Basically, yes, flossing helps, but self-flossing really doesn't do anything more than just brushing daily.
I'm a little disappointed at the number of comments here along the lines of, "Well, it's obvious! Why do we need to study it?" That's a very unscientific attitude.
I had the opposite reaction: how on earth has no one looked into this!?
But if you dig into it, it's horrifying how little "evidence" goes into treating a lot of common medical conditions. For another trivial example, the stuff in Sudafed PE (phenylephrine) http://www.sciencedirect.com/science/article/pii/S1081120610... is much worse than the psuedophedrine it replaced.
I wish the NIH (and other funding agencies) would consider running big, confirmatory trials on a lot of "obvious" things that affect people every day, the money clearly isn't there and it's politically difficult to get it there:
There are a fair number of ignorant Congressman in the US who love to rant about 'wastes' of government money on studies like these.
What are the phases in this study? There's no explanation of the phases in the abstract:
"Phase 1 results showed a difference between phenylephrine and placebo that was 64% of the difference between pseudoephedrine and placebo, substantially greater than the 17% difference observed for all phases. "
Edit: Phase 1 may mean "Testing of drug on healthy volunteers for dose-ranging", from wikipedia:
That study uses a crossover design, which means that everyone gets all three treatments (in this case, phenylephrine, pseudoephedrine, and placebo), but in different phases. You might get the placebo this week and the pseudoephedrine next week, while I get the opposite. Each one of these time steps is a "phase".
A similar study might use a "batch design" instead, where the subjects are each tested once, after being given a single treatment. They might put you in the pseudoephedrine group, while I get the placebo.
Crossover designs have a big advantage in that are more robust to individual variability, and thus have more statistical power to detect differences. In essence, the crossover design allows you to compare the average of each subjects' difference between conditions while the block designs force you to examine the difference between the average scores of each group.
This power comes at a price--you have to be careful that the different treatments do not interact so you can correctly associate causes and effects. None of the treatments remain in the subjects' system for a week, but they are worried that people might remember* how well pseudoephedrine worked and "downgrade" the other treatments. One way to check this is to analyze the first phase of your data, where each subject has had only one treatment, as a batch design, which is what they reported there.
* The measurement here is a self-reported scale of nasal congestion. Note that they don't do this for most of the quantitative/physiological measurements.
Remember "chocolate is good for you"? Turns out that: "While research shows that cocoa can have a beneficial effect with regards to maintaining healthy vascular tone and insulin sensitivity, the reverse is true for sugar. Eating sweetened chocolate is still not good for you." [1]
Yet plenty of people seem to have fallen over each other to share that article (and this article). It seems anything that says you can have your cake and eat it too will have plenty of social media shares. In this case, it looks like flossing may be lightly studied, but is still good for us. Perhaps we can change that famous old adage to, "if it sounds too good to be true, it's probably clickbait".
Here's another piece of research on flossing, "In regression analyses, brushing thoroughness, flossing ability and frequency, and dental visit frequency were predictors of lower plaque, gingivitis, and calculus scores. In turn, these scores were predictors of shallower pocket depths and less attachment loss." [2]
That's on a study of 319 people, flossing regularity is based on surveys and dental health based on examinations.
Your point about science reporting is also one of Dr. Ritchey's points. It's actually something that comes up fairly frequently on the SBM blog.
As for the paper you cited, it seems (from what is publicly available) to conflict with the Cochrane review he cites. I can;t tell if the review looked at that particular paper or not.
Or, people who were assigned a professional flosser every single school day were also more likely to brush their teeth better and were reminded constantly about their teeth and even possibly taught stuff about teeth and so maybe even ate less sugary things. I don't have access to the paper: did they at least have the professional flosser supervise the self-flossing to control for this? Otherwise this just seems like a much more likely reason for these results.
I can't find a PDF of the original study, but in the review, they mention that one quadrant of the mouth was professionally flossed. This presumably lets them do within-subject comparisons: are there more/less cavities (or whatever) within the flossed portion?
This should remove confounds like 'ate more sugary things'. It's possible, of course, that kids brushed more on the flossed side (or the unflossed side), but you could presumably quantify that too.
The reference is a systematic review, not a single study; only one study in the review was run as you indicate.
Beyond that, I am not sure what you are getting at. The point of the post I posted and the original article here is that self-flossing as an augmentation to brushing does effectively nothing. What you stated corroborates that. Am I missing something?
My point was that from the information in the article that isn't actually clear; it is like when people say that condoms are X% effective as a contraception technique, and so people assume that means that condoms have an X% failure rate, but what they really mean is that "couples who report using condoms as their primary means of contraception have an X% success rate at avoiding pregnancy". While it is interesting from a clinical perspective as to whether "sending a child home and telling them to floss by themselves" is a working strategy or not, it would be taking into account "children don't really floss" and doesn't tell us if an adult who actually knows they are flossing (such as an adult who actually knows they are using the condom every time) has a particular success rate.
Basically, yes, flossing helps, but self-flossing really doesn't do anything more than just brushing daily.
I'm a little disappointed at the number of comments here along the lines of, "Well, it's obvious! Why do we need to study it?" That's a very unscientific attitude.