Background: To investigate and compare the gap (i.e. fit) and thickness of six aligner systems (Airnivol, ALL IN, Arc Angel, F22, Invisalign and Nuvola) using industrial computed tomography (CT). The null hypothesis was that there would be no detectable differences in either measurement between the aligners investigated. Materials and methods: Passive aligners of each brand were fitted to one single resin cast prototyped from an STL file from a single patient. The samples obtained were examined under high-resolution micro-CT, and the resulting tomographic microphotographs and volumetric data were compared. 3D analysis investigated the gap volume, the mean gap width and the maximum gap width of each sample. A total of 204 linear 2D measurements were made on 18 microtomographic images to investigate the aligner gap and thickness among different systems. Investigated regions were the central incisor, canine and first molar. The resulting measurements were analysed by ANOVA and compared using Tukey's post hoc analysis (P < 0.05). Results: 3D analysis revealed that the F22 displayed lower gap volume and mean gap width, followed by Airnivol and Invisalign, whereas Airnivol the lowest maximum gap width. 2D analysis showed that F22 had the lowest mean gap and aligner thickness at all teeth investigated. Comparison of the 2D point values revealed statistically significant differences between brands in terms of both measurements (P < 0.05), with the exception of six points in the gap analysis and one in the thickness analysis. Conclusions: There are differences between the six aligner systems examined in terms of 2D and 3D measurements of aligner thickness and gap.

In many applications polymeric foams (such as expanded polystyrene, EPS, or polypropylene, EPP) are used for protection from impacts. Standard design requires the foam to maximize the energy absorption, thus achieving large deformations (typically up to 25% and above in compression) while maintaining the stress level below a threshold value. In this work steam chest moulded EPS and EPP were characterized in relation to their density, microstructure and applied strain rate. Typical mechanical parameters (elastic moduli and plateau stress in compression) were compared with existing models and data in the literature. The strain rate dependence was accurately described using Nagy's phenomenological model. The mechanical behaviour of the foams was then correlated with their microstructure, as investigated using scanning electron microscopy and X-ray micro-tomography. Structural parameters were obtained using both (2D and 3D) techniques and relevant results were compared.

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Objective To assess the effects of thermoforming on aligner thickness and gap width in six aligner systems with the same nominal thickness. Methods Six passive upper aligners of different brands were adapted to a single printed cast. Each sample was evaluated with high-resolution micro-computed tomography. To investigate aligner thickness and gap width, two-dimensional (2D) analysis was conducted assessing the effects of the following variables tooth type (central incisor, canine, and first molar), 2D reference points, and aligner type. Data were analyzed and compared using analysis of variance and Tukey’s post-hoc tests ( p < 0.05). Results Tooth type, dental region, and aligner type affected both the gap width and aligner thickness. The aligner thickness remained moderately stable across the arch only in the F22. Conclusions All thermoformed samples displayed smaller aligner thickness and gap width at anterior teeth and both gingival and coronal centers than at posterior teeth and occlusal surfaces.

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