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The Fine Print

April 1, 2010
The headline reads, “Periodontal Disease and Pancreatic Cancer Linked.” A colleague sends you this press release and you later discuss it with a patient.

Interpret clinical studies with ease

by Frieda Atherton Pickett, RDH, MS, and Lynne Slim, RDH, MS

The headline reads, “Periodontal Disease and Pancreatic Cancer Linked.” A colleague sends you this press release and you later discuss it with a patient. What can you tell your patient about this particular link? Even more important, should you even mention it? Is a press release about a single study linking periodontal disease to pancreatic cancer newsworthy, or is it sensational journalism? Let’s explore together how to interpret clinical studies, as well as conduct critical analysis of dental literature.

Anyone who’s been involved in the preparation of literature reviews is familiar with the process of searching the library for scientific studies on the topic being investigated. Thirty years ago, students went to the library, located a large volume called Index to Dental Literature, and searched for a topic. They wrote down the citations on 3x5 cards, and headed to the stacks to locate the publications. This search took a great deal of time, and sometimes studies were not available. They had to be retrieved via interlibrary loan, adding more time delay. Fast forward to the 2000s, and the process is completely different.

The process of retrieving reliable, evidence-based information on a topic of interest can now be done in the comfort of your home. The Internet has built-in advantages by providing a list of relevant citations after entering a topic’s key words.

Let’s say, for example, you’re puzzled about a patient who’s convinced that his mercury amalgams are making him sick. You’ve read a lot about the hysteria and pseudo-science on this topic, and your patient recommends that you watch the short video titled, “Smoking Teeth = Poison Gas,” on YouTube.

Something about this topic puzzles you. Since you’re skeptical, you decide to investigate further. With relative ease, it’s easy to navigate to the PubMed Web page sponsored by the National Institute of Health ( and find citations in dental, medical, and associated journals, as well as a special link to systematic reviews (SR) at this site.1 The Web page at www.MedLinePlus can also be used to access information (just enter “periodontal disease systematic reviews” in the search box). In some situations, a full text is free and available through these portals. If not, one can almost always access an abstract on a study that’s of interest. Money and time can be saved by visiting a dental or medical library that has journals you need within their library holdings that contain clinical trials. Clinical trials are research studies, using humans, designed to answer specific health questions. There are various types of clinical trials, and those with randomized controlled trial (RCT) designs have the highest level of quality and lowest level of bias, and are often described as “rigorous trial design.”

The highest levels of evidence

Clinical issues are often studied more than once and when identifying an issue to research, it’s important to find a wide body of evidence on the clinical question that needs to be answered. A systematic review (SR) is a comprehensive survey of a topic in which all of the primary studies of the highest level of evidence are systematically identified, appraised, and then summarized according to an explicit and reproducible methodology. Often studies not included in an SR are identified with a discussion of the reasons for the lack of inclusion, such as poor study design introducing bias and inadequate numbers in the study population, resulting in lack of statistical power.

The reader who is not familiar with these terms may be confused, but this presents an opportunity for the oral care professional to be cautious about making clinical decisions based on low levels of evidence and to learn important new information related to identifying reliable study designs without bias in the study methods (see Table I).

In the meta-analysis (MA) strategy, data from various studies with similar study designs are pooled or combined (treated as if the results were one study) in order to get a larger sample size and increase the rigor and reliability of the studies on an issue. In general, a good SR or MA will provide a better guide than an individual study.

Searching for systematic reviews isn’t always straightforward, such as when you use PubMed as a source. When using PubMed for the first time, go to the PubMed home page and click on tutorials. From there, you will learn more about different search strategies. Another good source for systematic reviews is the ADA Center for Evidence-Based Dentistry. ( Systematic reviews are alphabetically arranged by topic and are easy to find. For example, let’s say you’re interested in knowing if there are any systematic reviews on peri-implantitis. Once you type in the word peri-implantitis, your search will reveal about 17 results. Select the most recently published papers for the most up-to-date science.

The number of published systematic reviews has increased enormously every year, but the quality of these reviews is sometimes poor. The most reliable SR papers are published by the Cochrane Collaboration, the Agency for Health Research Quality (part of NIH in United States), and professional journals. Future of preparation requirements for systematic reviews will probably include specific guidelines requiring rigorous preparation.

Levels of evidence

All study designs are not the same and some provide higher levels of reliability than others. A pyramid for study types and levels of clinical evidence has been developed to guide the oral health-care professional in interpreting the strength of a study design.2 Systematic reviews (SR) provide a high level of reliable analysis of multiple studies on an issue. The MA protocol of combining data from multiple studies with similar designs is valuable and enables the dental hygienist to look at the preponderance of evidence and strength of large sample size evidence.

These two strategies represent the “gold standard” for levels of evidence to answer treatment questions.1 In these formats of literature review, studies are limited to only high quality (such as randomized controlled trials) to moderate quality study designs (such as cohort or case control studies) in humans. Recent tutorial guides to finding SRs using the PubMed or ADA Web site provide an excellent guide to finding this valuable literature.1,3

Clinical studies are analyzed by experts and organized in such a way that makes systematic reviews easy to find. When searching PubMed, there are great audio tutorials that walk you through the process of searching, and medical/dental libraries conduct workshops on research and information management tools.

Once you’ve learned how to obtain systematic reviews, share this skill with others. Start a dental hygiene study club and meet regularly to identify issues for investigation. Whether you’re blogging on your favorite Internet chat group or just attending a continuing education course, this newly discovered knowledge will help you question a speaker’s or writer’s assumptions and aid in improved clinical decision-making. After all, we are scientists since we use science as a basis for our clinical practice!


Forrest JL. Utilization of the internet for clinical decision-making. Access 2009;23(3):29-35.

Modified Evidence Pyramid. SUNHY Downstate Medical Center, Medical Research Library at Brooklyn ( Accessed 10/17/09.

Draper K. Accessing health information in the 21st century. Contemporary Oral Hyg. Apr 2007;17-23.

Frieda Atherton Pickett, RDH, MS, is a former associate professor at the Caruth School of Dental Hygiene, Baylor College of Dentistry, as well as an author and lecturer. Lynne Slim, RDH, MS, is the Periodontal Therapy columnist for RDH magazine.

Table 1

Clinical Study Designs

Randomized, controlled trial: Subjects are randomly assigned to two or more groups, with one or more receiving an intervention (experimental group) being tested (such as periodontal debridement or locally delivered antimicrobial), and one group receiving a placebo (controlled group). The groups are followed over time to determine if any differences exist between the intervention(s) and the controlled group.

Cohort study: A study in which a particular outcome, such as death from a heart attack, is compared in groups of people who are alike in most ways but differ by a certain characteristic, such as smoking.

Case control: In a case-control study, patients are assigned to one of two groups on the basis of their disease status: one group with the disease (the cases) and one without (the controls). The cases and controls are then compared to ascertain if certain factors occur more frequently in one group than the other.

Observational: This design addresses health issues in large populations in natural settings.

Interventional: This design evaluates experimental treatments or the safety of an established procedure.

Prospective study: A study with this design looks at the evidence of treatment or therapy over a period of time in the future.

Retrospective study: A study with this design examines the events of a therapy in the past, “looks back” at interventions experienced, and what happened to the individuals.

Case study: A patient experience or several patients with the same experience are reported in this type of study, and characteristics related to the clinical issue are described. These are considered “anecdotal” and do not usually use control groups or large sample sizes, so are low levels of evidence.

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