Ready to climb the evidence pyramid?

Ready to climb the evidence pyramid?

Are ultrasonic toothbrushes more effective than manual brushes? Is it ethical to recommend professional teeth cleaning every six months? Will a posterior composite last as long as the amalgam restoration? If any of those questions came across your mind, so you need a trusted opinion based on “evidence” and that is our topic today. Clinical decisions are not relying on personal opinions anymore, rather on evidence-based dentistry. So, without beating around the bush, let us CLIMB the pyramid. 

What’s the evidence-based pyramid or research hierarchy of evidence? 🤓

Now, when you open PubMed to search for an answer to the previous questions you will find many study designs. Which study should you read? During our journey to search for the “evidence”, we need to rely on the most reliable study designs. So, the evidence pyramid is a visual summary of the types of study/ research designs from the least reliable (base) to the most reliable (apex). There are many variations of the pyramid, but they all share a similar structure. 

So, why are we learning about this? Trust me on this. Its importance exceeds the exam marks. Anyone currently enrolled in a dental hygiene program is required to read, understand, and summarize a scientific article as an assignment. Some students push beyond those assignments and voluntarily search articles to find answers to the nagging questions in their heads. Many dental hygiene students have the opportunity to participate in conducting or writing a research paper. 

Now, Ready to climb the PYRAMID with me? 🧐Let’s start at the bottom, the least reliable research:
  1. Background information and expert opinions:
    The least reliable evidence comes from ideas, opinions, and experience. Sometimes we develop our ideas from what we’ve studied or heard and we accept those ideas with little questioning. Also, personal experience can come from a gut feeling without having a scientific explanation. So, NO OFFENSE, but we shall take the opinions we hear with a grain of salt. 
  1. Case report/ case series:
    An in-depth study of a single case (case report) or several similar cases (case series) usually focus on a rare disease. Tip: remember any of the syndromes you studied? Like  Osteogenesis Imperfecta or Reiter Syndrome? If you encountered one, you may want to write an article about it, but this type of research is considered to be a low level of evidence since it does not have a control group and it is retrospective.  

For study designs 3, 4, and 5: we “observe” if there is a relationship between:

  1. Outcome= dependent variable &
  2. Risk factor= independent variable

For example, imagine that you want to observe the relation between sticky food and caries. Here, the amount of caries is the outcome that DEPENDS on the sticky food, so the outcome is called the dependent variable. 

  1. Cross-sectional study:
    Imagine that you are taking a cross-section of the population. Here, we investigate both the risk factor and the outcome at the same time. A cross-sectional study is the least reliable study in the observational studies (the studies which observe certain conditions with no intervention or treatment). This study type poses low evidence since it does not have a control group. 
  1. Case-control study:
    These studies aim to measure subjects that either HAVE a disease or condition (cases) or DO NOT have the disease or condition (controls) being studied. Information is obtained about their previous exposure/non-exposure to the intervention or factor covered in the study. 
  1. Cohort studies:
    Cohort Studies are defined as a study that categorizes participants according to the exposure to risk factors then follows the participants over some time to observe the occurrence of the disease. Cohort studies can be prospective or retrospective. Prospective cohorts are observed at a time point to be exposed or not exposed to a risk factor while retrospective studies are usually done from medical records.  
🙂 Bonus tip!

I find a case-control study is self-explanatory, so please don’t confuse it with a cohort study. In a Case-control study, we divide the population into cases (disease or condition) and control (no disease), so the population is divided according to the disease (outcome) and not the risk factor (as in cohort studies).

  1. Randomized controlled trial (RCT):
    Medications always have side effects or limitations, so we need to search for new drugs. RCT is an experimental (intervention) research type where participants are randomized into two or more different groups with each group receiving a different intervention. The effects of the different interventions are then measured and recorded. 
  1. A systematic review and meta-analysis: 
    This is simply a “review” of the current literature in a “ systematic” way. Authors of systematic reviews know that you are busy doing a great job in the clinic, so they help you by appraising and summarizing the current evidence. You don’t have time to read 13 or 15 articles comparing green tea and chlorhexidine mouth wash. Sometimes, data from research can be combined and “analyzed” for a meta-analysis. So, they do that for you. Here is a link for a systematic review by me:

Acknowledgment: All figures were created using 

What is next? 🤗

Hands-on experience is very important in learning the evidence pyramid so I ask you to window-shop PubMed for different study designs. For now, it is enough to read the abstract, especially the methods section. 

Written by:

Heba Hussein is a Cochrane author and Cochrane translator and a member of the Cochrane Oral Health. She has been publishing many publications including systematic reviews and guidelines. She worked in the tenure track at the Oral Medicine Department at the Faculty of Dentistry, Cairo University, Cairo, Egypt since 2006. She is currently a Research Volunteer at UIC, Chicago, IL.

She had her BDS, Master’s in Oral Medicine and Periodontology, and a Ph.D. in Oral Medicine from Cairo University.  She is fluent in Arabic and English. She speaks intermediate Spanish.  She had the National Board of Dental Examination (NBDE) in 2014 and since then, she has been tutoring hundreds of dental and dental hygiene students on most of the known platforms. 

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