Abstract
The use of metal-free thermoplastic materials plays a key role in the orthodontic digital workflow due to the increasing demand for clear aligner treatments. Three thermoplastic polymers commonly used to fabricate clear aligners, namely Duran®, Biolon® and Zendura®, were investigated to evaluate the effect of thermoforming (T.), storage in artificial saliva (S.A.S.) and their combination on their mechanical properties. Elastic modulus and yield stress of the specimens were characterized. Each material was characterized for each condition through tensile tests (ISO527-1). The results showed that thermoforming does not lead to a significant decrease in yield stress, except for Zendura® that showed about a 30% decrease. An increase of the elastic modulus of Duran® and Zendura®, instead, was observed after thermoforming. The same increase was noticed for the yield stress of Duran®. For S.A.S. specimens, the elastic modulus generally decreases compared to supplier condition (A.S.) and simply thermoformed material. A decrease of yield stress, instead, is significant for Zendura®. The results demonstrated that the impact of the operating conditions on the mechanical properties can vary according to the specific polymer. To design reliable and effective orthodontic treatments, the materials should be selected after their mechanical properties are characterized in the simulated intraoral environment.
Highlights
Adolescent and adult patients who are aware of their malocclusion traits and dissatisfied with their dental appearance tend to have psychosocial concerns [1,2]
The aim of this study is to evaluate the effect of the thermoforming process and of storage in artificial saliva on the mechanical properties of three different thermoplastic materials, commonly used for clear aligners, or rather Duran®, Biolon® and Zendura®
The null hypothesis was rejected for the elastic modulus of Duran and significant differences were observed for any test condition (A.S. vs. T., T. vs. S.A.S., A.S. vs. S.A.S., p < 0.05)
Summary
Adolescent and adult patients who are aware of their malocclusion traits and dissatisfied with their dental appearance tend to have psychosocial concerns [1,2]. The use of an orthodontic appliance to treat a malocclusion may lead to an impairment of quality of life, which is less severe when clear aligner therapy is performed [3]. Despite the fact that orthodontic treatment with clear aligners is a quickly growing sector, there is still insufficient evidence with regard to the effectiveness and stability of the treatment compared with conventional brackets [4]. Aligner therapy might treat mild non-extraction cases faster and more efficiently, but it requires more time than fixed appliance treatment for more complex cases. There is still limited evidence of aligner efficacy in arch expansion through bodily tooth movement, extraction space closure, and larger antero-posterior and vertical discrepancies [5].
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