Surface evaluation of alkali-heat treated Ti-6Al-4V implants: Machined versus additive-manufactured

Objectives: This study aimed to compare the effects of alkali-heat treatment on the surface characteristics of titanium dental implants (Ti-6Al-4V) produced by two different fabrication methods—subtractive machining and additive manufacturing using laser powder bed fusion (LPBF)—with both horizontal and vertical build orientations. Methods: Disc-shaped Ti-6Al-4V specimens were prepared using machining and LPBF techniques. All samples underwent alkali treatment with 10 M NaOH at 90°C for 24 hours, followed by heat treatment at 600 °C. Surface morphology, elemental composition, crystalline structure, roughness, and wettability were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), laser confocal scanning microscopy, and contact angle goniometry. Data were expressed as mean ± SD, with significance set at p < 0.05. Results: Alkali-heat treatment generated nanostructures—such as nanospikes and micro-crevices—on all surfaces. EDS and XRD confirmed the formation of a sodium titanate layer, evidenced by increased oxygen and sodium content and a new diffraction peak at 48.3°. LPBF specimens exhibited greater roughness than machined ones (p < 0.001), and vertically printed LPBF samples were rougher than horizontally printed ones (p < 0.05). However, the treatment did not significantly change the baseline roughness (p > 0.1). Untreated surfaces were hydrophobic (contact angle > 90°), while treated machined samples became highly hydrophilic (10.13° ± 2.78, p < 0.0001), and treated LPBF specimens achieved complete wetting (0°). Conclusions: Alkali-heat treatment successfully induced nanostructural modifications and sodium titanate layer formation on Ti-6Al-4V implants, greatly enhancing surface hydrophilicity without altering roughness. The additive manufacturing method and build orientation significantly influenced surface topography. These results suggest that combining LPBF fabrication with alkali-heat treatment could optimize implant surface bioactivity for improved osseointegration.