Research Methods in Dentistry PDF

Fahimeh Tabatabaei Lobat Tayebi Research Methods in Dentistry Research Methods in Dentistry Fahimeh Tabatabaei Lobat Tayebi Research Methods in Dentistry Fahimeh Tabatabaei Lobat Tayebi School of Dentistry School of Dentistry Marquette University Marquette University Milwaukee, WI, USA Milwaukee, WI, USA ISBN 978-3-030-98027-6 ISBN 978-3-030-98028-3 (eBook) https://doi.org/10.1007/978-3-030-98028-3 © Springer Nature Switzerland AG 2022 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. 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This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland Preface Advances in dentistry are the result of great dentists and researchers’ collaboration efforts in the past, present, and future. Without their efforts, dentistry would not have achieved its present status. New science and technologies such as smart bioma- terials, biomimetic, functionally graded materials, tissue engineering, and 3D print- ing are rapidly finding their way into dentistry. However, many questions remain about the treatment of specific oral defects such as critical-sized ones or etiology of oral diseases and the most effective ways to prevent or treat them. Any dental mate- rial (new resin composite), pharmaceutical (triple antibiotic), and preventive prod- uct (varnish), or new treatment protocol (guided bone regeneration) needs to be validated by dental researchers. Having an effective role in the investigation of unre- solved challenges and participation in the evolution of dentistry require employing a reasonable research methodology. Therefore, learning the methodology of research is an integral part of dental education to prepare dentists for a dynamic future that is dependent on generating new knowledge in this field. Teaching the research methodology in dental schools is not only for conducting research but also for obtaining the critical thinking and reading skills necessary to incorporate new evidence into the clinic. After years of teaching and mentoring dental students, the authors of this book realized that the growing volume of research articles during the recent years has overwhelmed and confused many students in their research activities. They usually ask questions about how to read and cover all these papers, how to find the points needed in research among hundreds of existing documents, or how to be sure that what they are doing in their project has not already been done by other investigators. This book aims to help dental students and future dental practitioners to overcome such challenges and be competitive in today’s fast- growing research environment. The book presents the research methodology in dentistry in seven chapters. The chapters complement each other but can also be used independently. The first and second chapters explain the key concepts and common approaches in dental research, both in basic science and clinical dentistry. The third chapter familiarizes the readers with evidence-based research in dentistry and how to write a systematic review. The fourth chapter explains the process of designing and presenting a v vi Preface proposal. Chapters 5 and 6 discuss reporting the results of scientific studies and managing the references. The final chapter is about ethics in research, highlighting the significance of adherence to ethics in animal and human studies. This book pro- vides practical guidelines for dental researchers; however, it can also be beneficial for researchers in other fields (e.g., medical sciences and biomedical engineering). Milwaukee, WI, USA Fahimeh Tabatabaei Lobat Tayebi List of Abbreviations 3D Three-Dimensional ADA American Dental Association AFM Atomic Force Microscopy ANOVA Analysis of Variance APA American Psychological Association ARRIVE Animal Research Reporting of In Vivo Experiments CAD/CAM Computer-Aided Design/Computer-Aided Manufacturing CI Confidence Intervals COI Conflict of Interest CONSORT Consolidated Standards of Reporting Trials COPE Committee on Publication Ethics COVID Coronavirus Disease DOAJ Directory of Open Access Journal DOI Digital Object Identifier EARR External Apical Root Resorption EBD Evidence-Based Dentistry EDS Energy Dispersive Spectroscopy EMBASE Excerpta Medica dataBASE Er: YAG Erbium-doped Yttrium Aluminum Garnet laser FDA Food and Drug Administration GBR Guided Bone Regeneration GIC Glass Ionomer Cement GPa Gigapascals GTR Guided Tissue Regeneration H0 Null Hypothesis HIPAA Health Insurance Portability and Accountability Act of 1996 IADR International Association for Dental Research ICMJE International Committee of Medical Journal Editors ICTRP International Clinical Trials Registry Platform IEEE Institute of Electrical and Electronic Engineers IgM Immunoglobulin M vii viii List of Abbreviations IL Interleukin IPD Implant Probing Depth IRB Institutional Review Board ISO International Organization for Standardization JDE Journal of Dental Education JDR Journal of Dental Research JDS Journal of Dental Sciences JPEG Joint Photographic Experts Group KAP Knowledge, Attitude, Practice MEDLINE Medical Literature Analysis and Retrieval System Online MeSH Medical Subject Headings MPC 2-Methacryloyloxyethyl Phosphorylcholine polymer MTA Mineral Trioxide Aggregate MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bro- mide assay NCBI National Center for Biotechnology Information Nd: YAG Neodymium-doped Yttrium Aluminum Garnet laser NIDCR National Institute of Dental and Craniofacial Research NIH National Institutes of Health NiTi Nickel-Titanium NOS Newcastle-Ottawa Scale NSF National Science Foundation OIERR Orthodontic-Induced External Root Resorption PDF Portable Document Format PDL Periodontal Ligament PICO Patient/Population, Intervention, Comparison, Outcomes PMA Premarket Approval PMID PubMed identifier or PubMed unique identifier P–P Percentile-Percentile PRISMA Preferred Reporting Items for Systematic Reviews and Meta-Analyses qPCR Quantitative Polymerase Chain Reaction Q–Q Quantile-Quantile RCT Randomized Controlled Trial RevMan Review Manager RF Risk Factor RIS Research Information Systems SD Standard Deviation SE Standard Error SEM Scanning Electron Microscopy SJR SCImago Journal Rank SPSS Statistical Package for the Social Sciences STARD Standards for Reporting of Diagnostic Accuracy STAs Sequential Thermoplastic Aligners STROBE Strengthening the Reporting of Observational Studies in Epidemiology List of Abbreviations ix SYRCLE Systematic Review Centre for Laboratory Animal Experimentation TIFF Tag Image File Format WHO World Health Organization WMA World Medical Association WWH What-Who-How XML Extensible Markup Language Contents 1 Introduction to Dental Research 1 1.1 What Is Research? 1 1.2 Types of Dental Research 5 1.2.1 Based on the Time 5 1.2.2 Based on the Location 6 1.2.3 Based on the Type of Data 7 1.2.4 Based on the Application 7 1.2.5 Based on the Main Question or Objective 10 1.3 Selecting the Research Topic 22 1.3.1 How to Find the Field or Area of Interest? 23 1.3.2 How to Determine the Research Topic? 26 1.4 Handling Large Volume of Literatures as New Challenge in Performing Research 30 1.4.1 What Resources? 32 1.4.2 How to Read? 33 References 36 2 Design Cycle of Research 39 2.1 What Is the Design Cycle? 39 2.2 Investigation (Formulating the Hypothesis) 39 2.2.1 Analysis of the Collected Information 40 2.2.2 Formulating the Research Question 42 2.2.3 Decision-Making About the Different Solutions for the Research Question 44 2.2.4 Formulating the Hypothesis 46 2.3 Designing a Plan (Writing the Proposal) 50 2.4 Performing the Research (Hypothesis Testing) 51 2.5 Evaluation (Data Interpretation) 52 References 58 xi xii Contents 3 Systematic Review and Evidence-Based Research in Dentistry 61 3.1 What Is the Purpose and the Process? 61 3.2 Formulating Review Questions 63 3.3 Determining the Search Strategy (Documenting the Methodology) 68 3.3.1 Choosing the Keywords 69 3.3.2 Selecting Databases 70 3.3.3 Boolean Searching and Selection Criteria 72 3.4 Performing the Review and Searching Studies by Using MeSH 75 3.5 Quality Assessment 77 3.6 Extracting Data from Studies (Descriptive Analysis) 81 3.7 Data Synthesis and Evaluation 83 References 85 4 Writing a Research Proposal 87 4.1 What are the Requirements? 87 4.2 Title 88 4.3 Statement of the Problem/Significance 89 4.4 Specific Aims 92 4.5 Literature Review (Justification and Feasibility) 97 4.6 Research Design 99 4.6.1 Type of Research 99 4.6.2 Subjects, Sampling Method, Sample Size 100 4.6.3 Data Collection 104 4.6.4 Data Analysis 107 4.6.5 Potential Pitfalls and Alternate Approaches 108 4.7 Timetable 109 4.8 Budget and Personnel 109 4.9 Core Review Criteria 110 References 113 5 Scientific/Clinical Research Report 115 5.1 When Should You Start? 115 5.2 Title 118 5.3 Abstract 119 5.4 Introduction 122 5.5 Materials and Methods 124 5.6 Results 126 5.7 Discussion and Conclusion 129 5.8 Acknowledgment/Conflict of Interest 132 5.9 References 132 5.10 Submission of a Manuscript 133 References 136 Contents xiii 6 Reference Management in Scientific Writing 139 6.1 When and How Should You Cite a Reference in Your Text? 139 6.2 The Digital Style (Numbered Method) 141 6.3 Author-Date Style (Annotated Method) 141 6.4 EndNote Software 142 6.5 Mendeley Software 146 References 149 7 Ethics in Dental Research 151 7.1 Why Do We Need Ethics in Research? 151 7.2 Ethics in Human Studies 152 7.3 Ethics in Animal Studies 153 7.4 Ethics in Manuscript Writing 156 References 158 Index 161 Chapter 1 Introduction to Dental Research 1.1 What Is Research? Scientific research is a rational approach that allows the examination of problems to be solved and the discovery or formulation of precise answers to questions. It is built on the work of other scientists, can be generalized, and generates new ques- tions. The purpose of the research could be to earn doctorates or masters, meet curiosity, make discoveries, provide innovative solutions to complex problems, develop new products, save costs, advance science, acquire new knowledge, or improve the well-being of society. The ultimate goal of the research is to create the knowledge essential for improving health. Without this knowledge, this action is impossible because it has no logical basis. The process of research is characterized by the fact that it answers questions in an organized, scientific, and systematic manner. Questions are required for research, and research always arises from a problem to be solved. Without a specific question, your research will be aimless. In other words, there is no research where there is no question. Therefore, by stating your question, you will clarify what your study intends to address. Finding the answer to the research question will be the objective of your research. Organized research begins with a plan or proposal. Non-planned research is often inefficient, and it may never lead to the researcher’s correct answer. The scientific method means that the study is based on reproducibility, feasibil- ity, and reliability, which we will explain further in the following chapters. Finally, using a systematic process means following clearly defined steps in the research to achieve an accurate answer: If your approach is deductive, you should: (1) formulate the research question, (2) predict the answer to the research question in the form of a hypothesis, (3) design a plan, (4) test the hypothesis, and (5) evaluate and report the results which confirm or reject your hypothesis. For example, after treating a carious-exposed tooth using calcium hydroxide and composite, you noticed the dentin bridge formation under restoration. Your ques- © Springer Nature Switzerland AG 2022 1 F. Tabatabaei, L. Tayebi, Research Methods in Dentistry, https://doi.org/10.1007/978-3-030-98028-3_1 2 1 Introduction to Dental Research tion is: What is the reason for the formation of the dentinal bridge? You hypoth- esize that calcium hydroxide caused it. To test this hypothesis, you design a plan. After examining the effect of calcium hydroxide on dental pulp stem cells, you can report that your hypothesis has been confirmed or rejected. In an inductive approach, you should: (1) carefully observe a situation or an individual case, (2) gather the findings, (3) authenticate the underlying characteristics, (4) find a pat- tern in other cases, and (5) formulate your theory. The theory of gravity is an example of an inductive approach. By observing the fall of an apple from a tree and the recurrence of this fact in other objects, Newton concluded that there must be a gravitational force that causes this pattern to happen. Therefore, one of the basic steps in any research project is to choose the research approach. This choice depends above all on the nature of the problem and the phe- nomenon being studied. As the deductive approach is more prevalent in dental research, we will focus on this approach in this book. Similarly, researchers should be familiar with the different types of research and know their application in their field of study. Before dealing with the types of research, it is necessary to understand the exact meaning of the key concepts in the research literature, which are also used exten- sively in this book. Method: The word method may refer to a tool, instrument, experiment, tech- nique, and test to set up, conduct, collect, analyze, and evaluate data for answering the research question. Observations, experiments, and statistical approaches are all examples of the methods employed to conduct the research. For example, you may work with a “universal testing machine” to obtain the compressive strength of your new composite samples; you can use an MTT assay (3-(4,5-dimethylthiazol-2-yl)- 2,5-diphenyl-2H-tetrazolium bromide assay) for evaluating the cytotoxicity of these composite samples; or you may employ “one-way analysis of variance (ANOVA)” for analyzing your data. Methodology: The research methodology is broader than the method and refers to several methods used to efficiently investigate the research hypothesis and achieve the objective. Accordingly, the methodology may include subsections like “Research Design,” “Protection of Human Rights,” “Instrumentation,” “Data Collection and Analysis.” Methodology implies the correct application of the method, explanations behind the decision of your specific methods (the rationale), and the recognition of the criteria for choosing a method. Methodology asks: Why did you use the compression test? Is it the best way to solve the problem? If your material is brittle, you should consider the diametral compression test. Therefore, “methodology” or “approach” is the investigation’s work plan and justifies and sup- ports a particular method’s choice by citing relevant sources. Using a hook is a method of fishing, while how to use it is your methodology. The methods used should be valid and reliable, which means that they must precisely measure the expected properties and, if repeated, lead to the same results. Suppose that you are studying the effect of a substance on craniofacial regeneration. In that case, the method you are using should be such that anyone who uses it achieves the 1.1 What Is Research? 3 same results. Sometimes, the method is valid and reliable, and you are performing it correctly, but it does not answer your question, which means that your methodol- ogy is incorrect. When your objective is to investigate the effect of mineral trioxide aggregate (MTA) on the osteogenic differentiation of stem cells, the MTT test will not answer your question even if it is done correctly. The MTT test is not a proper method for measuring differentiation. For this purpose, you need to assess the osteogenic marker expression by real-time quantitative polymerase chain reaction (qPCR). Therefore, your research design guarantees that the correct choice of methods is genuinely and solely responsible for the results and leads to the correct answer to the research question. To employ a proper method, you need to under- stand the research problem accurately. Then, the selected methods should be ana- lyzed rigorously (clarifying the logic behind them) to ensure the results’ validity, reliability, and credibility. Variable is the measurable factor that can vary during research, can have more than one value, and is involved in answering the research question. The variable must also be directly observable (sex, color of eyes), or if it is not directly observ- able (time, temperature, proportion, pH), it can be measured by another measuring instrument (pH meter). The cause, risk factor, or the variable that can be manipu- lated in the research method is called the independent variable. The dependent vari- able is the effect, outcome, or the variable that responds to changes and would be analyzed to meet the objective. The independent variable can be changed/manipu- lated/controlled at given levels/doses/values/types by the researcher. Therefore, you can purposefully change the independent variable, which causes a change in the dependent variable (the reverse is impossible, which means the dependent variable cannot cause any change in the independent variable). The dependent variable should be measurable, and you should know how to measure it. When you study “the effect of MTA on the osteogenic differentiation of stem cells,” MTA is the independent variable, and the dependent variable (osteogenic differentiation) is measurable. You can observe or measure the dependent variable (effect) to report the correla- tion or association between the independent and dependent variables or find a dif- ference between them. We say that an association (correlation) exists between two variables when a change of one variable coincides with the shift in the other vari- able. An association can be positive or negative and proportional or non-proportional. The association is causal when a change in the independent variable (exposure) leads to or causes a difference in the dependent variable (disease). For example, you may assess patients regarding the use of restorative materials and the location of caries. If the results show that restoration selection depends on tooth type and sur- faces, there is an association between the two variables. When you assign sub- jects to groups and compare them to find the difference, the independent variable is the group classification; the dependent variable is that on which they differ. For instance, you may distribute several extracted teeth to four groups restored with dif- ferent bulk-fill resin-based composites (independent variable) and compare them in terms of internal adaptation (dependent variable). 4 1 Introduction to Dental Research Hypothesis, in simple terms, is a statement in response to the research question and should be stated based on the researcher experiences and the findings of previ- ous studies. This statement can be proven or rejected. To write a hypothesis, the researcher must determine the variable or groups and predict the relationship or the difference between them. The null hypothesis (H0) usually predicts no difference between the control and the study group, while the alternative hypothesis assumes a difference between groups or association among the variables. Hypothesis plays a guiding role in the research process and is only validated after experimentally test- ing. The role of hypotheses is to show the researcher the general direction for con- ducting research; they prevent the study of resources not related to research, help in the correct determination of the methods, and provide a framework for interpreting the information gathered and drawing conclusions. Based on the specific aims of your research, you may have several hypotheses. In a good research design, reject- ing a null hypothesis will construct another null hypothesis, and the study will continue. The participants/samples are drawn from a population with determined charac- teristics. As the population of interest is usually substantial, and it is impossible to work directly on all of them, most research studies involve observing a sample from a defined population. Sampling is the process of choosing portions of the population to observe and study. The sampling method can be probable (random) or non- probable. It is essential to be aware of the difference between random sampling and random assignment/allocation. While random sampling is considering a known chance (greater than zero) of participation for every member of the population to be selected as subjects, random assignment means that after selecting subjects, you should also determine a method of randomly assigning the sample into the study/ control groups. Finally, one of the most crucial parts of the research is the researcher. The researcher is any person carrying out studies respecting a rigorous methodology to provide new knowledge. The researcher only deals with facts within a framework defined by the scientific community. A researcher needs to be passionate about his/ her work, have a good plan, be patient while doing research, and be persistent in achieving the goal. Among the critical qualities of researcher leading to success in research, we can cite: A curious mind to find new facts. Integrity for the value of the scientific method. An analytical mind capable of practicing critical thinking. Receptivity to criticism at the professional level. Open-mindedness and the ability to see the meaning of unexpected observations. Objectivity. Now that we are familiar with the terminology of research, we can more easily get acquainted with different types of research. 1.2 Types of Dental Research 5 1.2 Types of Dental Research The type of research significantly impacts the method of data collection and analy- sis, and if not chosen correctly, it can lead to erroneous results or an inability to answer the research question. Therefore, it is imperative to decide on the type of research before starting the project because you cannot change it during the study. Let’s see what the primary types of research are. 1.2.1 Based on the Time One of the criteria for research is the issue of time. Based on the time, the researcher observes the subjects/patients at a given time (cross-sectional studies) or during a continuous period (longitudinal studies) (Fig. 1.1). In cross-sectional or prevalence studies, you want to define “what is happening.” Like taking a picture with a camera, you need to observe all samples of different groups once at the same point in time or over a short period at the present moment. When you simultaneously compare the salivary cytokine levels of periodontally healthy subjects and subjects with chronic periodontitis, your study is cross- sectional. Here, you measure the dependent and independent variables (the expo- sure and the outcome) at the same point in time and cannot predict which came first (the increase of salivary cytokine or chronic periodontitis). Consequently, you cannot infer causality. Another application of prevalence studies is the estimation of the prevalence of the outcome of interest but not its occurrence. For instance, you can observe the presence of common dental anomalies in a sample of non- orthodontic growing subjects by examining their panoramic radiographs. You can also use this type of study for knowledge and attitude evaluations by conducting surveys. If data collection is performed several times in cross-sectional studies, it can be named a pseudo-longitudinal study. For instance, you select a sample of adolescents to evaluate the improvement in the toothbrushing frequency and its associated factors over three studies. In longitudinal studies, the same group is observed continuously or repeatedly over a period (like a movie) to examine changes over time and understand the rela- tionship between variables. This study is more accurate than cross-sectional and can be utilized for discovering the predictors of diseases. When you select two groups of subjects with/without a high level of a salivary cytokine and recall them Fig. 1.1 Classification of research studies based on the time 6 1 Introduction to Dental Research periodically to evaluate the development of periodontitis in each group, subjects are enrolled in a longitudinal study. The longitudinal research can be retrospective or prospective: Retrospective studies concern any study for which exposure has occurred in the past, and data will be collected after the exposure or intervention through inter- views or recorded information of patients. This method aims to analyze and interpret past events to predict similar events in the future. In other words, this method expresses “what happened.” Assuming that you are selecting a group of patients who previously received direct posterior resin-based composite restora- tions, you are conducting a retrospective longitudinal study if you evaluate the survival rate of their restoration. In the prospective study, the research starts now, and the data will gradually be collected to determine the exposure. You aim to express “what will happen” regarding the etiology of a disease or the efficacy of an intervention. For instance, you can analyze salivary biomarkers of bone loss in two sample groups at risk or no risk of periodontal disease to see in which group more bone loss will occur. Prospective studies could be interventional (experimental) or non- interventional (observational). Non-interventional studies involve only ques- tionnaires completed at a consultation or routine follow-up of participants. On the other hand, in interventional (experimental) studies, the intervention is the researcher’s responsibility. If a group of patients recently received resin-based composite restorations, and you only examine their restorations every 6 months for 12 years, your study is observational, while, if you select a group of patients, repair their teeth by composite restorations after assigning them to different groups, and then follow up with them over a period, your study is prospective and interventional. 1.2.2 Based on the Location Based on the location of the data collection, the research can be divided into two categories: field research and library research (Fig. 1.2). Field research involves the researcher’s own observations and data collection. For example, to evaluate “the salivary cytokine levels in subjects with chronic peri- odontitis and periodontally healthy individuals,” you need to select the subjects, collect their saliva, measure the cytokine level in the samples, and then analyze the Fig. 1.2 Classification of research studies based on the location 1.2 Types of Dental Research 7 collected data. This type of research in which the researcher gathers data directly is also called a preliminary or original study. In library research, the data is already available and should only be categorized. Systematic review and meta-analysis are the common forms of library research, where the researcher refers to the libraries or bibliographic databases and uses exist- ing data that has already been submitted. Such studies that are based on the results of primary studies are also called secondary studies. It should be noted that the library research does not mean the obligation to be in the library, but rather the com- mitment to the library data. For instance, you can extract information from the his- topathological data available in the Oral Pathology database. 1.2.3 Based on the Type of Data Depending on the data type, two kinds of studies can be identified: qualitative and quantitative (Fig. 1.3). If the information received or collected is not subject to statistical analysis but is based on an analysis beyond numbers, we refer to it as qualitative research. Here, you do not deal with numbers and statistics but rely on data explanation and inter- pretation of a small sample size. Images obtained from the optic, scanning electron, or fluorescent microscopes; spectra obtained from X-ray diffraction and Fourier transformation infrared spectroscopy; and a result obtained by cell and tissue stain- ing are all examples of qualitative data. In contrast to qualitative research, the emphasis in quantitative research is on statistics. It aims to collect quantifiable data and statistically analyze them to search for correlation (association) between variables or differences between groups. In this approach, sampling is critical to be representative of the population. Data should be analyzed using statistical methods, and significant or nonsignificant dif- ferences between groups should be statistically summarized and compared. Therefore, to ensure the meaningfulness and usefulness of quantitative data, it is essential to choose the analysis method before data collection. 1.2.4 Based on the Application Based on the outcome or purpose of the study, the research can be categorized into three types: fundamental (basic), developmental, and applied (Fig. 1.4). Fig. 1.3 Classification of research studies based on the type of data 8 1 Introduction to Dental Research Fig. 1.4 Classification of research studies based on the application 1.2.4.1 Fundamental or Basic Research Fundamental research aims to identify new problems, discover facts, recognize phe- nomena, test theories, and generate knowledge. This research is concept-oriented and is the primary source to produce new knowledge for applied and developmental research. This type of research is about expanding the boundaries of knowledge without having concern about its immediate application. The keys to success in this type of research are new ideas, a highly motivated team, and access to modern tech- nologies. The scientific community uses its results. This type of study is entirely theoretical and cannot be used immediately after the project accomplishment. It is more time-consuming and has strategic goals. Governments often support this research and encourage institutions to address these fundamental issues. Fundamental research is usually conducted in a controlled environment such as a laboratory to strictly observe the samples and prevent the interaction of different variables. Examples of basic research in dentistry include: 1. How does Streptococcus mutans cause caries? 2. How do medications induce dry mouth (xerostomia)? 3. How does calcium hydroxide produce dentin bridge? 4. Is there any way to replace lost tooth structure instead of using syn- thetic materials? 1.2.4.2 Applied Research This problem-oriented research seeks to provide a practical solution to a specific problem, answer a direct question, and achieve the generally desired result quickly. The results can be used immediately after the project is completed. The purpose of this research is to put the practical application of knowledge into life. This research is more worthwhile, more objective, and more tangible. Therefore, in terms of effi- ciency, they have extraordinary value. In general, this research aims to improve the living conditions of human beings. It costs relatively less due to its short duration, and often a particular employer supports the costs incurred. However, the results may only be applicable at the time specified. These studies have the following characteristics: 1.2 Types of Dental Research 9 1. In terms of time, they should be performed earlier than other types of research. 2. They are profitable. 3. Mostly public and private organizations and factories, and sometimes uni- versities and research centers do this research. 4. The relationship between industry and academia follows this type of research. 5. Have a clear and generally professional employer. 6. Consider cross-sectional problems. 7. They are seriously looking for knowledge application in answering the problem, not the achievement of new knowledge. 8. Financial support is often guaranteed. 9. Most of their topics are about the validation or application of the results of basic research. Examples of applied research in dentistry include the investigations to determine: 1. The immunomodulating properties of dental pulp stem cells. 2. The treatment options for aggressive periodontitis. 3. The ways to improve the antibacterial effects of root filling materials. 1.2.4.3 Developmental Research Developmental research aims to improve and develop the previous devices, pro- cesses, systems, or existing situations. It is established upon applied research. For example, after identifying the cause of tooth caries in basic research and introducing possible solutions to treat caries in applied research, conducting a clinical trial to determine the best treatment or improve a current product is a form of developmen- tal research. In many cases, applied and developmental research are considered the same. Other examples of developmental research in dentistry are: 1. Improvement of an ultrasonic handpiece and its clinical evaluation. 2. Animal study for assessment of bone particles as implant material. 10 1 Introduction to Dental Research Fig. 1.5 Classification of research studies based on the main question of research (what the ques- tions in each category are) 1.2.5 Based on the Main Question or Objective Studies are based on different types of questions. Understanding this category of research is the foundation of any research program. The researchers must explain their aim clearly to be able to ask the correct question. Research in this category can be divided into exploratory, descriptive, and ana- lytical research (Fig. 1.5). Each of these types is structured in response to the main question of the study. 1.2.5.1 Exploratory Research Exploratory research consists of describing or characterizing a phenomenon so that it appears familiar. It is, in fact, the starting point of research, with which the researcher intends to add to the existing literature in some way. From this perspec- tive, it is perhaps the most explicit and most basic type of research. Being elemen- tary does not necessarily mean that it is simple, but rather that the researcher takes the first step to build the foundation of a subject. Exploratory research seeks to answer the question of whether there is a problem in the research community. Examples: Are there any viable cells in the pulp of necrotic teeth? Are there any bacteria inside the disinfected root canal of a tooth? Does the amount of fluoride in drinking water vary in different parts of the city? Obviously, in exploratory research, the researcher has no hypotheses, and his/her main goal is to gather information about the presence or absence of a phenomenon. Although the researcher has a presupposition in his/her mind, this assumption has no scientific basis. It is not permissible to interfere with one’s presuppositions in the exploratory research process. 1.2 Types of Dental Research 11 This research provides rich information about a disease. It makes the community aware of a problem that needs to be investigated in the next step on “how it arises” and “why” by conducting “descriptive” and “analytical” research. The researcher collects the data based on observations. Exploratory research can be classified into case reports and case series. A rare disease, a new symptom of a known disease, a new treatment, or the destructive effect of an intervention is reported in the case reports, and there is no control group. For example, you may aim to report on three cases of peri-implant bone loss and peri-implantitis. Case series are based on reports of a series of cases of a given pathology or a series of treated patients with- out a specific control group assignment. In this type of study, we only consider a limited number of cases, so it should not be used for a risk assessment. Here are the steps of exploratory research: Problem recognition: not clearly defined problem at a preliminary stage. Carrying out methods to explore the problem: –– No hypothesis. –– No control groups. –– No intervention or manipulation of variables. –– Produces qualitative data. –– No conclusive result. –– Leads to further research. 1.2.5.2 Descriptive Research When the researcher accepts the exploratory research results and begins to describe the created phenomenon, he/she enters the descriptive research process. For exam- ple, after we find out that there are bacteria inside the disinfected root canal of a tooth, now we ask about their type, numbers, and properties. Therefore, if the research question is not about “what” a phenomenon is, but rather about its charac- teristics, that will be named descriptive research. In other words, we only describe the available information in descriptive research, which is part of the observational studies. The results of this research only show the features of a situation at the time of the study. For example, what is the prevalence or rate of caries in a population? What are the characteristics of this population (age, race, socioeconomic)? What are the radiographic or clinical symptoms? Descriptive studies in epidemiology are often designed to express temporal, spa- tial, and disease distribution concerning individual risk factors and are examples of cross-sectional studies. The title of the descriptive research should be very detailed as follows: “Prevalence of oral diseases and oral-health-related quality of life in people with severe mental illness undertaking community-based psychiatric care”. 12 1 Introduction to Dental Research “Prevalence of total and untreated dental caries among youth: the United States, 2015–2016”. This type of research is a kind of observational study in which different charac- teristics of a sample of the population are observed. The questions such as “how many types,” “what types,” “how much,” and “what ratio” are raised in descriptive research. These questions are usually answered via observation of the participants, interviews, surveys, obtaining measurements of physical features, or simply by extracting information from existing sources, such as disease reporting registers, hospital medical records, or employment service records. Descriptive studies are cross-sectional surveys (opinion survey, knowledge, atti- tude, practice (KAP) survey), epidemiological descriptions of the occurrence of a disease, and studies of variations in health and disease trends as a function of time and territory. In cross-sectional surveys, cause-and-effect data are collected simul- taneously, without determining the time sequence. They do not attempt to test a hypothesis about an association. They provide a prevalence rate at a point in time (point prevalence) or over a period (periodic prevalence). As the name suggests, a cross-sectional survey requires data collection on a cross-section of a population. This population could be the entire population of a city or a part (sample) of it. In this type of descriptive study, we use surveys to assess the distribution of a disease, pathological state, immunological condition, nutritional state, etc. The researcher always tries to report the facts without any interference. The goal in conducting such research is to provide a realistic description of the characteristics of a situation or subject. For example, you may interview a group of women to determine if they have children with cleft palate and whether they have taken certain medications dur- ing pregnancy. In such a study, you may see an association between medication use (exposure) and cleft palate (disease). However, the cause-and-effect relationship is unclear, as you did not select groups in this study. The following example can better illustrate the steps of this study : Study objectives: evaluate the occlusal, periodontal, and implant-prosthetic parameters and marginal bone loss (MBL) around implants after prosthetic loading. Identify all patients who received implants restored with single-tooth or up to three splinted crowns. Calculate MBL in all patients considering occlusal, periodontal, and implant- prosthetic parameters. The critical point in this research is that, unlike exploratory research, the descrip- tive study is problem-oriented and hypothetical. The researcher must have a hypoth- esis, and his/her research will prove the main hypothesis, which is the answer to the main question. The analysis of descriptive data often leads to formulating a new hypothesis, which is the basis for analytical research. 1.2 Types of Dental Research 13 The steps of descriptive research are: Recognizing the problem. Defining the hypothesis. Planning methods to answer the question. –– No control groups. –– No intervention. –– Uncontrolled variables. –– Produces quantitative data. –– Conclusive result. 1.2.5.3 Analytical or Explanatory Research While the exploratory and descriptive studies give an image of the current situation, the purpose of the analytical research is to go beyond and look for the links that events may have. In this type of study, the objective is to test hypotheses about dif- ferences between two or more groups or associations between various factors within the same group. Analytical or explanatory research clarifies the relationships between phenom- ena and determines why such phenomena occur or under what conditions. In this type of research, the researcher seeks to answer the “WHY” question and discover the cause or determine the association between exposure to risk factors and disease. In other words, the objective of this type of research is to examine the causal rela- tionship of variables. Exploratory research has allowed you to detect the presence of bacteria in the root canal of disinfected teeth; by descriptive research, you have known their characteristics; now you ask yourself why these bacteria can remain in the root canal even after disinfection. Before reaching this stage, the previous two steps must have been completed. Suppose the study’s objective is to investigate the cause of the increase of dental caries among youth. In that case, the incidence of caries and their augmentation should be investigated earlier by exploratory and descriptive research. Accordingly, in this type of research, we need to know what others have done before. If you are sure about the increase of dental caries among youth and want to check the effect of immunoglobulin M (IgM) antibodies or the amount of fluoride in drinking water as causing factors, your study is analytical. In this study, the presence of a control group is mandatory, and the type of exposure to intervening variables is also essential (see the topic of variables). The essential step in an analytical study is to develop a hypothesis and design a study plan that allows control of the variables that would interfere with the risk fac- tor and disease. This approach varies depending on the analytical strategy adopted. Analytical research is divided into two types of observational and experimental (interventional) studies based on the assignment to exposure. Observational analytical studies, which implicate only observing what is hap- pening, do not involve any intervention. The researcher cannot control any of the third-party factors acting on any individuals under observation. In these studies, 14 1 Introduction to Dental Research groups of individuals are compared to identify differences in exposure or outcome. Here, the observations of cause and effect are lagged in time and may give rise to an inference of associations. This association may even be statistically “significant.” However, a high degree of relation between X and Y does not mean that X is the cause of Y or vice versa. You need an experimental study to verify causality. In observational analytical studies, samples are selected from a large group of people by random sampling; however, there is no randomization (random assignment of each subject to one of the groups). Therefore, groups have non-similar characteris- tics, and other factors besides the factor of interest may influence the results in these observational studies. Observational analytical studies could be prospective or ret- rospective, case-control, or cohort: In the case-control type, the case group has the disease of interest and the control group does not, and their history of exposure to the risk factor is determined. In other words, the groups are divided according to the dependent variable, and you will try to find out the possible cause of a disease. Case-control research is also called retrospective research, since cause and effect (independent and dependent variables) are examined after the occurrence. Here, you will determine the out- come before the determination of exposure to express “what happened” (Fig. 1.6). A higher risk factor frequency in disease cases than in controls indicates a rela- tionship between it and the disease/pathology. The groups are selected based on the dependent variable. Matching the case and control groups is essential. Matching means choosing controls with similar characteristics (gender, race, age, etc.) to cases and is a method to reduce the effect of confounding factors. The matching ensures the features’ comparability in the two groups; hence, a different distribution of these characteristics does not disturb the observed asso- ciation between the risk factor and the disease. Selecting several control groups that represent pathological conditions other than the one studied would increase the power of the study. Exposure data is collected by researching the history and/ Fig. 1.6 Case-control study. RF+: exposed to the risk factor, RF-: not exposed to the risk factor 1.2 Types of Dental Research 15 or consulting medical records through interviews, surveys, and/or file review. Sometimes the risk factor is a permanent condition, such as blood type, deter- mined by clinical or laboratory examination. In this type of research, following a blind method is very important. The blind method means that the examiner or investigator should not know whether a subject belongs to the study group or the control group. We can determine the associations between exposures and oral disease by using this study design. Suppose that you aim to “determine the relationship between amalgam restorations and periodontitis.” Your analytical research method is case-control if you start with the selection of patients with periodonti- tis (case group) and healthy people (control group). Here, amalgam restora- tion is an independent variable (the exposures of interest), and periodontitis is a dependent variable. It is recommended that people in the case group be newly diagnosed with periodontitis and do not have any other oral disease. Recently diagnosed cases are preferred to eliminate the possibility of exposure to the risk factor studied after the onset of the disease in patients who have lived with the disease for a long time. Here, you determine the percentage of people in both groups who are exposed to an amalgam filling. Back to the example of children with cleft palate, if you choose two groups of mothers with healthy or cleft palate children and ask them about taking a particular medication during pregnancy, your research method is case-control. The following example can better illustrate the steps of this study : –– Study objectives: investigate the role of alcohol consumption in implant failures. –– Matching criteria: age, gender, number of implants, the year implants were placed, bone augmentation. –– Identify all patients with implants with at least one failed implant removed or lost/exfoliated (case). –– Identify a control group of patients with the same characteristics and without any implant losses; select a random sample. –– Ask patients to report the amount of alcohol consumption per day. –– Calculate the frequency of alcohol consumption in each group and compare. Therefore, the steps in the case-control research are as follows: 1. A clear statement of the inclusion, exclusion, and matching criteria to improve the validity of the results. 2. Selection of people with the disease of interest (case). 3. Selection of people without the disease of interest (control). 4. Measurement of the interested risk factor in the past of both groups (retrospective). 5. Data analysis to investigate the cause-and-effect relationship. 16 1 Introduction to Dental Research Fig. 1.7 Prospective cohort study. RF: the risk factor In cohort research, another type of observational analytical study that is more common than case-control in dental research, groups are divided according to the independent variable. The classic strategy of cohort studies is first to take a reference population without a given disease. Some individuals of this popula- tion present characteristics of interest for the study (exposed group), while others do not present them (unexposed group or control). Both groups should be free from the pathology considered at the start of the study. Observation of the two groups (with or without exposure) continues to identify the disease’s incidence over a given period. Here, you will determine the outcome after the exposure or intervention to express “what will happen” (Fig. 1.7). In fact, in the cohort study, your goal is to show whether people exposed to a specific factor or exhibiting a particular characteristic have a greater risk of subsequently developing the dis- ease than those not exposed or not exhibiting the particular feature. Different methods are used to collect the data, including investigations with questioning and follow-up procedures, medical records checked over time, medical examina- tions and laboratory tests, and the consolidation of archives with exposure data- sets and outcome datasets. Let us consider a study to “determine the particle size ratio of composite fillers on the failure rate of restorations.” The research method would be cohort if you select the teeth repaired with composites of different particle sizes and determine the condition of repairs (success or failure) after a while. In this case, the particle size is the independent variable (the factor of interest), and the failure rate (incidence) will be the dependent variable. In a cohort study for determining the relationship between amalgam restorations and periodontitis, you select a reference population without periodontitis. A group of this population has amalgam fillings, while the other one is without it. Then, you can assess the presence or absence of periodontitis disease in both groups by fol- lowing them for a defined period. Regarding the relationship between cleft palate disease in children and the use of medication by the mother during pregnancy, if you select several children with or without cleft palate, and then ask their mothers about the use of the drug, the study is case-control type. In contrast, if you select a group of pregnant women, some of whom are on certain medications, and then examine whether their 1.2 Types of Dental Research 17 children will have cleft palate, your study will be a cohort study. When you plan a cohort study to evaluate the relationship between a population’s oral health and mortality rate, oral health is an independent variable, and mortality is a depen- dent variable. Another example of a cohort study could be the follow-up of healthy individuals with positive or negative gene polymorphism in specific interleukins and their examination at defined intervals for periodontal disease. In all these cases, subjects are disease-free at the start of the study, one of the groups is exposed to the factor of interest, and the number of new cases of disease (inci- dence) will be found out by follow-up time. The following example can better illustrate the steps of this study : –– Study objectives: investigate the effect of chronic periodontitis on the long- term implant prognosis. –– Matching criteria: type of implant, method of installation, suprastructure. –– Identify all patients with recent implant placement who lost their teeth due to chronic periodontitis. –– Identify patients with recent implant placement without a history of periodontitis. –– Compare the failure, success, and complication rates between two groups 1 and 10 years after implant placement. The steps in the prospective cohort study are as follows: 1. The population of interest is determined. 2. Disease-free samples are selected in this population. 3. Some individuals in the study population were in contact with the risk factor (exposed), and some were not exposed to the risk factor. 4. At different time points, the occurrence or nonoccurrence of the dis- ease is examined in each group. Although in all the above examples for the cohort study, the research begins now, and the information is collected in the future (prospective), it is essential to note that the cohort study can also be retrospective. If the study design requires that you select individuals belonging to a specific population at a particular point in the past and then follow these individuals from that point in the past to “today,” the study is called a retrospective cohort study. A retrospective/historical cohort study is only possible if the archives or data available make it possible to reconstruct a cohort exposed to a risk factor and monitor its effect over time. In other words, although the researcher did not attend the initial identification of the risk factor, he/she recon- structs the exposed and unexposed populations from the archives. Let us suppose you have access to the electronic records of adults at high caries risk, some of whom have received nonoperative anti-caries agents. You can perform a retrospective cohort study by determining whether they received anti-caries agents or not and calculating the caries outcomes in the data recorded from baseline to follow-up in 18 1 Introduction to Dental Research both groups. However, it may be challenging to prove that reducing tooth decay in all patients results from receiving anti-caries agents. To better understand the difference between the retrospective and prospective cohort, take note of the following example: –– The goal of the study: Analyze the effect of implant location on the marginal bone loss around the dental implant. –– Prospective cohort study: Identify patients who were recently surgically treated with at least one implant; split them into two groups: implants located anteriorly and implants located posteriorly; monitor and examine them over a period; cal- culate the incidence rate for the development of bone defect at the site of implan- tation in each group and compare them (risk ratio). –– Retrospective cohort study: Using the records of a dental clinic, identify all the patients with implants placed 10 years ago; divide them into two groups: those with implants located anteriorly and those with implants located posteriorly; examine the data recorded during their follow-up regarding the crestal bone level to understand which patients have developed bone defect at the site of implanta- tion and which have not; calculate the risk ratio in both groups. The results of case-control studies and cohort studies may suggest a possible relationship between cause and effect. However, the best study design to prove a causal relationship is the experimental (interventional) study. The main characteris- tic of this type of research is manipulating at least one variable and monitoring and controlling other dependent variables to measure the effect of the manipulated vari- able (independent variable also called experimental variable or cause) on the moni- tored one (dependent variable). The general principles of experimental research are intervention, experimental group, control group, and randomization. This type of research can be viewed as the ultimate or decisive step in the research process, as a mechanism for confirming or rejecting the validity of ideas and assumptions about subjects’ behavior or the effects on them. The researcher masters the subjects, the intervention, and the outcome measures, and he/she imposes the conditions under which the experiment takes place. More specifically, the researcher defines the sub- ject who will be exposed and the one who will not be exposed to the intervention. This selection is made in such a way as to minimize any bias effects when compar- ing outcome measures between the exposed group and the unexposed group. In experimental (interventional) research, which is always prospective, the impact of an intervention on the living laboratory cells or bacteria, animals, or human beings is investigated before and after the intervention. If human intervention is performed, the study is called a clinical trial. Clinical trials are often used to test new dental materials, medication, treatment, or preventive regimens. However, any new materi- als or drugs should be evaluated via in vitro experiments and in vivo animal studies before entering the clinical phase. In the experimental group, intervention is the primary condition, and there is no intervention (“sham” intervention) in the control group. The control group can receive a placebo or a gold-standard intervention in clinical trials. Examples of experimental research include: 1.2 Types of Dental Research 19 Material: effect of thermocycling on dental composites. Cells: examining the impact of mechanical forces on osteogenic differentiation of dental pulp stem cells. Animal: studying the rate of gingivitis in amalgam-restored teeth in guinea pigs. Human: analyzing the effect of an herbal mouthwash on reducing dental caries in individuals with orthodontic appliances. The following example can better illustrate the steps of this study : Study objectives: correlate marginal bone loss around dental implants positioned subcrestally to short abutments. Enroll patients according to inclusion/exclusion criteria. Insert implants in the posterior mandible with the same protocol and deliver metal-ceramic restorations 3 months after implant insertion (adapt the length of the prosthetic abutments to the soft tissue vertical thickness). Evaluate bone loss after 6 and 12 months of functional loading. Calculate the association between prosthetic abutment height and bone loss. A conventional clinical trial for a new therapy, device, or biomaterial goes through four phases: 1. Trials during phase I include studies involving limited healthy volunteers to evaluate the safety of a device. Giannakopoulos et al. conducted a phase 1 study for assessing “the cardiovascular effects and pharmacokinetics of intranasal tet- racaine plus oxymetazoline”. 2. Phase II trials are designed to assess the clinical efficacy of the drug or device, determine the appropriate dosage, and study its safety. Additional pharmacologi- cal information will be collected, particularly on the dose-response relationship of the drug. If it is a device, its clinical efficacy should be evaluated, and its configuration and possibilities for improvement should be tested. An example is the study of Ciancio et al. for assessing the “safety and efficacy of a novel nasal spray for maxillary dental anesthesia”. 3. Phase III is the phase in which rigorous inclusion and exclusion criteria are fol- lowed for the choice of participants. The purpose of this phase is to assess the actual performance of a drug, device, or new treatment and to assess the safety of its prolonged use against the current standard treatment in a larger and more heterogeneous population than in phase II. This phase requires more clinical and epidemiological skills as well as high laboratory technology. Marketing authori- zations for a new drug or medical device are based on evaluating the results of phase III trials. Therefore, phase III trials are subject to strict guidelines. Because phase III trials are time-limited, some side effects may not appear in the short term. Ciancio et al. conducted a phase III clinical trial “comparing three intrana- sal mists for anesthetizing maxillary teeth in adults”. 4. Although the market authorization of a drug or device is usually based on prom- ising results from phase III trials, government agencies and the World Health Organization (WHO) prioritize using an additional test phase—testing in the field or under normal operating conditions. The purpose of the phase IV clinical 20 1 Introduction to Dental Research trial is to reassess the functional performance, safety, acceptability, and continu- ity of use of a drug or device under normal conditions of use. An example of the phase IV trial is the study of “oral dexmedetomidine premedication effect on preoperative cooperation and emergence delirium in children undergoing dental procedures”. As in other research designs, it is rare for the researcher to study all the popula- tion in an experimental study. Therefore, you should select the samples representa- tive of the populations from the target population to be analyzed for experimental purposes. A probability sampling generally does this. If the groups are very similar and the outcomes vary, the sample size should be more noticeable. It is also impera- tive to randomly assign subjects to the control and treatment groups. Randomizing the treatment allocation is very important in the randomized controlled trial (RCT) as the most powerful scientific research tool. There are many unknown factors, such as genetics or lifestyle, that can influence the results. Proper randomization can reduce the risk of severe imbalance of these factors in the various study groups. If the subjects in question are all available before the study begins, they can be ran- domly assigned into the control and experimental group after matching in terms of intervening variables (randomized matched controlled trial (RMCT)). Therefore, by random assignment in RCT, you can be sure about non-systematic differences between the treatment and control groups. Figure 1.8 shows the clinical trial design with random sampling and random assignment. In most clinical trials, it is not possible to have the study group at the same time, and random assignment into the groups is not possible. In this quasi-experimental research, patients gradually come to the research site. It is necessary to gradually (non-randomly) assign individuals to intervention and control groups in such cases. Again, the groups must be matched in terms of intervention variables (group matched controlled trial). Suppose that you want to evaluate the efficacy of fluoride varnish on the primary dentition. If you randomly assign children to treatment and no treatment, your study is RCT. In contrast, when children are part of an ongo- ing program, you cannot randomly assign them to treatment and control groups, so your study is quasi-experimental. Fig. 1.8 Clinical trial design 1.2 Types of Dental Research 21 Blinding is another crucial characteristic of clinical trials. A double-blind trial is a study where both the researcher team (including the statisticians responsible for analyzing the data and the investigators who write down the trial results) and the patient do not know whether the patient is in the experimental group or the control group. This method is advantageous when the control group receives a placebo drug or an identical sham procedure. The steps in the experimental study are as follows: 1. Identifying the relevant population of interest. 2. Determining the study sample by random sampling. 3. Obtaining “informed consent” from each of the participants before submitting them to the experiments. 4. Samples are then randomly assigned to the different intervention factors and the control group. 5. Subjects in the control and experimental groups are then followed up under rigorous conditions for a specified period. 6. Appropriate statistical methods are used to compare the outcome measures of groups. The randomized split-mouth trial (a design of randomized controlled trial) is specific to research in dentistry. The split-mouth trial is defined as a study in which different sites in the oral cavity (tooth, quadrant, or jaw) of a patient’s mouth will be randomly assigned to either the experimental treatment or control. The split-mouth experimental design has been used in many areas of: Dental surgery: “prophylaxis versus placebo treatment for infective and inflam- matory complications of surgical third molar removal”. Periodontology: “antimicrobial photodynamic therapy as an adjunct to non- surgical treatment of aggressive periodontitis”. Orthodontics: “effect of micro-osteoperforation on the rate of canine retrac- tion”. Cariology: “effect of sodium fluoride or titanium tetrafluoride varnish and solu- tion on carious demineralization of enamel”. Pediatrics: “split-mouth design in pediatric dentistry clinical trials”. In all analytical studies, the presence of a control group is mandatory, and the matching of the groups in terms of confounding factors, which distort the relation- ship between the exposure and the outcome, is essential, even though the process of randomization in clinical trials can remove these confounding factors. Before con- ducting the study, it is necessary to determine the inclusion and exclusion criteria, which always include the age range. We have shown the classification of different studies based on the main question of research in Fig. 1.9. The process from simple observation to experimental research that follows a series of systematic steps is shown in Fig. 1.10. An observa- tion (case report) or a series of observations (case series) launches a hypothesis. A 22 1 Introduction to Dental Research Fig. 1.9 Classification of research studies based on the main question of research (name of the studies in each category); RCT: randomized controlled trial Fig. 1.10 The process from simple observation to carrying out experimental research cross-sectional study (descriptive study) is undertaken to record the information on the characteristics of a disease or phenomenon, which provides a more in-depth view of the problem and generates a correct hypothesis. An observational analytical study including planned comparisons between variables gives more convincing evi- dence, establishes associations, and confirms (or rejects) the hypothesis. Finally, after this observation and these comparisons between groups, an experiment will be conducted to test the hypothesis more accurately and find the cause of the problem (experimental study). Let us consider that your colleagues in dental school report cases of implant failures. Cross-sectional research could address the prevalence of dental implant failures. By conducting a case-control or cohort study, you may find an association between bone resorption and the performance of dental implants. To confirm this association, you need to perform an experimental study. After realizing the cause of the dental implant failures, you may consider some solutions. Still, you need to do in vitro and in vivo studies to determine your intervention’s efficacy. 1.3 Selecting the Research Topic As mentioned earlier, research is a pathway to answer a question, and without a specific question, research will be aimless. Knowledge deficit within the research area leads to raising the research question. But what is the approach to get to the research question? In the first step, the researcher must determine the field of 1.3 Selecting the Research Topic 23 Fig. 1.11 The process of building a research problem that begins with moving from the research area to the research topic and then to a specific research question interest or area of his/her research. Secondly, he/she must go through some steps to define the research topic, and finally, he/she can specify the research question that we will address in the next chapter. Your general “field of interest” will be the basis for choosing the “topic” of the research. Therefore, to start research, you must select the subject area of your research. Then, you need to define a research topic. For example, in the field or research area of “regenerative dentistry,” your research topic could be about “the effect of laser on periodontal regeneration,” “dental pulp stem cells for root canal therapy,” “ceramic scaffolds for bone regeneration,” or “biomimetic approach for dentin regeneration.” After identification of the research area and the research topic, you should follow some steps to refine your “research topic” to a “precise research question” (Sect. 2.2). Therefore, building a research problem involves moving from an interest in a research area to a research topic and then to a specific research question (Fig. 1.11). The closer the researcher is to the research question, the smaller the dimensions of the problem. 1.3.1 How to Find the Field or Area of Interest? The selection of the field or area of interest is the first step in conducting the research. Determining what you want to study (the subject area of research) and, subse- quently, the topic for implementing any research project depends on many factors. The choice is influenced by considerations such as the possession of domain knowl- edge, your experiences, studies, needs, interests, and educational environment. Knowledge of current work lets you know if research is possible in the area and can suggest the type of question to ask and the precise subject to study. But how do researchers usually find the subject of their research? The idea may come from personal experiences in everyday life, articles relating to the field of study, or research priorities of research centers. 1.3.1.1 By Accident or Personal Curiosity Sometimes the choice of the research subject is entirely random. Luckily, the sub- ject area of your project may be inspired by accident. For example, you notice that the number of referrals of children with molar tooth caries has increased. This 24 1 Introduction to Dental Research increase in referrals will arouse your curiosity. Has there been a change in the fluo- ride of the drinking water in the area? Sometimes paying attention to an ordinary situation can lead to a great discovery in science. For ages, people saw the apples fall from the tree. No one asked why objects always fall from the sky to the ground and not the other way around. But one person’s attention to this seemingly commonplace issue led to discovering the law of gravity. Keep in mind that dentists have been using the “tissue engineering” approach a long time before its discovery by using calcium hydroxide as a pulp capping material. But no one paid much attention to the question, “how does cal- cium hydroxide induce the dentinal bridge formation?” Later, with the discovery of tissue engineering in medical science, the reality of this story became clear to den- tists. The high alkaline pH of calcium hydroxide results in the release of growth factors from dentin, which subsequently lead to the recruitment and differentiation of dental pulp stem cells and regeneration of dentin (the formation of a dentinal bridge). For years scientists have known about the genetic programming of embry- onic stem cells, which results in their multilineage differentiation into skin cells, neuron, muscle cells, etc. However, Yamanaka and Takahashi’s curiosity to repro- gram and reverse engineer adult cells into stem cells led to the Nobel Prize. The critical point here is that the most beneficial research that will remain as the line of research and become the scientific heritage of a researcher is the one based on curiosity. Every dental researcher may deal with a variety of phenomena on a daily basis, which may stimulate his/her curiosity. The researcher should try to pur- sue a valuable issue that is vague to him/her for whatever reason, find something he/ she can be passionate about, and be persistent enough to understand, clarify, resolve, or at least find a convincing answer for himself/herself. The first sparks are ignited when you feel mentally challenged about a problem and want to find a solution. The researcher’s personal interest is compulsory for choosing a subject area, and this interest is the engine of continuity of research. Identifying a knowledge gap or being fascinated by a problem can motivate the researcher. In this case, he/she will devote a lot of time and energy researching and overcoming limitations and challenges because his/her personal interest is at stake. Otherwise, the researcher will not be sufficiently motivated to continue the study in a desirable and valuable way and carry out the research to the end. To find a field of research that attracts you, use the following questions: When dealing with dental patients or reading an article recently, did I encounter a topic that piqued my interest or made me think for hours? Is there an aspect of a subject in dentistry that I am interested in learning more about? Do I have a view on a current scientific controversy? 1.3 Selecting the Research Topic 25 After selecting a research area, to understand if you are undoubtedly inter- ested in that, ask the following questions: Why do I want to work on this subject? Will I still be interested in dealing with this subject in a few months, or even for years, as part of my career? 1.3.1.2 Previous Studies One of the most important sources for finding a topic or subject is a previous study because it is always limited and specific. Each research project answers one or more questions but at the same time creates other questions or offers suggestions for fur- ther studies based on the limitations of the research. Therefore, previous studies can be used—as a source—to find new questions and choose a new topic. Keep in mind that in every research paper, some questions remain unanswered. Consequently, if you read the articles critically, you can find new subject areas or topics for your research. Usually, the last paragraphs of the “discussion section” of scientific papers are about the “study limits” and the “recommendations for future research.” By reading these final paragraphs, you can determine the problems and questions that have not been addressed. Even if an article does not have a recommendation for future studies, by critically reviewing the existing literature and identifying the dis- agreements between researchers, you can think about what has not been studied yet or is missing in the literature. For example, in the studies on the effect of concen- trated growth factor (CGF) on stem cell differentiation, if you notice that research- ers have obtained different (controversial) results, you will be able to conduct a study that will close this debate by settling the question that remained unanswered. Systematic reviews that often focus on a particular topic are also excellent sources for finding new research subjects. They mention the remaining challenges after reviewing a wide range of research done on that topic. By reading articles, you may also decide to investigate the effect of other independent variables as causes of a dependent variable. 1.3.1.3 Research Priorities of Research Centers or Funding Centers In many cases, organizations and educational or research centers submit a list of their research priorities annually, and budgets are allocated for this purpose. Depending on their field of study, the researchers can choose a subject area from the list, determine the topic, and receive a reliable funding grant for their research by successful approval of their proposal. For instance, the areas supported by the National Institute of Dental and Craniofacial Research (NIDCR) are “oral cancer, orofacial pain, tooth decay, periodontal disease, salivary gland dysfunction, cranio- facial development and disorders, and the oral complications of systemic diseases” (https://www.nidcr.nih.gov/about-us/fast-facts). 26 1 Introduction to Dental Research 1.3.2 How to Determine the Research Topic? The research problem is an anomaly, an issue, a limitation, a difficulty, or clinical uncertainties that will be addressed through research. After choosing the area of interest or the field of research, the next step is to identify a problem that leads to the choice of the research topic. Let us suppose that you are interested in “dentin regen- eration” as your field of research. You need to determine the subject of your research in this area based on a problem (dentin demineralization by caries) that must be resolved. If you understand the importance of a problem, you can properly articulate the problem and talk about the need to do a project for solving the problem. You can select the research topic, considering factors such as: Importance of the problem and its impact. Urgent need for a solution. Relevance to the objectives of the funding organization. Possibility of dealing with the problem through a study. Project feasibility. Chances of success. Foreseeable consequences in case of success. Benefits in terms of training and other elements strengthening research capacities. To specify a research problem, we need to know “what is the process of selecting a research topic in dentistry?” Usually, the students are unaware of the importance of this process and haste to work on a research problem. Due to unfamiliarity with the process of selecting a research topic and lack of self-confidence, some students become afraid and anxious and decide to follow in the footsteps of other researchers and choose a topic that is not actually novel. The time you spend choosing a topic is critical. Three essential steps to reach the research topic include observing, thinking, and reading about your area of interest. After explaining the first two steps in this sec- tion, the third step will be described in more detail in Sect. 1.4. These steps would help you to limit your “research area” gradually. Each step will pave the way for the next step (Fig. 1.12). The more accurate and systematic the previous step, the easier and quicker the next step will be. If you look closely at the problem, it will be easier to think about it. And if you have thought about the problem and considered all aspects of it, reading about it will not take much time. The more deeply the researcher observes the problem, the more systematically and creatively he/she will think Fig. 1.12 The inverted pyramid of necessary steps of “observing,” “thinking,” and “reading” for determining the research topic 1.3 Selecting the Research Topic 27 about it. The more time he/she spends thinking deeply, the more purposeful the reading will be and the sooner the goal will be achieved. Finally, allocating more time to reading will speed up formulating the research hypothesis and planning the research project. From this perspective, the three stages of observing, thinking, and reading are repeated regularly in the researcher’s life, and each sequence in a new topic is based on the previous rounds. 1.3.2.1 Observing Observation is an active process and the first step in gathering information about the research problem. When a patient comes to you and complains of a dental problem, you first receive information about the chief complaint and medical and dental his- tory. Then by physical evaluation, clinical and radiographic examination, and the assessment of the performance of his/her existing restorations, you can have a com- plete view of the patient’s condition. You try to answer some questions by detailed observation: Is there any vitamin deficiency in medical history? Has your patient had a new illness like diabetes? Are there any cervical abfractions, erosion on ante- rior teeth, or wear patterns on occlusal surfaces of teeth? Has there been a change in the patient’s occlusion? Has he/she had bruxism recently due to stress? Has the patient developed new eating habits such as drinking acidic substances or smoking? How is the oral hygiene of your patient? Is there any infection? In the same way, when you face a potential research problem, the first step is to gather information by detailed observation. You should actively observe as many details as possible about the subject to detect and assimilate any information. For example, one of your patients reports that he has stopped using dental floss because it tears when used for posterior teeth. If you are a curious person interested in the subject, the first step is to look closely at the situation. You must carefully examine the patient’s teeth regarding too tight interproximal contacts, a marginal adaptation problem, or any overhang in proximal restorations. By thorough observation, you can collect some data about the situation. Observation is not limited to the synthesis of new materials. Let us suppose that you are responsible for purchasing a composite for a dental school. The question is: Which brand of composite shows better performance in posterior teeth? This ques- tion can be the basis for starting a research project. The importance of this research is especially evident when thousands of composites are purchased annually for a dental school. Before deciding about the change of composite supplier, the first step is to gather the results of the colleagues’ and students’ observations on the compos- ites’ performance so far. How is the handling of existing composites? Are there any differences in terms of postoperative sensitivity, solubility, color stability, or wear rate? Based on the observations, you can move on to the next step. 28 1 Introduction to Dental Research 1.3.2.2 Thinking When we carefully observe a problem, we can then analyze it, understand its impor- tance, and find solutions by creative thinking. Creative thinking is the ability to think in a unique way and beyond the established limits to arrive at authentic solu- tions. For innovation, we need to generate new ideas and new concepts through creative thinking on each question. As Albert Einstein said, “finding new questions or possibilities, and looking at old problems from a new angle requires a creative imagination.” This facet allows us to innovate and face challenges in different ways and get out of the routine. Generally, those who think more need to read and consult less, and those who think less seek to find the answer to their questions in the thoughts of others. Because creative thinking is not easy for many people, the shortcut is to get an answer from the product of others who have thought about it before. In this way, the researcher extracts his/her response from their works and puts it in front of his/her question. It seems that the precedence of reading over thinking saves time, but the disadvantage is that the imported answer is about another researcher’s question. Why don’t we often spend a lot of time thinking about the research problem? Maybe we don’t know what it means to think. It is widespread to confuse thinking with imagination. When you imagine that you have written your article and are now safely traveling and having fun or watching an exciting movie, you have not made an actual move; you are in the same position as before and only fly mentally in an unreal space. Thinking is a purposeful mental activity combined with developed imagination. The researcher should have a clear vision and manage it in the direc- tion of the research topic. Because if you don’t know where you are going, it will be impossible for you to reach your destination. For example, you are trying to figure out how or why dental floss tears in overhang areas. For this purpose, in addition to observation, you should think about the different aspects of it. What is the shape of the dental floss cross-section? Is it possible to change it? Is the dental floss single strand or multiple braided strands? Which one is better? What material is dental floss made of? Is it possible to use a different material? Is it possible to coat the cur- rent dental floss with a lubricant? The more significant and more profound the initial thinking is on a topic, the other research steps, including reading and writing a proposal, will be easier. More practical thinking can be expected if you have a good background and experience in a research subject. On the other hand, the less knowledge you have about a topic, the less effective it will be to think about it, and the sooner you will have to move on to the next step (which is reading). In this case, as you did not spend a lot of time on the thinking step, reading will naturally take more time. As mentioned before, it is not appropriate to prioritize reading before thinking; however, you can use brainstorming to get ideas from others to complete your vision. Teamwork is one of the main engines of creativity. By presenting the prob- lem or the situation to colleagues, they could observe it, draw conclusions, share their ideas, and give you a new light on the case. Reframing the issue by others 1.3 Selecting the Research Topic 29 increases the number of angles from which you’ll be able to consider the problem and discover new approaches. At this stage, accumulating knowledge is an opportu- nity to establish and to develop the research subject in mind and guess its various dimensions to explore the issue gradually. Here are four critical tips in moving forward: 1. How to think is generally a matter of taste, and tastes are different, so the way of thinking comes back to us. Taking a bath, working in a noisy environment, exer- cising, and walking are examples of thinking methods that could be different in every person. However, imposing some limitations or deadlines could be benefi- cial for creative thinking. 2. Intellectual work must be accompanied by manual effort. Consequently, we must take notes while thinking. It’s often helpful to use large notebooks with enough space to write a general description of various ideas. It is also beneficial to write each idea on a small card. Another way is to visually represent ideas in a diagram called the mind map. Usually, the main concept is in the center and sub-concepts radiate from the center. You can use keywords for preparing the mind map. That gives you an overview of a problem while helping to remember details. You can also link concepts to different branches. Using mind mapping software allows you to complete a mind map at any time. Take the time to develop several ideas through a mind map. You can highlight the potentials and weaknesses of each and create new ones if necessary. The words you have used during mind mapping can help you decide about your research methodology. If your keywords are more about the characteristics of a problem, you may choose descriptive research. In contrast, if you are more concerned about the relationship or association of several factors, your research methodology should be analytical. 3. The researcher must always be prepared for the emergence of new ideas. In other words, new ideas cannot be produced with prior intent. Therefore, it is recom- mended that the researcher always be prepared to deal with new ideas and thoughts and save them somewhere. 4. The researcher should try to generate new ideas without judging them. Avoiding being too rational can help you in this aspect. The final question is how the researcher can discern the novelty and well-being of the thought that has arisen and formed in his/her mind. To answer this question, we can mention several well-known criteria: 1. Be objective: For this purpose, you should recall your goal of thinking and facts about the problem. Determine the problem (what is the problem?), its possible causes, and eventual consequences (why did it happen? what are its impacts?). Then, consider the compatibility of your ideas produced from your thinking with answers to these questions. You should not feel contradiction in your thoughts. 2. Ask questions, analyze the answers, challenge assumptions: The researcher must explain all the facts and dimensions of the subject in his/her mind and reflect well on their relationship with each other. 30 1 Introduction to Dental Research 3. Be open-minded and communicate: Evaluate your thinking results by brain- storming to make its characteristics more transparent. 4. Think outside the box: To find an innovative topic, you need to consider its effect on others, not just how it affects you. Be concerned about at least one clinical relevance, research relevance, or educational relevance for your research topic. If there is no relevance (importance and usefulness), maybe you should recon- sider your choice and find a new topic that is more engaging. 5. Identify missing information: At the end of this step, you should have prepared a list of questions for the next step, the literature review. 1.4 andling Large Volume of Literatures as New Challenge H in Performing Research After observing a problem and understanding its importance, you start thinking about its various dimensions and then reading and collecting scientific evidence to increase your knowledge and ensure the choice of the topic (Fig. 1.13). Let’s go Fig. 1.13 The different steps of determining the research topic: from facing a problem to gather- ing the required information based on observation, thinking, and reading 1.4 Handling Large Volume of Literatures as New Challenge in Performing Research 31 back to the dental floss example. A researcher who has carefully observed and thought about the causes of floss rupture will now turn to read previously published articles to increase his/her knowledge. Reading at this stage means consulting the scientists who published on the related subject. The researcher should review the literature before starting the research design. By reading, you can understand “what has been done on your research subject so far?”, “how has it been done?”, and “what are the results?”. You will find out if there is enough information for your needs, set the perspective of your research, and have a more precise and more accurate topic. The more precise and purposeful the research topic is, the less time it will take to develop a coherent research design. Conversely, research design (Sect. 4.5) will be more time-consuming if the researcher spends less time reviewing the literature. We can briefly list the following advantages of literature review: 1. A better understanding of the research topic and increasing knowledge on the field of research: by examining the texts, the researcher expands his/her knowl- edge and becomes more informed about the subject. Consequently, the researcher can look at the problem with a broader perspective and begin to master the prob- lem and refine its presentation. 2. Awareness of the research topic background: the researcher will be familiar with the scope and quality of the work that has been done so far on that topic. 3. Recognition of further research suggested by previous researchers or gaps in the literature might form the researcher’s long-term goal and future research direction. 4. Learning how others have defined and measured key concepts allows the researcher to identify the desired variables in the study better, explain the cause- and-effect relationships between the variables in the form of theoretical models, and more easily formulate research hypotheses. 5. Assessing the appropriateness of the research topic and identifying the limita- tions and problems that other researchers have encountered while working on a similar issue will help the researcher complete his/her research with a clearer perspective, at a lower cost and greater efficiency. 6. Ensuring the innovation of the research question and its relevance to others: the

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