Abstract
In recent years, aesthetic concerns regarding orthodontic appliances have significantly increased due to the growing number of adult patients undergoing orthodontic therapy. Clear removable aligners have seen growing popularity as an aesthetic and comfortable alternative to traditional fixed appliances. Clear aligner therapy also appears more respectful of the patient’s periodontal health; in fact, clear aligners allow the patients to maintain proper daily oral hygiene thanks to being removable. Among the parameters that affect the clinical efficacy of aligners, the material employed for their manufacturing plays a key role. The present paper aims to review the most used materials in manufacturing clear aligners, focusing on their clinical and mechanical performances, according to the current state of literature. Furthermore, biological features of the different materials are also examined regarding their effects on dental and periodontal tissues, oral mucosa, and potential systemic effects.
Highlights
The idea to employ clear overlay orthodontic appliances to move progressively misaligned teeth was introduced in 1946 by Kesling, who described how consecutive tooth movement is possible by utilising positioners produced from setup models (Kesling, 1945; Kesling, 1946).In the last decades, thanks to the introduction and spread of CAD/CAM technologies in dentistry, the use of clear removable splints for orthodontic purposes has received a great impulse.The first digitally designed and manufactured aligners system was the Invisalign system, a series of removable polyurethane aligners launched in 1998 by Align Technology (Santa Clara, CA, United States)
The study of Dalaie et al investigated the thermomechanical properties of two Polyethylene terephthalate glycol (PET-G) aligners of two different thicknesses, 1 and 0.8 mm, in response to thermoforming; it has been seen that in both types, the hardness decreases by about 7.6% after thermoforming, but there are no significant differences in hardness into the two types of aligners
One in vitro study based its results on comparing eight different types of most used materials (PET-G, PC, PP, PUR, A +, C +, PE and EVA) from different manufacturers and placed them in contact with a solution that simulated the oral environment (Ryokawa et al, 2006). It assessed that the elastic modules of Polycarbonate (PC), polyethylene terephthalate (PET)-G and Essix A + in the intraoral environment exhibited significant increases compared to the original samples; in reverse, those of polypropylene (PP), C +, polyethylene (PE) and Ethylene Vinyl Acetate (EVA)were significantly reduced
Summary
The idea to employ clear overlay orthodontic appliances to move progressively misaligned teeth was introduced in 1946 by Kesling, who described how consecutive tooth movement is possible by utilising positioners produced from setup models (Kesling, 1945; Kesling, 1946). In 2001 it was introduced in Europe (Galan-Lopez et al, 2019) It is one of the most used clear aligners systems worldwide (Galan-Lopez et al, 2019; Nemec et al, 2020). The properties of materials used to produce clear aligners are among the essential aspects in determining their mechanical and clinical features. The present paper study reviews the most employed materials in the manufacturing of clear aligners, focusing on their mechanical performances and biological features about their effects on dental and periodontal tissues and oral mucosa
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