Enable next button when other slides have been visited

Hi,

I have a project I'm working on where on the third slide, I present the user with a navigation slide to four different pages. I have disabled the Next and Previous buttons that come with Storyline and have used my own. What I want to have happen is when the user visits all four of those pages in whatever order, the Next buttons on those visited pages become reactivated or "normal" when all of them have been visited. I know there is a way I can do this with variables. Or perhaps there is an easier way? I appreciate any help!