Facial Prosthetic Materials

Historically, a large number of materials such as porcelain, natural rubber, gelatin and latex have been employed in the fabrication of facial prostheses. But, two of them have established themselves methacrylates and silicones [Ij. Methacrylates have the advantage of being more durable, however, they are relatively hard. 

Chlorinated polyethylene elastomer (CPE) is one of the alternatives of the PDMS. Extraoral maxillofacial prostheses have been fabricated with silicone elastomer for 50 years, with few improvements. A controlled, randomized, prospective, double-blind, single-crossover, multicenter, phase 111 clinical trial was performed by Kiat-Amnuay et al. to determine the noninferiority of CPE to silicone elastomer [46]. For this purpose, 42 patients were randomly assigned to wear a custom-made prosthesis fabricated from both materials for four months and asked to rate their satisfaction (0 = not satisfied, 10 = completely satisfied). Of the 28 patients who completed the study, 68% had used silicone prostheses previously. Overall, patients rated the silicone prosthesis higher than CPE (difference 2.2, 95% confidence interval [Cl] 0.9 to 3.6, P =. 017). Previous users had a stronger preference for silicone (difference 3.3, 95% Cl 1.7 to 4.9, P = 

SiUcones on the other hand, are both soft and flexible and keep body temperature. Hair and skin features can be easily simulated and the edges can be thirmed as to become imperceptible. This enhances camouflage of the finishing border between the prosthesis and the surrounding skin. By using the modern polydimethylsiloxane (PDMS) elastomers, it is possible to fabricate facial prostheses of outstanding aesthetic quality [1,47,48]. 

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In addition, the prosthetic material must be insoluble and present low absorption capabdities. Facial prostheses may absorb saHva or sweat from the surrounding facial tissue, and also maybe vulnerable to liquids used for washing of the prosthesis. Absorbed water may deteriorate the physical properties or even affect the perfection of color matching to the surrounding facial tissue [7]. 

The application of polymeric materials in medicine is a fairly specialized area with a wide range of specific applications and requirements. Although the total volume of polymers used in this application may be small compared to the annual production of polyethylene, for example, the total amount of money spent annually on prosthetic and biomedical devices exceeds 16 billion in the United States alone. These applications include over a million dentures, nearly a half billion dental fillings, about six million contact lenses, over a million replacement joints (hip, knee, finger, etc.), about a half million plastic surgery operations (breast prosthesis, facial reconstruction, etc.), over 25,000 heart valves, and 60,000 pacemaker implantations. In addition, over AO,000 patients are on hemodialysis units (artificial kidney) on a regular basis, and over 90,000 coronary bypass operations (often using synthetic polymers) are performed each year (]J. 

External maxillofacial prosthetics is a science that uses substitutes for anatomical, functional or cosmetic restorations of those regions in the maxiUa, mandible and face that are missing or defective because of surgical intervention as a result of accident, disease or congenital malformation [4], Facial prostheses offer the advantage of immediate reversible solutions and less compHcated medical rehabihtation, but they require artistic skills by maxillofacial technicians and the materials used need to be designed with amenable physical properties. The primary materials for facial prostheses are silicone elastomers. 

Facial prostheses may fail due to the limitations in the properties of existing materials, especially the biocompatibility. Biocompatibility of PDMS elastomers (LIM 6050, MDX 4-4210, Silastic 732) was tested in subcutaneous tissue of rats [85]. A histomorphometric evaluation was conducted to analyze the biocompatibihty of the implants. Mesenchymal cells, eosinophils, and foreign-body giant cells were counted. Initially, all implanted materials exhibited an acceptable tissue inflammatory response, with tissue reactions varying from light to moderate. Afterward, a fibrous capsule around the sihcone was observed. In conclusion, the tested silicones were found biocompatible and suitable to use for implantation in both medical and dental areas. Their prosthetic indication is conditioned to their physical properties. Solid sihcone is easier to adapt and does not suffer apparent modifications inside the tissues [85]. 

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