Improvement of osseointegration of Ti-6Al-4V ELI alloy orthodontic mini-screws through anodization, cyclic pre-calcification, and heat treatments

Prog Orthod. 2022 Apr 4;23(1):11. doi: 10.1186/s40510-022-00405-8.

Abstract

Background: Mini-screws are widely used as temporary anchorages in orthodontic treatment, but have the disadvantage of showing a high failure rate of about 10%. Therefore, orthodontic mini-screws should have high biocompatibility and retention. Previous studies have demonstrated that the retention of mini-screws can be improved by imparting bioactivity to the surface. The method for imparting bioactivity proposed in this paper is to sequentially perform anodization, periodic pre-calcification, and heat treatments with a Ti-6Al-4V ELI alloy mini-screw.

Materials and methods: A TiO2 nanotube-structured layer was formed on the surface of the Ti-6Al-4V ELI alloy mini-screw through anodization in which a voltage of 20 V was applied to a glycerol solution containing 20 wt% H2O and 1.4 wt% NH4F for 60 min. Fine granular calcium phosphate precipitates of HA and octacalcium phosphate were generated as clusters on the surface through the cyclic pre-calcification and heat treatments. The cyclic pre-calcification treatment is a process of immersion in a 0.05 M NaH2PO4 solution and a saturated Ca(OH)2 solution at 90 °C for 1 min each.

Results: It was confirmed that the densely structured protrusions were precipitated, and Ca and P concentrations, which bind and concentrate endogenous bone morphogenetic proteins, increased on the surface after simulated body fluid (SBF) immersion test. In addition, the removal torque of the mini-screw fixed into rabbit tibias for 4 weeks was measured to be 8.70 ± 2.60 N cm.

Conclusions: A noteworthy point in this paper is that the Ca and P concentrations, which provide a scaffold suitable for endogenous bone formation, further increased over time after SBF immersion of the APH group specimens. The other point is that our mini-screws have a significantly higher removal torque compared to untreated mini-screws. These results represent that the mini-screw proposed in this paper can be used as a mini-screw for orthodontics.

Keywords: Anodization; Cyclic pre-calcification; Orthodontic mini-screw; Osseointegration; Ti–6Al–4V ELI alloy.

MeSH terms

  • Alloys
  • Animals
  • Biocompatible Materials
  • Bone Screws
  • Hot Temperature*
  • Humans
  • Osseointegration*
  • Rabbits
  • Titanium

Substances

  • Alloys
  • Biocompatible Materials
  • titanium alloy (TiAl6V4)
  • Titanium