Miniscrews have been introduced in orthodontics as temporary anchorage devices (TADs), in order to move the correct teeth and avoid other elements to slide toward a wrong direction. Moreover the ease of use of TADs encouraged clinicians to use miniscrews also for non-conventional purposes, as fixation in mandibular fracture, mini-implant supported temporary pontics, miniscrew-assisted rapid palatal expanders and distalizers. These applications develop higher forces, so TAD fracture can be an unwanted complication. Some authors analyzed torsional loads but no studies measured forces required to bend the screws and ultimate flexural strength. Accordingly, inthepresentreport, Ti-6Al-4VTADswere mechanicallyevaluated. Sevendifferentdiametersof screws were tested: 1.3mm (Aarhus Screw, Medicon), 1.5mm (Spider Screw, HDC), 1.6mm (Aarhus Screw, Medicon), 1.7mm (Ortho Easy, Forestadent), 1.8mm (Ortho Implant, 3M), 1.9mm (Spider Screw, HDC) and 2.0mm (Storm, Kristal). The forces to bend the titanium TADs were measured at 0.1mm, 0.2mm magnitude of deflections and at maximum load (as peak before screw fracture) in air with a universal testing machine. Statistical analyses were performed. Both at 0.1mm and at 0.2mm deflections and at maximum load, the significantly highest forces were reported with 1.7, 1.8, 1.9, and 2.0mm TADs. The lowest values were reported with 1.6, 1.5, and 1.3mm miniimplants. No significant differences were reported between 1.6mm and 1.7mm screws. It was found that load values in N versus stress in MPa were not fully comparable when screws with small and larger diameter were compared. Therefore, when placing a miniscrew for applications that need maximum shear bending resistance, these results would be considered in order to reduce risk of unwanted fracture.

Failure load and stress analysis of orthodontic miniscrews with different transmucosal collar diameter

Sfondrini, Maria Francesca;Gandini, Paola;Alcozer, Roberto;Scribante, Andrea
2018-01-01

Abstract

Miniscrews have been introduced in orthodontics as temporary anchorage devices (TADs), in order to move the correct teeth and avoid other elements to slide toward a wrong direction. Moreover the ease of use of TADs encouraged clinicians to use miniscrews also for non-conventional purposes, as fixation in mandibular fracture, mini-implant supported temporary pontics, miniscrew-assisted rapid palatal expanders and distalizers. These applications develop higher forces, so TAD fracture can be an unwanted complication. Some authors analyzed torsional loads but no studies measured forces required to bend the screws and ultimate flexural strength. Accordingly, inthepresentreport, Ti-6Al-4VTADswere mechanicallyevaluated. Sevendifferentdiametersof screws were tested: 1.3mm (Aarhus Screw, Medicon), 1.5mm (Spider Screw, HDC), 1.6mm (Aarhus Screw, Medicon), 1.7mm (Ortho Easy, Forestadent), 1.8mm (Ortho Implant, 3M), 1.9mm (Spider Screw, HDC) and 2.0mm (Storm, Kristal). The forces to bend the titanium TADs were measured at 0.1mm, 0.2mm magnitude of deflections and at maximum load (as peak before screw fracture) in air with a universal testing machine. Statistical analyses were performed. Both at 0.1mm and at 0.2mm deflections and at maximum load, the significantly highest forces were reported with 1.7, 1.8, 1.9, and 2.0mm TADs. The lowest values were reported with 1.6, 1.5, and 1.3mm miniimplants. No significant differences were reported between 1.6mm and 1.7mm screws. It was found that load values in N versus stress in MPa were not fully comparable when screws with small and larger diameter were compared. Therefore, when placing a miniscrew for applications that need maximum shear bending resistance, these results would be considered in order to reduce risk of unwanted fracture.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11571/1224629
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