Orthodontic Biology of Tooth and supporting structure

1. 1 Orthodontic biology of tooth Orthodontic biology of tooth and supporting structure and supporting structure Prepared by: Prepared by: Dr Mohammed Alruby Dr Mohammed Alruby لبقتسملا همحري نل يضاملا نم ملعتي مل نم D Dr. Mohammed Alruby r. Mohammed Alruby Orthodontic Biology of Tooth and s Orthodontic Biology of Tooth and supporting structure upporting structure

2. 2 Histology of supporting structure -Periodontal ligament -Alveolar bone = types of tooth movement = classification of force during treatment = factors affect tooth movement = hyalinization = types of root resorption = factors affect tooth movement according to pressure tension theory = role of chemical mediators in tooth movement = role of neurotransmitter in tooth movements D Dr. Mohammed Alruby r. Mohammed Alruby Orthodontic Biology of Tooth and s Orthodontic Biology of Tooth and supporting structure upporting structure

3. 3 The goal is to examine the relationship between orthodontic biomechanics and the underlying biological process When orthodontic force is applied to the crown of the tooth it is transmitted through the roots to the periodontal ligament and alveolar bone Histology of supporting structure: -Periodontal ligament -Alveolar bone I- Periodontal ligament: A-Cellular component: Forming cells: Osteoblast: bone forming cells Fibroblast: PDL fibers forming cells Cementoblast: in layer adjacent to the roots Resorptive cells: Osteoblast: large cell rich acid phosphatase enzyme that demineralize the bone and disintegrate of organic matrix Fibroblast: disintegrate fibers Cementoblast: resorb cementum Progenitor cells: undifferentiated mesenchymal cells UMC: small cells with closed nucleus and little cytoplasm & monocytes Epithelial rest of malassez: arise as a result of breakdown of epithelial root sheath at the time of cementogesis Defensive cells: as macrophages & mast cells B-Periodontal fibers: 1-Collagen fibers: the main bulk of PDL fibers and found in 5 groups: -Alveolar crest group: from cervix to alveolar crest -Horizontal group: from cementum to bone horizontally -Oblique group: the main attachment that run obliquely from cementum to bone in an apical direction -Apical group: circumscribed the apex and responsible for resistance to rotation -Inter-radicular group: inter-mediate plexus, observed midway between bone and root -Supra-alveolar group: Dento-gingival Dento-periosteal Transeptal Circular Alveolo-gingival 2-Oxytalan fibers: Immediate elastic fibers that resist dissolution by acids unlike collagen Run from cementum or bone to blood vessels Play a role in supporting the blood vessels against distortion and compressive strain c- Ground substances: organic matrix surrounding the PDL elements, it is chemically composed of CHO linked with protein. CHO- protein complex commonly divided into two groups: proteoglycan and glycoprotein D Dr. Mohammed Alruby r. Mohammed Alruby Orthodontic Biology of Tooth and s Orthodontic Biology of Tooth and supporting structure upporting structure

4. 4 ground substances of periodontal ligament is in a continuous state of remodeling process d- Neurovascular elements: myelinated: pain sensation non-myelinated: blood vessels wall PDL functions: -Supportive -Nutritive -Remodeling -Sensory II- Alveolar bone: = in human, marrow spaces are rare in the buccal and lingual plates, these spaces decreased with age = wider spaces are lined with a layer of fenestrated compact bone when PDL fibers are anchor these fibers is called bundle bone N: B: = collagen turn over in PDL is higher 4 times than skin and 2 times than gingiva and this due to the forces in PDL is multi-directional takes vertical and horizontal component = lake of marrow spaces implies that bone resorption takes more time so that the tooth movement in mesial and distal direction occur more than labial and lingual sides = the resorptive cells increase as the marrow spaces increase N: B: The new deposited tissue during tooth migration have 3 stages: Stage I osteoid: is the product of osteoblast, found on surface where new bone is deposited appear as white line or white outgrowth. Stage II: bundle: Appear calcified tissue is deposited –a wider opaque line indicate that calcified tissue has been added Stage III: lamellated: Cells and fibers will be incorporated in the bundle bone during its life cycle. When it is reach certain thickness and maturity the bundle bone recognized as lamellated bone This sequence is the same as that occurs after orthodontic tooth movement N: B: The tissue reaction during tooth movement was pointed out for the 1st time by Steiner and Weinman 1925, then Bjork 1955 on animal study N: B: PDL approximately 0.20 -0.25mm wide D Dr. Mohammed Alruby r. Mohammed Alruby Orthodontic Biology of Tooth and s Orthodontic Biology of Tooth and supporting structure upporting structure

5. 5 Types of tooth movements 1-Physiologic tooth movements: Movements of the tooth in the alveolus during function, in human beings and primates, the teeth in the posterior segment migrates mesially. The tissue reaction during physiologic movements is normal function of supporting structure. 2-Orthodontic tooth movements: It is intentionally induced movement that is performed through application of orthodontic forces using orthodontic appliances Basically there is no differences in tissue reaction between physiologic tooth movements and orthodontic tooth movements except: 1-Orthodontic movement is more rapid 2-Time needs for short bone formation takes from 8 -10 days Classification of forces during treatment I- According magnitude: 1-Orthodontic force: = according to Schwarz, the ideal orthodontic force: is that force which induce pressure in the PDL not exceed blood capillary pressure not more than 33mm/hg OR that force which result in tooth movement about 1mm / month He suggested that force to be 15-20gm /cm of the root surface = differential orthodontic force: is that force which causes: -Minimum discomfort -Minimum loosening of the tooth’ -Minimum damaged of tooth investing structure -Move the tooth more rapidly = each tooth has differential values: 150 -200gm for canine and 300gm for 1st molar = the initial actual orthodontic movement 6 -7 days after application of force and continuous for a period of 10-12 days after elimination of force 2-orthopedic force: force transmitted to the basal bone to move it or guide its growth and position, the magnitude of force range between (900 – 1350gm) but in cases of RME the force may increase II- according force duration: a-continuous force: = it maintains approximately the same magnitude over the period of force application as: nitinol coil spring b-dissipating force: that shows decrease amount of force within short time as: force of elastics and RME advantages: has period of recovery, re-organization and cell proliferation prior to force re- application c-intermittent force: = force associated with the use of removable appliances, the force is active when the appliance within the mouth and stop when it is removed = some intermittent action also seen as result of changes of tooth or appliance position during mastication. Extra-oral attraction force is intermittent force D Dr. Mohammed Alruby r. Mohammed Alruby Orthodontic Biology of Tooth and s Orthodontic Biology of Tooth and supporting structure upporting structure

6. 6 III- -tipping -translation -rotation -intrusion -torque -extrusion according to direction: Factors affect tooth movement 1-amount of force: light force: direct bone resorption -------- fast heavy force: hyalinization ------- undermining resorption ---- delayed movement followed by rapid movement and losing of teeth 2-duration of force: it is important for PDL to have recovery periods to establish the blood supply and to promote cell proliferation, so heavy force of short duration less damaging than light continuous force 3-direction of force: some forces are liable to occurs faster than other as: tipping movement is fast than the translation and torque 4-age: the biologic response to orthodontic force in adult is slower than children, because bone is denser and PDL is less cellular 5-occlusal function: movement of interdigitated teeth is more difficult than that of teeth with inter-occlusal clearance 6-application of drugs: = administration of aspirin like drugs reduce the rate of movement because it inhibits the synthesis of prostaglandin = administration of prostaglandin especially E2 enhance tooth movement = prostaglandin inhibitors: --- decrease tooth movements Hyalinization = Disappearance of cells with changes in intercellular substances = There are some changes in hyalinized zone: 1-gradual compression of periodontal fibers leading to shrinkage and disappearance of cell nuclei 2-osteoclast is formed in marrow spaces and adjacent areas of inner bone surface after period of 20 -30 hours 3-gradual increase in the number of young C T cells around the osteoclast area where the pressure is relieved by undermining bone resorption = hyalinization is related to force factor: if the tooth moved by muscular impulse exerting light intermittent force, hyalinization will not occur. Intermittent force elicited by removable appliances may produce either hyalinization of short duration or no hyalinization at all. N: B: During orthodontic treatment there is always certain tooth mobility, that occurs primarily as a result of widening of periodontal spaces by bone resorption. Mobility may be manifest during mastication when the tooth moves against an alveolar bone wall that is covered by a layer of recently formed elastic osteoid D Dr. Mohammed Alruby r. Mohammed Alruby Orthodontic Biology of Tooth and s Orthodontic Biology of Tooth and supporting structure upporting structure

7. 7 N: B: Bone formation: Cell proliferation takes place on tension side after 30 – 40 hours shortly after cell proliferation has started, the osteoid tissue will be deposited on tension side Tooth movability: -higher tissue activity during spring than others -higher rate of bone formation in patients with anterior growth rotation than in patients with posterior growth rotation -more bone formation obtained by moving the teeth with interrupted force than with continuous forces Extrusion of teeth: = after the age of 18 -20 years of age growth activity slow = extrusion of adult in mass movement may result in relapse after displacement and subsequent contraction of the whole free gingival fibers system, in such cases it has been observed that closure of an anterior open bite may be performed with greater success if anterior teeth are extruded individually and not in mass movement = the extrusion need minimal force 25 – 30gm to prevent disturbance of pulp structure, BUT in young patients 13 years of age it has been shown that permanent closure of the bite and a Deformed roots: Dilacerations or curvature of the roots may lead to delayed the movement and by increase the magnitude of force, the resistance is increase but by use of frequently light interrupted force lead to extrude the tooth or surgical resection of curved roots after endodontic treatment facilitate the orthodontic tooth movement. Intrusion: During intrusion there is tendency to shortening of roots as a result of apical root resorption so if carefully measured the forces there will be less tendency to such shortening of roots. Light force: 20 -30gm lead to short hyalinization periods and the teeth intruded rapidly N: B: Types of root resorption: a-very mild irregular apical root contour b-mild apical root blunting c-moderate apical root resorption d-severe apical root resorption e-lateral root resorption Thanks D Dr. Mohammed Alruby r. Mohammed Alruby Orthodontic Biology of Tooth and s Orthodontic Biology of Tooth and supporting structure upporting structure