Mechanics of Orthodontic tooth movement
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The document discusses the mechanics of orthodontic tooth movement. It covers topics such as the nature of orthodontic tooth movement, forces, center of resistance, moments, couples, types of tooth movement including tipping, translation, rotation, intrusion and extrusion. It also discusses force duration types including continuous, interrupted and intermittent forces. Threshold force values and moment to force ratios for different tooth movements are provided.
Mechanics of Orthodontic tooth movement
- 1. Mechanics Of Orhtodontic Tooth Shahzad Hussain Final Year BDS Roll No 52 Movement 10/29/2014 MEchanics Of orhtodontic tooth Movement 1
- 2. In the name of Al lah , The mos t gr ac ious , The mos t me rc i ful 10/29/2014 MEchanics Of orhtodontic tooth Movement 2
- 3. What is orthodontics ? Orthodontics is the specialty of dentistry concerned with the management and treatment of 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 10/29/2014 MEchanics Of orhtodontic tooth Movement 3
- 4. The nature of orthodontic tooth movement : it has a bio – mechanic nature. solely based upon stress- strain that occurs in the PDL environment the orthodontic tooth movement results from forces delivered to the teeth 10/29/2014 MEchanics Of orhtodontic tooth Movement 4
- 5. Andrew’s keys for ideal occlusion 10/29/2014 MEchanics Of orhtodontic tooth Movement 5
- 6. The forces are delivered via orthodontic appliances which are 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 10/29/2014 MEchanics Of orhtodontic tooth Movement 6
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- 8. 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.” 10/29/2014 MEchanics Of orhtodontic tooth Movement 8
- 9. 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. 10/29/2014 MEchanics Of orhtodontic tooth Movement 9
- 10. Location of the center of resistance depends on the alveolar bone height and root length 10/29/2014 MEchanics Of orhtodontic tooth Movement 10
- 11. 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 10/29/2014 MEchanics Of orhtodontic tooth Movement 11
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- 13. 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 10/29/2014 MEchanics Of orhtodontic tooth Movement 13
- 14. 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. 10/29/2014 MEchanics Of orhtodontic tooth Movement 14
- 15. 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 10/29/2014 MEchanics Of orhtodontic tooth Movement 15
- 16. 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 10/29/2014 MEchanics Of orhtodontic tooth Movement 16
- 17. 3 Couple 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 10/29/2014 MEchanics Of orhtodontic tooth Movement 17
- 18. Couples result in pure rotational movement about the center of resistance 10/29/2014 MEchanics Of orhtodontic tooth Movement 18
- 19. 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. 10/29/2014 MEchanics Of orhtodontic tooth Movement 19
- 20. 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 10/29/2014 MEchanics Of orhtodontic tooth Movement 20
- 21. Orthodontic wire bends 1st order 2nd order 3rd order 10/29/2014 MEchanics Of orhtodontic tooth Movement 21
- 22. Types of tooth movement : 1. tipping ( controlled & uncontrolled) 2. translation ( bodily ) 3. root movement 4. rotation 5. intrusion & extrusion 10/29/2014 MEchanics Of orhtodontic tooth Movement 22
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- 24. Tipping • simplest orthodontic movement • controlled occurs about the tooth apex • uncontrolled occurs about CER • Force needed is about 50 – 75 gm. 10/29/2014 MEchanics Of orhtodontic tooth Movement 24
- 25. Translation : • All PDL is uniformly loaded with the force •Force needed is about 100 – 150 gm. 10/29/2014 MEchanics Of orhtodontic tooth Movement 25
- 26. Rotation : needs high force • occurs around the CER • Force needed is about 50 – 100 gm 10/29/2014 MEchanics Of orhtodontic tooth Movement 26
- 27. Extrusion : • needs to produce tension in the PDL ligaments • Force needed is about 50 gm. 10/29/2014 MEchanics Of orhtodontic tooth Movement 27
- 28. 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 10/29/2014 MEchanics Of orhtodontic tooth Movement 28
- 29. Intrusion: • forces are nearly at the apex • needs minimum force application • Force needed is about 15 – 25 gm. 10/29/2014 MEchanics Of orhtodontic tooth Movement 29
- 30. Types of orthodontic forces acc. to Duration • continuous • interrupted • intermitted 10/29/2014 MEchanics Of orhtodontic tooth Movement 30
- 31. Moment / Force ratios needed for different kinds of tooth movement : tipping controlled 5 : 1 uncontrolled 7 : 1 translation 10 : 1 root movement 12 : 1 10/29/2014 MEchanics Of orhtodontic tooth Movement 31
- 32. 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. 10/29/2014 MEchanics Of orhtodontic tooth Movement 32
- 33. Continuous force : achievable via fixed orthodontics Never declines to zero. 10/29/2014 MEchanics Of orhtodontic tooth Movement 33
- 34. 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 . 10/29/2014 MEchanics Of orhtodontic tooth Movement 34
- 35. 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 10/29/2014 MEchanics Of orhtodontic tooth Movement 35
- 36. Thank You 10/29/2014 MEchanics Of orhtodontic tooth Movement 36