I brought a teeth whitening kit off the the internet, it is a gel pen. it includes 35% carbamide peroxide, glycerin, propylene glycol, carbomer, triethanolamine, xylitol, stevia rebaudiana. Its meant to be used 15 mins in the morning & 15 Mins at night then washed off, is this safe for my teeth? I am 18, an ex-smoker, but smoke weekends when I have a drink. thanks