I N THE NAME OF G OD 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

P ERIODONTAL 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

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

P ERIODONTAL L IGAMENT S TRUCTURE 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

E RUPTION : The phenomenon of tooth eruption makes it plain that forces generated within the P D L itself can produce tooth movement. A CTIVE STABILIZATION P ERIODONTAL L IGAMENT F UNCTION

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

R ESPONSE TO N ORMAL F UNCTION Since those are intermittent heavy 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

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

P IEZOELECTRIC 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: (1)a quick decay rate (2) production of an equivalent signal, opposite in direction 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: (1)a quick decay rate (2) production of an equivalent signal, opposite in direction Streaming potential: Ions in the fluids of the living bone 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. Endogenous electric signals Reverse piezoelectricity

P RESSURE -T ENSION T HEORY : The classic theory of tooth movement Chemical rather than electric signals Alterations in blood flow create changes in O2 level & chemical environment 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

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.

what happens between the onset of pressure and tension in the PDL and the appearance of second messengers a few hours later Prostaglandin and interleukin-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

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.

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

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 Where from are the osteoclasts derived when a heavy force is applied?

U NDERMINING RESORPTION  delay in tooth movement results by 1. a delay in stimulating differentiation of cells within the marrow spaces 2.a considerable thickness of bone must be removed from the underside before any tooth movement can take place.

C LINICAL TOOTH MOVEMENT, STEPWISE

R ELATIONSHIP OF T OOTH M OVEMENT TO F ORCE

D RUG E FFECTS ON THE R ESPONSE TO O RTHODONTIC F ORCE Vitamin D Direct injection of prostaglandin Enhance OTM rate OTM rate depressors: 1. Bisphosphonates (alendronate) 2. prostaglandin inhibitors 3. other classes of drugs can affect prostaglandin levels 4. anticonvulsant drug 5. some tetracyclines

OTM rate depressors: 1. Bisphosphonates (alendronate) synthetic analogues of pyrophosphate that bind to hydroxyapatite in 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.

B IOMECHANICS, BASIC DEFINITIONS Force Moment Centre of resistance Centre of rotation

D IFFERENT TYPES OF TOOTH MOVEMENT Tipping Bodily Root torque Rotation Intrusion extrusion

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.

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

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.

EXTRUSION

ROTATION

R OOT MOVEMENT ( ROOT TORQUE )

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.

A NCHORAGE : R ESISTANCE TO U NWANTED T OOTH M OVEMENT 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.

R ECIPROCAL T OOTH M OVEMENT. 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.

R EINFORCED A NCHORAGE. 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

S TATIONARY A NCHORAGE. 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 o 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

D IFFERENTIAL E FFECT OF V ERY L ARGE F ORCES. 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

C ORTICAL A NCHORAGE. 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 A BSOLUTE A NCHORAGE.

D ETRIMENTAL 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

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

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

S UBDIVISIONS 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

E FFECTS 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

S KELETAL 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

P REVENTION : H EADGEAR 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

A CCELERATION : 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

E FFECTS OF O RTHODONTIC F ORCE ON THE M ANDIBLE 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

P REVENTION : C HIN CUP Animal experiments, in which quite heavy and prolonged forces can be used, suggest that restraining forces can stop mandibular growth A. The duration of the chin cup force (hours/day) may be an important difference between children and experimental animals. B. 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

A CCELERATION : FUNCTIONAL Passive active

M C / MF, TYPES OF MOVEMENT

Mechanical Principles in Orthodontic Force Control The Basic Properties of Elastic Materials Strain Springiness = 1/Stiffness

M ECHANICAL P RINCIPLES IN O RTHODONTIC F ORCE C ONTROL Deflection

THREE MAJOR PROPERTIES OF BEAM MATERIALS FOR ORTHODONTIC PURPOSES : Strength stiffness (or its inverse, springiness) range These three major properties have an important relationship: Strength = Stiffness X Range

O RTHODONTIC A RCH WIRE M ATERIALS Precious Metal Alloys Stainless Steel (18% chromium and 8% nickel) Beta Titanum Cobalt-Chromium (Elgiloy) Nickel-Titanium (NiTi) Alloys.

N I T I ALLOYS SPECIAL FEATURES shape memory: Shape memory refers to the ability of the material to "remember" its original shape after being plastically deformed while in the martensitic form. In a typical application, a certain shape is set while the alloy is maintained at an elevated temperature, above the martensite-austenite transition temperature. When the alloy is cooled below the transition temperature, it can be plastically deformed, but when it is heated again the original shape is restored. superelasticity A-NiTi wires do not undergo plastic deformation until remarkably high force is applied. The wires can be shaped and their properties can be altered, however, by heat-treatment.

C OMPARISON OF CONTEMPORARY ARCHWIRES Stiffness formability

E FFECT OF LENGTH AND DIAMETER