Flashcards in metallic instruments and implants Deck (72):
What are the 3 main categories of stainless steel instruments?
martensitic, precipitation hardenable, austenitic
martensitic stainless steel has ______ corrosion resistance and is ______ magnetic.
the martensitic compositions contain what percentage chromium? describe their carbon content.
12 to 18%; a medium to high carbon content, and other minor elements
Common types of martensitic alloys of the 400 series of stainless steel include 420A, 431, and 440B. How does the nomenclature relate to it composition?
the higher three digit 4XX number indicates a higher chromium range for a given alloy (440 > 431 > 420).
the suffix letters A,B, or C define an increasing carbon range for a given alloy (420C > 420B > 420A).
T/F: martensitic stainless steel alloys are ideal for cutting instruments and for use in noncutting tools.
True; . Martensitic alloys are very hard and resistant to wear, which makes them ideal for cutting instruments (such as drills, taps, countersinks, reamers, chisels, and bone-cutting forceps) and for use in noncutting tools (such as screwdrivers and wrenches).
What is heat treating?
Heat treating is a hardening process that transforms the microstructure with temperatures in the range of 930° to 1150° C, followed by a controlled quench in air or a liquid. The hardened alloy is then tempered
at an intermediate temperature of 150° to 370° C to develop the final optimal properties
how does increasing the tempering temperature change the hardness of a given martensitic alloy?
the hardness decreases as the tempering temperature increases.
T/F: Precipitation hardenable (PH) stainless steels contain substantial amounts of chromium, nickel, and copper, plus controlled levels of secondary elements.
True; A commonly used PHgrade alloy contains 17% chromium plus 4% nickel (17-4PH) and is identified as Type 630.
T/F: The PH grades contain a high carbon content, so edge retention and wear resistance are superior when compared with the 400 series martensitic compositions.
False; The PH grades do not contain a high carbon content, so edge retention and wear resistance are inferior when compared with the 400 series martensitic compositions
T/F: PH stainless steels are used for a variety of noncutting instruments that require a moderate hardness level.
The term __________ describes the type of microstructure associated with 300 series stainless steel, which is ________ magnetic and has ________ corrosion resistance
austenitic; slightly; excellent
A commonly used __________ alloy contains 17% chromium plus 4% nickel (17-4PH) and is identified as Type 630.
precipitation hardenable alloy
What are the usual composition ranges of chromium and nickel in austenitic alloys?
16% to 18% chromium (similar to PH alloys); 8% to 10 % nickel (c.f. ~ 4% in PH alloys)
T/F: In austenitic alloys, the low carbon grades, such as 304L meet a compositional requirement of a maximum of 0.03% carbon.
True; (L indicates low carbon)
The austenitic alloys 316 and 316L contain what percent molybdenum?
2% to 3%
T/F: The austenitic alloys, except for 316 and 316L, which contain 2% to 3% molybdenum, also become slightly magnetic as the amount of coldwork increases.
T/F: the 300 series stainless steels have outstanding cutting and wear properties.
False; the 300 series are austenitic alloys and have poor cutting and wear properties because of the low carbon content.
T/F: Austenitic alloys can be strengthened by cold working, however they can become slightly magnetic as the amount of cold-working increases.
True; The 300 series stainless steels may be strengthened by cold working, but they do not have outstanding cutting or wear properties because of the low carbon content. The austenitic alloys, except for 316 and 316L, which contain 2% to 3% molybdenum, also become slightly magnetic as the amount of cold work increases. Some of the austenitic stainless steels can be cold-worked to a very high tensile strength and may be used for some noncutting applications including drill guides, clamps, hollow sleeves, springs, and washers
Aluminum _____ are frequently used for bone plate/rod templates. They are ____ in strength, highly _______ (malleable), nonmagnetic, and lightweight
templates; low; ductile;
*Aluminum grade 1100 meets a minimum aluminum content of 99% and is supplied in the soft annealed condition (O temper).
T/F: Pure aluminum has more strength and less ductility when compared with aluminum alloys.
False; Aluminum alloys have more strength and less ductility when compared with pure aluminum
T/F: Aluminum alloys nonmagnetic and lightweight. They are frequently used for depth gages, intramedullary (IM) nail-insertion instruments, hollow external-fixation rings, graphic case modules, and screw racks.
T/F: Aluminum contact with strong alkaline cleaners must be avoided to prevent aggressive chemical attack.
True; Chemical cleaning solutions containing chlorine, iodine, or certain metal salts may attack the anodized coating.
Implant quality 316L stainless steel is an iron-based stainless composition, aka wrought 18% chromium-14% nickel-2.5% molybdenum implant alloy. What qualities do the chromium, nickel, and molybdenum lend to the compound? What is its carbon content?
Chromium provides corrosion resistance; nickel lends greater microstructural stability; molybdenum improves resistance to pitting and crevice corrosion. This alloy has a low carbon content (maximum, 0.03% carbon) which improves resistance to intergranular corrosion.
Can you use a titanium plate with stainless steel screws?
No; For multicomponent devices, such as plates and screws, it is not advisable to mix stainless steel and titanium implants because an accelerated form of corrosion, known as galvanic corrosion, can occur.
T/F: The alloy may also be supplied in the cold-worked or moderate-strength condition to resist the stress loading encountered by bone plates and bone screws. Cold-working refers to a metalworking operation that permanently deforms the material at room temperature to increase the strength, usually by reducing the cross-sectional area by drawing or rolling
The excellent corrosion resistance of stainless steel is primarily a result of a _________ _____ film, known as the ________ layer, which is present on the surface.
Chromium oxide; passive
T/F: Chemical passivation in nitric acid is a commonly used method of surface finishing for stainless steel implants.
True; Immersion in 20 to 45 volume-percent nitric acid passivation solution removes surface contaminants, such as cutting tool transfer films, oxide from heat treatment, imbedded particles, and burned-in lubricants. The passivation process restores maximum corrosion resistance but does not affect part dimensions.
Immersion in 20 to 45 volume-percent ______ _______ passivation solution removes surface contaminants, such as cutting tool transfer films, oxide from heat treatment, imbedded particles, and burned-in lubricants. The passivation process restores maximum corrosion resistance but does not affect part dimensions.
____________ is a surface treatment that consists of applying an electric current to an implant immersed in a specially formulated chemical solution under specified conditions of time and voltage.
T/F: Electropolishing removes a microscopic amount of metal, decreases the surface roughness of the implant, provides a low coefficient of friction, improves corrosion resistance, and creates a chemically passivated surface.
T/F: repeated steam autoclaving will disrupt the passive film and alter the mechanical properties of stainless steel implants.
False; repeated steam autoclaving will not disrupt the passive film or alter the mechanical properties of stainless steel implants.
What does shot-peening before electropolishing do to stainless steel implants?
improves fatigue strength; In shot-peening the implant surface is subjected to high-velocity impaction by metallic or ceramic particles under well-defined conditions. Shot-peening produces a roughened surface with increased residual compressive stress for enhanced fatigue life.
T/F: Implant quality stainless steel is completely nonmagnetic in all conditions, and implants will not exhibit torsional movement or displacement during MR scans.
T/F: Signal artifacts may obscure complete MR visualization in the vicinity of the stainless implant.
T/F: The 15% nickel content may provoke a metal sensitivity reaction and is responsible for about 90% of the metal allergies that are clinically observed in people.
Commercially pure (CP) titanium, also known as unalloyed titanium, is available in five implant compositions designated Ti Grade 1 ELI, 1, 2, 3, and 4. What does ELI stand for? how do the grade changes affect the strength and ductility?
ELI = extra-low interstitial grade (it has the lowest content of nitrogen, carbon, iron, and oxygen).
The strength increases and the ductility decreases as the grade changes from the lowest designation (grade 1 ELI) to the highest designation (grade 4).
T/F: Stainless steel has better biocompatibility than CP titanium.
False; CP titanium has better biocompatibility than stainless steel and typically contains less than 0.05% nickel. Unalloyed titanium implants will not cause metal allergy reactions and are recommended for humans in situations where metal sensitivity is preoperatively verified or where 316 L stainless steel implants have provoked an allergic response.
T/F: Titanium's unique biocompatibility properties include soft tissue and bone adhesion to the implant surface, possibly resulting in less bacterial colonization and reduced infection.
T/F: Tissue adjacent to pure titanium implants becomes well vascularized, with less tendency toward capsule formation.
What is a major disadvantage associated with titanium implants?
titanium implant removal may be difficult, especially for well-osseointegrated implants
T/F: The pitting and crevice corrosion resistance of titanium is inferior to stainless steel.
False; The pitting and crevice corrosion resistance of titanium is superior to stainless steel.
T/F: Titanium implant materials have a lower density, have a lower modulus of elasticity, and provide significantly less MR artifact when compared to stainless steel.
How do the densities and weights compare between stainless steel and titanium implants?
The density of titanium is 57% of the density of stainless steel and represents a weight reduction of nearly 50% when implants of similar dimensions are compared.
The _________ __ __________ is a constant physical property that describes the stress per unit strain in the elastic region.
modulus of elasticity; A material with a high modulus of elasticity will transfer less stress from the implant to the bone.
A material with a high modulus of elasticity will transfer less stress from the implant to the bone. This may produce a condition known as ________ __________, which is not ideal because bone must be adequately stressed to consolidate properly during the bone healing stage.
How does the modulus of elasticity compare between titanium and stainless steel implants?
The modulus of elasticity of titanium is about 55% of stainless steel, and the low modulus is desirable because of increased stress transfer.
T/F: The anodizing treatment for titanium is different from the electrolytic anodizing treatment used for aluminum. The titanium implants are immersed in a chemical solution and a known electrical voltage is applied for a specified time.
T/F: The titanium anodizing process is capable of producing a variety of colors that permit the design of colorcoded implant systems.
True; Visible light diffraction within the oxide film creates a distinct color, which depends on the thickness of the oxide film. No pigments or organic coloring agents are present in the anodized titanium film.
T/F: Multiple steam sterilization cycles will significantly change the appearance of anodized titanium implants.
False; Multiple steam sterilization cycles will not significantly change the appearance of anodized titanium implants. However, fingerprint contamination from skin contact should be avoided when handling the implants between autoclave cycles. Gloved handling of anodized titanium implants prevents the discoloration of isolated areas during steam autoclaving.
In regard to titanium alloys, what does "ELI" indicate?
The ELI designation denotes lower oxygen content and lower hydrogen content
What are common titanium alloys (composition)?
Titanium-6 aluminum-4 vanadium alloys containing approximately 6% aluminum and 4% vanadium;
titanium, 6% aluminum, and 7% niobium
Titanium alloys have ______ tensile strength capability, _______ ductility, ______ modulus of elasticity, and equivalent density when compared to CP titanium.
higher; lower; similar;
Define notch sensitivity.
Notch sensitivity is a term that describes the relative effect that local irregularities or stress raisers have on mechanical properties.
T/F: The notch sensitivity resistance of implant quality stainless steel is similar to unalloyed titanium and is somewhat better than conventional titanium alloys.
_______ alloys are used primarily for prosthetic implants, such as total hips, total knees, and total disc replacement.
Co-28Cr-6Mo is the predominant Cobalt-base alloy that is fabricated for joint replacement applications. The nickel content of this alloy is typically less than what?
less than 0.5%
This alloy may be hot forged into complex shapes, the tensile strength can exceed 1172 MPa, and the wear resistance is outstanding.
Which has better corrosion resistance (cobalt-base alloys, stainless steel, titanium)?
Titanium > cobalt-base alloy > stainless steel
Unique properties of cobalt-base alloys include a high modulus of elasticity, which may be ___% ______ than stainless steel.
_____________ increases the strength of cobalt-base alloys, and thermal aging heat treatments can significantly _______ the yield strength and ultimate tensile strength.
T/F: Certain cobalt base alloys contain greater than 10% nickel, which may provoke a nickel allergy reaction.
T/F: The excellent corrosion resistance of the cobalt-base alloys is predominantly the result of the chromium content, which typically exceeds 19%.
T/F: Chromium and cobalt are considered metal- sensitizing agents but the clinical incidence of sensitivity reactions are relatively rare when compared with nickel.
T/F: Fatigue is a phenomenon leading to fracture under repeated or fluctuating stresses having a maximum value less than the ultimate tensile strength of the material.
True; The fatigue loads are well below the level that normally would be required to cause fracture within a single load cycle. The fatigue cycle is the time interval during which the stress is regularly repeated.
One common measure of the fatigue properties is known as the ____________ ________, which is the maximum stress below which a material can presumably endure an infinite number of stress cycles.
What is an S-N curve?
A common method of expressing the fatigue properties of a material is known as the S-N curve. The S-N curve is a best-fit plot of the individual test values, where S refers to the applied cyclic stress and N is the number of cycles required to fracture the test specimen or to achieve runout.
Runout is defined as the maximum cyclic stress that does not create fatigue fracture at a predetermined number of cycles (usually 10^6 cycles or greater).
In this type of testing, a bone plate is placed in a four-point bending fixture and oriented in a manner that mimics clinical bridging of a fracture site. The bone plate is subjected to a constant frequency cyclic load in four-point bending. The test method establishes a uniform four-point _____ _______ ______ to characterize and compare the fatigue performance of different plate designs.
bending fatigue test
T/F: When comparing bending fatigue curves for 3.5 mm DCP and 3.5 mm LC-DCP, the bone plate fatigue curves reveal that the DCP has increased resistance to maximum compressive fatigue loads when compared to LC-DCP in the low load–high cycle region (greater than 10^5 cycles).
True; Maximum runout load for the DCP (n = 4) was 323 N, whereas the maximum runout load for the LC-DCP (n = 5) occurred at 268 N.
T/F: The endurance limit for 316L stainless steel and CP titanium increases as the percentage of cold-work increases.
T/F: Titanium alloys exhibit a greater 0.2% yield strength when compared with CP titanium, and this factor is primarily responsible for the superior fatigue properties of titanium alloys when compared with CP titanium.