Mechanical properties of “two generations” of teeth aligners: Change analysis during oral permanence

Condò, Roberta; Pazzini, Luca; Cerroni, Loredana; Pasquantonio, Guido; Laganà, Giuseppina; Pecora, A.; Mussi, Valentina; Rinaldi, Antonio; Mecheri, Barbara; Licoccia, Silvia; Maiolo, Luca

doi:10.4012/dmj.2017-323

Cited by 57 publications

(52 citation statements)

References 35 publications

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“…SmartTrack (LD30; Align Technology) material is a multilayer aromatic thermoplastic polyurethane/ copolyester. 19 With respect to the previous EX30 material used, LD30 exhibited a more amorphous structure and a greater elastic recovery, 27 and its use is considered safe. 28 Polymer structures can be affected by different processes of production (molding, cooling, trimming).…”

Section: Discussionmentioning

confidence: 99%

Micro computed tomography evaluation of Invisalign aligner thickness homogeneity

Mantovani¹,

Parrini²,

Coda³

et al. 2021

The Angle Orthodontist

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Objectives To measure the thickness homogeneity of Invisalign (Align Technology Inc, San José, Calif) aligners with micro-computed tomography (micro-CT) scans. Materials and Methods Starting from micro-CT scanning of 20 different aligners, multiplanar reconstructions were obtained. An orthodontist blinded about the study measured aligner thickness in different regions (molar, canine, incisor) and in different sites (gingival–buccal, buccal, occlusal, lingual, and gingival–lingual). To assess various thicknesses in different aligner sites and regions, the sample was stratified into subgroups and linear regression analysis was performed. Results Descriptive analysis showed that mean thickness of aligners in the incisor region ranged from 0.582 mm to 0.639 mm, in the canine region from 0.569 mm to 0.644 mm, and in the molar region from 0.566 mm to 0.634 mm. Student's t-tests showed no significant differences in the aligner thickness of different regions when data were stratified by different sites. Student's t-tests showed significant differences in thickness homogeneity for the molar region when the data were stratified by tooth (mean difference = 0.068 mm; 95% confidence interval, 0.009–0.126 mm; P = .024). Conclusions Invisalign aligner thickness is characterized by small differences. The only significant difference was revealed in the molar region where thickness of the gingival–lingual edge is significantly thinner than that measured at the occlusal aspect. From a clinical perspective, the results of the present study could be considered to explain the reduced predictability of several orthodontic tooth movements in the molar region.

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Section: Discussionmentioning

confidence: 99%

Micro computed tomography evaluation of Invisalign aligner thickness homogeneity

Mantovani¹,

Parrini²,

Coda³

et al. 2021

The Angle Orthodontist

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“…Bradley et al [13] carried out a study on the same topic of Eliades and Bourauel [21] focusing on the comparison of chemical properties of Invisalign™ appliances before and after their use. Condò et al [22] made, instead, an in-vitro study focused on the analysis of mechanical and chemico-physical properties of two different polymeric orthodontic aligners, Exceed30 and Smart Track, before and after use. In particular, they used a transversal approach relying on different characterization techniques (i.e., Fourier transform infrared spectroscopy, micro-Raman spectroscopy, X-ray diffraction, tensile and indentation strength test) [21].…”

Section: Discussionmentioning

confidence: 99%

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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“…It is crucially important to measure thickness changes of the occlusal surface as they might be influenced not only by factors that can be easily studied in in vitro experiments, such as temperature and humidity, but also by different oral functional and parafunctional activities (chewing, talking, drinking, swallowing, clenching or grinding). Due to the difficulties in monitoring the intraoral environment, the previous researches assessing the mechanical and dimensional proprieties of orthodontic thermoplastic materials were performed in a simulated intraoral environment with artificial saliva and/or on fragments or specimens of retrieved aligners [13, 18, 20–22]. The methodology of the current study allowed to analyse the surface dimension of the entire aligner at different reference points, overtaking the limitations related to the not uniform structure of the aligner.…”

Section: Discussionmentioning

confidence: 99%

“…Numerous previous researches studied the mechanical and aesthetic properties of biomaterials for their application in the orthodontic field [14–16]. Nowadays, thermoplastic materials are widely used for the fabrication of CA due to their excellent characteristics [15, 17, 18]. In particular, polyester, copolyester, polycarbonate, thermoplastic polyurethanes and polypropylene are the dominant thermoplastic material mixtures used for the manufacture of CA [19].…”

Section: Introductionmentioning

confidence: 99%

Thickness of orthodontic clear aligners after thermoforming and after 10 days of intraoral exposure: a prospective clinical study

et al. 2019

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Background Clear aligners (CA) are among the most chosen orthodontic therapies for patients who require an invisible treatment. Previous studies showed that the thermoforming process and the complexity of the intraoral environment might alter the properties of these devices. The aim of the current prospective clinical study was to assess the thickness changes of the CA after 10 days of intraoral use. The secondary aim was to assess the reproducibility of the thermoforming process, in terms of aligner thickness. Materials and methods CA from 18 consecutive patients (13 women, 5 men, mean age 28.8 ± 9.6 years) were investigated. Before intraoral exposure (T0), the thickness of the unused CA was measured at different occlusal points on a 3D model with a dedicated software (Geomagic Qualify 2013; 3D Systems, Rock Hill, SC, USA). Two CA configurations were studied: passive maxillary aligner (P—no tooth movement; no shape for attachments) and active maxillary aligner (A—tooth movement; shape for attachments and divot). The used aligners were returned after 10 days (T1) and the thickness measurements were repeated. A Student’s t test for paired data (T1 vs. T0) was applied to compare the thicknesses of used and unused devices (significance level after Bonferroni correction for multiple comparison was set at p < 0.0014). Furthermore, to study the reproducibility of the thermoforming process, P and A aligners were thermoformed twice, and the thicknesses of the two unused thermoformed devices were compared by means of Student’s t test for paired data (significance level after Bonferroni correction for multiple comparison was set at p < 0.0014) and Dahlberg’s error. Results The thermoforming process showed good reproducibility for both aligner configurations, with a maximum Dahlberg’s error of 0.13 mm. After intraoral use, the thickness of P showed some statistically significant, but not clinically relevant, thickness changes as compared to the unused aligners, while A did not show any significant changes. Conclusion Considering the thickness changes, the thermoforming process is reliable both with active and passive aligner configurations. Also, the CA examined show good thickness stability after physiological intraoral ageing in a population of healthy adults.

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Mechanical properties of “two generations” of teeth aligners: Change analysis during oral permanence

Cited by 57 publications

References 35 publications

Micro computed tomography evaluation of Invisalign aligner thickness homogeneity

Micro computed tomography evaluation of Invisalign aligner thickness homogeneity

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

Thickness of orthodontic clear aligners after thermoforming and after 10 days of intraoral exposure: a prospective clinical study

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