smile strategy: The science behind attachment-free aligners

Nathalie Schüller, Dental Tribune International

Tue. 21. April 2026

save

At the seventh European Aligner Congress, discussions around aligner materials and digital workflows highlighted a question of growing relevance to orthodontic practice: how close are 3D-printed aligners to routine clinical use, and what still stands in the way? Known for bridging materials science and clinical application, Dr Rooz Khosravi addressed this area of technological advancement in a congress presentation, and in this interview, he covers some of the topics he raised, including the practical and clinical questions that still need to be resolved and the direction in which the technology may be heading.

Dr Khosravi, what are the differences between thermoformed and 3D-printed aligners?
These two materials are fundamentally different in nature. Thermoformed aligners are made by heating plastic sheets above their glass transition temperature and forming them into shape as they cool. 3D-printed aligners, by contrast, are produced by curing resin through a layer-by-layer photopolymerisation process. Both materials flex in response to force. When you push on a thermoformed aligner or a 3D-printed aligner and hold it in that deformed position, the material exerts a restoring force as it returns towards its original shape. This behaviour, of course, only holds while the material is below its glass transition temperature. In brief, these two classes of materials have distinctly different properties, and that translates into meaningful differences in clinical behaviour, including force retention, staining and thickness.

What limitations do clinicians currently face regarding 3D-printed aligners?
The core issues with 3D-printed aligners include extensive staining, unfavourable patient perception compared with thermoformed aligners and a lack of the sustained force needed to move teeth as efficiently as thermoformed aligners can. The fabrication process itself is another significant challenge, largely because the high viscosity of currently available 3D-printing resins can complicate processing. That said, we’ve come a long way in solving some of these issues, and I’m confident things will continue to improve.

What are the potential advantages of attachment-free aligner therapy?
The hypothesis behind using 3D-printed aligners without attachments is logical. It rests on the notion that 3D-printed aligners fit the teeth more precisely than thermoformed aligners do. But it is still a hypothesis, albeit grounded on the theory of better fit, and to the best of my knowledge, it has not yet been proved scientifically.

What challenges do orthodontists face in transitioning to in-office 3D-printing workflows?
In my view, an in-office 3D-printing system is a must-have in a modern orthodontic practice. This system can be built out to produce a wide range of products—retainers, aligners, flippers, temporary crowns and more—or used simply to print dental models. Either way, the transition comes with multiple challenges: the initial financial investment, hiring a team member capable of operating the system, and the relatively high amount of learning and effort required for each workflow you set up.

In what ways could in-office 3D printing reshape orthodontic practice overall?
Customisation and agility in delivering care are the core value propositions of in-office 3D printing. Having the ability to deliver multiple retainers to patients at relatively low cost is a great example of how 3D printing has already significantly improved the retention phase of care. Another example is digital indirect bonding. Indirect bonding is a sensitive and labour-intensive process, but by 3D-printing the trays, the clinician can eliminate some of the tedious steps and, arguably, bond brackets faster and more precisely—which in turn improves the experience of new patients.

How is 3D printing of aligners evolving, and what still needs to happen for the use of 3D-printed aligners to become routine in the clinic?
The progress over the last six years has been remarkable. Resins, printers and post-processing workflows have all matured substantially, and what was not yet a clinically acceptable option in 2020 now has real potential and is being used in practices today. But before 3D printing of aligners can become routine, we still need to answer a few fundamental questions. How do these materials deliver force over the full wear cycle? The low level of force generated by 3D-printed aligners is an undisputable fact. How predictable is tooth movement compared with thermoformed systems? How do these resins behave biologically and mechanically in the oral environment over weeks and months? Do 3D-printed aligners leach chemicals? These are the kinds of questions the field has to work through before 3D-printed aligners can be treated as a drop-in replacement.

But I would go one step further. I don’t think the question is how we can make 3D-printed aligners that perform like thermoformed aligners. The more interesting question is: what new appliance can we design that only 3D printing makes possible? Aligners were fundamentally shaped by the constraints of thermoforming: a uniform sheet of plastic wrapped over the teeth. 3D printing lifts almost all those constraints. We can vary thickness locally, integrate engagement features directly into the aligner, design lattice structures that deliver targeted flexibility or build segmental appliances that combine rigid and flexible zones within a single device.

This opens the door to a category of appliance that sits somewhere between aligners and fixed appliances—one that delivers the controlled, differentiated forces of a fixed appliance system without the visibility and hygiene trade-offs and with more biomechanical precision than a conventional aligner can offer. Whether we end up calling it a smart aligner, a hybrid appliance or something else entirely, that’s where I think the real upside of 3D printing lies. Replicating the aligner form factor with a new manufacturing method is an incremental win. Redesigning the appliance itself around what the technology can uniquely do is the step change.

Editorial note:

Dr Rooz Khosravi is a clinical associate professor in the Department of Orthodontics at the University of Washington School of Dentistry in Seattle in the US and has advanced training in both oral biology and orthodontics. His work focuses on the integration of digital technologies into orthodontics, particularly aligner therapy and 3D printing, and increasingly on in-office aligner production and attachment-free treatment. Through his research and teaching, Dr Khosravi continues to contribute to the evolution of modern orthodontics and to the development of more efficient, patient-centred approaches to care. He is the US ambassador for the European Aligner Society .

Topics:

Orthodontics

Tags:

Aligners Attachments Digital workflows Dr Rooz Khosravi EAS7 Orthodontics Shape Memory Aligner Thermoformed aligners

To post a reply please login or register

Raising the bar for endodontic success: Where we were, where we are and where we are going

Vince Lombardi so eloquently stated, “Practice does not make perfect. Only perfect practice makes perfect.” In other words, we can perform a ...

Digital workflow for dental offices and laboratories—where are we now?

During IDS 2023, Dental Tribune International talked to Niels Plate, group vice president of digital devices and equipment at Dentsply Sirona, about the ...

Print angulation affects fit and efficiency of 3D‑printed aligners—study

PHOENIX, US: As more practices bring 3D printing in-house, understanding how technical settings affect both accuracy and turnaround time is becoming a ...

3D-printed aligners: Study finds need for material-specific cleaning protocols

ZAGREB, Croatia: As 3D-printed aligners gain traction, many patients and clinicians continue to apply cleaning routines that were originally developed for ...

Leading the charge with 3D-printed prostheses

I have been a registered denturist for over 20 years. At our laboratory and clinic, we specialise in removable prosthetic solutions: partial dentures, ...

3D-printed hybrid composite restoration in a fully digital workflow

In recent years, 3D-printed polymer-infiltrated ceramic resins, also defined as hybrid composites, have emerged as a promising option for definitive dental ...

Midas: The 3D printer that transforms the analogue dentist into a digital workflow protagonist

This is not just another article about 3D printing. It is a practical, clinically grounded reflection on how the Midas 3D printer (SprintRay) has overcome ...

Digital workflows in dentistry and the future of oral care

In March last year, Dr Ahmad al-Hassiny, director of the Institute of Digital Dentistry, noted that over 90% of US dental laboratories and nearly 50% of ...

Education

Live webinar
Wed. 22 April 2026
11:00 am EST (New York)