What kind of materials are available for aligners?

Kesling was the first to propose using clear overlay rubber-based orthodontic appliances in order to progressively move malaligned teeth back in 1946, without a question, way out of his time. This at-the-time bizarre concept laid the groundwork for clear aligners to establish a place in the orthodontic society. And decades later, thanks to the introduction and development of CAD/CAM technologies in dentistry, clear aligner therapy (CAT) has now become the anchor of orthodontic treatment.

While clear aligners addressed a lot of issues with traditional braces, bringing into existence superior aesthetics, comfort of wear, and removability, it has also thrust into the limelight increasing and growing concern with the materials used. Undoubtedly, the properties of materials that are used to produce clear aligners are among the most essential aspects that contribute to the efficacy of aligner therapy. Due to the continued improvement of clear aligner systems to date, there are more demands for ease of use, and cheaper and more durable products without compromising the treatment outcome itself.

Clear aligners today are made from both high-strength and high-modulus materials, meaning that they are both strong as well as flexible, enough to produce large-scale tooth movements during the treatment. Let’s understand what makes these materials effective so much so that they have been widely acclaimed since the launch of clear aligners in the market with Invisalign® in 1999!

What are polymers and why are they used?

Throughout these years, as many as 30 clear aligner companies have been founded worldwide, all but with similar treatment philosophies. Based on the requirements, clear aligners should be made out of material that is lightweight, easy to mass-produce, cheap, versatile, and of course, transparent. Most of these criteria and more is fulfilled by a material known as a polymer. Due to their superior properties, polymers are often used in different medical applications such as implants, prostheses, and orthodontic appliances.

In terms of orthodontic needs, polymers will be required to be exposed to the intraoral environment, in the long term. While it is plain as day for one of the requirements of polymers to be biocompatible with the intraoral environment, it is also important for it to be resistant to chemical corrosions caused by the fluctuating acidity of the mouth.

Another important aspect is the thermal properties of the polymer. Although the internal temperature of the mouth remains relatively constant (near 37ºC), a polymer may be subject to a wide range of temperatures during intraoral application from sub-zero (while eating ice cream) to high levels (when drinking tea). These temperature variations can cause contraction and/or expansion of the material. Thus, the polymer should also be able to tolerate temperature alterations.

Lastly, the polymer should have good mechanical stability, meaning that it should be able to withstand high occlusal forces without deforming or fracturing. The material should also be able to resist unwanted changes due to the mechanical loads applied to the teeth during intraoral application. Other properties include transparency, good elasticity, and high resilience.

What materials are used to fabricate aligners?

Clear aligners are made up of thermoplastic materials like polymers. The most widely used polymers by aligner manufacturers currently include polyethylene terephthalate glycol-modified (PET-G), polypropylene, polycarbonate (PC), thermoplastic polyurethanes (TPU), ethylene vinyl acetate, etc.

Most aligners are made up of a material known as polymethyl methacrylate (PMMA). This material is also used to fabricate Plexiglas, acrylics, and lenses. It is transparent, durable, and strong. Some aligners are also made of polyethersulfone (PES), which is transparent but not as strong as PMMA ones. The main drawback of PMMA is that it is hard and brittle and may be expensive to replace.

PET-G is also a brilliant material used for clear aligners owing to its significant chemical resistance, durability, and formability for manufacturing. Due to the low forming temperatures of PET-G, it is easily vacuumed and pressure-formed or heat-bent, making it a popular choice for commercial use like in 3D printing.

The latest generation of aligners now uses a material known as trimethyl orthosilicate. This orthodontic plastic can be moulded into 3D shapes, making it a brilliant choice for clear aligners. It is also affordable, lightweight, highly durable, and less prone to breakage or fracture. The material also comes with lubricants embedded within it to reduce friction when you move your jaws while wearing them. This makes the wearing experience more comfortable than ever before.

Takeaway

The materials that are used to produce clear aligners can greatly affect their clinical performances. This is why these manufacturers curate products with materials that can withstand great force while also producing superior results.