While sequential aligner systems have demonstrated robust outcomes for a wide range of tooth movements, persistent discrepancies between digital treatment plans and clinical results highlight the importance of material behavior and physical adaptation in force transmission.
In particular, the fit of aligners within embrasure regions — narrow anatomical spaces where adjacent teeth converge — has a significant impact on how effectively force is transferred to achieve controlled tooth movement.
These embrasure zones present unique challenges due to their complex geometry and susceptibility to undercuts, yet they have received relatively little attention in quantitative research compared with buccolingual or occlusal surfaces.
Traditionally, aligners are produced by thermoforming thermoplastic sheets over dental models, a process that can lead to reduced material thickness and diminished adaptation in anatomically restricted regions.
In the present study, thermoformed aligners exhibited significantly lower thickness in embrasure regions (0.32–0.66 mm) compared with their three-dimensionally printed counterparts, highlighting a notable limitation of conventional fabrication methods.
By contrast, 3D-printed aligners — especially those designed with a deliberate internal surface offset (e.g., 0.05 mm) — offer the potential for enhanced customization of fit and thickness profiles.
In this investigation, microcomputed tomography (micro-CT) analysis revealed that 3D-printed aligners with a 0.05-mm offset achieved superior embrasure adaptation, with consistently smaller gap distances and higher embrasure fit ratios (73–93 %) than both no-offset 3D-printed aligners (58–86 %) and thermoformed aligners (44–85 %).
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Importantly, the offset design maintained similar fit across both coronal and cervical vertical levels, suggesting more uniform adaptation in critical anatomical sites.
The embrasure gap distances measured across different tooth pairs further underscore the advantage of optimized 3D printing: the 0.05-mm offset group showed markedly reduced embrasure gaps compared with the other groups, while the thermoformed aligners demonstrated the largest gaps at key cervical levels, especially in regions with pronounced undercuts.
Beyond gap fit, material thickness behavior also diverged substantially between fabrication techniques.
While thermoformed aligners underwent notable thickness reductions relative to the original sheet (36.5–88.5 %), 3D-printed aligners demonstrated significant thickness increases relative to their virtual design specifications (197–470 %).
Such differences in physical characteristics can meaningfully influence stiffness, force delivery, and long-term biomechanical performance.
Taken together, these findings suggest that digital design refinements — like controlled internal surface offsets in 3D-printed aligners — may enhance embrasure adaptation and material performance, with potential implications for improved treatment accuracy, predictability, and overall orthodontic outcomes.
Through high-resolution micro-CT evaluation, this study provides a detailed comparative assessment of two emerging fabrication paradigms, laying the groundwork for informed clinical decisions and future material innovations in clear aligner therapy.
👉 You can download and read the complete open-access PDF of this study at Springer’s journal site to explore the full methods, results tables, and imaging data.
