Fig. 1.

Serum cobalt concentrations. Line graph showing the concentrations of cobalt in the serum, in nanograms per milliliter (ng/mL, parts per billion), as a function of time in the four groups investigated. The hybrid group had cobalt levels that were 3.2 times higher at 120 months than they were at baseline and had cobalt concentrations that were significantly higher than the levels in the titanium (Ti) group at thirty-six, sixty, eighty-four, ninety-six, and 120 months (p < 0.01). *Cobalt levels in the hybrid group were significantly different than those in the titanium group (p < 0.05).