What's in a link?

Both my editor and I are a bit over the top when it comes to our dogs. Mark Hartley recently told me that he Skypes with his granddaughter just about every week, which includes holding up his two Boston Terriers so she knows who they are. My dachshunds are so spoiled that when I changed out the summer comforter on my bed to the thick and comfy duvet for winter, all four dogs slept in the following morning and weren't barking in their usual way for a breakfast food ration.

BY LYNNE SLIM, RDH, BSDH, MSDH

Both my editor and I are a bit over the top when it comes to our dogs. Mark Hartley recently told me that he Skypes with his granddaughter just about every week, which includes holding up his two Boston Terriers so she knows who they are. My dachshunds are so spoiled that when I changed out the summer comforter on my bed to the thick and comfy duvet for winter, all four dogs slept in the following morning and weren't barking in their usual way for a breakfast food ration.

Being a dog lover, it upset me when I heard the news that authorities in Spain euthanized a dog belonging to the Spanish nurse assistant who tested positive for Ebola. The authorities in Spain said that the dog, named Excalibur, posed a risk of transmission to humans even though, to date, there have been no reported links between Ebola infections and those found in dogs. In fact, there's no documented case of Ebola spreading to people from dogs and vice versa. I guess you could say that there's a potential for a link but to date there's absolutely no evidence to support a role for dogs in transmission of the Ebola virus to humans.

---------------------------------------------------

Other articles by Slim

---------------------------------------------------

So, what's in a link? Is a link the same as an "association," and what's required to prove causation? Considering the various perio/systemic links, there's one in particular that I want to focus on again: the perio/cardio link. Let's discuss the strength of the evidence surrounding this link and follow the research from observational research (associations) to what's required to establish cause/effect.

I learned the difference between a link and a statistical association while completing my bachelor's degree at Old Dominion University while in Eminent Professor Michele Darby's research methodology class. In simple terms, an association simply shows a link between two variables. In the case of the perio/cardio link, one variable is chronic periodontitis (PD) and the other is cardiovascular disease (CVD). In observational studies, researchers found that there was an association (also called correlation) between these two variables. Many hypothesized that treating PD nonsurgically would reduce future cardiovascular events.

Even throughout ancient history, associations between PD or dental caries and systemic health were proposed, and, at the end of the 19th century, a focal infection theory emerged.1 According to this theory, microorganisms localized in a certain area of the body (such as oral tissues) could be transmitted via the blood or lymphoid circulation to other distant areas, such as external tissues, subsequently causing various systemic conditions such as cardiovascular, pulmonary, or gastric diseases.1

In the first part of the 20th century, the focal infection theory was applied to dental clinical practice in an erroneous manner, including massive extractions of teeth, with the aim of preventing or treating systemic infections.2 During the second half of the 20th century, the concept of massive extractions was no longer popular.1,2

Fast forward to the 1980s when Finnish researchers reported an association between poor oral health and CVD.3,4 A surge of studies all over the globe followed, paving the way for another paradigm shift, and it was 'assumed' that treating PD and reducing periodontal inflammation would improve cardiovascular health outcomes.

In order to confirm causality (PD is a cause of CVD), intervention studies and randomized controlled intervention trials are required. To date, insufficient evidence has been found for improvement of systemic disease after periodontal treatment.3,5,6 Even though PD could affect CVD either directly through microbial challenge or indirectly by host response to microbial challenge, periodontal and cardiovascular diseases share multiple risk factors that are prevalent and powerful promoters of disease, including tobacco use, diabetes mellitus, and age.2,5

Determining causation requires evaluating the strength of the evidence and following Bradford Hill criteria, which were established by a British epidemiologist in 1965. You can view the criteria online but it takes individuals with specific skills in data analysis and interpretation of evidence to understand how they apply to oral/systemic link science.

The highest possible level of evidence is a systematic review (SR) or meta-analysis of randomized controlled trials (RCTs). The most current SR on the effect of periodontal therapy on CVD was recently performed in China for the Cochrane Oral Health Group. This organization is an international network of health-care professionals, researchers, and consumers who prepare, maintain, and disseminate SRs of randomized controlled trials (RCTs) in oral health.

Electronic databases were searched up through April, 7, 2014, and RCTs and quasi-RCTs were included in the SR. Only patients with a diagnosis of PD and CVD were included. Patients in the intervention group received active periodontal therapy. Data was extracted in a way to minimize bias by the authors who were completing the SR and a Cochrane tool for risk of bias assessment was also used for critical appraisal of the extracted evidence.6

In summary, the Cochrane SR reported very low quality evidence, which makes it impossible to support or refute whether periodontal therapy can prevent the recurrence of CVD in patients with PD.

Dental hygienists who want to read more details about criteria for clinical trials included in this SR can read the report on the Cochrane Oral Health webpage under updated reviews (ohg.cochrane.org/reviews).

Currently, only one randomized controlled trial (303 participants) was suitable for data extraction. This study had problems with its design and the Cochrane group found it to be at high risk of bias.6

If you think this information is hard to follow, try writing about it! Evidence-based decision making is a critical part of our destiny if we are serious about embracing "professionalism" and standing united in our area of expertise. We must embrace it, so slog along with me as we sometimes tackle tough topics in periodontal therapy.

Just as there's no evidence to support a role for dogs in transmission of the Ebola virus of humans, it's not possible to say whether or not periodontal therapy can prevent the recurrence or improve the symptoms/adverse effects of CVD in patients with periodontal disease.

A petition to save Excalibur, the pet dog of the Spanish nursing assistant who contracted Ebola was unsuccessful and euthanasia of this beloved pet was considered a precautionary measure. As his corpse was removed in a van for incineration, some members of the crowds who clashed with police yelled out, "Murderers!"

What are we saying to our patients about periodontal therapy and preventing CVD? Are we providing accurate evidence, or is it just hearsay or fear mongering? Is it appropriate to send the following message to a patient: "Floss or Die?" Even worse, are we "selling" periodontal therapy to patients and telling them that untreated PD can cause CVD? Are we suggesting to patients that periodontal treatment will improve cardiovascular disease?

According to the authors of the SR completed by a group of researchers (dentist, periodontist, cardiovascular physicians) oral health professionals should not be telling patients that treating PD will prevent CVD.5 Statements by oral health-care professionals that imply a causative association between PD and specific CVD events or claim that therapeutic interventions may be useful on the basis of that assumption are unwarranted.5RDH

References

1. O'Reilly PG, Claffey NM. A history of oral sepsis as a cause of disease. Periodontol 2000. 2000; 23: 13-18.

2. Kotsovilis S, Slim LH. Periodontal and cardiovascular diseases: statistical or causal association? A review and analysis. Can J Dent Hygiene 2012; 46 (2): 131-140.

3. Pickett FA. Discussion of state of science related to oral-systemic links. Can J Dent Hygiene 2012; 46(2): 89-90.

4. Muller P. Periodontology; matters arising. http://perioatuit.com/2014/05/

5. http://circ.ahajournals.org/content/early/2012/04/18/CIR.0b013e31825719f3.full.pdf

6. Chungie L. Periodontal therapy for the management of cardiovascular disease in patients with chronic periodontitis. Cochrane Database Syst Rev 2014. CD009197.


LYNNE SLIM, RDH, BSDH, MSDH, is an award-winning writer who has published extensively in dental/dental hygiene journals. Lynne is the CEO of Perio C Dent, a dental practice management company that specializes in the incorporation of conservative periodontal therapy into the hygiene department of dental practices. Lynne is also the owner and moderator of the Evidence-Based Dental Hygiene Group (EBDH) on LinkedIn. Evidence-based periodontal therapy will be part of the group's focus, and Lynne enjoys mentoring dental hygienists in EBDH. She can be reached at periocdent@mindspring.com or www.periocdent.com.

More in Patient Care