Direct-Printed vs. Thermoformed Aligners: A Clinical Comparison

Clear aligner fabrication has relied on a single dominant method for more than two decades: thermoforming a plastic sheet over a 3D-printed model. Direct 3D printing of the aligner itself is now emerging as a distinct manufacturing pathway, supported by purpose-built photopolymer resins from manufacturers such as Graphy Inc. (Seoul, South Korea). This article summarizes the manufacturing differences, the mechanical and biological evidence comparing the two methods, and the clinical considerations relevant to treatment planning.

1. Thermoformed Aligners: The Indirect Method

Thermoforming is an indirect fabrication process in which the aligner is not printed but shaped over a printed model:

1. The treatment plan is digitally staged into sequential tooth positions.
2. A physical model is 3D printed for each stage.
3. A thermoplastic sheet (commonly polyethylene terephthalate glycol, or PETG) is heated and formed over the model under vacuum or pressure.
4. The formed shell is trimmed to the designed gingival margin.

This remains the manufacturing basis for the majority of clear aligners currently produced, and it is the comparator arm ("gold standard") used in ongoing clinical trials evaluating newer fabrication methods.

2. Direct-Printed Aligners: Graphy and the Tera Harz System

Direct 3D printing removes the intermediate model-and-sheet step. The aligner geometry, including gingival margins, wall thickness, and localized pressure features, is printed directly from resin on an LCD or DLP printer, then cleaned of uncured resin and post-cured, typically in a nitrogen and/or glycerin bath to preserve clarity and flexibility.

Graphy Inc. is the manufacturer most closely associated with clinical adoption of this method. Its Tera Harz TC-85 resin was the first resin cleared for direct aligner manufacturing, and it has since been followed by TC-85DAC and TC-58. Graphy also supplies a companion digital workflow, including Digital Aligner Design (DAD) software and dedicated curing units (Cure M), and markets its own finished product line under the Graphy Clear Aligner name, which has been evaluated directly against other direct-printed systems and thermoformed materials in comparative laboratory studies.

Terminology note: "Direct-printed aligner" (DPA) refers to the manufacturing method. "Graphy aligner" or "Graphy Clear Aligner" refers to a specific commercial product built on that method using Graphy's resin and design software. Other DPA materials in the literature include iLuxClear and RightBio Clear Aligner resins, evaluated alongside Graphy's system in head-to-head studies.

3. Mechanical and Force-Profile Evidence

Several in vitro studies have directly compared the force output of thermoformed PETG aligners against direct-printed resins, including Graphy's TC-85DAC:

• Force magnitude: At intraoral temperature, direct-printed aligners have consistently generated significantly lower forces than thermoformed PETG aligners across displacement ranges of 0.10–0.30 mm.
• Force consistency: Thermoformed aligners show a marked, statistically significant increase in force with each incremental displacement, while direct-printed aligners maintain a comparatively flat, more consistent force profile across the same range.
• Shape memory: Graphy's TC-58 resin exhibits pronounced shape-memory recovery, approximately 90% of deformation recovered within 10 minutes and 96% within 60 minutes, compared with PETG, which does not spontaneously recover its original shape once deformed.
• Mechanical loading: A 14-day water-immersion study found that direct-printed resins (TC-85, TA-28, TR-07) delivered significantly lower mechanical loads than thermoformed materials, which researchers associate with a more favorable orthodontic force profile.

4. Surface and Biological Considerations

Comparative evaluation of three direct-printed materials, including Graphy Clear Aligner, against two thermoformed materials found measurable differences in surface roughness and bacterial adhesion following extended immersion in artificial saliva, indicating that material selection (not just fabrication method) continues to influence long-term hygiene and wear performance. This underscores that not all direct-printed resins, and not all thermoformed sheets, behave identically, product-level evidence matters.

5. Accuracy, Efficiency, and Waste

• Manufacturing waste: Because direct printing eliminates the need to print and discard a model at every stage, several studies report reduced material waste relative to thermoforming.
• Retention and fit: Retentive force and margin-design studies using Graphy's DAD software and TC-85DAC resin have evaluated how gingival margin geometry and attachment presence affect aligner retention in direct-printed systems, an area still being benchmarked against thermoformed equivalents.
• Clinical outcomes: Early clinical data on direct-printed aligners have reported meaningful reductions in Peer Assessment Rating (PAR) scores for moderate malocclusion cases, along with reduced reliance on attachments, though thermoformed aligners remain the active comparator in ongoing randomized trials assessing pain and tooth movement outcomes.

6. Summary Comparison

Factor	Thermoformed (e.g., PETG)	Direct-Printed (e.g., Graphy TC-85DAC)
Fabrication method	Indirect — sheet formed over printed model	Direct — resin printed as final aligner geometry
Force profile	Higher, escalates with displacement	Lower, more consistent across displacement range
Shape memory	Minimal — holds deformed shape	Pronounced — majority of shape recovered within 10–60 minutes
Material waste	Higher — model discarded per stage	Lower — no intermediate model required
Clinical track record	Extensive, long-established	Emerging, growing evidence base
Design flexibility	Limited to uniform sheet thickness	Variable wall thickness and surface features possible

7. Clinical Takeaway

The evidence to date suggests direct-printed resins, Graphy's Tera Harz system in particular, offer a lower and more consistent force profile with less manufacturing waste, which may translate to improved patient comfort and more predictable biomechanics. Thermoforming, however, remains the more established method, with a longer clinical track record and lower equipment overhead. Surface and biofilm data indicate that material selection within each category still meaningfully affects hygiene and wear performance, so method alone should not be treated as a proxy for material quality.

Sources: Progress in Orthodontics; Frontiers in Oral Health; ScienceDirect systematic review of 3D-printed vs. thermoformed clear aligners; ClinicalTrials.gov registrations (NCT07496892, NCT07637227); comparative in vitro studies on direct-printed and thermoformed aligner materials.