Teeth whitening is only achieved with either Hydrogen Peroxide (HP) or Carbamide Peroxide (CP) and requires custom-fitted trays to use. HP and CP produce the same results, however HP whitens 3x faster and requires 3x less strength to that of CP to achieve the same results. This is because of the time needed for the CP to break down into HP first.While formulas found in less effective LED whitening kits such as PAP and PAP+, are merely a temporary teeth "lightening" effect by dehydrating teeth rather than whitening and removing tooth stains. In the dental industry we call this "rebound" and people using those products find once their dehydrated teeth return to health 3–4 weeks later, their original tooth stains reappear (as they were never removed).With all factors considered, it's why Smileflex chooses Hydrogen Peroxide as its active whitening agent to achieve the best and longest lasting professional results.