Most of the materials such as silicone elastomer for facial prostheses are imported to Japan. We have been developing two novel silicone materials for facial prostheses: one is used by mixing Part A and Part B in a 10 : 1 ratio by weight （KRS-10）, and the other is filled in a 1 : 1 cartridge （KRS-C1）. The viscosities, viscoelastic properties, Shore A durometer hardness, elastic distortion and tensile properties were investigated. KRS-10 showed a lower viscosity, which suggested that it could be mixed easily. It also showed sufficient working time and sharp setting. After curing, the material became flexible and stretchable. KRS-C1 would be easy to use because there is no need for measurement, mixing and defoaming, though it had a higher viscosity than KRS-10. KRS-C1 had high tensile strength, but seemed to be too hard to use for facial prostheses; further modification is required.
The most common facial prosthetic material is silicone elastomer. The ideal characteristics and biological properties of facial prostheses should be similar to those of the facial part or tissue, including elasticity and dimensional and color stability. The purpose of this study was to evaluate the viscoelastic properties of three silicone materials for facial prostheses. Two experimental silicone materials （KRS-10 and KRS-C1, GC Corp） and a commercially available material （A-2186F, Factor Ⅱ） were examined. Cylindrical-shaped specimens were prepared. All specimens were stored in water at 37ºC, and measured after storage for 1 day, 1 week, 1 month, and 3 months. Five specimens of each material were tested with a creep meter. The viscoelastic properties among materials and storage conditions were analyzed with the two-way analysis of variance （ANOVA） and Tukey’s multiple comparison test. All silicone materials exhibited mainly elastic behavior. The viscoelastic properties of KRS-C1 and A-2186F showed almost the same behavior, and the elastic displacement of KRS-10 after 24 hours was greater than that of the others, but that after 1 week was not significantly different from that of the other materials. KRS-10 was the softest silicone material in this study, and was influenced by aging.
A facial prosthesis may have various problems with regard to retention. The use of osseointegrated implants improves retention, however, the implants are not permitted to be used for facial prostheses under the Pharmaceutical Affairs Law in Japan. Hence, the Japan Academy of Maxillofacial Prosthodontics proposed to develop a new silicone material with better characteristics for application to facial prostheses.
The aim of this study was to investigate the recovery from deformation and elongation of new silicone materials for facial prostheses. The permanent deformation of new silicone materials （KRS-10 and KRS-C1 manufactured by GC Co., Ltd. and conventional silicone material A-2186F manufactured by Factor Ⅱ） were recorded by tensile testing.
The rate of change at permanent deformation in KRS-10, KRS-C1, and A-2186F were 0.71±0.20％, 0.19±0.18％, and 0.73±0.18％ （ave.±SD）, respectively. Because an adhesive agent creates a large tensile stress while detaching, KRS-C1 would show better characteristics of recovery from deformation and elongation.
It is suggested that further improvement regarding recovery from deformation and elongation is required for the daily use of facial prostheses.
Conventional silicone-based materials for facial prostheses are normally debubblized after hand-mixing. However, this step requires sensitive techniques and special instruments. The incorporation of bubbles in a facial prosthesis affects the surface color and texture, and morphological reproducibility. Therefore, it is important to investigate the effects of mixing and debubblizing methods on silicone materials in order to control the quality of facial prostheses.
To determine a proper mixing method for the material, the effects of hand-mixing, use of a silicone dispenser as well as presence or absence of debubblizing procedures on bubble incorporation into the polymerized materials were examined in this study.
As experimental silicone materials for facial prostheses, KRS-10 （hand-mixing type, GC） and KRS-C1 （dispenser type, GC） were used. Three groups consisting of KRS-10 without debubblizing, KRS-10 with debubblizing and KRS-C1 without debubblizing were tested. As a result, KRS-C1 presented the least amount of bubble incorporation, followed by KRS-10 with debubblizing, and KRS-10 without debubblizing.
The use of a dispenser for mixing silicone is simple and minimizes the incorporation of bubbles. However, customized color matching by experienced clinicians requires hand-mixing and debubblizing for sites of high esthetic importance. Further improvements in both hand mixing with debubblizing and a method using a dispenser are required.
Color degradation of facial prosthetic silicone material is a severe problem for patients. Many factors have been examined, including the inherent chemical instability of silicones and pigments, exposure to cleansing agents, sunlight and dust. Ultraviolet exposure is one of the important factors of degradation. A novel silicone material has been developed through JAMP. This study reports the color changes caused by ultraviolet exposure. Samples were fabricated using two kinds of silicone material and intrinsic color using pigments and nylon flocking. The samples were exposed to artificial ultraviolet light of 2,313,900 kJ/m2 in total, which is equivalent to one year of outdoor use in Japan. The color change before and after exposure was evaluated using a spectrophotometer. In both materials, hue and chroma showed significant differences between before and after exposure rather than brightness. The samples including nylon flocking as intrinsic coloring were more affected by ultraviolet exposure than the samples with pigments.
Facial prostheses applied to defects of the facial region are always exposed to skin or oral mucosa, fresh air, and sunlight, so it is important to keep the prostheses clean to prevent infection.
The purpose of this study was to evaluate the handling of a new silicone material for facial prostheses. The influence of a denture cleanser, ethanol for disinfection and cleaning with a brush for dentures on test pieces was examined. In addition, we examined the influence of different preservation methods on the color changes of the material.
The denture cleansers and ethanol for sterilization had no influence, but the test piece cleaned with a brush for dentures lost its surface luster and turned yellow. Furthermore, the test piece that was left in the air turned yellow in comparison with a test piece that was immersed in water.
These results suggest that the material should be handled by immersing it in water, keeping it clean by ethanol for disinfection, and regularly cleaning it with denture cleanser.
The purpose of this study was to evaluate the effects on a trial silicone material （KRS-C1, GC Corp.） of deposition of three kinds of stain: coffee, powdered green tea, and curry. The test pieces were immersed in water as a control and these three stains for 4 weeks. Color changes of test pieces were evaluated by colorimeter at the baseline and 4 weeks later. There was no difference of brightness or color between before and at 4 weeks in the control group. However, although there were no differences in brightness, the test pieces dipped into coffee, powdered green tea and curry became yellow-green. It is suggested that this trial product might become stained with long-term use.
The fabrication and clinical application of a facial prosthesis for defects including a movable region are one of the most complicated treatments. The subject was a 63-year-old man who had a left facial skin concavity with an extensive facial and maxillary defect including the orbit after surgery for a left maxillary tumor. The mid-facial defect including the movable region was reconstructed by a two-piece facial prosthesis which could follow the movable region by dividing the amount of opening gap. This clinical report describes the method of fabricating the two-piece facial prosthesis made of a new silicone material manufactured by GC Co., Ltd. and its application to the patient. The prosthesis was successful with regard to suitability and ability to follow the movable region.