview. Semin Orthod. 2003;9(4):218-22

Thanks for
attention
◦ “There may be a great
fire in our soul, yet no
one ever comes to warm
himself at it,
and the passers-by see
only a wisp of smoke.”
― Vincent van Gogh.
Café, le soir, by Vincent Van Gogh 1888

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