Dr. Shnall's Dental Blog
Associated Press Advice to Stop Flossing is Misguided: Part One
By Dr. Jeff Shnall
On Aug 2 of this year the Associated Press (AP) put out an article entitled ”The medical benefits of floss unproven”.
The article sites the fact that the US Department of Dietary Guidelines for Americans has dropped its recommendation for people to floss because “the effectiveness of flossing has never been researched.”
The AP article then goes on to say:
“The AP looked at the most rigorous research conducted over the past decade, focusing on 25 studies that generally compared the use of a toothbrush with the combination of toothbrushes and floss. The findings? The evidence for flossing is "weak, very unreliable," of "very low" quality, and carries "a moderate to large potential for bias."
So essentially the AP is saying that they have looked at the most reliable dental research research that has been done that put people into two groups: one group that was told to brush only and the other group was told to brush and floss daily. After a number of weeks or months the two groups were examined and compared to see if the gums and teeth in one group were healthier than the other. If flossing was beneficial we should expect the group that flossed to have healthier gums.
The AP article implies that after they scoured all the best research done in the field of dentistry, the consensus is that flossing is a complete waste of time and that it does nothing to promote good dental health. The AP article also makes claims that it is in the interest of manufacturers of dental floss to promote the myth that flossing plays a role in maintaining dental health as floss sales are estimated to be worth a billion dollars a year in the US alone.
A lot of media outlets including newspapers and the evening news picked up the AP article and ran with it. I can understand why. Flossing is to many, one of life’s little drudgeries. It isn’t easy for some people to maneuver the floss; some people have trouble getting the floss in between tight contacts in between their back teeth; as well it takes time out of your day and can be tedious. I try to read or watch tv while I floss to beat the sheer boredom factor.
As a dentist I routinely ask my patients if they floss and the standard answers are: “not as often as I should”, “when i remember”, “after i eat corn on the cob” or “when i get food stuck between my teeth”. I do have few patients who are brave enough to give me a flat out “no’, and yes, I do also have some daily flossers in my practise.
After hearing the AP report I am sure some people were in a hurry to fling their their floss into the nearest garbage can or at least keep it around for some emergency repairs like sewing loose buttons or as an emergency shoelace substitute as it is strong and durable.
However recommending that everyone stop flossing due to alleged lack of scientific evidence not a trivial matter. As a practising dentist I think the AP article does not make a sound argument against daily flossing. I would like to point out some shortcomings of the AP article and also explain why I think flossing is a worthwhile endeavor based on what I have observed while caring for teeth and gums for at least half of my waking hours for the past 25 plus years.
As mentioned the AP states in their article that:
“The AP looked at the most rigorous research conducted over the past decade, focusing on 25 studies that generally compared the use of a toothbrush with the combination of toothbrushes and floss.”
I would like to comment on this quote. In fact, only some of the studies that the AP based their article on directly compared whether people who used a toothbrush and floss had healthier gums than those who only used a toothbrush. And the results of some of those studies do not support the AP notion that flossing is ineffective.
Moreover I will argue that almost half of the brushing versus flossing studies the AP looked at were conducted on young, healthy experimental subjects only, thus limiting any conclusions they made on the utility of flossing applicable to young, healthy people only (at most) and if at all.
As well, the bulk of the studies the AP looked at did not even consider whether flossing helps prevent cavities, which is a definite benefit of flossing.
So let us take a closer look at the question: does daily flossing make your gums healthier and can it prevent gum disease? ( I will discuss the AP article as it relates to cavity prevention in a future article in this series).
In my opinion, and I believe in the opinion of the majority of dentists and dental hygienists , flossing is a very worthwhile daily practise. It promotes healthier gums and most patients will benefit from daily flossing.
First, let’s discuss a little about the nature of gum disease and how many people are affected by it.
For the purpose of this discussion we can group people into four different categories based on the health of their gums:
Category 1: Healthy gums. No sign of gum swelling or bleeding. Gums pink in colour.
Category 2: Mild gingivitis or mild gum inflammation: one or more areas of red or puffy gums that might bleed when touched
Category 3: gum disease in one or more areas of the mouth i.e. may have bleeding or swelling at the gum line and early loss of bone that supports the teeth.
Category 4: generalized moderate or severe gum disease affecting many areas or the mouth; may include swelling and or bleeding a the gum line and moderate or severe loss of bone that supports the teeth
How prevalent is gum disease?
Health Canada reports that over 50 % of the adult population has some form of gum disease.
The Centers for Disease Control and Prevention (CDC) in the US reports the same figure.
So gum disease is a very common condition affecting adults but clearly not everyone has gum disease. Why is that?
This can be explained in part due to the nature of gum disease, that being it is an inflammatory disease.
GUM DISEASE IS AN INFLAMMATORY DISEASE
There are many reasons why some people have healthier gums than others.
Some people have gums that are more prone to inflammation than others and people who are more prone to inflammation in their gums are going to have a greater risk of gum disease.
What is Inflammation?
Inflammation is our body’s normal reaction to injury or attack by foreign invaders (such as bacteria) and is part of our body’s natural defense system.
When we are injured, our body’s defense system kicks in to the minimize the damage. If we suffer an injury, for example if we fall down and scrape our knee the following sequence of events occurs at the site of the injury:
Skin scraped ----> blood vessels in skin react by leaking fluid into the injured area (swelling and redness)
----> leaky blood vessels allow larger white blood cells into the injured area to clean up or neutralize any bacteria in the wound
This is a healthy defense mechanism that allows us to survive the bumps and scrapes that befall us through a lifetime. The response to a wound described above is called an inflammatory response.
So how does this relate to gum disease?
Our mouths are host/home to millions of bacteria that live on our teeth and along and under our gumline. We all have this bacteria.
The question of who will go on to develop gum irritation or gum disease is related in part to how your body responds to the bacteria and this response can differ from person to person.
I can see two patients at my office with the same amount of plaque or bacteria on their teeth. However in each of these two patients their gums may look and respond differently: One patient might have slight swelling, redness and bleeding in their gums while the other patient will have normal, pink and healthy looking gums that don’t bleed and are not swollen.
So why the difference between these two patients? Same bacteria and same amount of bacteria yet a different gum response?
This can be explained by the difference in the strength of each person’s inflammatory response or put another way, how prone they are to inflammation.
Inflammation is our body’s protective mechanism, however if we respond to very minor threats with an overblown inflammatory response we are going to get more swelling, more bleeding and the initiation of gum disease.
So who is the type of patient who will be more likely to have a stronger inflammatory response in their gums making them more prone to gum disease?
Medical and dental research has already provided this answer:
People who have a stronger inflammatory response to plaque or bacteria on their teeth and around their gum line also are more likely to have other illnesses linked to inflammation in other parts of their body, for example high blood pressure, diabetes and forms of heart disease such as clogged coronary arteries.
The consensus in the medical and dental community is that gum disease, heart disease and diabetes all have an underlying cause, namely inflammation.
So how does all of this relate to the original article in the Associated Press? Recall its opening lines:
“It's one of the most universal recommendations in all of public health: Floss daily to prevent gum disease and cavities. Except there's little proof that flossing works.”
In this assertion they go on to say that they looked at 25 of the most rigorous articles that examined whether flossing was any more effective in keeping gums healthy than brushing alone.
The problem is that about half of these “rigorous” studies only looked at whether flossing would benefit healthy people. People with systemic diseases such as diabetes or heart disease were intentionally left out of the studies the AP looked at. Let’s have a closer look at this.
The AP listed the research sources that they used to write their article.
They are listed here:
Let's look at one of these studies in a bit more detail It is called “The Cochrane Database Systematic Review. 2011 Dec 7;(12). Flossing for the management of periodontal diseases and dental caries in adults. (Third link in the above list)
The authors of this study ( Sambunjak, Dario et al) did not conduct their own research on the question of whether flossing helps people. Instead they in turn looked at 11 other studies that were done by others and tried to extract data from these studies to answer the flossing question.
Sambunjak, Dario et al state that they only used data from studies that had healthy experimental subjects.
So if someone did a study on whether flossing works that included people with diabetes, heart disease or high blood pressure Sambunjak, Dario et al would not even look at results or the data in that study.
So what did the eleven studies that Sambunjak, Dario et al) looked at find?
Well, first that people who were in the brush only group for a number of weeks or months did not have any more gum inflammation than people who brushing and flossing group. (A closer look at each the eleven studies does not exactly show this but more on this in a future article).
This is not a big surprise because they were already looking at a pool of patients who were healthy, who did not have any inflammatory related diseases such as diabetes or heart trouble, and who would be expected for this reason to do relatively well even without flossing; the people in these eleven studies likely had low inflammatory responses to plaque on their teeth and under their gum line.
The people in these studies were very likely the people I referred to early in this article as category 1 patients: ( Category 1: Healthy gums. No sign of gum swelling or bleeding. Gums pink in colour.)
If Sambunjak, Dario et al, in their 2011 study, included research studies conducted on diabetics or people with heart disease or high blood pressure they undoubtedly would have found that people in the floss and brush group would have less gum inflammation than people in the brush only group, because they would have been looking at a population that are more sensitive and reactive to dental plaque and more prone to gum inflammation when plaque levels are not kept under check by flossing. This is something observed in dental offices all over the world.
It has already been widely researched and known that if you get diabetics, for example, to keep their teeth cleaner (brushing, flossing) their gums will get healthier and their blood sugar levels will also improve.
Given that over 50% adults in Canada and the US have gum disease, 9% have diabetes (25 % of senior citizens in the US), over 20% have high blood pressure, and the majority of adults in North america have one or more risk factors for heart disease or stroke the Associated Press should actually be telling people: although young and healthy people (no systemic disease) might be able to get away without flossing at least in terms of not having an impact on the health of their gums in the short term (cavities are a different story), anyone with a risk factor for diabetes, high blood pressure or heart disease should be flossing daily as these people are prone to inflammatory diseases such as gum disease:
A second study cited by the AP to prove flossing is not worth your time is entitled:
Primary prevention of periodontitis: managing gingivitisIain L. C. Chapple, Fridus Van der Weijden et al (fifth link in the article list above).
The authors of this paper did not do direct research studying the health effect of flossing; they too, like the authors of the previous study discussed above looked at healthy subjects only, so any conclusions the authors drew from their research as well could only be applied to healthy people.
Well, I tried to bring a little clarity to what is actually a fairly complex question: whether flossing is effective in reducing plaque and promoting healthy gums. In my next article in this series i will comment on some other aspects of the AP article that in my opinion are not supported by facts.
Until then I do urge you to keep flossing daily or to start flossing daily.
I welcome any comments you may have on this topic.
Dr. Jeff Shnall
Toronto, Canada BeechDental.com