Purpose: This study measured the tensile force required to separate a custom implant abutment fixture that had been cast onto a machined component using the Impac custom abutment system (Vident, Baldwin Park, CA). The characteristics of the interface between the cast and machined components were also investigated by scanning electron microscopy x-ray and energy-dispersive (JEOL T330A, Peabody, MA) analysis (Kevex Delta Level I, San Carlos, CA).
Materials and methods: A polycarbonate custom abutment component, attached to a gold alloy component of the abutment, was invested in a phosphate-bonded investment and cast in a type III gold alloy (Argenco, Argen Precious Metals, San Diego, CA). Eight samples were cast after a burn-out of 900 degrees F and 13 samples were cast after a burn-out at 1300 degrees F. The abutment components were pulled in tension in a universal Testing Machine (Instron 4204, Canton, MA) until failure. The interface of as-cast and failed samples were examined by electron microscopy.
Results: Samples burned out at 1300 degrees F failed at a mean force of 2477 +/- 295 N (545 +/- 65 lb), and samples burned out at 900 degrees F failed at a mean force of 2182 +/- 91 N (484 +/- 20 lb). Electron microscopy of the interface between the cast and machined components showed retentive tags provided in the design of the machined components. There was also a zone of diffusion between components shown by a zone of void formation within the casting. Failure occurred at the interface of the cast and machined components for all samples.
Conclusion: The cast component was retained by a combination of mechanical and chemical mechanisms.