Bio-mechanical Principle in Orthodontic Treatment Xi'an Jiaotong University Stomatology hospital Orthodontic Department Zou Min

Bio-mechanical Principle in Bio-mechanical Principle in Orthodontic TreatmentOrthodontic Treatment

Xi'an Jiaotong University StomatolXi'an Jiaotong University Stomatology hospitalogy hospital

Orthodontic DepartmentOrthodontic Department Zou Min Zou Min

Force

tooth 、 Alveolar 、 bone Displacement

Appliance

Ⅰ Biological characteristics of Periodontal tissue


（一） Stability of Periodontal ligament Environment

Periodontal ligamentPeriodontal ligament （（ PDLPDL ））is made up of Fibrous connective

tissue ， mostly connect teeth to alveolar ， so that teeth fixed in the alveolar.



CellCell

Periodontal ligament has three cells (Three components) ：

1 compound cell

2 Absorption cell

3 Undifferentiated cells



Tissue fluid : Periodontal ligament is full of tissue fluid, which is to absorb external force. As the liquid is incompressible ， the force gave to teeth is quickly spread to the alveolar .


（二） Plasticity of alveolar

Bone especially alveolar has the general robustness of bone tissue and highly Plasticity.In the physiological state, constantly updated and translated ， through the conversion and absorption to achieve a new balance .


(( 三三 ) ) Resistance to stressResistance to stress of of the cementumcementum

Root surface is coveRoot surface is covered with a thin layer of cemenred with a thin layer of cementum tum ，， it fights against exterit fights against external forces nal forces ，， protect cementuprotect cementum not to be absorbed.m not to be absorbed.

Ⅱ Biological theory of teeth movement

1. Piezoelectric theoryPiezoelectric effect is the phenomenon by

crystal material deformation produced by

charge . Negatively charged concave, convex positively charged


Piezoelectric theory

Piezoelectric effect has two characteristics ：1 The loss of speed is very quickly. If the

force continues, it dose not continue to produce

electrical signals. 2 The disappearing of force brings the s

ame amount but the opposite direction of the signal .


1. Piezoelectric theory

Have a positive effect on the normal alveolar bone metabolism.The effect about the continuing orthodontic force is not clear .

Results show: Electrical changes in the environment can affect the permeability of cell membrane, causing

cell activation.


2. Mechanical - chemical theory of bone ： external force 　 teeth 　 blood c

hange of PDL 　 Chemical environment of PDL （ the level of oxygen and other relative levels of metabolites ， for example Concentration of Centr

al - phosphate ）　 Cell differentiation 　　　 Bone formation and absorption

2. Mechanical - chemical theory of bone:

Tension side ：The amount of blood increase blood oxyg

en content of the blood increase

Osteoblast differentiation bone formation

Ⅱ Biological theory of teeth 　　　　　　 movement

Pressure side ：Decreased blood flow

Decreased blood oxyg

en content Osteoclast differentiat

ion

Bone resorption

Ⅲ Organizational change in the process of orthodontic treatment

（一） The response of alveolar and periodontal ligament to orthodontic force

1. Pressure side

Periodontal ligament narrowed Reduce blood flow Degradation and absorbtion of collagen fibers Alveolar bending deformation Osteoclast differentiation Alveolar resorption

Multinuclear

osteoclasts

Movement of teeth


（一） Response to orthodontic force by alveolar and periodontal ligament

Large treatment force——Local vascular hemorrhage ， Periodontal tissue degeneration transparent ， Transgender organizations was absorbed by Phagocyte ， Newborn fibroblasts 、

Vascular invasive ， repair them——Indirect absorption happens on the pressure of the alveolar ，indirect absorption also known as“Absorption of prowling ”.root tip is the mostly area of the root of teeth.


Tension side ：Periodontal fiber elongation stretc

h Blood flow increased Fibroblast proliferation ， Alveolar bone bending deformation Osteoblast differentiation

The surface of bone trabeculae to form new Trabecular bone Osteogenic

（ 1 ） the response of alveolar and periodonta

l ligament to orthodontic force In the process of tooth movement ， Cells

generally appear within 36 hours after the burner.


（ 2 ） Other

1. Dental tissue Changes in cementum Changes in root Changes in pulp tissue 2. Impaction of deciduous tooth movemen

t to constant tooth germ

3. Changes in suture

4. Impact on the adjacent teeth


（ 3 ） Periodontal tissue alterations and recovery after teeth movement

Periodontal tissue alterations usually takes four weeks to complete, which is one-month clinical follow-up visits the patient basis on the biological for the physiological movement of teeth.


（三） Periodontal tissue alterations and recoveries after teeth movement

Periodontal ligament fibers to keep nine months is still anomaly.

New bone to maintain 9 months is not mature .normal combination of periodontal ligament and alveolar

need 3 months.

Root absorption and recovery are more than 3 months.

Therefore, after treatment it needs to keep more than 1 year .

Ⅳ Ⅳ The effect of strength of The effect of strength of orthodontic force orthodontic force

Strength of different organizations have different power levels of impaction. If the force is too smal

l, it can not cause periodontal tissue changes in the chemical environment, the teeth will not move. Excessive force can cause some periodontal tissue degeneration and necrosis, degeneration and necrosis of these organizations need to remove and repair a longer period of time, tooth movement will be slowed down, even not to move.

Ⅳ Ⅳ The effect of Strength of The effect of Strength of orthodontic force orthodontic force

( 一） The size of forces Ⅰ level ： too small to cause teeth moving Ⅱ level ： moderate and long-lasting ,and can cause organizations response in 5~6 hours generally Ⅲ level ： so large that local periodontal fiber denaturize and necrosis

Ⅳ level ： Periodontal ligament compression ， and cementum and alveolar adhesion

（二） the best strength of treatment In theory , it should be moderate and long-lasting, and the strength can not exceed the pressure of periodontal ligament capillary, so that the capillaries is in a semi-closed state, generally around 75-100g.



1. Indications of determine the appropriate corrective force in clinic

No significant pain consciously

No significant response to percussion

Forced teeth has no obvious loosening ?( < II )

Obvious teeth movement

There is no pathological changes of roots and periodontal tissue on X-ray


2.Appropriate orthodongtic force obse

rved by Histological The pressure side vessel is compressed, but n

ot closed

The cells have the greatest response

Organization is in a activity, but not nonecrosis

Direct absorption of alveolar more than the i

ndirect absorption

（三）（三） The type of tooth movement and the distThe type of tooth movement and the dist

ribution of powerribution of power 11 ConceptionConception Center of Resistance

It is the simplify center of the resistance movement of objects ,also known as resistance, the center of objects. It is inherent, and not impacted by outside force.


Ⅳ Ⅳ The effect of Strength of The effect of Strength of orthodontic force orthodontic force（三）（三） The type of tooth movement and the distThe type of tooth movement and the dist

ribution of powerribution of power 11 ConceptionConception Center of Rotation

Refers to objects in the external force by the next rotation around the point center of rotation with the external force and torque changes.


（三）（三） The type of tooth movement and tThe type of tooth movement and the distribution of powerhe distribution of power

11 ConceptionConceptionForce: size, direction, point

moment=force×arm (Resistance force from the center line of the vertical distance ) 。 Moment has two variables ： Force and distance. The direction of moment consistent with the direction and force of resistance centers +is Anti-clockwise rotation ， -is clockwise rotation.

couple ： Two forces with equal size but opposite direction operated on the same odjects. They are parallelled but not in a line. Couple of teeth can cause a simple rotation.

Couple moment ： one of the force×arm

Orthopedic Force ： Large and discontinuous, causing the power to change the b

one morphogenetic . Orthodontic force ： Smaller sustained,

causing the power to change the tooth and dental arch .


2. The type of tooth movement

（ 2 ） Incline movement ： Crown and root movement are in opposite

direction with a fulcrum which is in the border between the 1/3 of root and 1/3 of middle of root by a single horizontal force.The periodontal tissues of root apiex and alveolar was afforded the largest power which is about 50g .



（ 2 ） Bodily movement ： Crown and root movement are in

one direction at the same time. On the one side of the periodontal tissues is compressed, the other side is tracted.The power distribution can support greater forces which is generally believed that 100 - 150g or so.


2 The type of tooth movement

（ 3 ） Vertical movement ： Teeth instrusion ： In this movement , there is only a small amount periodontal ligament of apical squeezed. If the force is too large, the obstacles to the blood circulation will be easier to caused in the root zone, resulting in group symptoms of necrosis and pulp texture. Therefore the power to suppress should be very modest. generally power: 15 - 25g



（ 3 ） Vertical movement ： Teeth extrusion ： In the movement, the periodontal fibers was force to extrusion,and new alveolar bone was formated in Alveolar fossa which make the alveolar increased with the teeth extrusion. As Periodontal ligament supporting a large of forces , extrusion movement can endure a larger elongation force. Force value of 50 - 100g

rotation


2. The type of tooth movement （ 4 ） Rotation movement ： A couple of forces can made the crown and

root rotate along the tooth axis. Most of periodontal fiber was forced by the horizontal direction level of traction, and flat tooth root formation will make two pressure zone and one tension zone. The role of the force is between extrusion and intrusion



（ 5 ） Torque Torque movement is also known as root-cont

rolled movement, which can cause the root to move without the moving of the crown .Alveolar resorption occurred in the 1 / 3 of the roots first, and apical has the largest movement. Periodontal ligament has larger force area which is similar to the bodily movement.

Ⅴ Ⅴ Factors that affect the Factors that affect the tooth movementtooth movement

1. Force faction

strength of force large ： >350gmedium ： 60~350gweak ： <60g

bodily ： 150

tipping ： 50

extrusion ： 25

instrusion ： 100

rotation ： 100

torque ： 150

Type of forceMechanical force, biological force, and

orthodontic force, orthopedic force ,and so on

Forcing time（ Continuous force, intermittent force ）


2. Body condition Age

Health status

Partial anatomical factors: Root length,

alveolar height


3. External factors Hormones: parathyroid hormone, e

tc.

Drug: prostaglandins, such as

Salvia

Physical stimulation: electrical

stimulation, magnetic, etc.

Documents

Bio-mechanical Principle in Orthodontic Treatment Xi'an Jiaotong University Stomatology hospital Orthodontic Department Zou Min