Biological Effects of Anodic Oxidation on Titanium Miniscrews: An In Vitro Study on Human Cells

Abstract

This controlled in vitro study compared the effects of varying the thickness of a TiO₂ layer on cellular activity using commercially available miniscrew samples with identical surface features to derive information with direct clinical impact. Titanium grade V plates with four different thicknesses of TiO₂ layer/color were used: absent/gray (Control group), 40-50 nm/pink (Pink group), 130 nm/gold (Gold group) and 140 nm/rosé (Rosé group). In vitro experiments used Saos-2 cells and included cell growth analysis, phospho-Histone H3 and procollagen I staining, cell viability analysis, and a cell migration assay at 12, 24, 40 and to 48 h. Few differences were seen among the groups, with no clear behavior of cellular activity according to the TiO₂ thickness. The Control group showed a greater cell count. Phospho-Histone H3 staining was similar among the groups and procollagen I staining was greater in the Rosé group. Cell viability analysis showed a significant difference for live cell counts (greater in the Rosé group) and no difference for the dead cell counts. The cell migration assay showed a delay for the Rosé group up to 40 h, where full repopulation of cell-free areas was obtained at 48 h. The results suggest that the TiO₂ layers of the commercial miniscrews have minimal biological effects, including cytotoxicity, with possibly negligible or minimal clinical implications.

Keywords: anodic oxidation; cell growth; miniscrews; orthodontics; titanium.

Figure 1

The different plates used in the study.

Figure 2

Representative cell migration assay images at 12 and 48 h, showing the different groups. Smaller cell-free areas in images indicates better migration of cells. White dashed lines indicate the 500-µm cell-free area which existed after the removal of the silicon insert. Arrows identify Saos-2 migrating cells on the cell-free area during the initial repopulation of the cell-free area at 12 h. Red dashed squares designate full repopulation of the cell-free area at 48 h. Asterisks indicate areas for which the gap was originally larger than 500 µm (excluded from the recordings). Images at baseline, 24 h and 40 h omitted for clarity.