Cases in Bioethics: Health Research Ethics in Southeast Asia
Keywords

study design, washout period, orthodontics, clinical trial, people who wear braces/retainers

Orthodontic retainers are appliances that maintain the position of aligned teeth. Stabilization or retention, using retainers, is important for both the look and function of teeth after orthodontic treatment.1,2 Without retainers, teeth are likely to return to their original positions, known as relapse. The retention process can take several months,3 and normal growth and chewing may gradually move teeth throughout life.4 Current recommendations for removable retainers encourage patients to wear their retainers for at least 10 hours daily5 for as long as they want to maintain aligned teeth.

Removable vacuum-formed retainers (VFRs) are made of clear plastic that conforms to the shape of teeth and holds them tightly in position. They are typically molded over stone dental study models. A researcher is interested in using 3D printed models instead and wanted to understand patient preferences and effectiveness of both approaches. The researcher designed a crossover randomized controlled trial in which study participants joined a different study group within the trial5 after the end of an orthodontic treatment phase. Using this approach, each patient serves as his or her own control,6 avoiding confounding variables (e.g., age, sex, and race) and enabling smaller sample sizes.7 Patients were assigned to two groups such that half the participants received a stone-model fabricated VFR, and the other half received a 3D reconstructed VFR.

After removal of the fixed appliances (i.e., braces), research participants were divided into study groups, given a new VFR, and instructed to wear it for at least 10 hours daily for 3 months. At the first follow-up visit, the researcher recorded patient perceptions of the VFR and measured changes to teeth alignment. Carryover (or residual) effect in a crossover study occurs when a treatment effect from the first time period persists into the second period and affects the outcome of the second treatment.8 To minimize such carryover effects, the researcher introduced a 1-month washout period to minimize patient memory about using the first device. After the washout period, participants were given the second VFR and instructed to wear it at least 10 hours daily for 3 months. At the second follow-up visit, the researcher again recorded patient perceptions of the VFR and measured changes to teeth alignment.

Questions

  1. Is a crossover trial appropriate for this research question? Why or why not? What are some alternative study designs?

  2. Are there ethical concerns about using a washout period, as was done in this case? If so, what concerns do you have?

  3. If you were a member of the research ethics committee reviewing this study, what would you like to know about the social and scientific value of the study?

References

Brooks, Joseph L. “Counterbalancing for Serial Order Carryover Effects in Experimental Condition Orders.” Psychological Methods 17, no. 4 (2012): 600–614. https://doi.org/10.1037/a0029310.
Cleophas, T. J. “Carryover Bias in Clinical Investigations.” Journal of Clinical Pharmacology 33, no. 9 (September 1, 1993): 799–804. https://doi.org/10.1002/j.1552-4604.1993.tb01954.x.
Littlewood, Simon J., Declan T. Millett, Bridget Doubleday, David R. Bearn, and Helen V. Worthington. “Orthodontic Retention: A Systematic Review.” Journal of Orthodontics 33, no. 3 (September 2006): 205–12. https://doi.org/10.1179/146531205225021624.
Melrose, Colin, and Declan T. Millett. “Toward a Perspective on Orthodontic Retention?” American Journal of Orthodontics and Dentofacial Orthopedics 113, no. 5 (May 1, 1998): 507–14. https://doi.org/10.1016/S0889-5406(98)70261-6.
Mohd Tahir, Norhidayah, Wan Nurazreena Wan Hassan, and Roslan Saub. “Comparing Retainers Constructed on Conventional Stone Models and on 3D Printed Models: a Randomized Crossover Clinical Study.” European Journal of Orthodontics 41, no. 4 (October 12, 2018): 370–80. https://doi.org/10.1093/ejo/cjy063.
Pratt, Michael C., G. Thomas Kluemper, and Adam F. Lindstrom. “Patient Compliance with Orthodontic Retainers in the Postretention Phase.” American Journal of Orthodontics and Dentofacial Orthopedics 140, no. 2 (August 1, 2011): 196–201. https://doi.org/10.1016/j.ajodo.2010.02.035.
Thickett, E., and S. Power. “A Randomized Clinical Trial of Thermoplastic Retainer Wear.” The European Journal of Orthodontics 32, no. 1 (October 14, 2009): 1–5. https://doi.org/10.1093/ejo/cjp061.
Thiese, Matthew S. “Observational and Interventional Study Design Types; an Overview.” Biochemia Medica 24, no. 2 (2014): 199–210. https://doi.org/10.11613/bm.2014.022.
Wellek, Stefan, and Maria Blettner. “On the Proper Use of the Crossover Design in Clinical Trials.” Deutsches Aerzteblatt Online 109, no. 15 (April 13, 2012). https://doi.org/10.3238/arztebl.2012.0276.
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