Tooth movement in orthodontics how and why

Tooth movement in orthodontics

1. Orthodontic tooth movement PREPARED BY DR. WESAM GOUDA PhD IN ORTHODONTICS LECTURER IN ORTHODONTIC DEPARATMENT FACULTY OF DENTAL MEDICINE ALAZHR UNIVERSITY

2. Orthodontic treatment is based on the fact that it is possible, to move the teeth through the alveolar bone, by applying appropriate forces, without causing permanent damage to either the teeth or their supporting tissues.

3. When a force is applied to the crown of a tooth, it is transmitted through the root of the tooth to the periodontal ligament and alveolar bone. According to the direction of the force, there will be areas of pressure and areas of tension on these supporting structures.

4. For the tooth to be moved and to maintain the integrity of the attachment mechanism there must be resorption and deposition of alveolar bone in response to pressure and tension areas respectively. In effect, the socket of the tooth is moved, concomitant with tooth movement through the alveolar bone. In other words, successful orthodontic tooth movement is ended by moving the tooth with its investing tissues ( periodontium ) through the supporting bone.

5. Factor affecting tooth movement Manner of force application Continuous force: It is steady force applied to the tooth. It remains almost unchanged throughout its application period e.g. force of super elastic coil spring

6. Intermittent force: The force is applied with multiple period of complete release of the force. e.g. the force of removable appliance that is stopped on removal of appliance

7. Dissipating force: It is a force, which decrease gradually by time, and increase again by activation of force component. E.g. force of elastic bands

8. Amount of force application Light force It is the force, which is not sufficient to occlude blood capillary in PDL

9. Tissue reaction in response to light orthodontic force: Hyperemia occur within PDL then osteoclast and osteoblast appear in PDL frontal resorption beneath the areas of pressure due to increased osteoclastic activity Apposition of osteoid tissue occurs on the opposite surface of the socket beneath the area of tension due to increased osteoblastic activity. This tissue (becomes calcified) within about 10 days to form mature bone

10. remodeling occurs to re-establish and maintain the integrity of the socket wall. The periodontal ligament fibers attaching the tooth to the bone become reorganized

11. Tissue reaction in response to heavy orthodontic force: It is the force, which is sufficient to occlude blood capillary in PDL leading to: Occlusio n of the blood ves sels in the areas of press ure and Dilatation of vessels in the areas of tension .

12. Appearance of cell free zone in PDL in the pressure area (hyalinization )

13. hyalinization is followed by a Period of stasis , when the tooth does not move because no resorption occurs on the periosteal surface of the socket (no frontal resorption). resorption of the alveolar bone under the cell free zone (undermining resorption) The tooth may become slightly loosen Healing of the periodontal ligament, re-organization of fibers and remodeling of the socket wall occurs when forces are removed. These processes may take longer time than with the light force

14. Tissue reaction in response to grossly excessive orthodontic force: Necrosis of the periodontal ligament tissue Massive undermining resorption . Possible root resorption. Healing may be occur by ankylosis . Possible tooth devitalization.

15. So what is the ideal orthodontic force The ideal orthodontic force for successful tooth movement should not exceed capillary blood pressure (32 mmHg. of 50 : - 75 grams/Cm 2 ) It depend on the size and shape of the tooth and size and number of the roots

16. Duration of force application The periodontal ligament should have period of rest during this period it can recover and promote cell proliferation

17. Direction of force application Types of orthodontic tooth movement

18. Translation or bodily movement It is an even movement of all part of the tooth in the same direction. The force must be applied directly to more than one point at the bracket slot. Bodily movement of tooth requires two to three times the force needed for simple tipping of the same tooth. Center of resistance

19. Rotation movement It is the movement of the tooth around its long axis in its socket, by the use of force couple

20. Intrusion It is the movement of the tooth along its Long axis towards its apex. It requires light force to avoid tooth devitalization and root resorption

21. Extrusion It is the movement of the tooth along its Long axis towards occlusal plane

22. Torque ( third order bend ) It is the movement of the root with no OR little movement of the crown in the opposite direction NB. Torque is the opposite movement to the controlled tipping

23. Occlusion When there is Occlusal Interference during orthodontic tooth movement it leads to mobility of teeth. This can be overcome by the use of bite planes. Posterior bite plane Anterior bite plane

24. Age of the patient Biologic response to orthodontic forces in the adult is slower than in younger age so we should use light forces with longer periods of rest between appointments.

25. Sex of the patient Tooth movement was noticed to be lagged or slowed down during menstruation periods in females BUT No problem

26. Individual variations Bone density and vascularity may vary from one to another according to many factors as nutrition & life style