Dr. Shnall's Dental Blog
Associated Press Advice to Stop Flossing is Misguided: Part 2
This is the second in a series of articles where I respond to the Associated Press news story
entitled “Medical Benefits of Floss Unproven” I will turn my attention to what the AP article had
to say about flossing and cavity prevention. I will explain why the AP article was inaccurate and
misleading and why if you want to spend less time in the dentist chair you should definitely
make flossing a part of your daily routine.
As a practising dentist for over 25 years I was puzzled by the claims in the AP article, as i am sure
were most in the dental profession , for it is fairly evident for that flossing plays an important
role in cavity prevention.
The AP stated in their article:
“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."
(Note: the AP actually looked at five research papers that in turn pooled the results of 25 smaller studies.)
At the bottom of the AP article they listed five large studies they used to base their flossing
article on. Only one of these studies looked at whether flossing prevents cavities:
The study is titled: “Dental flossing and interproximal caries: A systematic review” (Hujoel,P.P.
et al, 2006).
In lay terms the study is trying to determine whether flossing has any effect on preventing
cavities from forming in between our teeth.
The authors, Hujoel et al did not conduct their own research to answer this question. Instead
they initially looked through 130 studies done by other researchers related to flossing and cavity
prevention . They narrowed their focus down to six studies they felt were the most suitable to
determine whether flossing reduces cavities.
Here is a summary of what the six studies found. I will list the full names of these six studies at
the end of this report.
Note: after reading the summary of these six studies you may be left wondering how the
Associated Press can claim there is no research to support daily flossing reduces cavities.
Study 1 Wright et al (1979)
Study 2 Wright et al (1980)
Wright et al used 5 and 6 year olds in their research.
In the two studies they ran, children had all the teeth on one side of their mouths
professionally flossed once a day at school, five days a week, for ten months (excluding
weekends and summer holidays).
The result: there were 40% fewer cavities on the side of the mouth that was flossed.
Comment: These two studies clearly show there was a benefit of daily flossing in these children
and negates the premise of the AP article
Study 3 Gisselsson et al (1988)
This study put 10 and 11 year olds into two groups.
In one group, children were asked to floss every night at home. Their flossing was not
supervised by the researchers. The other group of children did not floss.
The study lasted two years. As well, the experimenter put the children who had the fewest
cavities and fillings in the “flossing” group at the start of the experiment.
The results need to be looked at carefully.
There was no difference in cavity rate in the flossing versus non-flossing group.
However after the study was completed they found that most of the children who were put in
the flossing group were not flossing every day at home.
Out of 20 children in the flossing group:
Comment: the kids who were in the flossing group had the same number of cavities as children
in the non-flossing group after two years, however since children in the flossing group were not
flossing daily this study does not properly address the question whether daily flossing reduces
cavities. For this reason one may wonder why this study was included in the research paper
written by Hujoel et al.
Study 4 Gisselsson et al (1994)
Children 4 years of age took part in this study. Children in group 1 (experimental group) had
their teeth flossed once every 3 months with the floss dipped in a chlorhexidine gel.
Children in another group (control group 1) had their teeth flossed with a gel that did not contain
any medicinal ingredient.
Children in a third group (control group 2) did not have their teeth flossed at all.
The study ran for three years.
After three years the three groups were compared.
Children in the group that had their teeth flossed with the chlorhexidine gel had slightly fewer
cavities than children in the two other groups.
This study shows there is a small benefit to using a chlorhexidine gel delivered by floss four
times a year in children but it does not tell us anything about whether daily flossing reduces
cavities, as the children in the flossing group only had their teeth flossed 4 times a year in this
study. Again, completely irrelevant to the question of whether daily flossing is of value.
Study 5 Granath et al, 1979.
This study was conducted on 12 and 13 year old children.
The researchers were interested in finding out whether simply moving a piece of floss once up
and once down in between the teeth would have any effect on the rate of cavities In children.
(Note: It important to know that this is not the correct way to floss.
The purpose of flossing is to remove bacteria (plaque) that clings to the surfaces of our teeth
where the toothbrush doesn't reach.
Bringing a piece of floss up and down once in between the teeth might remove lodged food but
would not do much at all to disturb or loosen all the plaque that sticks to the tooth surface, as
plaque is made up of bacteria that produces chemicals that glue it quite effectively to the tooth.
The proper way of flossing is to bring the floss in between the teeth and rub the floss several
times against the side of one tooth and then the other to loosen the sticky plaque off the side
of the tooth.)
Each child in the study flossed their teeth only on one side of their mouth, at school under
supervision every day for two years. They did not floss the other side of the mouth.
Granath et al found no significant difference between the amount of decay or cavities on the
side that children used floss compared to the side they did not use floss.
The study found that the simple up and down once method of flossing is of no benefit in
reducing cavities. This does not mean we should give up on flossing; rather, it reinforces the fact
that flossing has to be done properly to achieve any cavity reducing effect.
Study 6 Gisselsson et al, 1983.
This study was focused on a group of 10 and 11 year olds who were found to be the most prone
to cavities and gum inflammation out of a pool of 627 children.
87 of the children most prone to cavities and gum inflammation had their teeth professionally
cleaned every two to four weeks based on individual need for the next two years and we're also
given diet counselling and reminders on how to brush properly. Approximately half of the
children (experimental group) were also shown how to floss and advised to floss daily at home
while other half were not (control group).
Gisselsson states that at the end of the two year program of regular dental cleanings (every 2 to
4 weeks), children in the daily flossing group (which was at home, unsupervised) had
significantly fewer cavities than the group of children in the “no flossing group.”
Then they waited another two years and again checked cavity rates in the two groups.
This time they found that children in the “flossing” group had more cavities than kids in the
“non-flossing” group, however when they further into the matter they found that very few of
kids in the “flossing” group reported to actually flossing at home more than once or twice a
It should be noted that within the “flossing group” children who said they flossed at least three
times a week did not develop any cavities after the second two year follow-up period.
This study shows children who flossed daily or several times a week indeed had significantly
fewer cavities than children who did not floss.
I looked at the six studies that Hujoel et al used in their research paper.
I would say that studies 1, 2 and 6 showed that children who flossed daily developed fewer
Study 3 was unsupervised home flossing and unfortunately not enough children who were
supposed to be flossing daily actually did so.
In study 4 kids in the “flossing group” had their teeth flossed a total of 4 times a year so any
results of the study do not shed light on the question regarding whether daily flossing prevents
Study 5 showed that if you use poor flossing technique you are not going to get a reduction in
So, in light of the studies discussed in this paper what is the take home message about flossing
and does it agree with the Associated Press article that claims flossing to be ineffective and
I would say that based on the six research studies that Hujoel et al selected, we can conclude
could conclude that the Associated Press did not dig very deep when writing their article that
disparaged flossing and clearly could not have read the six source studies used by Hujoel et al in
their research paper.
These four recommendations I listed above can be expected to reduce the number of cavities
children get, whereas not flossing daily or at all will assuredly increase the risk of developing
In this article discussed we only discussed flossing in children. The AP did not cite any research
that answered the question whether daily flossing prevents cavities in adults. However, It is
obvious to anyone who practises dentistry that daily flossing in adults is an important part of a
cavity reduction program and compliments daily brushing, as our toothbrush cannot effectively
remove plaque and food between our teeth.
In my next article(s) on this topic I will address more misinformation contained in the AP article
and further the case for daily flossing.
Dr. Jeff Shnall Aug 2016 email: Dr.Shnall@gmail.com
BeechDental.com 350 Beech Ave Lower Suite, Toronto, Ontario M4E 3T8 tel 416-691-2886
Articles Used in the Research Paper by Hujoel et al:
The abstracts to these studies are available online.
Studies 1 and 2: Wright,GZ, Banting DW, Feasby WH (1979). The Dorchester dental flossing final report. Clin Prev Dent 1: 23-26
Study 3: Gisselsson H, Birkhed D, Bjorn AL (1988) Effect of professional flossing with
chlorhexidine gel on approximal caries in 12 to 15-year-old schoolchildren. Caries res 22: 187-192
Study 4: Gisselsson H, Birkhed D, Bjorn AL (1994) Effect of a 3 year professional flossing program with chlorhexidine gel on approximal caries and cost of treatment in preschool children. Caries res 28: 394-399
Study 5: Granath LE, Martinsson T,Matsson L et al (1979) Intraindividual effect of daily supervised flossing on caries in school children. Community Dent Oral Epidemiol 7:147-150
Study 6: Gisselsson H, Bjorn AL, Birkhed D (1983) Immediate and prolonged effect of individual preventive measures in caries and gingivitis susceptible children. Swed Dent J 7: 13-21