Thermoplastic Disks Used for Commercial Orthodontic Aligners: Complete Physicochemical and Mechanical Characterization.

Invisible orthodontic aligners (IOAs) have been introduced in the orthodontic field as an innovative alternative for fixed brackets, in relation to their ability to be easily inserted/removed from the oral cavity without affecting the chewing ability and the aesthetic of the patients. The paper provides a complete physicochemical and mechanical characterization of thermoplastic materials in the form of disks used for commercial IOAs. A wide palette of specific techniques is considered, from tensile tests and dynamic-mechanical analysis, to X-Ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transformation infrared spectroscopy (FTIR-ATR) analyses and water absorption tests. The disks are investigated before and after immersion into staining beverages (red wine, coffee, nicotine and artificial saliva), in terms of colour variations, transparency, and microscopic surface modifications by means of colorimetry, UV-VIS absorbance and scanning electron microscopy (SEM). Among all the samples, polyurethane (PU) exhibited the highest crystallinity and the highest values of mechanical and thermal resistance, while the poly(ethylene terephthalate)-glycol (PETG) samples presented better transparency and less ability to absorb water. Moreover, red wine and coffee give noticeable colour variations after 14 days of immersion, together with a slight reduction of transparency.

Influence of aeration cycles on mechanical characteristics of elastomeric diffusers in biological intermittent processes: Accelerated tests in real environment.

The paper deals with the evaluation of the effect of on/off switching of diffuser membranes, in the intermittent aeration process of the urban wastewater treatments. Accelerated tests were done using two types of commercial EPDM diffusers, which were submitted to several consecutive cycles up to the simulation of more than 8 years of real working conditions. The effect of this switching on the mechanical characteristics of the membranes was evaluated in terms of pressure increment of the air operating at different flow rates (2, 3.5 and 6 m3/h/diff): during accelerated tests, such increment ranged from 2% to 18%. The intermittent phases emphasized the loss both of the original mechanical proprieties of the diffusers and of the initial pore shapes. The main cause of pressure increment was attributed to the fouling of the internal channels of the pores. Further analyses performed by scanning electron microscopy and by mechanical tests on EPDM membrane, using a traditional tensile test and a non destructive optical method, from which the Young's Modulus was obtained, supported previous conclusions. Any changes in terms of oxygen transfer parameters (KLa and SOTE%) were specifically founded by causing to the repeated on/off switching.

Superimposed fringe projection for three-dimensional shape acquisition by image analysis.

The aim in this work is the development of an image analysis technique for 3D shape acquisition, based on luminous fringe projections. In more detail, the method is based on the simultaneous use of several projectors, which is desirable whenever the surface under inspection has a complex geometry, with undercuts or shadow areas. In these cases, the usual fringe projection technique needs to perform several acquisitions, each time moving the projector or using several projectors alternately. Besides the procedure of fringe projection and phase calculation, an unwrap algorithm has been developed in order to obtain continuous phase maps needed in following calculations for shape extraction. With the technique of simultaneous projections, oriented in such a way to cover all of the surface, it is possible to increase the speed of the acquisition process and avoid the postprocessing problems related to the matching of different point clouds.