This may be gross, so I apologize in advance. A few weeks ago, i had a filling fall out, and had it replaced. Its my next to back molar, and prior to having it fall out, it was a really tight squeeze to floss between it and the very back tooth and i almost couldn't get it in. In fact, the filling popped out while flossing. So now i am more careful, and rather than pulling out the floss, i slide it out but was afraid to do between those two teeth, in case it fell out again.
well today i decided to test it out, and there actually is more space, and i can easily slide the floss between those two teeth. (the gross was for not flossing between those teeth for a couple of weeks). I also realized the generic floss i had been using was much thicker than the brand name sample i used today. which of course is empty so i now have to buy more.