Been using for 1.5-2 years, no sign of decay thus far. It leaves the teeth with a smooth glassy feel. It is sometimes a chore to have to brush before eating, and adapting to not rinsing took a while, but worth it to avoid dental problems. So far as I can tell, it is a near faultless decay preventative when used as directed, BUT, that does mean brushing before breakfast, and not rinsing. That can take a while to adapt to, but the price is small for the benefits. Tony Mx 2018