For almost thirty years now, the aligners’ market has been constantly evolving, which has also contributed to the development of new materials, among others. In this document, we will try to highlight the different foils used in this context, including advantages and disadvantages. .
There are several thicknesses of foils used for aligners production: ranging from 0.4 mm to 1.0 mm. Usually, on the front teeth, where more stretching occurs, the thickness falls to approx. 0.63 mm. On the other hand, in the molars’ region, less stretching is detected at about 0.68 mm. In general, it is not recommended to employ thicker sheets, due to the patient's discomfort. Also, there is a significant gap between the arches by approx. 2 mm if 1.0 mm sheets are utilized on both arches.
When patients have their third molars in place, it is very likely that they will not even be able to close the teeth. If a thinner foil is used, for example, a 0.5 mm, then the aligners will be too soft and easily deformable. This can cause more discomfort to the patient, and in addition, decreases the chance for the aligners’ movements to properly track. Therefore, a 0.75 mm thickness in this sense is the optimal and therefore offered by most vendors.
There is a wide selection of aligner foils available in many shapes and forms: round, square, 120 mm, 125 mm etc. The standards themselves are mainly set by the vacuum forming equipment vendors, for example, Scheu Dental with their MiniStar unit, using a standard round sheet of 125 mm. Another German manufacturer, Dreve uses 120 mm round sheets. There are universal vacuum formers, which are suitable for any plate of any form factor.
Aligners foils also differ in the type of materials they are made of. Two formulas are prevalent in this arena, namely PETG and PTU. The former is a hypoallergenic polymer, its chemical composition is very close to the production of the polymer used for making water bottles. Typical examples of this family include "Biolon" from Dreve, "Duran" from Scheu Dental, "ESSIX" from Dentsply Sirona, and "Track A" from Forestadent. In addition, there are Korean manufacturers, of which there is a huge number on the market so, the choice is quite large. There is no key difference between them, although all the plates differ slightly in flexibility.
After extensive testing and experimenting, "Biolon" appears to be the winner amongst all PETG options. This foil appears to be the most flexible, which enhances patient comfort, and less breakable than other foils. Plus, the price-quality ratio is probably one of the best with one sheet costing slightly over USD 1.2.
The second type of material is classified as PTU, with the best known example being "Zendura FLX" from Bay Materials (also known as “Clear Quartz” when used with “Clear Correct” aligners). They usually come in round 120-125 mm sheets, and squares. The formula of the PTU material is more complex than PETG - it is made similar to a triplex glass - a solid material on top and the bottom, and a layer of very flexible soft material in the middle. Thanks to this composition, completely different properties are obtained in comparison with PETG: the material is far more flexible and comfortable to wear. Furthermore, due to its triplex structure, it is almost unbreakable: the effect is the same as that of a car glass – the internal very flexible layer prevents most breaking damage. Because of its advanced properties, PTU foils are more difficult to produce, so there are only a few manufacturers available. In addition to "Zendura", there is also the "CA Pro" material from Scheu Dental and Ghost aligners from Italy. It is of no surprise therefore that PTU is far more expensive than PETG, with the average retail price being about $5 per sheet (the Ghost foil is even more costly). The “Smart Track” material used by Align Technology for the Invisalign system is also a PTU-derivative.
In the context of aligners’ treatment, perhaps the most important advantage of PTU foils is that they retain their elasticity and original shape over a longer period of time. Different manufacturers have different parameters, but on average, whereas a PETG splint loses its potential after three days, a PTU device will have an impact during seven days, so the predictability of movements of PTU aligner is significantly higher.
Regardless of the PTU brand ultimately selected, eXceed recommends using one aligner for 14 days. If you work with our Company and use PTU material in your practice, please let us know and we will apply accelerated movements in your 3D plans. This means that the range of movements in a single step can be increased by about 25%. However, it should be understood that more radical corrections still require a suitable retention period, to fix the teeth in the new position. When the wearing of aligners is reduced, retention and therefore treatment results could be compromised. Wearing aligners can be shortened by the doctor only based on specific analysis of the patient's bone tissue and treatment progress. For more information on this subject, we also advise you to watch our free webinar: LINK ON A WEBINAR
PTU foils are produced in different thicknesses, with the most prevalent one used for aligners production being 0.75 mm. On the other hand, the initial attachment template is made of a thinner material. Bay Materials, for example, offers 0.35 mm Zendura foils while other manufacturers produce PTU sheets ranging from 0.4 mm to 0.5 mm.
There is also a material for making a "soft" attachment template, for example, Scheu Dental has a 0.5 mm "Copyplast" foil. The degree of rigidity mostly depends on personal preference. Some clinicians are used to working with a standard, yet thinner, PTEG material, for example, 0.4 mm. For some, it is more convenient to work with flexible sheets such as "Copyplast" or similar foils.
In addition, there are also sheets equipped with a protective layer so when the printed model is vacuum formed, the layer is removed only at this point. That way, the aligner remains as transparent and clear as possible. When using sheets without a protective layer, no matter if the aligners are washed and the printed model is cleaned - some dust and polymer particles remain, making the aligners less transparent.
Another point worth mentioning is the fact that PTU sheets require more controlled storage and use conditions. Normally, PTEG plates can be stored anywhere and are not prone to frost, heat, or moisture. On the other hand, PTU sheets are vacuum-packed at the factory in a special dry air chamber. After opening the vacuum bag, PTU foils must be used within a few hours. to combat their hydrophilic tendencies. If this is not followed upon, the sheets will become saturated with moisture and partially lose their properties.
One should also mention the method by which different thicknesses of aligners are used on a single step. The main difference between this method lies precisely in the modeling and production processes, and not in the material itself. Most manufacturers adhere to the classic approach, where one step is one aligner. The second method, when three aligners made of different thicknesses represent a single step (0.5 mm, 0.65 mm, and 0.75 mm), usually implements a larger step per one movement, that is, three times more movements per one aligner. Accordingly, one model is printed, but three aligners are made – soft, medium, and hard. This is somewhat similar to the logic of fixed appliances therapy using braces when there are three types of wires: activation, movement, and retention period.
This approach had made sense in earlier periods, when three-dimensional printers were not as accurate, or precision printers were too expensive, so achieving a step accuracy of 250 microns (0.25 millimeters) was not easy. Previously, this had some economic feasibility, when composites for three-dimensional printers were quite expensive, this technique allows one to save on printing resin – instead of three models, only one was printed. Today, almost any desktop printer provides high-quality printed models for the production of aligners, and polymers for three-dimensional printers have fallen in price drastically. That is, it does not allow to save money, but it adds manual work and complexity in purchasing a large variety of materials at once. In our experience, the “single aligner per step” approach works more predictably and reliably than the “three aligners per step” doctrine. One exception would be in the case of young children treated with aligners. We recommend using the second method due to the fact that children have much softer bones and easily moveable teeth - so more movements per step can be accommodated.