New fabrication method can improve clear aligner treatment

Anisha Hall Hoppe, Dental Tribune International

Fri. 30 August 2024

save

According to a recent study, aligner force depends on the type of material and the direction of movement, and multilayer materials are superior to single-layer ones owing to their lower initial force for enhanced patient comfort and their ability to maintain consistent force application even after ageing. Dental Tribune International spoke with lead author Dr Tarek Elshazly, who conducted wide-scale research on different aligner materials at the University Hospital Bonn in Germany, about the implications of the research findings on orthodontic treatment with aligners.

Dr Tarek Elshazly. (Image: Tarek Elshazly)

Dr Elshazly, could you tell our readers a bit about your background and how you ended up in the very specific research area of materials development for dentistry?
I am a dentist with a strong interest in materials engineering. I earned my bachelor’s degree in dentistry from Ain Shams University in Cairo in Egypt, where I also completed a master’s degree in dental biomaterials. After this, I moved to Germany to pursue a doctoral degree (Dr. med. dent.) and a PhD in oral technology at the University of Bonn. To identify a suitable and novel research topic for my PhD, I reviewed the literature extensively and brainstormed ideas. I discovered that the use of aligners was gaining significant global traction as a promising alternative to traditional orthodontic treatments. However, there were still notable drawbacks and limitations associated with the materials used and the biomechanical behaviour of these appliances. This led to my focusing my PhD research on this topic under the supervision of Prof. Christoph Bourauel, a renowned scientist in dental biomechanics. As part of my research, we collaborated with various companies to test new and innovative materials, employing different techniques and specialised methodologies to study the forces generated by these aligners.

In your research you found that there was a significant reduction in force transmission after 48 hours of thermal and mechanical ageing of aligner materials. Do these findings hold significance for the schedule of wearing aligners?
We are constrained not only by the aligner material but also by the periodontal ligament. Orthodontic tooth movement occurs through a biomechanical process within the periodontal ligament and bone when an appropriate force is applied to the tooth. Therefore, the ideal scenario is to use a material that can consistently apply the optimal force over the desired time frame. Based on our research, we suggest changing the aligner every week or seeking a material capable of maintaining the necessary force over a longer period. Otherwise, the force is most effective only during the first few days of use—typically two or three—after which the aligner merely functions as a retainer.

Some researchers argue that this is acceptable because tooth movement primarily occurs within the first few days and that the aligners are only needed to maintain the new position to allow for bone resorption over the remainder of the period, usually ten days to two weeks. In my opinion, it would be more effective to change the aligner weekly. However, this approach would lead to increased material consumption, raising costs and negatively affecting the environment. The best solution would be to develop a superior material that can sustain the necessary force for a longer duration. Multilayer materials have been introduced relatively recently to address some of the limitations of single-layer materials. While they are not yet ideal, they do offer better force sustainability.

“What concerns me most right now is the high consumption of plastic in the aligner industry.”

Could you explain a bit more about the specific benefits of using multilayer materials over single layer materials, and should clinicians consider changing their choice of materials?
The type of material used does not significantly alter the overall process. Typically, aligners are quite rigid during the first few days as they move the teeth. However, multilayer materials are more flexible, offering greater comfort, whereas, in our research, we showed that single-layer materials provide better control over tooth movement. Based on these findings, we recommend using a combination of two materials for each single step. Treatment should start with a multilayer material for one week, followed by a single-layer material for another week or just three days. This approach enhances movement control and maintains the necessary force. I believe that Angel Aligners is already implementing this technique.

Are there any new topics of research in materials development on the horizon that you are particularly excited about?
What concerns me most right now is the high consumption of plastic in the aligner industry, which is why we are actively seeking solutions. One potential solution is to use 3D-printed shape memory materials to reduce material waste. This approach would also allow for better control over the design, leading to improved tooth movement, increased treatment accuracy and fewer refinements and thus minimising the need for retreatment to achieve optimal alignment. By ensuring precise control of tooth movement from the outset, we can reduce the number of aligners required and, consequently, the amount of material wasted.

Another area of great interest to me is the development of recyclable aligner materials. I recently encountered an American company at a dental show that has innovatively introduced an eco-friendly, recyclable thermoformed aligner material. I haven’t found any research on this material in the literature yet, so we are planning to initiate studies on it soon.

Editorial note:

The study, titled “Effect of thermomechanical ageing on force transmission by orthodontic aligners made of different thermoformed materials: An experimental study”, was published on 18 June 2024 in Orthodontics and Craniofacial Research, ahead of inclusion in an issue.