Through the years, one of the questions that I have been asked the most is whether you should brush first or floss first. I was always happy when people would ask that question because it made me realize that some people actually do floss at home. However, I never really had a good answer for that question. I would always say that if you flossed first, the spaces between the teeth would be cleaner for the fluoride toothpaste to penetrate between the teeth. But then I would say that if you brushed first, you would have the fluoride toothpaste in your mouth from brushing and the floss would pull the fluoride toothpaste between the teeth where a brush can't reach. And then I would sum it up by saying that there are probably benefits either way and it probably doesn’t matter that much which is done first. I would always say that I was just happy that patients were attempting to floss.
However, in May 2018 there was a research article published in the Journal of Periodontology, the publication that focuses on the treatment of gum disease and the tissues around teeth. The focus of this research article was to determine whether there was an advantage to brushing first or flossing first. The research concentrated on the reduction of plaque bacteria, the cause of gum disease and tooth decay, as well as fluoride retention on the tooth surfaces after either brushing first or flossing first.
What they found was that flossing before you brush resulted in a statistically significant reduction of plaque bacteria between teeth when compared to flossing after brushing. So, that meant that flossing first did a better job of cleaning teeth in the research. In addition, flossing first also resulted in a statically significant increase in the amount of fluoride retained on the surfaces between teeth when compared to flossing after brushing. So, again, it is better to floss first because the teeth are left with more fluoride on them to help fight decay. Here is a link to a summary of the article https://www.perio.org/consumer/brush-or-floss-first
So now we have an answer based on science.
It is better to floss BEFORE you brush your teeth.