Slot fidelity and ligation-dependent tribology in personalized brackets made by casting versus selective laser melting: an in vitro study

TL;DR

This study compares two manufacturing methods for orthodontic brackets, finding differences in slot accuracy and friction behavior that could affect treatment outcomes.

Contribution

The study introduces a novel in vitro comparison of casting and selective laser melting for orthodontic brackets, revealing fabrication-ligation interactions affecting friction.

Findings

Casting and SLM produced similar slot height accuracy but SLM had greater angle errors.

Friction behavior varied by ligation type and fabrication method, reversing rankings between steel and elastomeric ligatures.

Support-facing walls showed reduced accuracy in both methods, suggesting design adjustments for SLM brackets.

Abstract

Reliable chairside adoption of digital orthodontics depends on micrometre-scale slot fidelity and stable bracket–wire tribology. A single computer-aided design for a personalized second-premolar bracket was manufactured by lost-wax casting and by selective laser melting (SLM) (n = 36 per method). Slot height and inter-wall angle were measured on both the support-facing and non-support surfaces. Static and dynamic friction were evaluated using stainless-steel rectangular wires ligated either with tightly twisted stainless-steel ties or with elastomeric modules. Mean slot height was 480.88 ± 73.90 µm for casting and 421.47 ± 32.03 µm for SLM, against a nominal 480 µm. Overall height error did not differ between methods (P = 0.673), whereas angle er-ror was greater for SLM (17.76 ± 11.29°) than for casting (9.56 ± 8.88°, P < 0.001). The support-facing wall consistently showed reduced accuracy: in casting, height error in-creased on the support side (P = 0.001); in SLM, both height and angle errors increased on the support side (both P < 0.001). Across conditions, static friction exceeded dynamic friction (all P < 0.001). With steel ligation, friction was higher for casting than SLM (median static 6.00 N vs 4.35 N, P = 0.007; median dynamic 5.03 N vs 3.83 N, P = 0.011). With elastomeric ligation, the ranking reversed, with higher friction for SLM (median static 2.95 N vs 2.05 N, P < 0.001; median dynamic 2.54 N vs 2.03 N, P = 0.003). In this standardized local in vitro model, findings suggest a surface-dependent reduction in accuracy at the support-facing wall and a fabrication-by-ligation interaction that may alter the frictional ranking between steel and elastomeric ligations. Cast brackets showed more consistent full-wire seating, whereas SLM brackets may benefit from calibrated design offsets and targeted finishing to limit undersized or tapered slots; validation beyond this setup is needed.

The online version contains supplementary material available at 10.1038/s41598-025-34810-w.

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