ArticleBMC oral health2026
Thermoforming time variability of PET-G and TPU aligner sheets across consecutive thermoforming cycles: an in vitro study.
Article in BMC oral health, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
backgroundThermoforming time is a critical parameter in the fabrication of thermoformed orthodontic aligners, as it influences polymer softening, material adaptation, and dimensional consistency. Manufacturer-recommended heating durations are typically based on standardized conditions and may not reflect the dynamic thermal behavior of thermoforming units during consecutive fabrication cycles. Empirical data quantifying heating-time variation and stabilization patterns remain limited.
methodsThis in vitro study evaluated heating-time variation across 20 consecutive thermoforming cycles in two commercially available thermoplastic aligner materials: a multilayer polyethylene terephthalate glycol/thermoplastic polyurethane composite (Zendura FLX) and a single-layer thermoplastic polyurethane sheet (Maxflex), both with a nominal thickness of 0.76 mm. Each material underwent ten independent experimental sessions (total n = 200 cycles per material) using a standardized pressure-forming unit under controlled environmental conditions (23 ± 1 °C; 50 ± 5% humidity). Heating was terminated at a predefined sag depth of 16 mm, determined using a laser-based measurement system. Linear mixed-effects models were used to assess cycle-dependent variation, and simple linear regression was applied to the pre-stabilization phase.
resultsHeating time progressively decreased across consecutive thermoforming cycles for both materials. Zendura FLX stabilized from cycle 6 onward, with a steady-state mean of 64.59 ± 3.58 s. Maxflex stabilized from cycle 12 onward, with a steady-state mean of 69.37 ± 1.12 s. During the transient phase, heating time decreased linearly by 8.66 s per cycle for Zendura FLX (R² = 0.78) and 4.17 s per cycle for Maxflex (R² = 0.97). Both transient and steady-state heating durations were significantly longer than Supplier-Recommended Thermoforming Times (p < 0.0001).
conclusionsHeating time during thermoforming decreased across consecutive cycles before reaching material-specific stabilization thresholds. For both materials, experimentally determined heating durations exceeded manufacturer-recommended times under controlled laboratory conditions, suggesting that thermoforming behavior may vary dynamically during repeated fabrication cycles.
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