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