THEORIES OF TOOTH MOVEMENT.pptx

THEORIES OF TOOTH MOVEMENT

1. GOOD MORNING

2. THEORIES OF ORTHODONTIC TOOTH MOVEMENT MEHDI MUSTAFA JR1

3. CONTENTS OBJECTIVE INTRODUCTION HISTORY KINGSLEY AND WALKHOFF HYPOTHESIS WORKS OF SANDSTEDT(1904-05) OPPENHEIMS TRANSFORMATION HYPOTHESIS COMPARISON BETWEEN SANDSTEDT AND OPPENHEIM MODEL SCHWARZ (1932) PRESSURE TENSION HYPOYHESIS DRAWBACK OF PRESSURE TENSION HYPOTHESIS BONE BENDING /PIEZOELECTRIC THEORY DRAWBACKS OF BONE BENDING THEORY FLUID DYNAMIC THEORY SECOND MESSENGER CONCEPT IN ORTHODONTICS CONCLUSION

4. OBJECTIVE TO HAVE AN OVERVIEW OF SOME OF THE IMPORTANT THEORIES OF ORTHODONTIC TOOTH MOVEMENT

5. INTRODUCTION Orthodontic tooth movement is the result of a biological response to interference in the physiological equilibirium of the dentofacial complex by an externally applied force(Profitt,2013) The biological foundations of force induced orthodontic tooth movement along with some of the concepts related to it has been investigated extensively since the onset of 20 th century

6. HISTORY The old pressure hypothesis of Schwalbe Flourens , which postulated that pressure moves teeth preceded the concept that alveolar bone resorption takes place on one side of the dental root while deposition takes place on the opposite side

7. KINGSLEY (1881) Based on his vast clinical experience,Kingsley stated that Slow Orthodontic Tooth Movement is associated with favourable tissue remodeling changes( resorption and deposition of alveolar bone),while Q uick movements displace entire bony lamellae along with the teeth. The functional and structural integrity is retained.He attributed these features to elasticity,compressibility and flexibility of bone tissue

8. WALKHOFF’S HYPOTHESIS(1890) Walkhoff stated that “Movement of a tooth consists in creation of different tensions in the bony tissue ,its consolidation in the compensation of these tensions . Walkhoff’s hypothesis was larglely based on the elasticity ,flexibility and compressibility of bone. He also stated that alveolar bone,after all the remodeling changes,maintains its thickness,due to transformation or apposition of bone during the consolidating period.

9. SANDSTEDT (1904-05) Histological examination of paradental tissues during orthodontic tooth movement was reported for the first time by Sandstedt who tipped teeth uncontrollably in dogs,and later studied their tissues by light microscopy In Sandstedt’s experimental model a labial arch was bent to engage the six maxillary incisors of a dog and inserted into horizontal tubes attached to bands on the canines ..

10. Distal to the tubes was a screw mechanism ,which when tightened moved incisors lingually and canines mesially

11. Results of Sandstedt’s experimental model TENSION SIDE PRESSURE SIDE LIGHT FORCE BONE DEPOSITED ON ALVEOLAR WALL ALVEOLAR BONE RESORBED HEAVY FORCE BONE DEPOSITED ON ALVEOLAR WALL HYALINIZATION

12. PRESSURE SIDE – Resorptive bone surface with numerous osteoclasts in Howship’s lacunae TENSION SIDE -New bony trabeculae oriented along the principal fibres of the ligament HISTOLOGICAL PICTURE

13. OPPENHEIM’S TRANSFORMATION HYPOTHESIS Oppenheim (1911 , 1930 ) published the results of experimental work carried out on the primary teeth of monkeys. He found that where a tooth had been tipped labially , the original bone disappeared completely from the labial surface and was replaced by new bone. According to him,this takes place by resorption of the bone present and deposition of new bone tissue; both processes occured simultaneously .

14. COMPARISON BETWEEN SANDSTEDT AND OPPENHEIM’S MODEL Sandstedt : In the regions of pressure in the PDL,the old alveolar bone is resorbed and in the regions of tension ,new alveolar bone is added Oppenheim : On the side of the pull, bone is resorbed and new bone is added by resorption of the bone present and deposition of new bone tissue; both processes occur simultaneously

15. Schwarz (1932) Schwarz (1932) attempted to explain the difference between the findings of Sandstedt and Oppenheim by the fact that Oppenheim had euthanized his experimental animals several days after the appliance had been last activated Moreover Oppenheim ignored the acute phase reactions and focused only on the stage of regeneration after the force had been exhausted.

16. Following Schwarz publication Oppenheim worked further(1944) on tissue reactions in mature monkeys to light and heavy forces LIGHT FORCES HEAVY FORCES Osteoclasts mobilized at a fast pace and attack bone by uniform lacunar resorption Resulted in undermining resorption

17. PRESSURE TENSION HYPOTHESIS The studies of tooth movement through histological analysis by Carl Sandstedt,Oppenheim and Schwarz led them to hypothesise that tooth moves within the periodontal space by generating a “pressure side” and a tension side”

18. Diagram illustrating pressure-tension hypothesis. Application of orthodontic force results in pressure on certain areas of the periodontal ligament while tension on the others.Bone under pressure shows resorption while on the tension side,deposition takes place

19. On the pressure side PDL displays disorganization and diminution of fibre production There is vascular constriction Decrease in cell replication On the tension side Stimulation produced by stretching of PDL fibre bundles results in an increase in cell replication This eventually leads to an increased fibre production

20. Schwarz detailed the concept further ,by correlating the tissue response to the magnitude of the force applied with the capillary blood pressure According to him forces that are delivered as a part of orthodontic treatment should not exceed the capillary blood pressure (20-25gm/cm2) If this pressure is exceeded compression could cause necrosis through “suffocation of the strangulated periodontium ” Application of even greater force levels will result areas of undermining resorption or hyalinization in adjacent marrow spaces

21. DRAWBACK OF PRESSURE TENSION HYPOTHESIS According to Baumrind,the periodontal ligament is a continuous hydrostatic system and not a solid one O nly part of the periodontium where differential pressures as mentioned in the pressure tension hypothesis can be developed ,is solid i.e bone,tooth , and discrete solid fractures of PDL

22. BONE BENDING /PIEZOELECTRIC THEORY Farrar(1876) first suggested that bone bending maybe a possible mechanism for bringing about tooth movement Baumrind proposed a hypothesis in 1969,known as bone bending theory Baumrind (1969) also observed that the crown of the first molar was displaced, on average, 10 times more than the average reduction in PDL width on the pressure side,suggesting that bone deforms more readily than the PDL

23. According to this hypothesis orthodontic forces routinely produce alveolar bone deflection accompanied by resultant changes in the PDL bending of the bone,tooth,as well as of solid structures of PDL Bone was found to be more elastic than the other two tissues,which bend far more readily in response to force application

24. Zengo et al measured the electric potential in mechanically stressed alveolar bone and demonstrated that concave side of the orthodontically treated bone is electronegative and favours osteoblastic activity The convex side is electropositive and showed elevated osteoclastic activity

25. HYPOTHETICAL MODEL OF THE ROLE OF STRESS INDUCED BIO ELECTRIC POTENTIALS IN REGULATING ALVEOLAR BONE REMODELLING ELECTRONEGATIVE/CONCAVE BONE SURFACE Characterized by osteoblastc activity ELECTROPOSITIVE/CONVEX BONE SURFACE Characterized by osteoclastic activity

26. The findings led to the suggestion that bioelectric potentials( piezo -electricity and streaming potentials) propagated by bone bending incident to orthodontic force application might be functioning as pivotal cellular first messengers

27. Piezoelectric potentials According to this concept when a crystal structure is deformed,electrons migrate from one location to another resulting in an electric charge The mineral content of bone in hydroxyapatite crystalline form as well as collagen matrix,have piezoelectric properties Also,the mucopolysaccharides of ground substance can generate piezo -electricity when deformed

28. Two features of piezoelectricity are Quick decay rate : When a force is applied,piezoelectricity is generated,which immediately goes to zero level ,even if the force is applied.This property is called quick decay rate. Reverse piezoelectricity : When the force is removed ,the crystals after returning to its original positions produce flow of electrons in the opposite direction .This is reverse piezoelectricity

29. Though piezo-elelectrical model enjoyed support initially ,there were problems from a biological point of view Piezoelectricity doesnot require the presence of living cell;dead bone displays the same activity Wether the electrical phenomenon is sufficiently discriminatory to be able to regulate the metabolic activity of cell types as diverse as osteoblasts and osteoclasts is doubtful

30. DRAWBACKS OF BONE BENDING THEORY The main drawback is that this theory was based on stress generated signals which are produced by vibratory type of tooth movement, but for optimum tooth movement light continuous forces are applied A simple relationship between stress generated potentials and cellular activation seemed unlikely since higher potentials are seen in dentin than in other dental tissues,yet remodeling of dentin doesnot occur in response to stress

31. FLUID DYNAMIC THEORY Bien in 1966 found out that there are three distinct but interacting fluid systems involved in providing response to intrusive forces in PDL Vascular system enclosed within the blood and lymph vessels The system of periodontal membrane, comprised of cells and periodontal fibres Interstitial fluid continuum that permeates the spaces between the cells,fibres,blood vessels,tooth and bone

32. During intrusive cycle ,exhaustion of extracellular fluids from the PDL membrane into the vascular reservoir of the marrow space occurs .This damping rate is dependent upon size and number of perforations. As a momentary effect the fluid that is trapped between the tooth and the socket tends to move to the boundaries of the film at neck of the tooth and the apex while acting to cushion the load and is referred to as “ squeeze film effect ”

33. As the squeeze film becomes depleted and the pressure continued ,the second damping effect occurs after exhaustion of the extracellular fluid and the ordinarily slack fibres tighten. These fibres which criss-cross the blood vessels tighten ,then compress and constrict the blood vessel which run between them,causing stenosis of the blood vessel . This causes vessels to balloon creating a back pressure.

34. At the stenosis a drop of pressure would occur in the vessel in accordance with Bernoulli’s principle Bien suggested that there is an alteration in the chemical environment at the site of the vascular stenosis due to decreased oxygen level in the compressed areas as compared to the tension side The formation of these aneurysms and vascular stenosis causes blood gases to escape into interstitial fluid thereby creating a favourable local environment for resorption

35. SECOND MESSENGER CONCEPT IN ORTHODONTICS According to this concept,increase in the tissue or cellular concentrations of second messengers are generally viewed as evidence that an applied extracellular ‘first messenger’,such as an orthodontic force,has stimulated target cells.

36. Arachidonic acid metabolites i.e prostaglandins and leukotriens play a key role in conversion of orthodontic pressure stimuli into a cell mediated response However considering the different response of osteoblasts and osteoclasts to the same chemical stimuli that leads to deposition of bone on tension side and resorption on pressure side it has been suggested that it is the messenger system that modulates the behavior of cells The messenger system translates a wide array of external stimuli(first messenger) into a narrow range of internal signals(second messengers)

37. CELLULAR RESPONSE TO MECHANICAL FORCE APPLICATION

38. The second messenger hypothesis postulates that target cells respond to external stimuli,chemical or physical,by enzymatic transformation of certain membrane bound and cytoplasmic molecules to derivatives capable of promoting the phosphorylation of cascades of intracellular enzymes

39. CONCLUSION After 100 years of attempts by Sandstedt , we have reasonably good understanding of the sequence of events involved in orthodontic tooth movement at the tissue and cellular levels on both the tensile and compression sides of the periodontium Tooth movement is not confined to events within the periodontal ligament. Orthodontic tooth movement involves two interrelated processes: deflection or bending of the alveolar bone and remodelling of the periodontal tissues

40. REFERENCES Biological Mechanisms of Tooth Movement,2 nd Edition; Vinod Krishnan,Ze’ev Davidovitch The tissue, cellular, and molecular regulation of orthodontic tooth movement: 100 years after Carl Sandstedt : Murray C. Meikle , Department of Oral Sciences, Faculty of Dentistry, University of Otago , Dunedin, New Zealand Baumrind S 1969 A reconsideration of the propriety of the “ pressure tension” hypothesis. American Journal of Orthodontics 55 : 12 – 22 Orthodontics:Diagnosis and Management of Malocclusion an Dentofacial Deformities-Om Prakash Kharbanda Orthodontics:Current Principles and Techniques;Graber , Vanarsdall,Vig,Huang Bien S M 1966 Hydrodynamic damping of tooth movement. Journal of Dental Research 45 : 907 – 914

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