| Silicone elastomers are the most widely used materials to replace missing facial parts which have been lost through disease or trauma. Addition-type silicone elastomers have superior properties and are more suitable for maxillofacial prostheses than condensation-type ones. Most prosthetic silicone rubbers belong to addition-vulcanized type, such as MDX4-4210 and A-2186. But there is no domestic-made addition-type product. So the objective of this study was to develop a new addition-type prosthetic silicone rubber, and compared its properties with commonly used materials A-2186 and SY-1. Furthermore it is imperative that facial tissue substitutes should be mimic as closely as possible the natural behaviour of facial soft tissues, so different hardness of silicone materials were needed.This thesis was composed of five correlative parts.Part 1. Development of ZY-1 addition-type silicone elastomers.Addition-type silicone ealstomers were comprised of vinylsiloxane, silica, activator, polymerization retarder and hydrogen containing silicone fluid. It was a pourable two-component silicone rubber. The mechanical properties of a silicone elastomer were dependent on many factors. An important one of these was the molecular weight distribution which affected the mechanical properties of the elastomer. The blending of long and short chains of the same polymer gived a broader, bimodal molecular weight distribution, and a network prepared from such a blend was known as a bimodal network. The practical significance of such networks was to achieve elastomers possessing a combination of good mechanical properties such as tear strength, tensile behaviour and resilience. A second factor affecting mechanical properties was the incorporation of hydrophobic surface treated silica filler with a low particle size and therefore a high surface area. This prevented incorporation of water and increases the strength of the elastomer. Clinically acceptable mechanical properties were achieved only at the correct filler concentration. The third main factor was the degree of cross-linking between polymer chains. A high cross-link density produced an inelastic brittle material whilst a very low cross-link density would produce a very weak material with low tear and tensile strength. Based on the results mentioned above, the compoundings of ZY-1 was developed. Shore A hardness of ZY-1 was (24.6±0.5). Tensile strength was (5.5±0.5) MPa, and tear strength was (17.5±3.2) KN/m.Part 2. Measurements of mechanical and physical properties of ZY-1 silicone rubber.Important properties essential in a prosthetic silicone elastomer are high tear strength, high tensile strength, low water solution and sorption and aging abilities. In this study, the mechanical and physical properties of ZY-1 were tested and evaluated by a series of national standard experiments compared with those of A-2186 and SY-1 silicone elastomers. The results showed: tensile strength, elongation at break, permanent deformation rate, tear resistance and aging abilites of ZY-1 silicone elastomers were similar with those of A-2186 and a little better than that of SY-1. Moreover, the water sorption and solubility of ZY-1 addition-type silicone elastomers were markedly superior to that of SY-1. So we can conclude that ZY-1 silicone elastomers had good mechanical and physical properties and could satisfied the use of maxillofacial prostheses.Part 3. Developments of ZY-2 and ZY-3 silicone elastomers and evaluations of their properties.The differences in the hardness readings may be due to differences in the cross-linking system, cross-link density, molecular weight of the polymer and differences in the grade and concentration of the silica filler. Through the adjustment of the compoundings of ZY-1, we got ZY-2 and ZY-3 addition-type silicone elastomers. ZY-2, ZY-1 and ZY-3 had the shore A hardness grads of 30.4,24.6 and 19.0, Which was corresponded with the hardness range of facial tissues. From the results, we could conclude that ZY-2 and ZY-3 also had as good mechanical and physical properties as A-2186.Part 4. Evaluations on the biocompatibility of ZY-1, ZY-2 and ZY-3 addition-type silicone elastomers.Before the clinical application, a series of experiments should be done to determine the biocompatibility of the three new silicone elastomers.So this part was arranged and the results showed that ZY-1, ZY-2 and ZY-3 had good biocompatibility and were suitable for restoration of maxillofacial soft tissue defects.1. In the cytotoxicity test, the results of the MTT cytological assays indicated there was slight cytotoxicity in eluate concentration of ZY-1, ZY-2 and ZY-3 at four inbubation time points. 2. In the skin irritation tests, the primary irritation index of ZY-1, ZY-2 and ZY-3 were all zero. The response types of irritation tests were all minimal. The data showed that these materials didn't have skin irritaion under the experimental condition.3. In the intradermal reaction tests, the primary irritation index of ZY-1, ZY-2 and ZY-3 were all zero. The data showed that these materials didn't have intradermal irritaion under the experimental condition.4. In the skin sensitization tests, the scores of skin reaction of ZY-1, ZY-2 and ZY-3 were all zero. Sensitization rates of the three groups were also zero. There are no potential of skin sensitization to the new materials under the experimental conditions.5. In the Oral mucous membrane irritation tests, there were no local or systemic abnormal response in the groups of ZY-1, ZY-2 and ZY-3. The scores of erythematous response were all zero and the histopathological findings were also normal. The materials had no irritating response to oral mucous membrane under the experimental conditions.Part 5. Fabrications of two maxillofacial prostheses applied with the new developed elastomers mentioned above.The final target of these series of study was to apply the new addition-type silicone elastomers to clinical use.The two patients were all satisfied with the prostheses made by the new materials. And no side effects happened during the using time. The sevice time of the ear prostheses was over a year.
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