Table of Contents
Zendura materials are engineered from the molecular level up — and measured, tested, and validated just as rigorously. This page collects the published material science, independent research, and real-world clinical experience behind Zendura aligner and retainer materials.
Material properties (standardized testing)#
Our flagship materials are characterized against internationally recognized ASTM standards. The table below summarizes values historically published for the rigid monolayer retainer material Zendura A and the patented tri-layer aligner material Zendura FLX:
| Property | ASTM standard | Zendura A (monolayer) | Zendura FLX (tri-layer) |
|---|---|---|---|
| Tensile modulus | D638 | ~2,400–2,650 MPa | ~1,000–1,200 MPa |
| Tensile strength (yield) | D638 | ~41–48 MPa | ~10–15 MPa |
| Tensile strength (break) | D638 | ~50 MPa | ~40–45 MPa |
| Flexural modulus | D790 | ~2,260 MPa (pre-forming) | ~1,100–1,200 MPa |
| Flexural strength | D790 | ~90–110 MPa | ~35–45 MPa |
| Elongation at break | D638 | ~100–130% | >130–150% |
| Specific gravity | D792 | 1.20 g/cm³ | ~1.19 g/cm³ |
| Hardness (outer layer) | D2240 | 82 Shore D | ~80 Shore D |
| Water absorption (24 h) | D570 | 0.18% | ~0.20% |
| Light transmission | D1003 | >90% | >90% |
| Haze | D1003 | <1.0% | <1.0% |
The contrast is intentional, not incidental: Zendura A’s toughness and rigidity make it the gold standard for long-term post-treatment retainers, while Zendura FLX’s patented structure — rigid outer shells over an elastomeric inner core — is tuned for active tooth movement.
Force delivery and stress relaxation#
Clear aligner therapy depends on a material’s ability to keep delivering light, continuous force inside a warm, wet environment (37 °C, ~100% relative humidity) for days at a time. Many materials lose most of their tooth-moving force within the first days of wear.
In stress-relaxation testing under in-mouth conditions (1–5% strain, 37 °C, 95–100% relative humidity, 24-hour cycles), historically published results show:
- Zendura FLX requires ~40% lower initial insertion force for patient comfort, yet delivers up to 150% more continuous orthodontic force over a standard 7–10 day wear period than commodity PETG-based sheets, whose force decays rapidly.
- Zendura A delivers high initial force and retains its shape against tooth-induced strain for up to three years of retainer wear without cracking.
Overcoming “creep” in hydrophilic polyurethane was itself an engineering breakthrough: conventional dry annealing fails because polyurethane loses its stress alignment on re-hydration, so Bay Materials developed and patented a process of annealing in a controlled, humid environment that preserves the hydrated structure while redistributing internal stress (US Patent No. 8,716,425).
Independent research#
Gingival-margin trim design has a larger effect on aligner retention than attachments. In a study published in the Journal of Clinical Orthodontics (Cowley, Mah & O’Toole, 2012), researchers measured the retention of thermoformed aligners with different margin designs:
- Without attachments, a straight cut line 2 mm above the gingival zenith was about twice as retentive as a scalloped cut along the gingival margin.
- With attachments, the same 2 mm trim was over four times as retentive as a scalloped cut.
In other words, how the appliance is trimmed can matter more to retention than adding composite attachments — a finding that directly informs our trimming guidance for Zendura appliances.
Clinical experience: in-office aligner fabrication#
Published field experience from True Dental Care (Jersey City, NJ), a general practice that moved the majority of its clear aligner production to an in-office digital workflow using Zendura FLX:
- Patients reported little to no pain wearing FLX aligners.
- The practice safely planned up to 0.5 mm of tooth movement per aligner.
- The material delivered tooth-moving forces for well over 10 days of wear.
- Sustained force retention and low discomfort allowed the wear cycle to be shortened from 14 days to 7 days per aligner.
Operationally, switching to in-office fabrication with Zendura FLX cut retainer turnaround from 2–3 weeks (outsourced) to 1–2 days — and grew aligner treatment to more than 20% of the practice’s business.
The data on this page reflects values and studies published to date; some figures originate from earlier product literature and are provided for reference. For the latest validation data, regulatory filings, or test certificates for a specific material, contact our team — and see each material’s Instructions for Use and Safety Data Sheet.
