Materials research in maxillofacial prosthesis
Ideal requirement of materials used in maxillofacial prosthesisIdeal 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.Acrylic resin
Molds must be made in dental flasks to permit processing under pressure .Acrylic resin can be used as a temporary prosthesis, clinicians favors the permanent material because its durable ,color stable and cosmetic.
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) Polyurethane elastomers
These elastomers are donated as polyurethanes because they contain urethane linkages. Polyurethane liners improve the durability of silicone-based facial prostheses. Used commercially and medically but only (Epithane 3 ) is used in facial prosthesis.Polyurethane elastomers
Advantages: 1) They are quite elastic without compromising the edge strength, thus permitting thinning of the exposed margins is possible. 2) Flexibility suited in case of movable tissue bed . 3) they can be colored both intrinsically and extrinsically . 4) superior cosmetic results can be obtained.Polyurethane elastomers
Disadvantages: 1) difficult to process. 2) moisture sensitive which is difficult to control in humid environment . 3) not color stable with ultraviolet light and surface oxidation . 4) poor compatibility with the available adhesive systems . 5) Cleaning is difficult and may remove the extrinsic coloration .6) 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).7) 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
PrimersIts for the bonding of the silicone and other maxillofacial prosthesis material .
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.