The aim of our study was to determine the wear resistance of vacuum-formed retainers (VFRs) made out of polyethylene terephthalate glycol (PETG), from four different manufacturers (Essix, Leone, Erkodent, Bio-Art), under high load forces (600 N), for 10000 cycles. Forty thermoplastic sheets were divided in four groups, each group consisting of a set of ten sheets from each manufacturer, thermoformed on two matching study models with an ideal occlusion. The Instron 8874 equipment was used to simulate the accelerated wear of VFR surfaces. The surfaces of the VFRs were visually inspected using a KEYENCE VHX-600 digital microscope, but this proved difficult because of the surface shine. 3D models were generated using a GOM industrial laser surface scanner. Several wear areas were identified, having various degrees of roughness, with no evident tear points or perforations. One-way ANOVA analysis showed no statistically significant differences in net mass loss between the four groups.
Orthodontic appliances usually require the joining of different stainless-steel parts in order to achieve adequate control over tooth movement during the active treatment. The aim of this study was to assess the tensile and shear breaking force of the joints between forty orthodontic bands and forty attachments (buccal tubes), joined by laser and TIG welding, without filler material. For the laser welding technique, we used an XXS Laser (OROTIG) welding unit and for the TIG welding technique, a PUK D2 (LAMPERT) welding unit. The tensile and shear breaking force of the welded joints was determined using the Z010 Zwick/Roell testing machine. The independent-samples t-test showed statistically significant differences between the laser and TIG groups for both the tensile and the shear breaking force tests, the laser welded samples having better mechanical strength than the TIG welded samples. For practical use, under normal loading forces, both techniques are suitable for this particular application in orthodontics. In patients with parafunctional habits, that could develop higher bite forces, the failure of the welded joints might occur if the welding surface is not increased, especially for the TIG welding technique.
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