Abstract
Clear and removable tooth aligners for orthodontics treatments have become an increasingly popular alternative to fixed appliances. Even if protocols suggest removing aligners before eating or drinking, most patients retain them when they drink beverages. Alterations in the material during the daily use could determine a reduction in the application forces, affecting the desired orthodontic movement; the knowledge of how this material reacts when subjected to different aging processes is mandatory to establish the predictability of the orthodontic treatment. According to this, the aim of the present study was to assess a new objective approach, coupling spectroscopic and chemometric tools, to evaluate the changes occurring in Invisalign® aligners, the most widely used brand, exposed in vitro to coffee, tea, Coca Cola® and UV radiation for 24 and 48 h. In particular, ATR-FTIR spectroscopy was utilized to characterize, at the molecular level, the chemical and color modifications in the surfaces of the appliances; the obtained data were submitted to PCA and one-way ANOVA and Tukey’s multiple comparison test. Moreover, a colorimetry analysis was carried out to evaluate any changes in color and transparency. Coffee and tea samples displayed the major color changes between the tested groups. The differences highlighted in the spectral features of coffee, tea and UV-treated samples were mainly ascribable to color and transparency changes, because the chemical properties remained unaltered.
Highlights
The development of CAD/CAM technology has permitted the use of thermoplastic materials to fabricate clear and removable tooth aligners for orthodontics treatments, which have become an increasingly popular alternative treatment to fixed appliances [? ? ]
Samples were analyzed by attenuated total reflectance–Fourier-transform infrared spectroscopy
Bonds in aromatic rings) [? ? ? ? ]. The comparison of this average IR spectrum with the spectral library of the KnowItAll software (Wiley Sciences Solutions, John Wiley & Sons, Inc., Hoboken, NJ, USA) fitted with a copolymer formed by aromatic polyurethanes and polyesters (Hit Quality Index, HQI > 85.0)
Summary
The development of CAD/CAM technology has permitted the use of thermoplastic materials to fabricate clear and removable tooth aligners for orthodontics treatments, which have become an increasingly popular alternative treatment to fixed appliances [? ? ]. With respect to traditional orthodontic treatment modalities, it offers various advantages, such as less patient discomfort, better aesthetics, easier periodontal maintenance, and less chair time for dentists [? ]. The first report regarding the use of a flexible aligners for orthodontic treatment dates back to 1945 [? There are more than 27 different clear aligner brands available in the global market: Invisalign® is the most widely used brand, with over five million patients worldwide [? ]. Polyurethane, a versatile engineering thermoplastic polymer with excellent physical properties, chemical and abrasion resistance and ease of process, is the first material that was used for clear aligners [? It has been proven that polyurethane is not an inert material; it is affected by heat, moisture, and prolonged contact with salivary enzymes [? ]
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