So now, let's look at the results of both days side by side. I have repeated this many times, and I think we can definitively say that flossing then brushing gets way better results
than brushing and then flossing. Let's talk about why? After thinking about it more in-depth, there are a lot of reasons. When cleaning your teeth, it is the floss that does most of the work to knock the plaque loose in between your teeth. The toothbrush isn’t near as effective at cleaning plaque further between your teeth.
As you can see from day two, the floss will move the whole colony of plaque almost as one attached unit. Because the plaque colony is all attached, the floss doesn’t necessarily have to contact all of the plaque to move it. Then the brush's job is much easier to do the detailed clean-up work if any plaque remains. When you brush first, it breaks up and detaches the plaque colony from each other between your teeth, which fragments the plaque colony, making it impossible for the floss to do the heavy lifting of the whole colony as one complete unit. When flossing second, the floss must contact each tiny leftover plaque fragment and cannot heavily remove plaque between the teeth. As an analogy, if you were redoing your yard, you wouldn’t use a plow truck to dig holes for the plants, nor would you use a shovel to plow the whole yard. Floss is the plow truck when it comes to plaque between the teeth.
You may not know this, but electric toothbrushes propel the saliva-and-toothpaste mixture through the small gaps between the teeth. As saliva with toothpaste moves between your teeth, it does two things only if you have flossed before you brush your teeth. First, the actual flow of toothpaste from a mechanical toothbrush is enough to remove some of the debris itself. Second, toothpaste typically has fluoride that strengthens tooth enamel. However, if plaque is still sitting in between your teeth, it will block the toothpaste fluoride from strengthening that part of the tooth. Thus fluoridated toothpaste does not fortify between your teeth near as much if you brush first.