Our proprietary Gel Formula has been formulated to gently whiten both inner and outer teeth stains, whilst maintaining no damage to the enamel and is offered in three different strengths: 16%, 35%, and 44% . The percentages prefer to the concentration of whitening agent in the formula, the higher the % the more effective it is at whitening. Additionally the longer the formula is applied under our LED lighting the briter your teeth will be.