Chemical composition and in vitro staining resistance of SmartTrack and ClearQuartz multilayered orthodontic clear aligners

Abstract

Clear aligner therapy is a popular alternative to traditional metal braces because of its esthetic appeal and convenience. However, the chemical composition of these aligners is not well understood, and their resistance to staining by coloring compounds present in the oral environment remains a concern. In this study, we aimed to analyze the chemical composition of multilayer aligner materials using chemical imaging and evaluate their staining resistance to common food and beverage items. The in vitro staining resistance of SmartTrack (Invisalign; Align Technology, Santa Clara, Calif) and ClearQuartz (ClearCorrect; Straumann Group, Basel, Switzerland) was tested by immersing the aligners in coffee, cola, red wine, and mustard for 24 hours. The color change was assessed using spectrophotometry. The aligners were analyzed using Raman microscopy to identify the chemical composition of the individual layers and relate them to staining resistance. Raman microscopy revealed that ClearQuartz consists of a soft elastomeric polyurethane layer sandwiched between two polyester layers, whereas SmartTrack has the opposite configuration. ClearQuartz exhibited less staining in all the tested foods and beverages than SmartTrack, which showed marked staining in mustard and coffee. Stain uptake was primarily observed in the polyurethane layer, possibly because of its chemical affinity with the coloring compounds. Clinicians should consider the patients’ dietary habits and aligner material composition before recommending a clear aligner treatment. Aligners with polyurethane elastomer as the outer layer are not recommended for patients who consume food and beverages rich in colorants, such as coffee and mustard, as this may detrimentally impact patient satisfaction and compliance.