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Are clear aligners environment friendly?

American Journal of Orthodontics and Dentofacial Orthopedics, 2022-05-01, Volume 161, Issue 5, Pages 619-620, Copyright © 2021 American Association of Orthodontists

Clear aligner therapy has revolutionized orthodontic care delivery over the last 2 decades. With the increase in demand for clear aligner therapy, there is a concern about the plastic burden on the environment. Hence, we initiated research to investigate its environmental impact. This short communication aims to discuss the rationale of our ongoing study.


  • Environmental plastic is a burden because of the increased consumption of single-use plastics.

  • There is an increase in aligner trays with a change from bi-weekly to per-week protocol.

  • There is a need for an aligner uptake policy by suppliers to reduce the environmental impact.

The conventional fixed appliance therapy (FAT) has not undergone radical changes in its concepts and manner of force application since Edward H. Angle until the emergence of clear aligner therapy (CAT). The history of CAT dates back to 1945 when Harold D. Kesling first introduced a series of thermoplastic tooth positioners made on working models to sequentially move teeth. The “invisible retainer,” a thermoformed plastic appliance, was introduced by Ponitz in 1971. Later, in the early 1990s, Sheridan et al developed a procedure that involved slenderization followed by sequential tooth movement using the clear Essix appliance.

The CAT witnessed a giant leap forward when Zia Chishti and Kelsey Wirth, 2 Master of Business Administration graduates from Stanford University, came up with Invisalign (Align Technology, Inc, Santa Clara, Calif) in 1997. This was approved by the Food and Drug Administration and came into clinical use in the subsequent year. The use of 3-dimensional computer technology and artificial intelligence to plan and visualize tooth movements virtually gave it the extra edge.

Align Technology uses computer-aided design and manufacturing stereolithographic models to manufacture Invisalign, overcoming the manual shortcomings of its predecessors. Furthermore, the paradigm shift in artificial intelligence from symbolic to machine learning has contributed to the greater predictability of treatment using aligners. Digital scanning, SmartForce features, and SmartTrack material have greatly enhanced its overall treatment accuracy over the years from 41% in 2009 to 50% in 2020.

In-house aligners are a recent addition to the CAT family, wherein the aligners are designed and printed in-office without the involvement of a third-party laboratory. Though they operate on a similar mechanism as the former, the efficiency of in-house aligners needs to be time-tested. The do-it-yourself aligners, though unethical, is a sad reality of today.

Clear aligner materials: the “plastic” orthodontics

Aligners are made of different compositions of plastics such as polyesters, polyurethanes, polypropylenes, and so on, although the exact composition remains a trade secret. The one currently used by Invisalign is a highly elastic thermoplastic polyurethane termed SmartTrack. Most other aligner companies use glycol-modified polyethylene terephthalate. The aligner trays come in different thicknesses from 0.5 to 1.5 mm. The bi-weekly tray change schedule was the most accepted protocol initially. Studies have found that the 7-day protocol reduced the treatment duration to almost half compared with the 14-day regimen. Thus, the total number of aligner trays for each case is highly variable depending on the malocclusion type and the frequency of change. In addition, the number can increase further depending on the midcourse refinements (revision aligners).

It is well known that plastic, a nonbiodegradable material, takes a long time to decompose. In particular, polyethylene terephthalate belongs to the category of resistant plastics because of its resistance to degradation. The complete degradation of plastic can take up to 1000 years. It is estimated that a plastic bottle roughly takes 450 years to degrade. In addition, the incineration of the same can release toxic fumes such as polychlorinated biphenyls, dioxins, and so on, into the atmosphere, posing a threat to all forms of life. Nonetheless, its exceptional mechanical properties have made its use widespread in different sectors, including the fabrication of clear aligners.

The 4R principle

Reports from the United Nations and the World Resources Institute show that at least 127 countries across the globe have implemented some form of regulations on the use of single-use plastics. The Government of India has proposed the Plastic Waste Management Amendment Rules 2021, thereby prohibiting the use of identified single-use plastics, which is likely to come into effect from July 1, 2022. Given the aforementioned adverse effects and restrictions, it is high time we embrace the 4R principle in plastic waste management (ie, reduce, reuse, recycle, and recover). However, the possibility of implementing this principle in orthodontic CAT is yet to be probed. Out of the 4R’s, only reduce will be a possible option regarding aligners.

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