SGD Orthodontic: Material

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SGD Orthodontic: Material. Hamzi , Zulkhairi , Azizul , Haziq , Aishah , Anis, Asmat , Masyitah. Lecture outline: material. Wire fracture Mechanics of spring Bauchinger effect How does the material affect stability and the stiffness of the component?. Wire fracture. - PowerPoint PPT Presentation

Text of SGD Orthodontic: Material

  • SGD Orthodontic: MaterialHamzi, Zulkhairi, Azizul, Haziq, Aishah, Anis, Asmat, Masyitah

  • Lecture outline: material

    Wire fracture

    Mechanics of spring

    Bauchinger effect

    How does the material affect stability and the stiffness of the component?

  • Wire fracture

  • Small loads the stress is below the elastic limit of the material, reversible elastic strain occurs that disappears completely when specimen is unloaded.

    High stressA ductile material begins to undergo irreversible plastic or permanent deformationA brittle material will fracture without any significant permanent deformation

  • Stainless steel wireOrthodontic wire are generally shaped by bending and the wire should possess sufficient ductility to resist fracture during this bending procedure.

    The amount of residual ductility remaining in a wire depends in part on the ductility used up in its manufacture.

  • Mechanics of spring

  • Mechanics of springForce= (deflection)(radius4) @ F=dr4/l3length3

    Force:Single rooted: 25-40gExcess force: delay movement, overload anchorage & discomfort.

    Deflection:Common spring activation: 3mmGreater activation -> pt insert it incorrectly -> unwanted movementSmaller activation -> force applied decrease -> wanted tooth movement (1-2mm/month)

  • BAUSCHINGER EFFECT

  • Named after German Engineer, Johann Bauschinger.

    Applies to very small deformations.

  • May be stated as follows

    By applying a tensile or compressive load beyond the elastic limit, the elastic limit for compression or for tension, respectively, is reduced considerably, and the more the load exceeds the elastic limit, the greater the reduction

  • Tensile stressCompressive stressTensile strainCompressive strainIn this graph, lets treat tensile stress and strain as POSITIVE and compressive stress and strain as NEGATIVE

  • If an annealed specimen is loaded from 0 to B beyond its elastic limit,Bdesignated by point A,Aand unloaded,Its condition is represent by C.CNote that the elastic limit of the material in tensile is given by SeT

  • BACIf the same specimen is next loaded in compression, it follows the path CDE,where D is the elastic limit point on the compression curve,so that the elastic limit in compression is now SeCAccording to Bauschinger effect, SeC < SeT

  • BACIf an annealed specimen instead of being loaded in tension and then in compression, as stated above, was directly loaded in compression,The elastic limit in compression of the annealed material should be SeC ,And would be equal to magnitude to SeT . Hence, SeC = SeT ,and SeC < SeT and SeC < SeC

  • Similar reasoning will happen if the annealed specimen was initially loaded in compression past the elastic limit, unloaded and loaded next in tension.

    The resulting elastic limit in tension would be smaller than the elastic limit of annealed material in compression

  • Whereas Bauschinger effect was originally stated in terms of the elastic limit, the discussion of this effect in the literature has involve the use of terms elastic limit and yield strength interchangeably.

    The reason for this anomaly lies in the elastic limit and the yield point being located very close to each other on the stress-strain curve.

  • The important thing is that one should not lose sight of the fact that Bauschinger effect applies to VERY small strains only.

  • How does the material affect stability and the stiffness of the component?

  • How does the material affect stability and the stiffness of the component?The stability ratio of a spring in mechanical terms :Stiffness in the direction of unwanted displacementStiffness in the intended direction of tooth movement

    The spring must be guided so that its action is exerted only in the appropriate direction by:Place the spring in an undercut of the tooth so that it does not slip occlusally during activationUse a guide to hold the spring in its position during activationBond an attachment to the tooth surface to engage the spring

  • In PracticeHigh stability spring eg. Finger spring Straightforward to adjust/movement

    Low stability spring eg. Buccal canine retractorDifficult to position precisely on the tooth to be moved

    The spring should be adjusted so that the point of application will give the desired direction of tooth movement.

  • Self supported springThese springs are made up of thicker wire to avoid distortion by the patient

    Supported springThese springs are made up of thinner wire , a guidewire maybe provided. Alternatively, they maybe supported by an additional sleeve or boxed of acrylic to ensure adequate stability