What do you know about the materials used for invisible braces?

Materials for Invisible Braces

How much do you know?

Many people, upon first glance at invisible braces, might easily mistake them for being made of plastic and wonder how such "plastic" braces could move their teeth. What they don't realize is that each set of invisible braces is actually made from highly sophisticated, patented materials, consisting of high molecular polymers.

To understand the materials used for invisible braces, we should first delve into what they are and their history of development!

Development of Invisible Braces Materials

PC (Polycarbonate) material is known for its sturdiness and "strength." However, its flaw lies in its tendency to break during the process of putting on or taking off the braces. Subsequently, PETG (a type of amorphous copolyester) was introduced, which presented some improvements over PC but issues with breakage and loosening of the braces still needed to be addressed.

TPU (Thermoplastic Polyurethane Elastomer Rubber) largely solved the breakage issue with its reversible intermolecular hydrogen bonding or mild crosslinking between macromolecular chains, which can adapt to changes in temperature. This material has good elastic recovery and several other favorable properties. However, the issue with TPU is that the material's force can decay over time, losing its effectiveness.

Since invisible braces and retainers need to resist short and intense deformation without breaking during the process of putting on or taking off, and must deliver a light yet consistent corrective force over a long period, it is essential to have high yield stress, appropriate elastic modulus, and as low a stress relaxation rate as possible. Thus, brands specializing in invisible orthodontics began to independently develop new generations of films based on their first and second-generation products.

Modified TPU films not only retain the strength of the original TPU material but also make the material softer.

Besides, there is also the IPN film.

IPN Film

IPN (Interpenetrating Polymer Network) refers to a network structure formed by two or more blended polymers, where the molecular chains penetrate each other, and at least one type of the polymer chain is crosslinked chemically.

This results in six main advantages: enhanced tear resistance, higher resilience, thinner and more durable, better fit, and increased resistance to staining.

Strong Tear Resistance

Only with strong tear resistance can patients avoid issues with invisible braces breaking or loosening due to frequent removal or complex malocclusions during daily wear.

High Resilience

Precise application of force ensures the suitable rigidity and flexibility for tooth movement. The IPN film can maintain a 100% recovery rate within a relatively large range of deformation.

More Durable

The stress relaxation curve shows that, compared to other films, the IPN film possesses more durable and stable mechanical output. As shown in the graph below, while ordinary orthodontic materials experience a significant decay in corrective force within 10 days of wear, the IPN film can maintain a consistent force daily, allowing for continuous tooth movement.

Better Fit

Unique surface adaptability and excellent thermoplasticity significantly improve the wrapping performance of molds, which is more conducive to mechanical expression. After patients wear it, due to the soft and hard match of the braces and the unique cutting technology of Merlic, the braces can fit more closely to the tooth surface, freeing up the gums and making the correction safer and more comfortable.

√ After forming, the IPN film can intelligently match the corresponding rigidity and elasticity, achieving both comfort and effective force application.