Facial Prostheses

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. 

Dentures acrylic, ultrahigh molecular weight polyethylene (UHMWPE), epoxy Facial prosthesis acrylic, PVC, polyurethane (PUR)... 

Deformities of virtually any bone can be corrected. Even facial bones that are malformed can be reshaped or replaced to provide a normal face or to correct defects in the oral cavity. Bone transplants from one individual to another are commonplace. The patient who loses a limb from a disease such as cancer can have a normal-appearing prosthesis fitted and can be taught how to use it and attain a near-normal lifestyle. 

Generally, the patient has to be present when the process of tinting the prosthesis is carried out in the clinic to get the proper shade for the prosthesis. This stage may be facilitated if a reliable reproduction of the skin color can be made. So that, the patient needs only to be present when the facial shade is selected just before the processing of the prosthesis. 

Schaff NG. (1970) Color characterizing silicone rubber facial prosthesis. 1 Prosthet Dent 24 198-202... 

The tensile strength of the silicone elastomer ensures an overall strength of the material. Moreover, a high elongation at break is desirable, especially when peeling a nasal or eye prosthesis from the facial tissue. 

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]. 

In clinical practice, it has been observed that facial prostheses can cause irritation, abrasion and sometimes ulceration of the supporting tissues. If the tissue side of the facial prosthesis is left as a negative of the actual tissue texture, it will act as sandpaper as it abrades the tissue surface in function. Therefore, the tissue side of the prosthesis must be smoothed and polished to eliminate abrasion. In addition, the hydrophobic characteristics of polysiloxane... 

The effect of disinfection and accelerated aging on the hardness and deterioration of a facial sihcone prosthesis fabricated with and without incorporation of pigments was carried out by Goiato et al. [56]. The above authors concluded that the pigmented samples had significantly higher hardness and deterioration values than those of nonpigmented samples. 

Keywords Silicone elastomer, polydimethyl siloxane, facial prosthesis, epithesis, facial prosthetics, anaplastology... 

Some cancer surgery may cause facial defects integrated with an intraoral maxillary defect. Such defects are named midfacial defects, which occur in the horizontal plane of the middle third of the face and include two main categories midline and lateral. Midline defects refer to the complete or partial involvement of the nose, and/or upper lip, along with intraoral maxillary defects [7,8]. A lateral defect may include complete or partial contents of the cheek and or orbit, and may embrace an intraoral defect of the maxilla [9, 10]. Midfacial defects usually require a facial prosthesis to restore function and appearance, and also, an intraoral prosthesis such as an obturator to restore speech... 

Distribution of 35 facial prostheses were reported by Leonard et al. [19] of these, 12 were congenital, and consequently 8 were traumatic, 8 were resected neoplasms and 7 were infectious defect prostheses. Karakoca et al. [20] reported the 60 facial prostheses as 32 auricular, 25 orbital and 13 nasal. Also, Hatamleh et al. [21] studied the types of facial prostheses that were constructed by maxillofacial prosthodontists and technologists as an alternative treatment when mctxiUofacial defects cannot be fulfilled surgically. In that study, 1193 prostheses were recorded and were followed. Of these, 42% of them were ocular, 31% were auricular, 13% were orbital, 12% were nasal and 1% was composite, that is, more than one facial prosthesis. 

Figure 21.1 Skin-penetrating osseointegrated implants for a facial prosthesis.

Maintaining a reliable and long-lasting osseointegration in between the implant-bone interface is the first step of the success of any bone-anchored facial prosthesis. Of 142 implants that were used on 50 patients, osseointegration was observed in 95.7% of nonirradiated patients and 81.6% in irradiated ones, presenting radiotherapy as a potential factor which reduces the rate of osseointegration [30]. 

Osseointegrated implants are used in different regions of the face to fix a facial prosthesis. However, they should correspond to the requirements of the facial prosthesis. 

Toljanic et al. [32] reported the survival rates of the facial implants in a retrospective study. Implant failure rate in the orbital region was found to be 23% after 5 years and 42% after 10 years. Charpiot et al. [30] found the ossointegra-tion rate of 142 implants used for 51 facial prostheses was 95.7%. Leonard et al. [19] reported that implant failure was observed for 2 of the 3 implants placed to support a nasal epithesis in a patient with hepatitis C virus who also had serious periodontal disease and had experienced a post-infective necrosis of the nose after a liver transplantation. An implant failure was also observed in a diabetic patient with an extensive midfacial defect due to a mycotic infection, but it did not compromise the retention of the prosthesis. 

Akman et al. [15] reported the treatment of a patient with osseointegrated extraoral implants supporting a framework retainer and acrylic resin mesostructures and a large silicone midfacial prosthesis. A metal framework was used to splint the implants together and provided satisfactory retention for the facial prosthesis. There were several case reports about the implant-retained auricular prostheses [2, 3, 29] and the implant-retained nasal prostheses [13,28,31]. 

The mechanical performance of various attachment systems was studied comparatively [39, 40]. Goiato et al. [39] aimed to assess the behavior and stress distribution of three retention systems associated with implant for facial prosthesis by using the photoelasticity method. A photoelastic... 

To design a prototype is essential prior to the fabrication of the definitive facial prosthesis. Prototype designing may be performed by either real or virtual techniques. For fabrication of a real prototype, it is necessary to make an impression and to pour a facial moulage in dental stone. Afterwards, a... 

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]. 

Although widely used, these materials are far from ideal. The quality of these materials depends greatly on their two basic components, the PDMS chains and the silica fillers. The interactions between these two components affect the overall strength and service dimation of the material [55]. The essential physical properties of the material used for the construction of facial prosthesis were described as tear strength, tensile strength, hardness, water absorption and surface wettability [55,56]. 

The water absorption of a facial prosthesis is important since they may absorb saliva, sweat and/or nasal secretions from the surrounding tissue and also during washing the prosthesis in water. Any absorbed water may affect the physical properties and subsequently influence the color matching to the surrounding facial tissue [57]. 

Detail reproduction and the stability of color, flexibility and dimension are the most approved specifications of a facial prosthesis made with PDMS elastomer. The detail reproduction is directly related to the esthetic performance of the prothesis since the material mimics the details of the patients skin appearance in order to provide a lifelike appearance. StabiUty of color and flexibiUty of the PDMS are also important factors for longevity of facial prostheses. The dimensional stability is an important property of a material to provide prosthesis fitting over time, protection of the bloody tissues as well as esthetics [54,61]. Nevertheless, the average time of replacing the facial prostheses wcis reported between... 

Tear resistance of a facial prosthesis may also be increased by tulle. Margins of the prosthesis may be more stable, more resistant to tearing, and less likely to deform while adhesive, cosmetics, and cleaning agents are applied and removed [79, 84]. 

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