They used 30% h2o2 and it showed organic and mineral demineralization of dentin. The dentin dissolves due to the reactivity, solubility, and acidity of H2O2. However, this is the 30% in the study, the 3% I've seen in stores is probably a really weak version. The H2O2 (Hydrogen-Peroxid) can rapidly hit the dentin through the enamel and cause tooth sensitivity.
The 3% H2O2 (Hydrogen-Peroxid) can be diluted in 1/2 H2O and become 1.5% H2O2. It is a good mouth wash and disinfectant however that may prevent inflammation and plaque. Probably better than most toothpastes anyway.