Imp Tech U1 Flashcards
What are the 3 factors than need to be considered in implant design?
Structural, kinematic, biocompatibility
What are the components of structural factors that need to be considered in implant design?
Strength, stiffness, lubrication, wear, fatigue
What are the two types of bone and how are they distributed?
Compact; shafts on long bones (prevent deformation under bending/torsional loads)
Cancellous; at the ends of bone for shock absorbing (then cortical underneath to prevent deformation)
What type of loading is bone strongest under (in order of strength)?
Longitudinal loading (the direction bones are naturally loaded) Compressive, tensile, shear
How are trabeculae arranged?
Along lines of greatest stress
What material properties is cortical bone?
Viscoelastic (the faster it is loaded, the stiffer it becomes)
What type of loading can occur at an interface?
Compressive or shear loading
For compressive loading at an interface what happens if the stiffer material is on top, or on the bottom?
On top; the bottom material will bulge out underneath generating shear stresses due to uneven deformation - the load will be evenly distributed across the interface regardless of where it is applied
On bottom; top material will bulge, means that stress will be concentrated at the applied region - more concentrated load means higher interface stress than if stiff material on top
When 2 bars of different stiffness are bonded together and undergo shear loading, how is the stress distributed?
If off different stiffness they deform differently under the load - as joined together gives rise to shear stress
Load transfer occurs at the end regions where the bars join, there is no shear stress in the middle where there is land sharing
What determines how much load is transferred to the implant in the load sharing region?
The relative stiffness of the 2 materials;
- if the bone is stiffer, then less stress is shared so less stress shielding occurs
What geometrical properties affect stiffness?
Length and cross sectional area (S = EA/L)
S= stiffness, E = young’s modulus, A = cross sectional area, L= length
What is used to measure material stiffness under shear or axial loading?
Axial loading = E (Young’s modulus)
Shear (or torsion) = G (Shear modulus)
How is rigidity calculated in axial, bending and torsional loading?
Axial: R = EA
Bending: R = EI
Torsional: R = GJ
How is the amount of load sharing calculated?
The Load on the bone, vs the total load (so the % take by the bone) is calculated by the ratio of the rigidity of the bone vs the total rigidity (of the bone + stem)
Lbone/Ltotal = Rbone / Rbone + Rstem
How are temporary vs permanent implants fixed?
Temporary; screws, nuts, bolts
Permanent; interference fit, bone cement, biological fixation