Previous Electron Paramagnetic Resonance (EPR) studies identified the carbon dangling bond center as the main paramagnetic interface defect in 3C, 4H, 6H-SiC/SiO2, We demonstrate that this defect, called P-bC center, can be passivated by forming gas annealing at 400 degrees C. We have measured the PbC density at annealed 4H- and 3C-SiC/SiO2 interfaces and attributed its reduction to the transformation of the dangling bonds into EPR inactive C-H bonds. We have also studied the reverse phenomenon occurring during vacuum annealing at temperatures ranging from 600 degrees C up to 1000 degrees C and have determined a dissociation energy of approximate to 4.3 eV for the 3C and 4H polytypes.