Orthodontic tooth
movement
Abdurrahman MosaadOrthodontics department
Armed forces medical complex – Kobry al Qubba
I n t h e n a m e o f A l l a h , m o s t g r a c i o u s , m o s t m e r c i f u l
# What is orthodontics :
= Orthodontics is the specialty of dentistry concerned with the management and treatmentof malocclusion.
=In the majority of cases, a malocclusion does not in itself represent a disease state, but rather a variation from what is considered ideal
- Andrew’s keys for ideal occlusion
- The nature of orthodontic tooth movement :
= it has a bio – mechanic nature.
= solely based upon stress- strain occurs in the PDL environment
= the orthodontic tooth movement results from forces delivered to the teeth
= the forces are delivered via orthodontic app. Either fixed or removable
= PDL undergoes biological respond upon the mechanical application of a force i.e to achieve a precise biological respond the mechanical forces to be delivered should be precise
= Knowledge of the mechanical principles governing forces is necessary for the control of orthodontic treatment
= The proper application of biomechanics principles increases treatment efficiency through improved planning and delivery of care
= Knowledge of the mechanical principles governing forces is necessary for the control of orthodontic treatment
= The proper application of biomechanics principles increases treatment efficiency through improved planning and delivery of care
1 = center of resistance. - All objects have a center of mass.
- This is the point through which an applied force must pass for a free object to move linearly without any rotation,
- i.e., the center of mass is an object’s “balance point.”
analytic studies have determined that the center of resistance for single-rooted teeth with normal alveolar bone levels is about 1/4 to 1/3 the distance from the cementoenamel junction (CEJ) to the root apex.
Location of the center of resistance depends on the alveolar bone height and root length . = Location of the center of resistance with alveolar bone loss = with a shortened root
2 - Forces
= they are actions applied to bodies
= they equals ( mass X acceleration) F =ma
= in clinical orthodontics its unit is Grams = forces has the characteristics of vectors i.e magnitude & direction
Note : the diagram shows that the force vectors characteristics – magnitude , point of origin & direction
= 2 vectors could added by placing one vector at the head of the another i.e sum of them called resultant
= a vector could be resolved into components along x , y & z axes
= Clinically the determination of the horizontal,
vertical, and transverse components of a force
improves the understanding of the direction of
tooth movement
= An important point of view that the
orthodontic tooth movement is not applied on
the center of rotation of the tooth as it is
usually delivered through the tooth crown
= as the orthodontic forces
are delivered through the
tooth crown they will not
produce a pure linear
movement ,, some rotational
movement will be present ,,
those rotational movements
are called Moment of the
force
= The moment of the force
is the tendency for a force to
produce rotation.
= Its direction is found by
following the line of action
around the center of resistance
toward the point of origin
=It is determined by
multiplying the magnitude of
the force by the perpendicular
distance of the line of action to
the center of resistance
= The importance of the moment of a
force is often not recognized in clinical
orthodontics, but awareness of it is
needed to develop effective and
efficient appliance designs
Clinical examples of moments of the forces
3 – Couple
- A couple is
two parallel forces of equal
magnitude acting in opposite
directions and separated by a
distance (i.e. different lines of
action)
- The magnitude of a couple is
calculated by multiplying the
magnitude of force(s) by the
distance between them
Couples result in pure rotational
movement about the center of resistance
c l in i ca l examples o f coup les
4 – Torque
= Torque is a common synonym for
moment (both moments of forces and of
couples)
= Torque is erroneously described in
terms of degrees by many orthodontists.
= The appropriate unit for the applied torque is gram/millimeters (force × distance). It is the description of the
moments that more accurately describes the rotational components of a force
system and appliance design
Orthodontic wire bends
-1st order
-- 2nd order
-- 3rd order
# Anchorage
-Anchorage is the site of delivery from which force is exerted
- degree of resistance to displacement offered by an anatomic unit for the purpose of tooth movement.
# Classification of ortho. Anchorage
-acc. to manner of force application : * simple * stationary * reciprocal
- according to jaws involved : * intermaxillary * intramaxillary
- according to site : * intraoral * extaraoral * muscular - according to anchorage units : * primary * compound *reinforced (multiple)
# anchorage planning :
-Increasing no. of teeth to be move requires more anchorage- teeth having more surface area requires more anchorage - bodly movement requires more anchorage- prolonged tx. Plan requires more anchorage- vertical growth pattern requires more anchorage due to the less tonicity of muscles - N.B. Good occlusion = Good anchorage
# Anchorage loss :-Its is the unwanted tooth movements during orthodontics that cause space loss -Maximum anch. * anch. Demand is very high *not more than ¼ of ext space should be lost * augmentation of anchor units is usually done
-Moderate anch. * ¼ - ½ of ext space should be lost
- Minimum anch. * more than ½ ext space could be lost
Maximum anch.
Moderate anch.
Minimum anch.
# Equivalent Force systems
= A useful method for
predicting the type of tooth
movement that will occur with
appliance activation is to
determine the equivalent force
system at the tooth’s center of
resistance
= The force system at the
center of resistance accurately
reflects the type of movement
eg. Intrusion arch force system
# Types of tooth movement :
1 – tipping ( controlled & uncontrolled) 2 – translation ( bodily ) 3 – root movement 4 - rotation 5 - intrusion & extrusion
-The relationship between the applied force system and the type of movement can be described by the moment/force ratio
-The movement that occurs is dependent on the (moment/force ) ratio #and# the quality of the periodontal Support
1- Tipping :
* simplest orthodontic movement * controlled occurs about the tooth apex *uncontrolled occurs about CER
* Force needed is about 50 – 75 gm.
Controlled tipping
Uncontrolled tipping
2- Translation : * all PDL is uniformly loaded with the force * Force needed is about 100 – 150 gm.
3 – Rotation :
* needs high force * occurs around the CER * Force needed is about 50 – 100 gm.
4 – Extrusion :
* needs to produce tension in the PDL ligaments * Force needed is about 50 gm.
5 – Intrusion : * forces are nearly at the apex * needs minimum force application * Force needed is about 15 – 25 gm.
6- Root movement : * usually expressed as torque * the crown is held stationary and the root moves * CER is the bracket itself * done by increasing the Moment/Force ratio
Moment / Force ratios needed for different kinds of tooth movement :
1 – tipping
* controlled 5 : 1
* uncontrolled 7 : 1
2 – translation 10 : 1
3 – root movement 12 : 1
Types of orthodontic forces acc. to Duration
- continuous - interrupted - intermitted
* Threshold --- 6 hrs per day. * No tooth movement if forces are applied less than 6 hrs/d. * From 6 to 24 hrs/d, the longer the force is applied, the more the teeth will move.
- Continuous force : * achievable via fixed orthodontics *Never declines to zero.
- Interrupted force :
* force starts heavy then decline to optimal
after that may reach zero .
*achievable via removable appliance.
* produces some kind of undermining
resorption .
* reactivated every specific time .
-Intermittent forces : * declines to zero
* very high force 250 – 500 gm.( anch –
dist )
* achievable via extraoral appliance
* needs at least 12 hrs/day to be effective
* 14 hrs/day is optimal
-Force level : * Light, continuous forces are currently
considered to be most effective in inducing
tooth movement.
*Heavy forces cause damages and fail to move
the teeth.
N.B. Optimal force : “High enough to stimulate cellular activity without completely occluding blood vessels in the PDL”
Heavy Forces * B.V of PDL is totally occluded --- then * causes cellular necrosis within the bone --- then * hyalinization i.e undermining resorption occur
Phase 1Phase 3
Phase 2
Tooth
movem
en
t (m
m)
Time (Arbitrary Unit)
Light, continuous forces • Osteoclasts formed• *Removing lamina dura. *Tooth movement begins *This process is called “FRONTAL RESORPTION”. ( remodeling process )
Phase 3
Phase 2
Tooth
mov.
Time
-Phases of orthodontic tooth movement :- * Displacement - no clinical movement - instantaneous * Delay – no clinical movement - short ( partial B.Vs occ. ) or long 1-2 weeks ( more B.Vs occ. ) * Acceleration – rapid tooth displacement - differs among individuals
Phase 1
Phase 3 Phase 2
To
oth
movem
en
t (m
m)
Time (Arbitrary Unit)
Orthodontic tooth movement adverse effects : * Pulp - transient inf. response , can cause loss of vitality - in cases of compromised tooth ,, heavy force ,, wrong mech. * Root - usually repaired by cementum during rest periods - resorption may occur up to 2 mm. in permanent cases - At risk : thin roots ,, heavy force ,, Hx. of prev. idiopathic resorption
Material considerations : 1 – orthodontic wires *material of the wire * effect of increasing wire diameter 2 – orthodontic brackets * edgewise vs pre-adjusted (roth) * self ligating brackets * size of slots * interbracket distance * torque of the brackets
Modulus of elasticity of the wire
force
deflection
14’’ 50gm 16’’ 85gm 71% increase 18’’ 137gm 173% increase
Effect of increasing wire diameter
Perc
en
tag
e in
cre
ase in
sti
ffn
ess
100
%
20
0%
300%
400%
Wire diameter
14’’ 16’’ 18’’ 20’’ 22’’
Torque selection of lower teeth brackets
Torque selection of upper teeth brackets
Finally :
Optimal force is the lightest force that will move a tooth to a desired position in the shortest possible time without iatrogenic effects
So ,,, we should think optimal ,, it is orthodontics so we ( work smarter not harder )
Thank You
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