Far Eastern manufacturers of cosmetic surgery products are comparatively few. The principal one is Koken Co. Ltd. of Tokyo, Japan. This firm has been marketing its products in parallel with U.S. and European firms since the seventies. In the eighties, marketing agreements were evidently obtained with North American and European distributors and the products became more frequently used outside of the Far East. The main U.S. distributor is Porex Medical of Fairburn , Georgia, a subsidiary of Porex Technologies. Earlier distribution rights were granted to Minogue Medical of Montreal, Canada. Both firms were successful in significantly increasing the usage of Koken products amongst North American plastic surgery practices. 

Porex participated in Food and Drug Administration (FDA) discussions during the peak regulatory activities on breast prostheses in the late-eighties. Porex also marketed Koken products under "name brand" packaging and under different catalogue coding systems. The regulatory responsibility for the products in the U.S. has been delegated to Porex. A similar situation exists for Minogue Medical in Canada. These firms are exclusive distributorships. 

Koken has a long history of association with marginal plastic surgery products. Its original incorporation dates to the late-sixties and some of its products reached European and North American users from about 1968. It owns several patents and appears to have filed additional patent applications on implant technology. In the seventies, the activities of the company came to the attention of North American regulatory agencies when silicone-based oils promoted for direct tissue injection were discovered subsequent to investigations of adverse reactions. Significant importation of a product marketed under the trade name of Koken Young™, a silicone oil mixture with added fibrotic agents (Sakurai Formula silicone) intended for facial injection and indicated for removal of wrinkles, was discovered. Several shipments of the substance were intercepted in Montreal by the Canadian authorities. This material had been in widespread clinical use in most North American metropolitan centers since the mid-seventies and had evidently been imported into Canada and the U.S. in small amounts by individual medical practitioners. Injectable silicones from other sources as well as from Koken had been implicated in numerous adverse reactions in the early-seventies and had resulted in FDA advisory notices contraindicating the use of the products for any medical purpose. Subsequently, Nevada legislative amendments were enacted forbidding the practice. Koken Young injectables and their generic equivalents are still available from some plastic surgeons in North America and Latin America.

The current Koken mammary implant lines were developed in the late-seventies and papers describing their use were published between 1977 and 1985. Outwardly, the devices appeared similar to U.S. and European products but the composition and the assembly technology differed significantly. Late generations of gel prostheses were based on discrete sequentially made layers of silicone-based elastomeric substances. Some of these substances appeared to be phenyl substituted siloxanes. Fluoro-substituted siloxanes may also have been used in some products but the incorporation of the constituents into finished shells was significantly different from the technology developed by the Minnesota Mining and Manufacturing Corporation (3M) and McGhan Medical Corporation. The end result was a thick, multi-component shell with intervening layers acting as adhesives. Earlier products from the firm were closer to generic mammary implants based on conventional silicones with popular gel formulations. The elastomer technology differed marginally from U.S. made products. These prostheses are rarely encountered in North America. However, the recent versions are much more common. In the late-eighties, significant penetration of the products in the U.S. marketplace was substantial, mainly in the South Eastern states and continued until the FDA Moratorium on gel implants of 1992.  

Explanted late-issue Koken implants are comparatively rare at present and no information on the results. However, their number has been rising in recent years, possibly because of increased usage. The modes of failure are significantly different from the North American counterparts. As predicted, delamination of the shells is noted. However, the process appears to take place early. The tissue reactions to the prosthetic material also appeared to be significantly different. Most noteworthy is the singular characteristic of the products to form delaminated pockets between the multiple shells and for these spaces to become tissue and fluid-invaded. Under such conditions, gross denaturation of tissue followed by egress of degraded silicone-derived substances would be expected and would lead to extensive contamination of the breast and possibly systemic adverse reactions from the denatured autogenous material. 

The role of Porex Medical in the North American use of the Japanese-made products is unusual. Unlike other small marketing agencies, Porex evidently had technical expertise and participated extensively in discussions with regulatory agencies and the plastic surgery community during the implant controversy. In some respects, they would be considered with smaller U.S. breast prostheses manufacturers such as Mentor, Cox Uphoff and Bioplasty. The marketing of Koken products under the Porex label, the development of special product inserts and labelling, as well as highly visible and effective promotional activities, suggest that the firm played an informed role in the commercialization of the products and was not solely a distributorship.