|Year : 2009 | Volume
| Issue : 1 | Page : 2-5
Maxillofacial prosthetic materials
SK Khindria, Sanjay Bansal, Megha Kansal
Department of Prosthodontics, MM College of Dental Sciences and Research, Mullana, Ambala, India
|Date of Web Publication||23-Jun-2009|
H. No. 30, Sector 7, HUDA, Karnal, Haryana
Source of Support: None, Conflict of Interest: None
Acquired and congenital defects of the face create an unfortunate condition for an individual. For the individual to lead a comfortable life requires facial rehabilitation, thus a reassessment of materials used in the field of maxillofacial prosthesis seems desirable. The materials have traveled a long way from wood, wax, primitive metal, leather, rubber, etc. to the latest biomedical material such as polymers. While the new materials have exhibited some excellent properties they have also exhibited some frustrating deficiencies. We still are in search of a material comprising all the ideal properties so as to best restore a maxillofacial defect.
Keywords: Maxillofacial prosthetic material, resins, silicones
|How to cite this article:|
Khindria S K, Bansal S, Kansal M. Maxillofacial prosthetic materials. J Indian Prosthodont Soc 2009;9:2-5
| Introduction|| |
Maxillofacial prosthetics is defined as that branch of prosthodontics concerned with restoration and/or replacement of the stomatognathic and craniofacial structures with prosthesis that may or may not be removed on a regular or elective basis. 
Maxillofacial prosthesis is defined as any prosthesis used to replace part or all of any stomatognathic and/or craniofacial structures. 
Facial defects can result from trauma, treatment of neoplasm or congenital malformation. The prosthodontist is limited by inadequate material available for facial restorations, movable tissue below, difficulty in retaining large prostheses and the patient's capacity to accept the final result. Materials for maxillofacial prosthetic reconstruction span the full range of chemical structures, with physical properties ranging from hard, stiff alloys, ceramics and polymers to soft, flexible polymers and their formulation as latex and plastisols. But, as yet, no material has emerged that possesses all the distinct and desirable characteristics.
Desirable properties of maxillofacial prosthetic material
- Physical properties - The material should be flexible, dimensionally stable, light in weight, with low thermal conductivity and good strength.
- Biological and Chemical properties - The material should remain stable when exposed to environmental assaults, adhesives and their solvents. It should be non-toxic, non-allergenic and biocompatible. It should exhibit good life of at least six months without significant compromise of esthetic and physical properties.
- Fabrication characteristics - Polymerization should occur at a temperature low enough to permit reusability of molds. Blending of individual components should be easy, allowing some margin of error. It should have suitable working time and be easy to color.
- Esthetic characteristics - The complete prosthesis should be unnoticeable in public, faithfully representing lost structure in the finest detail. Its color, texture, form and translucence must duplicate that of missing structure and adjacent skin.
Ambroise Pare (1510-1590),  a famous French surgeon, made nasal prostheses using gold, silver, paper and liner cloth glued together.
1600 to 1800
Pierre Fauchard (1678-1761)  made a silver mask painted with oil paints to replace the lost portion of mandible of a French soldier, by making margins inconspicuous using facial hair.
1800 to 1900
William Morton (1819-1868)  fabricated a nasal prosthesis using enameled porcelain to match the patient's complexion. Kingsley (1880)  made a combination nasal prosthesis using ceramic material. Claude Martin (1889)  fabricated a nasal prosthesis using ceramic material.
1900 to 1940
By the end of the 19 th century, vulcanite rubber was being used. Upham  fabricated a nasal and auricular prosthesis made from vulcanite rubber. In 1913 gelatin glycerin compounds were introduced for use in facial prostheses to mimic the softness and flexibility of human skin, but their lifespan was too short for practical clinical application.
1940 to 1960
In 1937 acrylic resin was introduced and replaced vulcanite rubber. Tylman  introduced the use of resilient vinyl copolymer for facial prosthesis. Adolph Brown  used colorants certified by the Food and Drug Administration for coloring facial prostheses.
Braiser  used acrylic resin polymer stains for intrinsic coloring and oil colors mixed with acrylic resin monomer for external tinting of facial prostheses.
1960 to 1970
Various kinds of elastomers were introduced. Barnhart (1960)  introduced silicone rubber for constructing facial prosthesis.
1970 to 1990
Lontz  used modified polysiloxane elastomers. Gonzalez  described the use of polyurethane elastomers. Lewis and Castleberry  described the use of siphenylenes for facial prosthesis.
Turner , documented the use of isophorone polyurethane. Udagama and Drane , introduced the use of Silastic Medical Adhesive Silicone Type A for fabrication of facial prosthesis.
-1990 to present
A new generation of acrylic resins are being investigated by Antonucci and Stansbury.  Gentleman  described the use of polyphosphazenes. Silicone block copolymer is also being evaluated.
Acrylic resins are employed for specific types of facial defects, particularly those in which little movement occurs in the tissue bed during function (e.g. fabrication of orbital prosthesis) and for temporary facial prostheses.
Acrylic resin is easily available, easy to stain and color, has good strength to be fabricated with feather margin and a good life of about two years. Its rigidity and high thermal conductivity is a drawback.
Visible light cured resin is also being used, which has an organic filler made of acrylic resin beads of different sizes that become part of the polymer network structure upon curing. The matrix is a urethane dimethacrylate with microfine silica and contains a camphoroquinone amine as photoinitiator. 
Acrylic copolymers are soft and elastic but have not received wide acceptance because of poor edge strength, poor durability and being subject to degradation when exposed to sunlight. In addition complete restoration is often tacky predisposing to direct collection and staining.
Polyvinylchloride and copolymer
Earlier these consisted of a combination of polyvinyl chloride and a plasticizer. But these days 5 to 20% vinyl acetate is being added. They exhibit many desirable properties like flexibility, easy coloration and acceptable initial appearance. The primary deficiency arises from migration of plasticizer leading to discoloration and hardening of the prosthesis.
Lewis and Castleberry  reported chlorinated polyethylene, a material similar to polyvinylchloride in which coloration can be done using oil soluble dyes.
Polyurethane elastomers contain a urethane linkage. The reactants are a polymer terminating with hydroxyl group and others terminating with isocyanate in the presence of a catalyst. They can be synthesized with a wide range of physical properties by varying the reactants and their amounts. They have excellent properties like elasticity and ease of coloration but have certain deficiencies like isocyanates, and are moisture sensitive leading to gas bubbles when water contaminated and can also cause local irritation as described by Gonzalez. 
Barnhart (1960)  was the first to use silicone elastomers for extra-oral prostheses. They are a combination of organic and inorganic compounds. Chemically, they are termed as polydimethyl siloxane.  They are of two basic types.
- Room temperature vulcanizing (RTV)
- Heat vulcanizing (HTV)
Room temperature vulcanizing silicone elastomers (RTV)
They are viscous silicone polymer including a filler, a stannous octate catalyst and an orthoalkyl silicate cross linking agent. Fillers are usually diatomaceous earth which improves strength.
- Silastic 382, 399:- They are viscous silicone polymers which are color stable and biologically inert.
- MDX4 - 4210 - In a survey by Andres,  41% of clinicians used this material for maxilla prosthesis fabrication. Moore  reported that it exhibits improved qualities relative to coloration and edge strength. The material is not heavily filled, hence it is translucent. It exhibits adequate tensile strength, is non-toxic, color stable and biologically compatible.
- Silastic 891 - Udagama and Drane  first reported its use, also known as Silastic Medical Adhesive Silicone Type A and it is compatible with wide range of colorants.
- Cosmesil - It is a RTV silicone which can be processed to varying degree of hardness as described by Woofaardt. 
Heat-temperature vulcanizing silicone elastomers (HTV)
Designed for higher tear resistance in engineering applications, this type of polymer requires more intense mechanical milling of the solid HTV stock elastomers compared with the soft putty RTV silicone, especially for incorporating the required catalyst for cross link.
- Silastic 370, 372, 373, 4 - 4514, 4 - 4515 - They are usually white, opaque material with a highly viscous, putty - like consistency. The catalytic agent is dichlorobenzoyl peroxide. They exhibit excellent thermal stability and are biologically inert but do not possess sufficient elasticity to function in movable tissue beds.
- PDM Siloxane - This HTV silicone was developed by Veterans' Administration and reported by Lontz and Schweiger  and Lontz.  Independent evaluation of physical and mechanical properties were reported by Abdelnnabi. 
- Q7 - 4635, Q7 - 4650, Q7 - 4735, SE - 4524U-This new generation of HTV silicone evaluated by Bell  which showed improved physical and mechanical properties compared to MDX4 - 4210 and MDX4 - 4514 (RTV Silicone elastomers).
- Silastic 386 - The purpose of the foam forming silicones is to reduce the weight of the prosthesis.  However, the foamed material has reduced strength and is susceptible to training, leading to weakening of the material. This weakness can be overcome partially by coating foam with another silicone which adds strength but increase stiffness.
- Siphenylenes - Siphenylenes are siloxane copolymers that contain methyl and phenyl groups. These exhibit improved edge strength, low modules of elasticity and color ability over the more conventional polydimethyl siloxane.
Silicone block copolymers
Silicone block copolymers are new materials under development to improve on some of the weaknesses of silicone elastomers, such as a low tear strength, low elongation and the potential to support bacterial and fungal growth. They are more tear resistant than conventional cross-linked silicone polymers.
Polyphosphazene fluoroelastomers have been developed for use as resilient denture liners and have the potential to be used as maxillofacial prosthetic materials.
Other products used
With the introduction of urethane-line silicone prosthesis,  there has been an increased interest in primers used for promotion of bonding between silicone and other maxillofacial prosthetic material 1200, 1205, S-2260, 4040, Z6032 and Z 607.
A variety of adhesive systems have been employed to retain facial prostheses in position. They are commonly classified by the method in which they are dispensed: Parts, liquid, emulsions, sprayers and double sided tapes. Double sided tape is the most commonly used (41%) among patients with facial prostheses  because of its ease of application, removal and maintenance. Most cured silicones, because of their low solubility and low surface energy, will not adhere to conventional tissue adhesive. The single component RTV silicones were developed to serve as adhesives for silicon prostheses (Medical Adhesive Type A).
Realistic coloration of external facial prosthesis is an important feature for patient satisfaction and acceptability. From the standpoint of attaining ideality for any extra-oral prosthesis, it ranks high and indeed is the final, emotional arbiter in successful rehabilitation. The base shade selected for a patient should be slightly lighter than the highest skin tones of the patient because the prosthesis will darken as color is added. Cosmetic realism involves exacting replication of intrinsic (sub dermal) coloration and extrinsic coloration. Intrinsic coloration is longer lasting and is preferred, but is more difficult to achieve than extrinsic.
| Summary|| |
From the overview it is deduced that the materials currently available still do not completely meet our needs. It might be a dream but the possibility of fabricating a high quality lifelike prosthesis directly on the face would require no more skills than a prosthodontist already has, if the dental material scientist can help us by providing a perfect material with all the ideal properties to rehabilitate the patient with orofacial defect who deserves the best we can offer.
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