To replenish the defects caused by losses of bone, cartilage and soft tissue, either autogenous tissue or alloplastic material can be used. Although the autogenous tissue is the ideal choice for their reconstruction, the availability and problems associated with donor sites limit its use. Therefore, the alloplastic materials have been used widely for the tissue replacement. Many synthetic materials have been developed for alloplasty; among these, the silicone rubber has been the most popular alloplastic material for plastic surgeons. Inherent problems related to the use of silicone are infection, exposure, implant migration, capsule formation, and poor penetration of bony or soft tissue into the implant. To circumvent these problems, many efforts have been made. One of the efforts was that the surface of silicone implatn was roughened to modify the capsular reaction aroud the implant.
  Developed in 1970's, the linear high density polyethylene(HDPE, Medpor, Porex, Atlanta) is a porous substance, and it has the advantages of less implant migration by the penetration of connective tissue into the pores, less capsule formation, and reduced chance of infection due to high vasculartiy. The purpose of this study is to compare the tissue reaction of HDPE with that of slilcone rubber in rats. 1.0.m diametered discs of slicone rubber and HDPE were implanted in the back of rat, and en bloc tissue-specimens were obtanined including the implants and their surrounding capsules in 4 weeks and 8 weeks after the implantation, The specimens were examined grossly and microscopically. The microscopic slides were prepared with H-E and Masson's trichrome stains.
  Grossly, the capsules around the silicone rubber were easily peeled off while the capsules around the HDPE were strongly adherent to the implant. Under the microscpe, the thickness of capsules were compared. The capsules of both implants were thicker in 4 weeks than 8 weeks. The capsules of silicone rubber were significantly thicker than HDPE in 4 weeks(306.7±8.17㎛ vs 115±5.48㎛) and 8 weeks (143.3±87.85㎛ vs 58.3±16.02㎛). The regression test on the differences in thickrness were also significant in both 4 weeks and 8weeks.
  Histologically, the cspsule of silicone rubber consisted of denser connective tissue and showed lesser foreign body reaction than the HDPE. Many multinucleated giant cells were found around the HDPE while none of them was found around the silicone rubber. Fibroblasts in the capsule of silicone rubber were more mature forms than the HDPE. The capsule of HDPE showed more new capillary formation than the silicone rubber. Both capsules of silicone rubber and HDPE showed many eosinophils. The capsule of HDPE showed more new  capillary formation than the silicone rubber. Both capsules of silicone rubber and HDPE showed many eosinophils. The capsule of HDPE was composed of dense connective tissue, and the portion of capsule near the implant contained the multinucleated giant cells. In the core porticons of capsule around the HDPE, the capsule composed of less collagenous tissue and contained more inflammatory cells and young fibroblasts.
  From this study, HDPE will be advantageous in clinical usages by virtue of decreased chance of infection, migration, and exposure.