MECHANICAL PRINCIPLES IN OTHODONTICS FORCE CONTROL

Views:
 
     
 

Presentation Description

No description available.

Comments

Presentation Transcript

MECHANICAL PRINCIPLES IN OTHODONTICS FORCE CONTROL:

MECHANICAL PRINCIPLES IN OTHODONTICS FORCE CONTROL Syeda Tooba zaidi Deptt of OrthoDontics

OVERVIEW:

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 bruxism

FORCE SYSTEM IN ORTHODONTICS AND FUNCTIONAL JAW ORTHOPEDIC APPLIANCES:

FORCE SYSTEM IN ORTHODONTICS AND FUNCTIONAL JAW ORTHOPEDIC APPLIANCES Natural Biomechanical

Slide 6:

NATURAL Energy generated by contraction of jaw and facial muscles may be transferred through functional appliances

Slide 7:

BIOMECHANICAL Artificial forces . Clinically induced forces derived from mechanical devices. Eg archwires , coil spring, auxillary springs vertical loop in arch wires, elastics, screws etc

Strategies 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 movement

Materials & 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/length

Slide 12:

• Force applied to a beam = stress • Measure deflection = strain; examples: • Bending • Twisting • Change in length

Beam properties in orthodontics:

Beam properties in orthodontics • Defined in force deflection or stress strain diagrams • Useful properties: – Stiffness – Range -spring back – Strength

Bending 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/E

Stiffness 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= stiffer

Range 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 breaks

Relationship of Strength, Stiffness & Range:

Relationship of Strength, Stiffness & Range • Strength = stiffness x range

Resilience, 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 required

Biomechanical 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, ounces

FORCE:

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 direction

Biomechanical 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 movement

TOOTH 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 edge

Determining Crot:

Determining C rot Connect the before and after positions of 2 points The intersection of the perpendicular bisectors of these lines is C rot

Translation or Bodily Tooth Movement :

Translation or Bodily Tooth Movement Point of application of force: Closer to Cres Smaller moment Less rotation More translation

If 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 bracket

CONTACT 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 friction

ORTHODONTIC FORCE:

ORTHODONTIC FORCE Tipping Translation Rotation Extrusion Intrusion Torque

Slide 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 force

Slide 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

authorStream Live Help