Effects of thermoforming on the physical and mechanical properties of thermoplastic materials for transparent orthodontic aligners

Ryu, Joo-Hyung; Kwon, Jae‐Sung; Jiang, Heng Bo; Yul, Jung; Kim, Kwang Mahn

doi:10.4041/kjod.2018.48.5.316

Cited by 109 publications

(133 citation statements)

References 28 publications

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“…Other studies, like the ones of Fang et al [23] and of Lombardo et al [24], with different approaches, investigated the stress relaxation of thermoplastic polymers used for orthodontics in temperature-regulated baths specifically designed to get a simulated oral environment. Ryu et al [12], instead, focused their attention on the evaluation of the change in mechanical properties before and after thermoforming, with the aim to deepen the effect of the manufacturing process on the final mechanical behavior of the materials used. Our work also focuses on this aspect, but also analyzes the change in mechanical properties for specimens where thermoforming was combined with storage in a simulated intraoral environment.…”

Section: Discussionmentioning

confidence: 99%

“…Since the mechanical properties of the materials used for production of clear aligners are of utmost importance to evaluate the efficacy of an orthodontic treatment based on these devices, the technical data provided by materials' suppliers cannot always be used as a reference, but the materials need to be experimentally assessed within the different conditions in which they are used. Mechanical properties of thermoplastic polymers can change after thermoforming, suggesting the need to test them after this procedure [12]. Furthermore, in the oral cavity, aligners are subjected to an aggressive environment that could lead to a high degradation of their properties causing a negative influence on treatment efficacy [13].…”

Section: Introductionmentioning

confidence: 99%

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Mechanical Properties of Thermoplastic Polymers for Aligner Manufacturing: In Vitro Study

et al. 2020

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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.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mechanical Properties of Thermoplastic Polymers for Aligner Manufacturing: In Vitro Study

et al. 2020

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“…The tensile test and dynamic-mechanical analysis were performed to characterise the main mechanical properties of the as-received disks by following previous results from literature [11,19,21,[26][27][28][29][30] and UNI EN ISO 527-2 [31]. The tensile test was completed using the same thickness as the manufacturer, and the specimens were bone-shaped (geometry 1BA from standard UNI EN ISO 527-2 [31]) and their gauge was 6 mm wide and 30 mm long.…”

Section: Mechanical Characterization Of the As-received Disksmentioning

confidence: 99%

Thermoplastic Disks Used for Commercial Orthodontic Aligners: Complete Physicochemical and Mechanical Characterization

et al. 2020

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Invisible orthodontic aligners (IOAs) have been introduced in the orthodontic field as an innovative alternative for fixed brackets, in relation to their ability to be easily inserted/removed from the oral cavity without affecting the chewing ability and the aesthetic of the patients. The paper provides a complete physicochemical and mechanical characterization of thermoplastic materials in the form of disks used for commercial IOAs. A wide palette of specific techniques is considered, from tensile tests and dynamic-mechanical analysis, to X-Ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transformation infrared spectroscopy (FTIR-ATR) analyses and water absorption tests. The disks are investigated before and after immersion into staining beverages (red wine, coffee, nicotine and artificial saliva), in terms of colour variations, transparency, and microscopic surface modifications by means of colorimetry, UV-VIS absorbance and scanning electron microscopy (SEM). Among all the samples, polyurethane (PU) exhibited the highest crystallinity and the highest values of mechanical and thermal resistance, while the poly(ethylene terephthalate)-glycol (PETG) samples presented better transparency and less ability to absorb water. Moreover, red wine and coffee give noticeable colour variations after 14 days of immersion, together with a slight reduction of transparency.

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“…In view of the increasing use of thermoplastic aligners either as orthodontic treatment adjuncts for "invisible" orthodontics or as passive appliances used at the retention phase, this systematic review comes timely for a comprehensive assessment on safety considerations after quite a few years of clinical use. As evidence from in-vitro studies seems to accrue, albeit within a limited speed rate, data from clinical trials on safety of thermoplastic appliances used for orthodontic-related reasons, currently lags behind; Notwithstanding this, physical and mechanical properties of thermoplastic adjuncts prior to or after intraoral service, have gained a considerably higher amount of interest in the scientific community, allied with their clinical use, with material conformation and thermoforming effect being the most eminent prognostic factors for the appliances' properties' variability [30,31]. On safety grounds, with regard to BPA leaching, only one high risk of bias and low quality of the evidence trial has been published up to date.…”

Section: Summary Of the Evidencementioning

confidence: 99%

Safety Considerations for Thermoplastic-Type Appliances Used as Orthodontic Aligners or Retainers. A Systematic Review and Meta-Analysis of Clinical and In-Vitro Research

et al. 2020

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Use of thermoplastic material in orthodontics, either as aligner or as retainer appliances, is common practice and is likely to increase in the years to come. However, no systematic assessment on safety considerations of these adjuncts has been implemented up to date. The aim of this systematic review was to collectively appraise the existing evidence from both clinical and laboratory studies, on whether these appliances are associated with any estrogenic/cytotoxic effects or bisphenol-A (BPA) and monomer leaching. Eight electronic databases were searched with no limits in December 22, 2019, for published and unpublished research. Eligibility criteria comprised of studies of any design, describing use of any type of thermoplastic aligner. Study selection, data extraction and risk of bias (RoB) assessment was done independently, either in duplicate or confirmed by a second reviewer. Random effects meta-analyses of weighted mean differences (WMD) with associated 95% Confidence Intervals (CIs) were planned. Quality of the evidence was evaluated with Grading of Recommendations Assessment, Development and Evaluation (GRADE). A total of 58 articles were initially identified, while 5 were included in qualitative synthesis and 2 of those contributed to the quantitative syntheses. Four studies were in-vitro, while one was a randomized controlled trial; all assessed some type of orthodontic aligner or retainer, either as-received or retrieved. Risk of bias recordings ranged between unclear and high for all studies. Proliferation induction capacity of thermoplastic appliances’ eluents on MCF-7 cells failed to be confirmed compared to beta-estradiol (2 studies: 5% v/v, WMD: −182.08; 95% CI: −198.83, −165.33; p-value < 0.001; and 20% v/v, WMD: −184.53; 95% CI: −206.17, −162.88; p-value < 0.001). No cytotoxic activity was detected as well. In addition, although evidence from in-vitro studies was indicative of no traceable detection of BPA or other monomers, the findings from a single clinical trial were allied to increased levels of BPA in whole stimulated saliva, after up to 30 days of thermoplastic retainer usage, compared to standard Hawley retainer. The quality of the evidence overall was low to medium. Current data from in-vitro research are indicative of an absence of an estrogenic or cytotoxic effect of thermoplastic aligners or retainers. Regarding BPA or monomer release, evidence from clinical and laboratory studies appear inconsistent.

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Effects of thermoforming on the physical and mechanical properties of thermoplastic materials for transparent orthodontic aligners

Cited by 109 publications

References 28 publications

Mechanical Properties of Thermoplastic Polymers for Aligner Manufacturing: In Vitro Study

Mechanical Properties of Thermoplastic Polymers for Aligner Manufacturing: In Vitro Study

Thermoplastic Disks Used for Commercial Orthodontic Aligners: Complete Physicochemical and Mechanical Characterization

Safety Considerations for Thermoplastic-Type Appliances Used as Orthodontic Aligners or Retainers. A Systematic Review and Meta-Analysis of Clinical and In-Vitro Research

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