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

Appliance Force Displacement tooth、Alveolar 、bone

Ⅰ Biological characteristics of Periodontal tissue

Ⅰ Biological characteristics of Periodontal tissue （一）Stability of Periodontal ligament Environment Periodontal ligament （PDL） is made up of Fibrous connective tissue ，mostly connect teeth to alveolar ，so that teeth fixed in the alveolar.

Ⅰ Biological characteristics of Periodontal tissue （一）Stability of Periodontal ligament Environment Cell Periodontal ligament has three cells (Three components) ： 1 compound cell 2 Absorption cell 3 Undifferentiated cells

Ⅰ Biological characteristics of Periodontal tissue （一）Stability of Periodontal ligament Environment 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 .

Ⅰ Biological characteristics of Periodontal tissue （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 .

Ⅰ Biological characteristics of Periodontal tissue (三) Resistance to stress of the cementum Root surface is covered with a thin layer of cementum ，it fights against external forces ，protect cementum not to be absorbed.

Ⅱ Biological theory of teeth movement 1. Piezoelectric theory Piezoelectric effect is the phenomenon by crystal material deformation produced by charge . Negatively charged concave, convex positively charged

Ⅱ Biological theory of teeth movement 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 same amount but the opposite direction of the signal .

Ⅱ Biological theory of teeth movement 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.

Ⅱ Biological theory of teeth movement 2. Mechanical - chemical theory of bone： external force 　teeth 　blood change of PDL 　Chemical environment of PDL（the level of oxygen and other relative levels of metabolites ，for example  Concentration of Central - phosphate ） 　Cell differentiation 　　　 Bone formation and absorption

Ⅱ Biological theory of teeth movement 2. Mechanical - chemical theory of bone: Tension side ： The amount of blood increase blood oxygen content of the blood increase Osteoblast differentiation bone formation

Pressure side ： Decreased blood flow Decreased blood oxygen content Osteoclast differentiation 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

Movement of teeth Multinuclear osteoclasts

Ⅲ Organizational change in the process of orthodontic treatment （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.

Ⅲ Organizational change in the process of orthodontic treatment Tension side ： Periodontal fiber elongation stretch 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 periodontal ligament to orthodontic force In the process of tooth movement ，Cells generally appear within 36 hours after the burner.

Ⅲ Organizational change in the process of orthodontic treatment （2）Other 1. Dental tissue Changes in cementum Changes in root Changes in pulp tissue 2. Impaction of deciduous tooth movement to constant tooth germ 3. Changes in suture 4. Impact on the adjacent teeth

Ⅲ Organizational change in the process of orthodontic treatment （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.

Ⅲ Organizational change in the process of orthodontic treatment （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 The effect of strength of orthodontic force Strength of different organizations have different power levels of impaction. If the force is too small, 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 The effect of Strength of 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

Ⅳ The effect of Strength of orthodontic force （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.

Ⅳ The effect of Strength of orthodontic force 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

Ⅳ The effect of Strength of orthodontic force 2.Appropriate orthodongtic force observed by Histological The pressure side vessel is compressed, but not closed The cells have the greatest response Organization is in a activity, but not nonecrosis Direct absorption of alveolar more than the indirect absorption

Ⅳ The effect of Strength of orthodontic force （三）The type of tooth movement and the distribution of power 1 Conception 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 The effect of Strength of orthodontic force （三）The type of tooth movement and the distribution of power 1 Conception 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.

Ⅳ The effect of Strength of orthodontic force （三） The type of tooth movement and the distribution of power 1 Conception Force: 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 bone morphogenetic . Orthodontic force ：Smaller sustained, causing the power to change the tooth and dental arch .

Ⅳ The effect of Strength of orthodontic force 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 .

Ⅳ The effect of Strength of orthodontic force 2.  The type of tooth movement （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.

Ⅳ The effect of Strength of orthodontic force 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

Ⅳ The effect of Strength of orthodontic force 2. The type of tooth movement （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

Ⅳ The effect of Strength of orthodontic force 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

Ⅳ The effect of Strength of orthodontic force 2. The type of tooth movement （5）Torque Torque movement is also known as root-controlled 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 Factors that affect the tooth movement 1. Force faction strength of force bodily：150 tipping：50 extrusion：25 instrusion：100 rotation：100 torque：150 large：>350g medium：60~350g weak：<60g

Type of force Mechanical force, biological force, and orthodontic force, orthopedic force ,and so on

（Continuous force, intermittent force） Forcing time （Continuous force, intermittent force）

Ⅳ The effect of Strength of orthodontic force 2. Body condition Age   Health status   Partial anatomical factors: Root length, alveolar height

Ⅳ The effect of Strength of orthodontic force 3. External factors Hormones: parathyroid hormone, etc. Drug: prostaglandins, such as Salvia Physical stimulation: electrical stimulation, magnetic, etc.