Defects in hexed gold prosthetic screws: A metallographic and tensile analysis

Prosthetic gold screw fracture remains a clinical problem in implant prosthodontics.

This study examined hexed gold prosthetic screws for internal defects and determined the effect of these defects on tensile strength. The microstructure, microhardness, and major constituents of the alloys also were determined.

Four intact hexed gold prosthetic screws, 1 from each of 2 different lots from 2 manufacturers (Implant Innovations and Nobel Biocare), were examined with standard metallographic techniques for defects, microstructure, microhardness, and major alloy constituents. Thirty-six screws, 9 from each of the 2 different lots of both manufacturers, were subjected to tensile testing to determine fracture load values. Analysis of variance and Tukey tests were used to identify differences between manufacturers and lots (P<.05). The fracture sites were examined retrospectively with a scanning electron microscope to identify defects that could have contributed to failure. The mode of fracture was characterized.

There were no significant defects in the screws tested, but differences were observed in the microstructure, microhardness, alloy composition, and fracture load values for both manufacturers. Screws from the 2 manufacturers demonstrated distinctly different metallurgical characteristics, which highlighted differences in the manufacturing processes. Fracture load values ranged from 850 +/- 20 N to 1093 +/- 64 N. A significant difference was noted for mean fracture load values for the different lots of Implant Innovations screws (P<.05). Ductile fracture was the mode of failure.

The results of this study suggest that variability in the physical properties of similar hexed gold prosthetic screws made by different manufacturers, as well as different lots from the same manufacturer, may affect clinical success.