The first of these studies concluded that both Invisalign (Align Technology, San Jose, CA, USA) and CA-Clear Aligner (Scheu-Dental, Iserlohn, Germany) systems provided good fit. The only studies focusing on the topic have been carried out using a scanning electron microscope (SEM) to obtain microphotography of buccolingual sections of passive aligners, created by a cutting machine and fitted to stereolithographic models. The fit is determined by the thermoforming process (pressure and temperature), the elastic modulus of the materials used, the presence of divots or attachments and the hygroscopic expansion that occurs in contact with saliva. the gap between the inner surface of aligners and the external surface of the tooth. Īnother factor that may influence the predictability of clinical outcomes with aligners is the fit, i.e. suggest using aligners of nominal thickness 0.4 mm in order to minimise the initial overload on the periodontal tissues typical of the early stages of CAT. advise keeping programmed movements within the range 0.2–0.5 mm, and Elkholy et al. In fact, it has been reported that acceptable forces for tipping (0.5–0.75 N) and intrusion (0.1–0.25 N) may be exceeded by as much as tenfold. The thickness of the aligner material can affect not only their optical properties, but also the forces and moments expressed by the device, which often exceed those considered as optimal in the literature. There are many factors that influence the predictability of CAT, including the characteristics of the set-up (the staging of tooth movements and the types of programmed movement), the use of grip points and auxiliaries such as elastics and buttons, aligners’ physical properties, the manufacturing method of the thermoplastic materials used to make them, and the extension of their gingival margins. That being said, it is generally agreed that aligners are particularly efficient at resolving malocclusions of slight to moderate complexity in non-extraction cases due to their good capacity to expand, align and level the arches. In contrast, the literature contains differing reports on the efficacy of aligners in achieving extrusion. Īs regards the analysis of single movements, the literature agrees that rotation of cone-shaped teeth and movements that require good root control are those most difficult to obtain with aligners, while crown tipping and intrusion are the most predictable. Nowadays, they are a therapeutic option even in complex cases that involve distalization and space closure movements. Initially, CAT was mainly indicated in simple non-extraction cases, but over the years they have evolved, and there is now good evidence of their efficacy and efficiency. Indeed, the rise in popularity of clear aligner therapy (CAT) has been fuelled by the increasing demand of adult patients for more aesthetic treatments that do not negatively affect their social lives or relationships, and that are associated with fewer periodontal complications and a lower risk of root resorption. The demand for such orthodontic devices has grown, and they now occupy a significant portion of the market as a valid alternative to traditional fixed appliances. With the introduction of Computer-Aided Design and Computer-Aided Manufacturing (CAD/CAM) technology to Orthodontics, Align Technology (Santa Clara, CA, USA) launched its first clear orthodontic aligner in 1998.
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