Materials research in maxillofacial prosthesis

Maxillofacial prosthetics the science and art of anatomical, functional, or cosmetic reconstruction by means of artificial substitutes of head and neck structures that are missing or defective.

Ideal requirement of materials used in maxillofacial prosthesis Ideal physical and mechanical properties. Ideal processing character. Ideal biological properties. Ideal esthetic requirement.

Ideal physical and mechanical properties Dynamic properties comparable to tissues. High edge strength. High elongation. High resistance to abrasion. High tear strength. High tensile strength. Low coefficient of friction.

Ideal physical and mechanical properties, cont. 8. Low glass transition temperature. 9. Low specific gravity. 10. Low surface tension. 11. Low thermal conductivity. 12. Odorless. 13. Non-inflammable. 14. No water sorption.

Ideal physical and mechanical properties 15. Softness compatible to tissues. 16. Translucent.

Ideal processing characteristics: Adjustability. Chemically inert after processing. Ease of intrinsic and extrinsic coloring with commercially available colorants. Ease of mold fabrication. Ease of processing. Ease of repair or re-fabrication if needed. Fidelity of detail reproduction.

Ideal processing characteristics, cont. 8. High enough viscosity for maintaining even dispersion of colorant. 9. Long shelf life. 10. Long working time. 11. Low enough viscosity for ease of processing. 12. Low processing temperature. 13. Low sensitivity to contamination during processing. 14. No inflammable.

Ideal processing characteristics, cont. 15. No polymerization by products. 16. Non toxic components. 17. Non-porous after processing. 18. No color changes after processing. 19. Odorless before and after processing . 20. Reusable molds. 21. Retain intrinsic and extrinsic coloration during use short processing time.

Ideal biological properties: Non allergenic. Non toxic Compatible with supporting tissue. Cleansibility without loss of details at surface or margins. Cleansible with disinfectants. Color stability. Dimensionally stable. Flexibility comparable to tissues. Flexibility stable at extreme of temperature.

Ideal biological properties, cont: 10. Inert to solvents and skin adhesiveness. 11. Inexpensive. 12. Permeable to moisture release from underlying tissues. 13. Resistance to environmental discoloration. 14. resistance to growth of microorganisms. 15. Softness maintained during use. 16. Usable life of 2 or more years.

Ideal esthetic requirements Un-noticeable to public. Reproducing the lost structure in the finest details. Color, texture, form and translusency must duplicate the missing structure adjacent skin.

Materials available for maxillofacial prosthesis : Acrylic resin Acrylic co-polymers. Polyvinyl chloride and copolymers-realistic, mediplast prototype III. Chlorinated polyethylene. Polyurethane elastomers Silicon elastomers. Foaming silicones.

1) Acrylic resin Acrylic resin can be successfully employed for specific type of facial defects, particularly those in which little movement occurs during function such as the ocular defects.

Acrylic resin The material is readily available . Both intrinsic and extrinsic coloration can be easily done. Its compatible with most adhesive systems . it remains serviceable for up to 2 years, but they require occasional face repainting. Disadvantages: 1) Rigidity is disadvantage as it cant be used in movable tissues. 2)High thermal conductivity produces discomfort to cold climates.

2) Acrylic copolymers Soft and elastic but has not received wide acceptance because of the number of objectionable properties: 1) poor durability 2) subjected to degradation when exposed to sunlight 3) processing and coloration are difficult.

3) Polyvinyl chloride and copolymers-realistic, mediplast prototype III. its popular and widely used for facial restorations. It consist of combination of polyvinylchloride and plasticizers. Advantages : 1) flexible 2)adaptable to both intrinsic and extrinsic coloration. 3) present an acceptable initial appearance when properly manipulated.

Polyvinyl chloride and copolymers-realistic, mediplast prototype III. Disadvantages: 1)these compounds are easily stained and degrade when exposed to ultraviolet light , peroxides and ozone. 2)poor dimensional stability of the polyvinylchlorides .

4) Chlorinated polyethylene. Its similar to polyvinylchloride in both chemical composition and physical properties. The processing procedure : involves high heat curing of pigmented sheets of the thermoplastic polymer in metal models. Coloration : using oil soluble dyes. Repeated molding is being disadvantage of the system.

5) Silicon elastomers. Silicone elastomers have been used for over 50 years to fabricate facial prostheses for individuals with facial defects resulting from resection, trauma, or congenital anomalies. It’s a combination of organic and inorganic compound. Disadvantages: -poor tear resistance. -staining.

Silicon elastomers The process of cross-linking the polymer is known as vulcanization . The silicon elastomers available in 2 forms : 1) those who is requiring heat to effect vulcanization (HTV). 2) those who vulcanize in room temperature (RTV).

6) Foaming silicones. The form has a limited use in maxillofacial prosthesis The purpose of the foam forming silicon is to reduce the weight of the prosthesis however, it reduces the strength and its susceptibility to tear.

New materials Silicone block copolymers Polyphosphazenes A fiber-reinforced composite prosthesis.

Silicone block copolymers They are new materials under development to improve some of the weakness of the silicon elastomers such as : 1) low tear strength. 2) low percent elongation. 3) the potential to support bacterial and fungal block. the silicon block copolymer is done by incorporating the poly methyl methacrylate (PMMA) into silicon blocks.

Polyphosphazenes It has been introduced as a resilient liner . It has the potential to be used in maxillofacial prosthesis . Modification of the physical and the mechanical properties of this commercially available elastomers may be needed to satisfy the requirement for fabrication of maxillofacial prosthesis .

A fiber-reinforced composite prosthesis

Adhesives They are commonly classified by the method in which they are dispensed :pastes, liquid emulsion, spray-ons, and double-sided tapes. Double-sided is the most used (41%) among patients with facial prosthesis but its poorly flexible. If the patient is not candidate for implant intervention (tumor prognosis, compromised tissue beds, financial limitation) many of them have relay on skin adhesives to retain their facial prosthesis.

Osseo-integrated implants Alternative to reduce the need of adhesive is the use of Osseo-integrated implants to retain the facial prosthesis like bar-clips or magnets.

Coloration Basic skin tone should be developed into the shade guide.

Coloration The base shade selected for the patient should be slightly lighter than the lightest skin tones of the patient because the prosthesis will darken as color is added. Surface details character will be added either intrinsic or extrinsic coloration. Intrinsic coloration is longer lasting and therefore preferred but more difficult to accomplish than the extrinsic coloration.