Maxillofacial Prosthetic Materials
Maxillofacial prosthetic materials are used to correct facial defects or deformities which occur due to cancer, surgery, accident or congenital deformities. Nose, ears, eyes or any other part of head and neck may be reconstructed by this prosthesis.
Ideal Requirements of Maxillofacial Materials:
- These materials must be biocompatible, easy and inexpensive to fabricate, strong and durable.
- Prosthesis must be skin like in appearance and texture.
- It must be color stable as it is subjected to sunlight (including ultraviolet light) heat, and cold.
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- It must be easy to clean and manage by the patient.
- Facial prostheses are often constructed with thin margins to enable blending to the skin.
- This is then attached to the skin with adhesives.
- On removing at night, the thin edges can tear. It must be resilient enough to prevent tearing.’
- The water absorption of the prosthetic material is important since facial prostheses may absorb saliva or sweat from surrounding facial tissue.
- During washing, the prosthesis can absorb water.
- Any absorbed water may affect the physical properties and also affect the perception of color matching to the surrounding facial tissue.
- It should be hygienic and prevent the growth of microorganisms.
- It should have the translucent properties of the part it is replacing.
- No material so far has all of these characteristics.
Classification of Maxillofacial Prosthetic Materials:
Maxillofacial prosthetic materials are classified on the basis of their usage as:
- Intraoral: Materials are PMMA, tantalum, titanium, vitallium, Silicones, and titanium, stainless steel
- Extraoral: Materials are polyvinyl chloride, PMMA, Silicones, and polyurethane.”
Description of Materials:
PMMA:
- It was once commonly used for maxillofacial prosthesis.
- It is readily available, easy to manipulate, strong, color, stable, hygienic and durable.
- Its usefulness in extraoral prosthesis is limited because acrylic is hard and heavy, does not move when the face moves and does not have the feel of skin.
- It is particularly used in cases where there is least movement of tissue bed during function.
Plasticized MMA:
- This is formulated by foaming agent.
- Due to the heat released or by initiating chemical, a foaming agent releases the gas which gets incorporated in the material as it get cured.
- The final product formed is spongy with solid skin wherever the material contacts with mold surface.
Latex:
- Lat exes are soft, inexpensive and easy to manipulate.
- They are realistic and form life like prostheses.
- However, the finished product is weak, degenerates rapidly with age and changes color.
- Latex is no longer a major facial prosthetic material.
Vinyl Polymers
- Polyvinyl chloride is a rigid plastic and is made more flexible by adding a plasticizer.
- Other ingredients added to polyvinyl chloride include cross-linking against (for strength) and ultraviolet stabilizers (for color stability).
- Color pigments can be incorporated to match individual skin tones.
- It is supplied as fiely divided polyvinyl chloride particles suspended in a solvent.
- When the fluid is heated above a critical temperature, the polyvinyl chloride dissolves in the solvent.
- When the mix is cooled, an elastic solid is formed.
- The prosthesis becomes hard with age because the plasticizers are lost from the surface of the prosthesis.
Chlorinated Polyethylene:
- This material was introduced in the 1970s and 1980s as an alternative to silicone.
- Processing involves high heat curing pigmented sheets in metal molds.
- Dow’s chemicals’ chlorinated polyethylene elastomer is an industrial grade thermoplastic elastomer.
- It is less irritating to the mucosa than silicone, less toxic than thermos setting silicone materials and non-carcinogenic.
- Chlorinated polyethylene elastomer appears to be a suitable substitute for silicons for the fabrication of extraoral maxillofacial prosthesis in situations where the cost of silicone is prohibitive.
- Its advantages are higher edge strength, permanent elasticity and lower fungus growth
Polyurethane:
- It is the most recent addition.
- One of its components is acrylate which needs careful handling to prevent a toxic reaction to the operator.
- Although the material is cured at room temperature it requires accurate temperature control because a slight change in temperature can alter the chemical reaction.
- A metal mold is used to avoid moisture in the air affecting the process.
- It has life like feel and appearance and the color stability is better than that of polyvinyl chloride.
- But it is susceptible to deterioration with time.
Silicone:
It is a long chain molecule which is composed of chain of alternating silicone and oxygen atoms. By adjusting the length of silicone it can be produced in the form of fluid, resin or elastomers. They are of two types, i.e.
- Room temperature vulcanizing silicone or RTV silicones:
- These polymers set by condensation polymerization.
- They have stannous octate as catalyst and or tho alkyl silicate as cross-linking agent.
- RTV silicones are easy to process and also undergo intrinsic coloration
- Heat vulcanizing silicone or HTV silicones:
- These materials need heat for vulcanization
- HTV silicones are highly viscous, white and opaque.
- HTV silicones composed of dichlorobenzoic acid for condensation polymerization and platinum salts for addition polymerization.
- Advance equipments are needed for processing of HTV silicones.
- Physical properties of HTV silicones are better than RTV silicones.
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