Browsing by Author "Willems, Guy"
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Item Morphological and Structural Characterization of Two Types of As-Received and In vivo Orthodontic Stainless Steel Brackets.(2012-10) Hoste, Sofie; Celis, Jean-Pierre; Willems, GuyAims: To perform a) a topographical analysis of the bracket slot of 12 as-received stainless steel brackets and of in vivo used stainless steel brackets from 7 patients and b) a compositional characterization of the constituting materials of two types of brackets. Study Design: In vitro laboratory study. Methodology: 12 as-received brackets and in vivo used brackets of seven patients were analysed. Two commercially available brackets were used for this study. A SEM analysis evaluated the topographic features of each bracket slot while an EDAX analysis was performed to analyse the constituting parts of each bracket. Results: As-received ORMCO brackets show more traces of plastic deformation than GAC brackets. On the contrary, pits, crevices and grain boundaries were observed on all as-received brackets. An increased plastic deformation and amount of scratches was noticed on ORMCO and GAC brackets after orthodontic treatment. Elemental analysis revealed that base and wing materials were not identical in GAC nor in Ormco brackets. In addition, both ORMCO and GAC brackets consist each of two parts assembled using a different brazing material. Conclusion: Both as-received brackets show different damage patterns on their slot surface. Increase of damage patterns was visualized after intra-oral use. As a consequence of the use of different constituting materials for the manufacturing of the two types of brackets investigated, galvanic corrosion is likely to occur.Item Transformation Behaviour, Bending Properties and Surface Quality of 22 Commercial Nickel- Titanium Wires: A Batch-to-Batch Evaluation.(2012-10) Brosens, Veronique; Ghijselings, Ines; Voet, Martine; Leemans, Pieter; Humbeeck, Jan Van; Willems, GuyAims: The aims of this study were to investigate batch-to-batch differences in mechanical and thermal properties of 22 commercial nickel-titanium wires and evaluate the surface quality. Secondly the percentages of superelasticity at mouth temperature were measured. Study Design: In vitro laboratory study. Place and Duration of Study: Sample: Department of Oral Health Sciences – Orthodontics and Metallurgy and Materials Engineering KU Leuven, between January 2010 and May 2011. Methodology: The sample comprised 22 NiTi wires of the upper jaw from 7 different manufacturers. For each brand two different batches were investigated (LOT A, LOT B). Three different investigations were carried out. First transformation behaviour and transition temperatures were determined by differential scanning calorimetry, second a three point bending test was done to evaluate the mechanical properties and third scanning electron microscopy was performed on all samples to evaluate surface quality. Results: Absolute batch-to-batch differences in the investigated properties were all deviating from zero, although most differences were clinically acceptable. Significant interbatch differences in thermal properties were found in 4 wires. Mechanical interbatch differences were found remarkable for 5 wires. Percentage of elasticity showed a non- superelastic curve below a deflection of 1500 μm, which represents clinical small deflections. Surface topography showed also interbatch differences for 4 wires. Conclusion: This study shows that batch-to-batch differences are obvious in each sample. One has to be careful in the selection of archwires. Therefore more standardized consument information should be provided.