logging in or signing up MECHANICAL PRINCIPLES IN OTHODONTICS FORCE CONTROL stbzaidi Download Post to : URL : Related Presentations : Let's Connect Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Copy embed code: Embed: Flash iPad Dynamic Copy Does not support media & animations Automatically changes to Flash or non-Flash embed WordPress Embed Customize Embed URL: Copy Thumbnail: Copy The presentation is successfully added In Your Favorites. Views: 1337 Category: Science & Tech.. License: All Rights Reserved Like it (0) Dislike it (0) Added: August 27, 2011 This Presentation is Public Favorites: 0 Presentation Description No description available. Comments Posting comment... Premium member Presentation Transcript MECHANICAL PRINCIPLES IN OTHODONTICS FORCE CONTROL: MECHANICAL PRINCIPLES IN OTHODONTICS FORCE CONTROL Syeda Tooba zaidi Deptt of OrthoDonticsOVERVIEW: OVERVIEW Introduction. Strategies of force control. Orthodontic properties of wire. Definitions. Tooth movement. Adverse effect of tooth movement.What is needed: What is needed Tooth Healthy periodontal ligament Bone Applied force Tooth movement dependant upon physiology of the periodontal ligament and bone i.e turnover.FORCES WITHIN THE MASTICATORY SYSTEM: FORCES WITHIN THE MASTICATORY SYSTEM 1 INHERENT NATURAL FORCES. Originating from the action of the muscles of mastication. Originating from the teeth. Originating from circumoral musculature. Equilibrium theory. 2. ABNORMAL FORCES. Tongue- thrusting. Digital sucking Occlusal dysfunctiuon Traumatic occlusion bruxismFORCE SYSTEM IN ORTHODONTICS AND FUNCTIONAL JAW ORTHOPEDIC APPLIANCES: FORCE SYSTEM IN ORTHODONTICS AND FUNCTIONAL JAW ORTHOPEDIC APPLIANCES Natural BiomechanicalSlide 6: NATURAL Energy generated by contraction of jaw and facial muscles may be transferred through functional appliancesSlide 7: BIOMECHANICAL Artificial forces . Clinically induced forces derived from mechanical devices. Eg archwires , coil spring, auxillary springs vertical loop in arch wires, elastics, screws etcStrategies for controlling forces in clinical practice: Strategies for controlling forces in clinical practice 1. Elimination of unwanted forces, as a habit control appliance. 2. Redistribution of natural forces in all functional appliances. 3. Stimulation and strengthening of natural forces. 4. Introduction of artificial forces e.g brackets, lingual archwires , or screws inserted in “functional appliances” Control of appliance remains the pt own “neuromuscular system” Adjusted by amount and duration of force by dentist.Principles of mechanics in fixed orthodontics: Principles of mechanics in fixed orthodontics Orthodontic appliance is a system storing and delivering force against the teeth, muscles and bone and creating a reaction within the PDL and alveolar bone that causes movement of the teeth or alters bone morph and growth.General character of good orthodontic forces: General character of good orthodontic forces • Optimal: light, continuous – Ideal material • Maintains elasticity • Maintains force over a range of tooth force over a range of tooth movementMaterials & Production of Orthodontic Force: Materials & Production of Orthodontic Force • Elastic behavior – Defined by stress-strain response to external load • Stress= internal distribution of the load; force/unit area • Strain= internal distortion produced by the load; deflection/lengthSlide 12: • Force applied to a beam = stress • Measure deflection = strain; examples: • Bending • Twisting • Change in lengthBeam properties in orthodontics: Beam properties in orthodontics • Defined in force deflection or stress strain diagrams • Useful properties: – Stiffness – Range -spring back – StrengthBending Properties of an Orthodontic Wire: Bending Properties of an Orthodontic Wire Defined by 3 points 1. Proportional limit •Point at which permanent deformation is first observed • Similar to “elastic limit” 2. Yield strength • Point at which 0.1% deformation occurs 3. Ultimate tensile (yield) strength • Maximum load wire can Sustain.Stiffness of an Orthodontic Wire: Stiffness of an Orthodontic Wire Modulus of elasticity (E) – Young’s modulus – Stiffness below proportional limit – Slope of load deflection curve – Stiffness α E – Springiness α 1/EStiffness versus Springiness: Stiffness versus Springiness Reciprocal relationship – Springiness= 1/stiffness • Related to elastic portion of force deflection curve (slope) – More horizontal= greater springiness – More vertical= stifferRange versus Spring back: Range versus Spring back • Range – Distance wire will bend elastically before permanent deformation • Spring back – Found after wire deflected beyond its yield point – Clinically useful • Wires often deflected past yield point Failure Point - At this the wire breaksRelationship of Strength, Stiffness & Range: Relationship of Strength, Stiffness & Range • Strength = stiffness x rangeResilience, Formability: Resilience, Formability Resilience – Area under stress strain curve to proportional limit – Represents energy storage capacity • Formability – The amount of permanent deformation a wire can withstand before Breaking.Ideal Orthodontic Wire Material: Ideal Orthodontic Wire Material • Deflection properties: – High strength – Low stiffness (usually) – High range – High formability • Other properties: – Weldable , solderable – Reasonable cost • No one wire meets all criteria! – Select for purpose requiredBiomechanical Design Factors in Orthodontic Appliance: Biomechanical Design Factors in Orthodontic Appliance Terms: – Force (F): load applied to object that will tend to move it to a different position in space • Units: g , grams, ouncesFORCE: FORCE Force is a energy or strength brought to bear causing motion or change in body----- a push or pull acting in a straight line. A force has a magnitude , point of application and direction ( sense and line of action).Slide 23: If you apply 2 forces in 2 different directions the resultant force will be in another directionBiomechanical Design Factors in Orthodontic Appliance: Biomechanical Design Factors in Orthodontic Appliance – Center of resistance (CR): point at which resistance to movement can be concentrated Tooth root: CR=one third to one half the way from alveolar crest to the apex. MR= just apically to the furcation . Term used in place of center of mass or center of gravity. Since teeth are not free bodies . They are perfectly balanced on a point for they are constrained by PDL attachment to roots.Slide 25: By definition , a force acting through C res moves tooth with no change in orientation = translation. A point at which resistance to movement can be concentrated for mathematical analysis (= C res )DESIGN FACTORS IN ORTHODONTIC APPLIANCES: DESIGN FACTORS IN ORTHODONTIC APPLIANCES – Moment : product of force times the perpendicular distance from the point of force application to the center of resistance Units: gm-mm • Created when line of action of a force does not pass through the center of resistance – Force will translate and tend to rotate object around center of resistance.Slide 28: Direction: Clockwise or anti clockwise Magnitude = perpendicular distance from C res to the line of action X magnitude of force (unit = gram mm)DESIGN FACTORS IN ORTHODONTIC APPLIANCES: DESIGN FACTORS IN ORTHODONTIC APPLIANCES – Couple : two forces equal in magnitude but opposite in direction • No translation • Produces pure rotation around center of resistance.DESIGN FACTORS IN ORTHODONTIC APPLIANCES: DESIGN FACTORS IN ORTHODONTIC APPLIANCES – Center of rotation: point around which rotation occurs when object is being moved This point will vary depending on the force/moment/couple being applied -Bodily movement or translation -Tipping movementTOOTH MOVEMENT AND Crot: TOOTH MOVEMENT AND Crot Type of Movement Translation Uncontrolled tipping Controlled tipping Root movement Center of Rotation Infinity Slightly apical to C res Apex Incisal edgeDetermining Crot: Determining C rot Connect the before and after positions of 2 points The intersection of the perpendicular bisectors of these lines is C rotTranslation or Bodily Tooth Movement : Translation or Bodily Tooth Movement Point of application of force: Closer to Cres Smaller moment Less rotation More translationIf you apply a force through the Cres, what type of tooth movement do you get? : If you apply a force through the Cres , what type of tooth movement do you get? -- Translation = Bodily Tooth Movement A force applied in line with the center of resistance: the tooth is translated with no rotation relative to the force If you do not apply a force through the Cres . what movements can you anticipate? By applying a couple you can get rotation Tipping results because the line of action in orthodontics is at the level of the bracketCONTACT ANGLE: CONTACT ANGLE • When sliding a tooth on an archwire : – Tooth tips – Further tipping prevented by moment created as bracket contacts wire = contact angle – Increase contact angle = increase resistance • Greater force needed to overcome frictionORTHODONTIC FORCE: ORTHODONTIC FORCE Tipping Translation Rotation Extrusion Intrusion TorqueSlide 39: Tipping Translation Rotation Extrusion intrusion Tipping is a simple type of tooth movement where a single force is applied to the crown in which, results in movement of the force and the root in opposite direction 1 controlled tipping—lingual movement of crown with minimal tooth movement 2. Uncontrolled tipping---- crown moving in one direction while roots move in opposite direction.Slide 40: A force that doesn’t pass through C res causes translation + rotation = tipping i.e., tends to tip the tooth, movement with a rotational component.Slide 41: Tipping Translation Rotation Extrusion Intrusion When the crown and root going are going in same direction at the same time.Slide 42: A force applied in line with the center of resistance ; the tooth is translated with no rotation relative to the forceSlide 43: Tipping Translation Rotation Extrusion Intrusion Rotation are labial or lingual movements of a tooth around its long axis.Slide 44: Tipping Translation Rotation Extrusion Intrusion Bodily displacement of a tooth along its long axis in an occlusal direction.Slide 45: Tipping Translation Rotation Extrusion Intrusion Bodily displacement if a tooth along its long axis in an apical direction.Slide 46: Torque. Reverse tipping characterized by lingual movement of the root.EFFECTS of force magnitude: EFFECTS of force magnitude Excessive force can result in Crushing of blood vessels Death of cells CT comprssion . Hyalinization. no active movement can’t take place. Underminig resorption occur We don’t want hyalinization in orthodontics.Slide 48: THANK YOU You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.