The Japan Academy of Maxillofacial Prosthetics started a project to develop silicone elastomers for facial prostheses in 2010. In 2015, GC Corporation launched Silfy® in the market as a soft relining material. In order to improve the quality of silicone materials for facial prostheses and to launch the materials, further basic and clinical research is required. The purpose of this study was to evaluate the viscoelastic properties of four experimental silicone materials （KRS-10, KRS-10F, KRS-C2B1, and KRS-C2P1, GC Corp）, and the effects of a thixotropic agent on the viscoelastic properties of KRS-10 and KRS-10F. Seven cylindrical-shaped specimens of each material were prepared. All specimens were stored in water at 37℃, and measured with a creep meter after 1 day, 1 week, and 1 month. The viscoelastic properties among materials and storage periods 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 all the experimental materials examined showed almost the same behavior, and there were no differences between the cartridge and manual mixing types. The viscoelastic properties of these materials in this study were not influenced by aging within 1 month.

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A 59-year-old female with mandibulectomy presented to the Maxillofacial Prosthetics Clinic in Tokyo Medical and Dental University （TMDU） Hospital, Faculty of Dentistry for functional and esthetic rehabilitation. Secondary to right mandibular oral squamous cell carcinoma, she had segmental resection of the right mandible, supraomohyoid neck dissection and reconstruction with a graft from the scapula. A resin-based dento-maxillary prosthesis was fabricated, fitted and adjusted at regular intervals. During the treatment period, the gum-chewing test, masticatory ability test and University of Washington Quality of Life questionnaire were used for assessment. The results showed some level of functional improvement. In addition, psychological changes were investigated using salivary cortisol levels as a stress marker. Salivary cortisol was measured twice, at 17 days after delivery of the prosthesis and two years later. Within the limitations of this study, the changes in salivary cortisol levels suggested a reduction in the patient's stress condition.
This case report showed that delivery of a dento-maxillary prosthesis was effective for functional improvement and provided useful data for assessing the stress of dento-maxillary prosthesis wearers after head and neck cancer surgery.

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