Korean J Orthod.  2014 Sep;44(5):246-253. 10.4041/kjod.2014.44.5.246.

Enhanced compatibility and initial stability of Ti6Al4V alloy orthodontic miniscrews subjected to anodization, cyclic precalcification, and heat treatment

• Oh EJ
• Nguyen TD
• Lee SY
• Jeon YM
• Bae TS
• Kim JG

• KMID: 1726418
• DOI: http://doi.org/10.4041/kjod.2014.44.5.246

Abstract

OBJECTIVE
To evaluate the bioactivity, and the biomechanical and bone-regenerative properties of Ti6Al4V miniscrews subjected to anodization, cyclic precalcification, and heat treatment (APH treatment) and their potential clinical use.
METHODS
The surfaces of Ti6Al4V alloys were modified by APH treatment. Bioactivity was assessed after immersion in simulated body fluid for 3 days. The hydrophilicity and the roughness of APH-treated surfaces were compared with those of untreated (UT) and anodized and heat-treated (AH) samples. For in vivo tests, 32 miniscrews (16 UT and 16 APH) were inserted into 16 Wistar rats, one UT and one APH-treated miniscrew in either tibia. The miniscrews were extracted after 3 and 6 weeks and their osseointegration (n = 8 for each time point and group) was investigated by surface and histological analyses and removal torque measurements.
RESULTS
APH treatment formed a dense surface array of nanotubular TiO2 layer covered with a compact apatite-like film. APH-treated samples showed better bioactivity and biocompatibility compared with UT and AH samples. In vivo, APH-treated miniscrews showed higher removal torque and bone-to-implant contact than did UT miniscrews, after both 3 and 6 weeks (p < 0.05). Also, early deposition of densely mineralized bone around APH-treated miniscrews was observed, implying good bonding to the treated surface.
CONCLUSIONS
APH treatment enhanced the bioactivity, and the biomechanical and bone regenerative properties of the Ti6Al4V alloy miniscrews. The enhanced initial stability afforded should be valuable in orthodontic applications.

Keyword

Orthodontic mini-implant; Stability; Biocompatibility; Surface treatment

MeSH Terms

Alloys*
Body Fluids
Hot Temperature*
Hydrophobic and Hydrophilic Interactions
Immersion
Osseointegration
Rats, Wistar
Tibia
Torque
Alloys

Figure

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  Figure 1 Field emission scanning electron microscope images of Ti6Al4V miniscrews: (A) untreated, and (B, C) nanotubes formed on the surface; (B) top and (C) cross-sectional views.

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  Figure 2 Ca-P coating on nanotubular Ti6Al4V miniscrews (A, B) after anodization, cyclic precalcification, and heat (APH) treatment and (C, D) after APH treatment and 3-day immersion in simulated body fluid. The arrow marks the interface between the nanotube layer and the newly formed crystal layer. The cross marks the point where the high magnification image (C) was taken.

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  Figure 3 X-ray diffraction patterns of (A) UT, (B) AH, and (C) APH samples. UT, Untreatment; AH, anodization and heat treatment; APH, anodization, cyclic precalcification and heat treatment; OCP, octa calcium phosphate; HA, hydroxyapatite; A, TiO2 anatase; Ti, titanium.

• 

  Figure 4 Removal torque values 3 and 6 weeks after miniscrew implantation. Asterisks (*) indicate significant differences between the groups (p < 0.05). UT, Untreatment; APH, anodization, cyclic precalcification and heat treatment.

• 

  Figure 5 Morphology and chemical composition of the surface of extracted miniscrews. A, Field emission scanning electron microscope images of (a, c) UT and (b, d) APH samples in (a, b) 3 weeks and (c, d) 6 weeks after insertion. B, Corresponding results by energy dispersive X-ray spectrometer. UT, Untreatment; APH, anodization, cyclic precalcification and heat treatment.

• 

  Figure 6 A, Histologic images (Villanueva staining, ×100) of the bone-miniscrew interface for (a, c) UT and (b, d) APH samples (a, b) in 3 weeks and (c, d) 6 weeks after insertion. B, Percentage of bone-implant contact (BIC%) measured on 5 threads of UT and APH-treated miniscrew interfaces. Values are presented as mean ± standard deviation. *,†,‡Each marks indicate significant differences between groups (p < 0.05). UT, Untreatment; APH, anodization, cyclic precalcification and heat treatment.

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