The course

The one-day course was delivered by Björn and a star studied cast of orthodontists. Björn delivered the introduction and a live walk through the digital planning and processing stages of Graphy from his office, hosting around 20 people. The digital set up planning took place using OnyxCeph software on laptops provided by Björn (I hoped the laptops would be an upgrade on the token ‘pen’ given at courses, but alas they had to be returned, the consolation was I took several pens). Ravi Nanda presented recent published research on the topic, as well as the biomechanical issues with conventional aligners, and the possible advantages of Direct To Print aligners. Kenji Ojima and Ki Beom Kim gave online presentations of their uses of the material and learning they have from trailing it with patients.

What are Direct To Print aligners?

Direct To Print aligners have, until now, been spoken of as the ‘next big thing’ in aligners. Well, they have now arrived, in the form of Tera Harz^TM TC-85DAP from the company Graphy – a South Korean based company. The CEO Sim un seob, a 3D design engineer, was present and it made for several interesting conversations at the course.

Direct To Print aligners come with the following claimed advantages.

• Customised aligner design: This is the most exciting aspect of Direct To Print aligners. Both thickness and trim line can be customised to enable greater biomechanical possibilities. This is discussed later in the design section.
• Material Properties: Shape memory and elastic properties: The material claims that the original shape can be recovered through simply placing the aligner in hot water. One of the issues with conventional aligners is the loss of force with time ‘stress-relaxation’, which Direct To Print aligners can avoid through elastic recovery with hot water. The force delivery of Direct To Print aligners is less, which possibly enables greater activation e.g. 0.4-0.5mm, compared to conventional aligners which are limited to 0.2mm-0.3mm due to material stiffness. A difference like activation with Nickel Titanium Vs Stainless Steel archwires.
• Accuracy: Direct To Print aligners have greater overall ‘trueness’ than conventional aligners 0.14mm Vs 0.19- 0.21mm Ki Beom Kim 2022
• Cost saving: Without the need of physical 3D models, less cost and processing of aligners.
• Biocompatible: No Cytotoxicity and non estrogenicity  Pratsinis 2022

Material

Graphy is resin material which can be printed as an aligner. It is transparent and has elastic properties (like conventional aligner materials), with the key difference of being resin based rather than plastic.

• Direct to Print (Graphy): Photopolymer resin
• Conventional aligners: Polyethylene / polyurethane (plastic)

Design

Aligner thickness: With aligner 3D design now possible as well as 3D model design (as opposed to only 3D model design for conventional aligners), the possibilities of altering the thickness of the aligner become possible. To demonstrate this Ki Beom Kim showed a case where posterior aligner thickness was increased to aid posterior intrusion in an anterior openbite case. This feature is for me the ‘game changer’. Thickening / thinning aligner aspects changes the force delivered and opens the ability to manipulate different aspects of the aligner, for anchorage, greater activation as well as to create a counter-moment for root movement – one of the current limitations of conventional aligner treatment Dai 2021

Trimline: What is the best place to finish the margin of the aligner? Conventional aligner companies either place the trimline at the gingival margin, 1mm above or below the margin. It is unclear what the ‘best’ trimline is. What is understood is the trimline of a conventional aligner is the thinnest and least ridged aspect, and therefore offers little in terms of force delivery.  However, with Direct To Print aligners the aligner margin thickness can be customised This opens up the possibility of greater size and therefore force delivery. Giving the trimline a new role in aligners, whether it is anchorage through extending the trimline or retention, potentially engaging undercuts if desired.

Software: Access to software to design aligners with Direct To Print materials is very much limited and one of the most significant drawbacks using them right now. Currently OnyxCeph, delatface, BlueSky plan and uLab have a patch for their platforms, which are not openly available. Part of the planning process requires manual supports to be added, which is a time-consuming process (10-15 minutes when familiar), however Scheu-Dental have described an automated process for this coming soon.

Post – processing

Aligner production, direct or conventional, require a series of stages following the digital set up. This is due to 3D printed materials not being robust or biocompatible straight out of the printer. Estimate times have been provided.

Conventional aligners: 5 stages of post-production (broadly speaking)

1. Resin 3D model printing: 2-4 hours
2. Isopropyl alcohol wash: Removes excess resin material from the 3D printed model 5-10 minutes
3. UV light curing: Not all resin in the model is successfully polymerised, UV lightcuring completes the process resulting in a more dimensionally stable and biocompatible model. 10-60 minutes
4. Pressure / vacuum forming: The aligner material (usually 0.5-1mm) is pushed or pulled over the 3D printed. 5 minutes
5. Trimming and polishing: The aligner is removed from the model, and the excess plastic is trimmed and the trim line is established 1-2 minutes.

 Overall estimate time: 140-315 minutes

Direct To Print aligners however have less post-production stages, mainly due to no physical model being produced. Although the stages are less for post-production, but non-the-less essential, without which the resin printed material lacks transparency and structural strength.

Direct To Print aligners: 4 stages

1. Resin 3D aligner printing: 30-60 minutes
2. Centrifuge: 6 minutes
3. UV light curing Nitrogen chamber: To complete the process of curing UV light is combined with a Nitrogen chamber. 15 minutes
4. Boiling water: The Graphy material exerts shape memory, which manifests when heated in boiling water. 60 seconds

 Overall time: 52-82 minutes

Commercial availability

Graphy or Tera Harz^TM TC-85DAP to be more precise, is commercially available now. Distributors are Forestadent and Scheu-Dental. Currently distributors require a certification of attending the Graphy course prior to being able to order the material. This appears restrictive, as there is no equivalent for other aligner / resin materials, however the decision from Graphy was due to users not being familiar with the difference in post-production when compared to conventional aligners. A decision which I understand Forestadent will be changing soon.

Verdict

Graphy: Direct To Print has arrived and it was exciting to see eminent orthodontists Björn and Co working with the material at this early stage. The potential advantages offer a new way of delivering orthodontics with aligners, a 2.0 relative to the current aligner systems.  However It appears to still be in its infancy, both in terms of processes and research. The software was challenging to use and required significant time in digital planning.  Production although much quicker than conventional aligner production, was a much more technique sensitive process. The question ‘can they do it better’ still yet to be answered. Further research is needed, and at the top of the list for me is the force delivery of Direct To Print aligners, can they produce the same or better forces  than current aligners, a question also posed by Ki Beom Kim in his 2022 KJO paper. Dimensional stability of the aligner through wear, an issue with current aligners as they degrade with time Qi 2005, is this better, same or worse with Direct To Print resin aligners.

The Course: It was an excellently planned and delivered talk, an organic and passionate course by Björn and Co.  The excitement of the potential application of Direct To Print aligners could not be hidden by the speakers, however the issues and unknowns were discussed in detail. In doing so Björn had crafted an inspiring course, one he would probably describe in his own words as ‘Pirate Style‘, After the course Björn had a party at the office, where it was great to speak to the Graphy team and Björn’s father! 

I would recommend attending the course for anyone interested the future of aligners and in house printing.

 Edit / Update

The course will be run again

Date: Friday 16/12/2022

Location: Traben-Trarbach/Germany

Duration: 9 AM to about 5 PM

Fee: €500

 https://www.paypal.com/paypalme/ORTHOsummerschool
There is no financial interest 

Contributions

Edited/contents: Farooq Ahmed,