In the name of God

1. In the name of God Tooth response to orthodontic force Biomechanics in orthodontics Different types of tooth movement Anchorage and its control Deleterious effects of orthodontic force By: Dr. Sepideh Arab

2. Periodontal and bone response to normal function • Periodontal ligament structure and function • Response to normal function • Role of the periodontal ligament in eruption and stabilization of the teeth • Periodontal ligament and bone response to sustained orthodontic force • Effects of force magnitude • Force duration and force decay • Drug effects on the response to orthodontic force

3. Orthodontic treatment is based on the principle that if prolonged pressure is applied to a tooth, tooth movement will occur as the bone around the tooth remodels. Forces applied to the teeth can also affect the pattern of bone apposition and resorption at sites distant from the teeth

4. Periodontal Ligament Structure Approximately 0.5 mm The major component of the ligament is a network of parallel collagenous fibers Cementum Lamina dura Two other major components: • (1) the cellular elements, including mesenchymal cells of various types along with vascular and neural elements UMC fibroblasts and osteoblasts Hematogenous origin osteoblasts & cementoblasts • (2) the tissue fluids

5. Periodontal Ligament Function Active stabilization Eruption: The phenomenon of tooth eruption makes it plain that forces generated within the P D L itself can produce tooth movement.

6. continuous interrupted Different types of forces based on The force consistency intermittent

7. Response to Normal Function Since those are intermittentheavy forces, response to these forces depends on the duration of force exertion The body of the mandible bends as the mouth is opened and closed

8. PERIODONTAL LIGAMENT AND BONE RESPONSE TO SUSTAINEDORTHODONTIC FORCE • Piezoelectric signals • Pressure-Tension Theory

9. Piezoelectric signals: Endogenous electric signals deformation of the crystal structure (organic or inorganic) produces a flow of electric current as electrons are displaced from one pan of the crystal lattice to another Characteristics: a quick decay rate (2) production of an equivalent signal, opposite in direction Streaming potential: Ions in the fluids of the livingbone interact with the complex electric field generated when the bone bends, causing temperature changes as well as electric signals. bioelectric potential: can be observed in bone that is not being stressed. Metabolically active bone or connective tissue cells. Reverse piezoelectricity

10. Pressure-Tension Theory: • The classic theory of tooth movement • Chemical rather than electric signals • Alterations in blood flow create changes in O2 level & chemical environment Pressure side decrease Tension side increase

11. PERIODONTAL LIGAMENT AND BONE RESPONSE TO SUSTAINEDORTHODONTIC FORCE Depends on the magnitude of force (cAMP), the "second messenger" for many important cellular functions including differentiation, appear after about 4 hours of sustained pressure.

12. what happens between the onset of pressure and tension in the PDL and the appearance of second messengers a few hours later Prostaglandin andinterleukin-1 beta levels increase within the PDL within a short time after the application of pressure prostaglandin E2 is an important mediator of the cellular response. Changes in cell shape probably play a role. prostaglandins are released when cells are mechanically deformed (i.e., prostaglandin release may be a primary rather than a secondary response to pressure). mobilization of membrane phospholipids, which leads to the formation of inositol phosphates, is another pathway toward the eventual cellular response. Other chemical messengers, particularly members of the cytokine family but also nitric oxide (NO) and other regulators of cellular activity, also are involved

13. Where from are the osteoclasts derived when a light force is applied? Osteoclasts appear within the compressed PDL via two waves: 1)some may be derived from a local cell population 2)others (the larger second wave) are brought in from distant areas via blood flow These cells attack the adjacent lamina dura, removing bone in the process of "frontal resorption," and tooth movement begins soon thereafter.

14. PERIODONTAL LIGAMENT AND BONE RESPONSE TO SUSTAINEDORTHODONTIC FORCE Depends on the magnitude of force

15. Where from are the osteoclasts derived when a heavy force is applied? Complete occlusion of blood vessels lead to a sterile necrosis ensues within the compressed area. Remodeling of bone bordering the necrotic area of the P D L must be accomplished by cells derived from adjacent undamaged areas. Osteoclasts appear within the adjacent bone marrow spaces and begin an attack on the underside of the bone immediately adjacent to the necrotic PDL area creating undermining bone resorption

16. Undermining resorption • delay in tooth movement results by • a delay in stimulating differentiation of cells within the marrow spaces • a considerable thickness of bone must be removed from the underside before any tooth movement can take place.

17. Clinical tooth movement, stepwise

18. Relationship of Tooth Movement to Force

19. Drug Effects on the Response to Orthodontic Force Enhance OTM rate Vitamin D Direct injection of prostaglandin OTM rate depressors: 1. Bisphosphonates (alendronate) 2. prostaglandin inhibitors 3. other classes of drugs can affect prostaglandin levels 4.anticonvulsant drug 5. some tetracyclines

20. OTM rate depressors: 1. Bisphosphonates (alendronate) • synthetic analogues of pyrophosphate that bind to hydroxyapatitein bone • They act as specific inhibitors of osteoclast-mediated bone resorption • explore with her physician for switching to estrogen, at least temporarily. 2. prostaglandin inhibitors • Corticosteroids (chronic steroid therapy) • NSAIDs (especially potent prostaglandin inhibitors like indomethacin) • agents that have mixed agonistic and antagonistic effects on various prostaglandins 3. other classes of drugs can affect prostaglandin levels • Tricyclic antidepressants (doxepin, amitriptyline,imipramine) • anti-arrhythmic agents (procaine) • antimalarial drugs (quinine, quinidine, chloroquine) • methyl xanthines 4.anticonvulsant drug (phenytoin) 5.some tetracyclines (e.g., doxycycline) inhibit osteoclast recruitment, an effect similar to bisphosphonates.

21. Biomechanics, basic definitions • Force • Moment • Centre of resistance • Centre of rotation

22. Different types of tooth movement • Tipping • Bodily • Root torque • Rotation • Intrusion • extrusion

23. tipping • The simplest form of orthodontic movement. • Tipping movements are produced when a single force (e.g., a spring extending from a removable appliance) is applied against the crown of a tooth. • Maximum pressure in the P D L is created at the alveolar crest and at the root apex • The loading diagram, therefore, consists of two triangles as shown.

24. BODILY MOVEMENT (TRANSLATION) • the root apex and crown move in the same direction and with the same amount. • the total PDL area is loaded uniformly • rectangular loading diagram

25. INTRUSION • Light force is required for intrusion because the force will be concentrated in a small area at the tooth apex • As with extrusion, the tooth probably will tip somewhat as it is intruded • the loading diagram nevertheless will show high force concentration at the apex. • Only if the force is kept very light can intrusion be expected.

26. extrusion

27. rotation

28. Root movement(root torque)

29. TABLE 9-3 Optimum Forces for Orthodontic Tooth Movement 'Values depend in part on the size of the tooth; smaller values appropriate for incisors, higher values for multirooted posterior teeth.

30. Anchorage: Resistance to UnwantedTooth Movement • For every (desired) action there is an equal and opposite reaction. Inevitably, reaction forces can move other teeth as well if the appliance contacts them. • Anchorage, then, is the resistance to reaction forces • provided (usually) by other teeth, or (sometimes) by the palate, head or neck (via extraoral force), or implants in bone.

31. Reciprocal Tooth Movement. • In a reciprocal situation, the forces applied to teeth and to arch segments are equal, and so is the force distribution in the PDL . • example is what would occur if two maxillary central incisors • if a spring were placed across a first premolar extraction site, pitting the central incisor, lateral incisor, and canine in the anterior arch segment against the second premolar and first molarposteriorly.

32. Reinforced Anchorage. • reinforcing anchorage by adding more resistance units is effective because with more teeth (or extra oral structures) in the anchorage, the reaction force is distributed over a larger PDL area. • if it was desired to differentially retract the anterior teeth, the anchorage of the posterior teeth could be reinforced by adding the second molar to the posterior unit

33. Stationary Anchorage. • can be obtained by pitting bodily movement of one group of teeth against tipping of another to differentially retract the anterior teeth, the anchorage of the posterior teeth could be reinforced by adding the second molar to the posterior unit • example of a premolar extraction site, if the appliance were arranged so that the anterior teeth could tip lingually while the posterior teeth could only move bodily

34. Differential Effect of Very Large Forces. • If tooth movement were actually impeded by very high levels of pressure, it might be possible to structure an anchorage situation so that there was more movement of the arch segment with the larger PDL area. Not recommended

35. Cortical Anchorage. • The different response of cortical compared with medullary bone • If a root is persistently forced against either of these cortical plates, tooth movement is greatly slowed and root resorption is likely Absolute Anchorage.

36. Detrimental effects of orthdontic forces • Mobility Reorganization of the PDL itself Radiographically, it can be observed that the P D L space widens during orthodontic tooth movement • Excessive mobility is an indication that excessive forces • may occur because the patient is clenching or grinding against a tooth that has moved into a position of traumatic occlusion • Pain Caused by ischemia of PDL • If heavy pressure is applied to a tooth, pain develops almost immediately • If appropriate orthodontic force is applied, the patient feels little or nothing immediately • Allergy (soft tissue) Latex Nickel

37. effects of orthdontic forces on pulp • Necrotic tooth 1) If a tooth is subjected to heavy continuous force 2) Root apex, moving outside the alveolar process • What about the teeth with RCT? Moving endodontically treated teeth is perfectly feasible

38. effects of orthdontic forces on root structure Types of root resorption: cementum adjacent to hyalinized (necrotic) areas of the PDL is "marked" by this contact and that clast cells attack this marked cementum • Moderate generalized resorption Individuals who have undergone comprehensive orthodontic treatment shows that most of the teeth show some loss of root length, and this is greater in patients whose treatment duration was longer • severe generalized resorption At this point the etiology of severe generalized resorption must be considered entirely unknown. Orthodontic treatment is not the major etiologic factor • severe localized resorption excessive force during orthodontic treatment

39. Subdivisions of root resorption • 1, slight blunting • 2, moderate resorption, up to 1/4 of root length • 3, severe resorption, greater than 1/4 of root length

40. Effects of orthodontic force on alveolar bone height Since the presence of orthodontic appliances increases the amount of gingival inflammation, this potential side effect of treatment might seem even more likely. Fortunately, excessive loss of crestal bone height is almost never seen as a complication of orthodontic treatment. Loss of alveolar crest height in one large series of patients averaged less than 0.5 mm and almost never exceeded 1 mm, with the greatest changes at extraction sites. • Lateral missing • Extrusion and intrusion • Intrusion of teeth with periodontal problem

41. Skeletal effects orthodontic forces • Effects of Orthodontic Force on the Maxilla and Midface : amount of force, duration of force Because tooth movement is an undesirable side effect, it would be convenient if part-time application of heavy force produced relatively more skeletal than dental effect. • Acceleration: facemask • Prevention : Headgear

42. Prevention : Headgear Force of 500 to 1000 gm total (half that per side) Force direction slightly above the occlusal plane Force duration at least 12 hours per day

44. Acceleration: facemask Suitable age? 7 years (before interdigitation of sutures) An ankylosed tooth or implant/onplant would provide perfect anchorage Maxillary soft tissue is the most preventing factor

46. Effects of Orthodontic Forceon the Mandible • Prevention : Chin cup • Acceleration: functional Attachment of the mandible to the rest of the facial skeleton via the temporomandibular joint is very different from the sutural attachment of the maxilla

47. Prevention : Chin cup • Animal experiments, in which quite heavy and prolonged forces can be used, suggest that restraining forces can stop mandibular growth • The duration of the chin cup force (hours/day) may be an important difference between children and experimental animals. • the presence of the articular disk complicates the situation, making it difficult to determine exactly what areas in and around the temporomandibular joint It is fair to say that controlling excessive mandibular growth is an important unsolved problem in contemporary orthodontics. At this point, we simply cannot restrain mandibular growth It is possible to use a chin cup to deliberately rotate the mandible down and back, redirecting rather than directly restraining mandibular growth

48. Acceleration: functional • Passive • active