Reading the Dental LIterature

Reading the Dental LiteratureA Brief Guide to Critical Literature Review

Cathy Hollister, RDH, MSPH, PhDNashville Area Dental Support Center

Session GoalTo review key concepts in interpreting current, relevant dental research so that clinicians can use appropriate publications for clinical decision making. Learning ObjectivesAt the end of this session, participants will be able to:Name a strength and weakness of review articles and original research reportsExplain the benefits of a quasi-experimental study designExplain the importance of internal and external validityInterpret a p value

Key Points to Consider: Peer Reviewed PublicationsIs the material primary or secondary?What was the study design?Internal Validity: does the study measure want was intendedExternal Validity: can the results be generalizedStatisticsAre the results statistically significant?Are the results clinically significant?What is the Publication Type?Primary ResearchStrengthsIncludes a full description of researchFocusedControls for confounding variables (the ability to control for other variables differs by study design)WeaknessesScope is limitedMay not be generalizable to other populations or times

Review ArticlesStrengthsIncludes relevant material from many types of studiesPresents studies conducted over a period of timeWeaknessesThe reader may be unable to evaluate appropriateness of the articles included in the reviewMay present only one point of view

Review ArticleConsider the review article: Mercury Toxicity and Treatment: A review of the literatureNotice the lack of strict criteria that opens the possibility of author bias to stress a particular point of viewNotice also that for the reader, it can be very difficult to evaluate the quality of the reviewed articlesOverall conclusion: Mercury is toxic

Systematic ReviewsA specific type of review article that has strict inclusion criteria resulting in:Only high quality research is includedSelection bias is reduced

Systematic ReviewThe Cochrane Collaboration conducts systematic reviews on a variety of topics. WeaknessFew studies meet inclusion criteria, therefore it can bedifficult to draw strong conclusionsExample: Dental Amalgam and Multiple Sclerosis: A Systematic Review and Meta-AnalysisOverall Conclusion: Insufficient evidence, need more study

Original ResearchNow consider Neurobehavioral Effects of Dental Amalgam in ChildrenThis Randomized Clinical Trial measured the impact of mercury exposure in dental amalgam on neurobehavioral assessments.Notice the narrow focus of the research and the specific means of measuring the impact of mercury exposure.Overall conclusion: Dental amalgam poses no significant neurobehavioral risk in children over the age of 7 in Portugal

3 Articles: Different ConclusionsThese articles had a common topic: dental amalgam and the possible consequences to exposure to mercuryThese were all published in peer reviewed journalsConsider the similarities and differences in the conclusions.What would you consider to be a strength and weakness of each article?What overall conclusions could you draw after reading these 3 publications? Primary ResearchKey Points to ConsiderStudy DesignValidityInternal ExternalStatisticsWhat is the Study Design?Experiments:RCTStrengthsDetermines CausalityRisk of other factors is minimizedDetermines dose responseWeaknessesExpensiveMay be unethicalMay have small sample sizesMay not replicate real life situationsQuasi-Experimental DesignCohortA group with similar characteristics followed through timeCase ControlIdentify people with a condition (cases) and very similar people without the condition (controls)Compare previous exposuresTime SeriesMultiple cross sectional surveysQuasi-Experimental DesignStrengthsLess expensiveAvoids ethical concernsMore likely to replicate real situationsWeaknessesUsually includes biasesMany variables not under strict controlConfounding variables may not be eliminated

Confounders: Crime & Ice CreamCrime increases in the summerIce cream consumption increases in the summerTherefore: Eating ice cream causes crimeORCriminals like ice cream

Article Review: Maternal Amalgam Study design, Validity, Statistical significance, clinical significanceAre the conclusions are supported by the data?Potential sources of bias?Are there confounders?What can you learn from this study?What questions ARE NOT answered in this study?

Study DesignDescriptive, observationalRetrospective (to determine previous exposures)StrengthsReflects real life situationInexpensive and no ethical concernsWeaknessesCannot determine causalityBias and confoundersValidity: Internal and ExternalInternalIs the study free from bias?Did the study measure what was intended?External Can you generalize the results to other groups? Internal ValidityDid the study measure what was intended?Even with the best study design, sources of bias may be unavoidable and may affect studys impact

Common Threats to Internal ValiditySelection Bias: some participants were systematically excluded from the studyMeasurement error: study does not measure what was intended to be measuredRecall Bias: people do not remember past events accuratelyAmbiguity about the direction of the causal relationship: Which came first, chicken or egg? External ValidityHow generalizable are the results of the study?Even with excellent internal validity, the results may not be applicable to your population of interest due to systematic differences. Example:Race, gender, and socioeconomic status are common risk factors for many diseases. Results of a periodontal study on healthy adults may not apply to adults with diabetes.

ProbabilityStatistics are based on probability.Some natural variation will always occur within groups.Statistics are used to test the likelihood that findings are the result of the intervention and not a result of this natural variation. Statistics are used to project if similar findings would occur in any other sample or in the overall population.

P Value A p value is a measure of the likelihood that the results of the study happened BECAUSE of the intervention, and not because of normal variations in the study group. The smaller the p value, the more significant the finding. A report of p