PurposeThis 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 1, San Carlos, CA).Materials and MethodsA 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°F and 13 samples were cast after a burn‐out at 1300°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.ResultsSamples burned out at 1300°F failed at a mean force of 2477 ± 295 N (545 ± 65 Ib), and samples burned out at 900°F failed at a mean force of 2182 ± 91 N (484 ± 20 Ib). 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.ConclusionsThe cast component was retained by a combination of mechanical and