Weirdness in teeth! Help?!?

A few months ago I got an x-ray and it wasn't determined or not if I had any cavities. And there was this huge hole on the side of my tooth. But mysteriously as I just added mouthwash in my routine of brush and floss this hole got smaller and started rebuilding the tooth. The doctor and orthodontist agreed that my hole has been shrinking. And I wanna know if this hole disappearing is normal, along with the rebuilding of the tooth?