by Trisha E. O'Hehir
I have frequently been asked what is the incidence of periodontal disease in the United States. Sounds like a simple question, doesn't it? I read the research, so I should know the answer, right? What number are you thinking of right now? If your guess is between 20 percent and 87 percent, there is research to support it. A popular figure that comes to mind is 80 percent. I just read an article today that quotes the figure at 30 to 40 percent, and a big review article says it is reasonable to conclude that about half of the U.S. population 30 years and older have periodontitis.
Who is right and why are there so many different figures?
There are several reasons. Some are quite apparent when you read the studies, and others fall into the "you just had to be there" category. By "being there," I mean you had to have sat in the audience when one researcher presented his or her findings, only to be questioned by a researcher in the audience who had done a similar study and had gotten different results. Hockey games are known for the fights that occur, but research presentations with heated debate are admittedly rare. When it does happen, it makes for quite a rousing break from what you can imagine is a whole lot less than exciting.
Let's start with the obvious. Did they use a probe or just a mouth mirror? Important difference. Early studies in the 1950s used the Russell Index, which looks but doesn't probe. That definitely may influence the outcome of the study. These researchers found the highest rate of periodontal disease in 45- to 49-year-olds. That rate was just over 40 percent, and it dropped down to under 25 percent for 70- to 80-year-olds. Also important to note was the number of edentulous people increasing steadily after age 45 to a level of nearly 40 percent by age 70. Maybe this is where we get the saying, "Periodontal disease is the greatest cause of tooth loss after age 45."
That early study also pointed out the age groups and various figures for each. Depending on age, the figures change, so you may want to find out if the percentage speakers or writers throw out is for the general population or for a specific age group.
Besides the age, who the people are makes a difference. It's very difficult to get a true cross section of our population. The Veterans Administration did a study in the 1950s that included only those people who came in to see the dentist. That leaves out those who don't go to the dentist and, therefore, is not considered a representative sample.
Be careful what definitions are used. Some studies report 90 percent gingivitis levels, defined as one or more teeth with bleeding. The figure for gingivitis goes down to 60 percent when using a definition of bleeding at six teeth or more. The same goes for definitions of periodontitis. Is it 3 millimeters or deeper, or 4 millimeters, or 6 millimeters? Just a little thing can change the meaning of the bottom line figure.
Even in the studies that used a probe, there are issues. A common approach is to probe only two quadrants, and only probe two sites per tooth: mid-buccal and mesial-buccal surfaces. That makes it easier when examining 30,000 patients, but not completely accurate. When compared to full mouth probing, the severity of the disease was similar, but the extent or prevalence rate was underestimated by about 13 percent. So, in some of those studies, the low rate of 36 percent for periodontitis might actually be 49 percent.
Another probing issue that can be as exciting as hockey — given the right researchers — is where to place the probe. This argument surfaced years ago at a research meeting where the big news was that incidence of periodontal disease was on the decline. Figures in 1974 indicated that 36 percent of the population had periodontal disease, and the new figures in 1994 were 23 percent.
The audience gasped. How could that be? Or more to the point, where could that be?
"Surely not in my office" was the mumbled response from the audience.
A researcher in the audience raised his hand and asked just one question that explained it all. He simply asked if the examining dentists aimed the probe to the middle of the interproximal surface, or if they probed at the line angle. The answer from the researcher at the podium was that to ensure consistency and reproducibility, line angle probing was done.
To a researcher, that makes perfect sense. To a clinician, that is tantamount to malpractice. That means you miss the exact place where pockets form — the area just below the contact. Some of you were even taught line angle probing when you were in school. The difference can be several millimeters.
The researcher who asked about the probing technique published a study in 1994 reporting on the prevalence of periodontal disease in the elderly. His figures showed 87 percent of the group having at least one site measuring 4 millimeters or more. My guess is that his examiners aimed the probe to the mid-interproximal area.
Several other studies of elderly Americans reported figures ranging from 32 percent to 86 percent with probing depths of 4 millimeters or more.
My bias is to aim the probe at the middle of the proximal surface. Rather than holding the probe parallel to the long axis of the tooth, slide it into the interproximal and push the side of the probe up against the contact. While you have the side of the probe against the side of the contact, aim the tip right under the contact. This way you will measure the deepest area.
I trust you will never take a prevalence statistic for granted anymore.
You now have several questions to ask when figures are given for who has periodontal disease. Is it 23 percent? Is it 36 percent? Is it 30 to 40 percent? Is it 86 percent? Or is it 87 percent?
All of these numbers are correct based on the group examined, the definitions of disease, and how the examiners probed. Now you know why there are so many different answers to what seemed to be such a simple question.
Trisha E. O'Hehir, RDH, BS, is a senior consulting editor of RDH. She is also an international speaker, author, instrument designer, inventor, and oral health detective. Her Web sites are www.perioreports.com and www.toothpastesecret.com. She can be reached at (800) 374-4290 or at [email protected].
