Korean J Orthod.  2017 Jul;47(4):238-247. 10.4041/kjod.2017.47.4.238.

Effects of recycling on the biomechanical characteristics of retrieved orthodontic miniscrews

• Yun SD
• Choi SH
• Cha JY
• Yu HS
• Kim KM
• Kim J
• Hwang CJ

• KMID: 2379556
• DOI: http://doi.org/10.4041/kjod.2017.47.4.238

Abstract

OBJECTIVE
The aim of this study was to compare recycled and unused orthodontic miniscrews to determine the feasibility of reuse. The comparisons included both miniscrews with machined surfaces (MS), and those with etched surfaces (ES).
METHODS
Retrieved MS and ES were further divided into three subgroups according to the assigned recycling procedure: group A, air-water spray; group B, mechanical cleaning; and group C, mechanical and chemical cleaning. Unused screws were used as controls. Scanning electron microscopy, energy-dispersive X-ray spectrometry, insertion time and maximum insertion torque measurements in artificial bone, and biological responses in the form of periotest values (PTV), bone-implant contact ratio (BIC), and bone volume ratio (BV) were assessed.
RESULTS
Morphological changes after recycling mainly occurred at the screw tip, and the cortical bone penetration success rate of recycled screws was lower than that of unused screws. Retrieved ES needed more thorough cleaning than retrieved MS to produce a surface composition similar to that of unused screws. There were no significant differences in PTV or BIC between recycled and unused screws, while the BV of the former was significantly lower than that of the latter (p < 0.05).
CONCLUSIONS
These results indicate that reuse of recycled orthodontic miniscrews may not be feasible from the biomechanical aspect.

Keyword

Retrieved orthodontic miniscrew; Recycling; Surface characteristics; Biomechanical characteristics

MeSH Terms

Microscopy, Electron, Scanning
Recycling*
Spectrum Analysis
Torque

Figure

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  Figure 1 Schematic diagrams of orthodontic miniscrews with (A) machined and (B) etched surfaces. Ø, Diameter.

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  Figure 2 Placement of orthodontic miniscrews in the maxilla.

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  Figure 3 Flowchart of the experiment.

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  Figure 4 Images of the recycling processes used in the present study. A, Retrieved screws; B, air-flow with glycine powder (mechanical cleaning); C, immersion in 37% phosphoric acid (10 min; chemical cleaning); and D, immersion in 6% sodium hypochlorite (15 min; chemical cleaning).

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  Figure 5 Assessment of mechanical characteristics. A, Photograph of the torque tester used in the study; B, graph showing insertion time and insertion torque.

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  Figure 6 Measurements of (A) bone–implant contact ratio (BIC), T1 + T2 + T3 (yellow line) / T4 (blue line) and (B) bone volume ratio (BV), yellow area / area within the green line. Hematoxylin and eosin staining.

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  Figure 7 Scanning electron microscopy images of the lateral side of orthodontic miniscrews with a machined surface (×80, ×200, ×500, and ×1,000). Group A, air-water spray only and distilled water irrigation; group B, mechanical cleaning; group C, mechanical cleaning + chemical cleaning; group D, unused screw (control).

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  Figure 8 Scanning electron microscopy images of the lateral side of orthodontic miniscrews with an etched surface (×80, ×200, ×500, and ×1,000). Group A, air-water spray only and distilled water irrigation; group B, mechanical cleaning; group C, mechanical cleaning + chemical cleaning; group D, unused screw (control).

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  Figure 9 Scanning electron microscopy images of the tips of orthodontic miniscrews with (A) a machined surface and (B) an etched surface (×80, ×200). Group A, air-water spray only and distilled water irrigation; group B, mechanical cleaning; group C, mechanical cleaning + chemical cleaning; group D, unused screw (control).

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