Advances in orthodontic clear aligner materials

Abstract

Rapid technological improvements in biomaterials, computer-aided design (CAD) and manufacturing (CAM) have endorsed clear aligner therapy (CAT) as a mainstay of orthodontic treatment, and the materials employed for aligner fabrication play an all-important role in determining the clinical performance of clear aligners. This narrative review has attempted to comprehensively encompass the entire gamut of materials currently used for the fabrication of clear aligners and elucidate their characteristics that are crucial in determining their performance in an oral environment. Historical developments and current protocols in aligner fabrication, features of contemporary bioactive materials, and emerging trends related to CAT are discussed. Advances in aligner material chemistry and engineering possess the potential to bring about radical transformations in the therapeutic applications of CAT; in the absence of which, clear aligners would continue to underperform clinically, due to their inherent biomechanical constraints. Finally, while innovations in aligner materials such as shape memory polymers, direct three-dimensional (3D) printed clear aligners and bioactive materials combined with clear aligner materials are essential to further advance the applications of CAT; increased awareness of environmental responsibilities among aligner manufacturers, aligner prescribing clinicians and aligner users is essential for better alignment of our climate change goals towards a sustainable planet.

Keywords: Bioactive materials; Clear aligners; Direct 3D printing; Environment; Review; Shape memory polymers.

Graphical abstract

Fig. 1

Workflow of fabrication of clear aligners by the thermoforming process.

Fig. 2

Stepwise fabrication process of 3D direct printed clear aligners.

Fig. 3

Gold nanoparticle-modified dental aligner can prevent porphyromonas gingivalis biofilm formation: (a) SEM images of bacterial cells accumulated on the coated AuDAPTs sample surface compared to uncoated control when immersed into bacterial suspension of different density of bacterial suspension (104 CFU/ml and 105 CFU/ml). (b) Comparison of the bacterial growth area ratio of the AuDAPT-coated samples and untreated samples. (c) CV staining images, SEM images, and confocal images of biofilms formed on AuDAPTs and control sample surface. (d) Biocompatibility of AuDAPT-coated aligners compared with control [76].

Fig. 4

An illustration of the relative comparison of the stress-strain curves of different orthodontic materials does not reflect absolute values. It is based on the reference data from the literature [52,81,85,86]. SS, stainless steel. Beta-Ti, Beta titanuim. Niti, Nickel titanium. Essix, clear retainer material. PETG, polyethylene terephthalate glycol (thermoplastic aligner material). TC-85, photocurable resin (3D-printed aligner material).

Fig. 5

A multidisciplinary case treated with orthodontic appliance and 3D direct printed stent aided periodontal surgery. (a) Intra-oral photos before treatment. (b) Intra-oral photos after treatment. (c) 3D design simulates the amount of crown lengthening procedure. (d) 3D printer and 3D direct printed stent. (e) Frontal close-up view of before, during, and after the procedure. (f) Frontal smiling photos before and after orthodontic-periodontal combined treatment.

Fig. 6

A multidisciplinary case treated with orthodontic appliance and 3D Digital Smile Design, digital wax-up and direct printed periodontal crown lengthening guide, and restorative stent for injection moulded composite restoration.

Fig. 7

A relapsed anterior open bite case treated with modified 3DIH aligners (Graphy, Seoul, South Korea) with biting springs. (a) Digitally designed modified clear aligner with OnyxCeph3™ (Ghemnitx, Germany). (b) Frontal view after relapse. (c) Frontal view after retreatment, anterior open bite is closed. (d) Preview of the virtually designed model with the inclusion of supporting structures to facilitate printing. (e) Aligners printed with TC-85 (Graphy) on the build platform of a stereolithography 3D printer (SprintRay Pro, SprintRay, Los Angeles, CA, USA). (f) The final modified 3DIH aligners including 0.036″ TMA wires.

Fig. 8

Schematic diagrams illustrate the relationship between the clear aligner and the environment. (a) Recycling process and the threat of plastic to the environment. (b) Micro-plastic hazards to human bodies.