4. For the following materials: a) Titanium alloy; b) Cobalt alloy; c) stainless

Question

4. For the following materials: a) Titanium alloy; b) Cobalt alloy; c) stainless steel, d) TiNOL; e) amalgam; f) Aluminum oxide; g) pyrolytic carbon; h) hydroxyapatite. Which of these materials would you choose for the following applications? Why? (1) Dental implant (2) Hip implant stem (3) Hip implant femoral head (4) Heart valve coating (5) Bone substitute (6) Stent (7) Bone fixation plate In the artificial knee shown below, what materials can be used to make the joint? What type of materials cannot be used? Explain your answer. 5. Femoral flange Tibial Backup

Explanation / Answer

4.

1. Dental implant-(e)Amalgum

Reason: Dentistry has used alloys of mercury with metals such as silver, copper, indium, tin and zinc. Amalgam is an "excellent and versatile restorative material" and is used in dentistry for a number of reasons. It is inexpensive and relatively easy to use and manipulate during placement; it remains soft for a short time so it can be packed to fill any irregular volume, and then forms a hard compound. Amalgam possesses greater longevity when compared to other direct restorative materials, such as composite.

2.Hip implant stem-(B) Cobalt Alloys

Reason Cobalt alloys are most commonly used to make artificial joints including knee and hip joints due to high wear-resistance and biocompatibility.Cobalt alloys tend to be corrosion resistant, which reduces complication with the surrounding tissues when implanted, and chemically inert that they minimize the possibility of irritation, allergic reaction, and immune response.

3.Hip Implant femoral head-(f) Aluminium oxide

Reason: Alumina(Al2O3) are oxidized ceramics; their high oxidation level renders them chemically inert, resistant to corrosion and stable over the long term. Alumina is commonly used ceramic for THR owning to its low friction and wear coefficient, makes its suitable alternative for the orthopedic bearing

4.Heart valve coating-(g)Pyrolytic carbon

Reason: Blood clots do not easily form on Pyrolytic carbon it is often advisable to line a blood-contacting prosthesis with this material in order to reduce the risk of thrombosis. It finds use in artificial hearts and artificial heart valves.

5.Bone substitute-(h) Hydroxyapatite.

Reason: . Hydroxyapatite is composed of calcium phosphate and is incorporated into bone as a physiological mineral. It is not antigenic, carcinogenic or osteogenic. The material used in this study differs from other hydroxyapatite ceramics in that it is an interconnected porous system.It is also used to fill bone defects after trauma, for non-union in the lumbosacral area, for anterior vertebral fusions, in limb sparing operations for malignant bone tumours, and in exchange operations after failed joint endoprostheses

6.Stent-(d) NiTiNol

Reason: significant application of nitinol in medicine is in stents: a collapsed stent can be inserted into an artery or vein, where body temperature warms the stent and the stent returns to its original expanded shape following removal of a constraining sheath; the stent then helps support the artery or vein to improve blood flow. It is also used as a replacement for sutures - nitinol wire can be woven through two structures then allowed to transform into its preformed shape, which should hold the structures in place.

7. Bone fixation plate-(a) Titanium alloy

Reason:Wrought products formed by metallurgy treatments come with an extensive material loss during machining into the final shape of the product and for cast samples the acquirement of a product in its final shape somewhat limits further processing and treatment (e.g. precipitation hardening), yet casting is more material effective.

5.Knee replacement implants:

Artificial replacement parts can be made of strong plastic, metal, or ceramic. All knee replacements, partial or total, will have parts made of a few different materials (likely metals and plastic). In most cases, each component is built from titanium, cobalt-chromium alloys, or a titanium and cobalt mixed metal. The chosen materials must be durable, allow for some flexibility with movement and be biocompatible (meaning it will not be rejected, corrode nor react with the body).

Cobalt-Chromium Alloys— Chromium alloys are one of the most commonly used materials in implant components. This metal is biocompatible, tough, durable and will not be broken down inside the body. This material is commonly used for the femoral implant since it is very sturdy and the femoral implant has a lot of traction against the plastic spacer during movement. For those with nickel allergies, some particles from this metal can get into the bloodstream and cause a reaction. Please let your surgeon know if you have an allergy as there are alternatives.

Titanium and Titanium Cobalt— Pure titanium is not used nearly as commonly as titanium cobalt. Titanium cobalt is used as frequently as cobalt-chromium alloys in joint replacement components. Titanium alloys are biocompatible, will not corrode, nor change inside the body. Titanium cobalt is more elastic and favorable to the natural bone surrounding the implant. Since this metal is softer, it tends to make up the tibial part of the replacement where the plastic insert locks in. In the tibial component, the metal choice is less important since there is little traction or rubbing during movement.

Polyethylene— This is a type of strong plastic found in the the tibial patellar (kneecap) component and the plastic spacer. The plastic components allow the metal pieces to glide smoothly throughout movement. This material is metal-free.

Uncemented implants:

Implants designed to attach directly to the bone without the use of cement are uncemented implants.

Eg:1. Hydroxyapatite- surface of the titanium is modified by coating the implant with hydroxyapatite, a bioactive surfacing agent that will ultimately bond as the bone grows into it.

2.Tantalum:Tantalum is a type of pure metal, which has excellent biological and physical properties, namely flexibility, corrosion resistant, and biocompatibility. Recently, a new porous substance has been made of tantalum named Trabecular Metal. It contains pores, the size of which makes this material very good for bone in-growth. In addition, Trabecular Metal has an elastic nature which aids bone remodeling.

Materials that are not used for entire knee replacement:

1. Stainless Steel:

Reason: Due to limited ability to withstand corrosion in the human body in the long term, stainless steel is not often used in knee replacement implants. It is more suited to being used as temporary implants such as fracture plates and screws.

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