A Study of Tensile Degradation of Bioresorbable Materials Used for ...

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Degradation of Bioresorbable Tensile Bars Introduction Bioresorbable materials have been in use as medical applications for the past twenty years; however, they are used sparingly because these polymers are much more expensive than the more common material, titanium. Bioresorbable polymers comprise several varieties of compounds, including the PLA/PGA mixture. This specific compound has been shown to always unite bones by the end of the healing period. Most surgeries that use a bioresorbable fixation system have few complications and high success rates (British Association of Oral and Maxillofacial Surgeons, 2000, p. 4). One study on mandibular fractures in humans showed that the complication rate of using resorbable fixation was approximately 22.5 %. The average complication rate when using titanium fixation varies from 13.7% to a high 43% (Ferretti, 2008, p. 242). These statistics present the evidence that bioresorbable polymers can be used as a secure replacement to titanium fixation. Research has been focused on the improvement of bioresorbable polymers over the past four decades. Even though they have been researched for over forty years, the absorbable materials have only been in use by the public for approximately twenty years. These materials are still rarely used because they are much more expensive than their alternative fixation device, titanium. PLA/PGA co-polymers are desirable in areas of the body that are non-weightbearing and suffer little stress, such as the face. Maxillofacial implants are one of the most common uses of bioresorbable fixation. This is beneficial because the implants will dissolve after the facial fracture is healed, avoiding a subsequent surgery on the face to remove the fixation device (Bayram et al., 2009, p. 67). There are numerous applications of the bioresorbable polymers in addition to maxillofacial implants. The polymers were tested on non-weightbearing facial implants first because of the uncertainty that they would be able to withstand the stress of weightbearing body parts. The continuous research on biomaterials has led to numerous improvements on the qualities of bioresorbable polymers such as easier handling techniques, slower degradation processes, and stronger structural design. This allows the biomaterials to be used in more demanding applications (Eppley, 1997, p. 945). 3
Degradation of Bioresorbable Tensile Bars Literature Review Benefits and Uses of Titanium The practice of internal fixation comprises numerous devices such as resorbable fixation systems, sutures, and titanium fixation rods. Titanium is the most commonly used metal in medical applications. It is the metal of choice across the world and is known for its strength and flexibility. It is the most biocompatible material by far compared to all other metals that have been used for medical purposes. In the 1940s, titanium was being used for the first time in dentistry. Only one decade later, titanium found its way into the surgical field. Now it is the most widely accepted metal by medical professionals. Titanium can be used for prosthetics, internal fixation systems, and surgical instruments (International Titanium Association, 1999, p. 1). Several qualities put titanium at the top of the list for medical applications. For example, titanium is completely unaffected by bodily fluids, and it can resist the body environment under all conditions, including stress and fatigue. When exposed to any amount of oxygen, a naturally formed protective oxide layer develops around the titanium. Reaction to tissue in the body is prevented by this film that adheres to the titanium and resists alteration due to chemical changes. Moreover, titanium binds itself to bones, making it very difficult to break the bond between them. This quality makes titanium preferable to other materials that require an additional adhesive. Titanium also has the highest strength to weight ratio of any other metal that is tolerated by the human body. The density of titanium is very similar to the density of bone which makes it a natural choice for bone fixation. Titanium is also only 56% as dense as stainless steel, making it much lighter in weight than other strong metals. Even though titanium is less dense than other metals, its strength is not compromised. It is approximately 25% stronger than stainless steel. Bone growth is not an issue when titanium is used because it is flexible enough that it will accommodate the growth of the bones it adheres to. Furthermore, the thermal expansion of titanium is comparable to that of human bone. Because it is not magnetic, titanium is not affected by outside interference. Titanium is clearly the metal of choice to be used in human surgeries (International Titanium Association, 1999, p. 2). Because titanium is easily worked, reshaped, and combined to form different alloys, it is used in several diverse medical applications. The most common use of titanium today is in hip replacements. Of all the knee replacements performed each day, nearly half use titanium. Spinal fixation is also one of the frequent uses for titanium. To support broken bones, reconstructive titanium bone plates are used. These are only a few of the countless applications in which titanium is employed (International Titanium Association, 1999, p. 2). Negative Effects of Titanium Despite the benefits and characteristics of titanium that make it the number one choice of metals to be used in medical applications, it also has some downfalls. For example, once a titanium plate or other form of titanium has been put into the body, the piece of titanium resides in the body for the rest of the patient’s life. The titanium will stay in the body long after the problem it was designed to fix has healed. If the patient wants the titanium removed, he or she must undergo a second surgery that will remove the titanium. Titanium is a natural adhesive that forms a strong bond at the area of bone attachment. This also makes it very difficult to remove from the system. Even though it is not harmful to leave the titanium in the human body, it is not necessary for it to be present once the bone fracture is healed; however, it is unfortunate for a patient to endure another surgery to remove the internal fixation device. 4
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