Mechanical properties and biocompatibility of a novel miniscrew made of Zr₇₀Ni₁₆Cu₆Al₈ bulk metallic glass for orthodontic anchorage

The purpose of the present study was to fabricate a miniscrew possible for clinical application using Zr₇₀Ni₁₆Cu₆Al₈ bulk metallic glass (BMG), which has high mechanical strength, low elastic modulus, and high biocompatibility. First, the elastic moduli of Zr-based metallic glass rods made of Zr₅₅Ni₅Cu₃₀Al₁₀, Zr₆₀Ni₁₀Cu₂₀Al₁₀, Zr₆₅Ni₁₀Cu_17.5Al_7.5, Zr₆₈Ni₁₂Cu₁₂Al₈, and Zr₇₀Ni₁₆Cu₆Al₈ were measured. Zr₇₀Ni₁₆Cu₆Al₈ had the lowest elastic modulus among them. Then, we fabricated Zr₇₀Ni₁₆Cu₆Al₈ BMG miniscrews with diameters from 0.9 to 1.3 mm, conducted a torsion test, and implanted them into the alveolar bone of beagle dogs to compare insertion torque, removal torque, Periotest, new bone formation around the miniscrew, and failure rate compared with 1.3 mm diameter Ti-6Al-4 V miniscrew. The Zr₇₀Ni₁₆Cu₆Al₈ BMG miniscrew exhibited a high torsion torque even if the miniscrew had a small diameter. Zr₇₀Ni₁₆Cu₆Al₈ BMG miniscrews with a diameter of 1.1 mm or less had higher stability and lower failure rate than 1.3 mm diameter Ti-6Al-4 V miniscrews. Furthermore, the smaller diameter Zr₇₀Ni₁₆Cu₆Al₈ BMG miniscrew was shown, for the first time, to have a higher success rate and to form more new bone around the miniscrew. These findings suggested the usefulness of our novel small miniscrew made of Zr₇₀Ni₁₆Cu₆Al₈ BMG for orthodontic anchorage.