Just because you don't have dust now doesn't mean it won't get in there.
Here's a simple way to test if the ffc is sealed. Breathe on it, the ffc / ear speaker, with an open mouth...you know...haaaaaaaa. If it's not sealed, like mine, the glass above the ffc will fog up, on what appears to be the bottom side of the touch screen glass.
Doing this should also clear very minimal dust. I've had one or two specs of dust in their twice, from putting the phone in linty jean pockets with the ffc end of the phone, top, at the bottom of the pocket where $*** collects. After being cognizant of how I put the phone in my pocket, top of phone facing up, I have never had any more dust appear inside the ffc headspace.