We would like to address Dr Turpin’s editorial in the August 2009 issue regarding the usefulness of in-vivo vs in-vitro studies of self-ligating brackets (In-vivo studies offer best measure of self-ligation.. Am J Orthod Dentofacial Orthop 2009;136:141-2).
Our research objective was to develop a measurement system to analyze the complex force systems associated with continuous-wire orthodontic mechanics. Based on requests from the peer reviewers of the AJO-DO , our article provided a pilot study measuring the 3-dimensional forces around the dental arch associated with moving a maxillary canine vertically with different ligation methods. In this instance, in-vitro and in-vivo correlations are impossible to establish, since we could not find an in-vivo study of the orthodontic force systems produced by various ligation methods. Therefore, stating that our research outcome was out of sync with reality (assuming that reality is synonymous with in-vivo research) was a mistake, since we believe that the editor was comparing research studies that focused on different questions. Our research did not attempt to answer any questions tackled by the in-vivo studies cited in the editorial; therefore, it is impossible to be out of sync with those studies.
Our research was concerned with the qualitative assessment of the force systems produced by different ligation methods, and the in-vivo studies mentioned by the editor focused on plaque accumulation and treatment efficiency of various ligation methods. Clearly, our research and our outcome had nothing in common with those in-vivo studies; therefore, we believe that comparing them and discounting our outcome was a scientific mistake.
The basic principle driving modern medical research is the translation of fundamental research conducted in the laboratory to effective clinical treatment. Deep understanding of the biologic principles and, in our case, quantification of complex orthodontic force systems provides the basis for hypotheses to be tested in the clinical environment. The observations from the clinical environment then generate questions regarding “why and how,” which go back to the laboratory for further fundamental research. New hypotheses are developed to drive new clinical research. A typical example of this process is the development of new drugs. Basic research in cell and molecular biology allows researchers to design compounds (drugs) that target a specific cell function and, ultimately, a disease process. The testing flows from the biochemistry laboratory to animal testing and finally to human research. The observations from clinical trials are then used to drive further fundamental research with modifications to the compound followed by further clinical testing.
In the orthodontic biomechanics, the ability to quantify the complex force systems acting at the bracket is necessary to establish an understanding of the magnitudes of forces and moments being delivered to the tooth. The parallel laboratory research involves the biologic response to orthodontic strains imposed on the periodontal ligament based on force per unit of surface area. Animal research without quantitative force system research has no practical value. The combined understanding of the magnitude of force with a particular treatment and the biologic response to specific force magnitudes will allow the orthodontic specialty to move from the trial-and-error approach of testing treatment modalities and biased “expert” opinions to a true scientific-driven specialty.
The inherent problem is not the value and relevance of in-vitro research; it is the inappropriate interpretation of these research findings into clinical practice. Clinicians who are functioning as high-level “clinical scientists” will use the outcome of fundamental research (biologic and engineering) to generate hypotheses that are then tested with well-designed clinical studies.
Although we agree with the editor on the importance of in-vivo studies, it is important to recognize that (just like any other research method) clinical studies in orthodontics have many limitations. The main attribute of clinical trials is the control of bias through randomization and blinding. Whereas randomization is possible in orthodontic research, blinding is impossible. It is simply impossible to blind the clinicians making the treatment decisions necessary to complete the orthodontic treatment for a number of subjects with 2 types of orthodontic brackets. Randomized clinical trials do not provide all the answers, but they typically answer a specific question quantitatively, and, when a study is looking at a quality-of-care issue in which the criteria for success have not been clearly established, a randomized clinical trial is inappropriate.
The use of “between method triangulation” has received much attention in the medical literature; the idea is that, rather than being opposites, the mixing of paradigms might complement each other. By combining multiple observers, theories, methods, and empirical materials, researchers can hope to overcome the weaknesses or intrinsic biases and the problems that come from single-method, single-observer, and single-theory studies. Therefore, we believe that clinical evidence does not eliminate the need or invalidate in-vitro evidence. Most of the evidence base in orthodontics is the result of in-vitro research; the sum of in-vivo and in-vitro research studies is the evidence on which we should base our conclusions.
When we embarked on the task of developing a 3-dimensional orthodontic force measurement device, we kept in mind that the orthodontic force system by nature is extremely complicated, and measuring it is no easy task. Therefore, we followed a systematic plan to build a device with rigid tooth connectors, and, without tooth-to-tooth contacts, we built the device in a way that allows us to add more variables to our system as we go forward, such as periodontal ligament compliance and tooth-to-tooth contacts. We are already working on building those variables into our device to develop the system 1 step at a time; this helps to more closely simulate the oral environment, although we will never be able to totally simulate it.
Our data, for the first time in the history of our specialty, show clinicians the actual forces applied on the teeth with the straight-wire appliance. Using our data, we can plan clinical experiments to test specific hypotheses. We also can “engineer” orthodontic force systems to deliver the desired force magnitudes. As we continue to refine our measurement of orthodontic forces, we are using the finite element method to analyze the pressure per unit of area of projected root surfaces. This will move us closer to predicting the biologic effect of the complex force systems used in contemporary orthodontic mechanics.
Without laboratory research, the specialty would be restricted to clinical observational research without ever developing a fundamental understanding of “why.”