Average shear stress may be calculated from the force required to punch a cylinder out of a disk or plate of material. Tests on aluminum and methacrylate sheets enabled the comparison of dental restoratives with human dentin. Human dentin was found to have a greater shear strength than dental restoratives other than gold alloys.

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SummaryAn implant test, in which 0.3-0.5 g of solidifying or polymerizing material was injected into the belly wall of rats, was used to compare the tissue reactions to four materials. A histological survey was made of the tissue reactions to stainless steel pins, zinc oxide-eugenol mixtures, cold-cure acrylic resin, silicate dental cement, and to a polymer-filler system (dental restorative). The irritant effects of the implant on the fibrous encapsulation about these foreign bodies were used to assess the toxicity of the material. Implanted stainless steel pins acted as a control for comparison. Zinc oxide-eugenol and silicate cement produced necrosis when injected in the mixed but unset state; the irritation continued for 30 days after implantation and was sufficient to impede fibrous encapsulation. Fibrous encapsulation about injections of cold cure acrylic resin and an experimental composite of polymer and filler occurred 5 days after similar encapsulation about implanted stainless steel implants. The inclusion of a relatively inert filler decreased the initial reaction to a monomer-catalyst mixture.

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