Effect of printing orientation on mechanical properties of 3D-printed orthodontic aligners

PURPOSE

The purpose of this study was to assess differences in the fundamental mechanical properties of resin-made three-dimensional (3D) printed orthodontic aligners according to the printing orientation.

METHODS

Twenty resin 3D-printed dumbbell-shaped specimens and 20 orthodontic aligners were fabricated and postcured in nitrogen. Half of the specimens and aligners were built in horizontal (H), the other half in vertical (V) directions. The dumbbell-shaped specimens were loaded in a tensile testing machine, while parts of the aligners were embedded in acrylic resin, ground, polished, and then underwent instrumented indentation testing (IIT). Mechanical properties that were assessed included the yield strength (YS), breaking strength (BS), plastic strain (ε), Martens hardness (HM), indentation modulus (EIT), elastic index (ηIT), and indentation relaxation (RIT). Data were analyzed statistically with independent t‑tests or Mann-Whitney tests at α = 5%.

RESULTS

No significant differences were found between specimens or aligners printed either in a horizontal or a vertical direction (P > 0.05 in all instances). Overall, the 3D-printed aligners showed acceptable mechanical propertied in terms of YS (mean 19.2 MPa; standard deviation [SD] 1.7 MPa), BS (mean 19.6 MPa; SD 1.2 MPa), ε (mean 77%; SD 11%), HM (median 89.0 N/mm2; interquartile range [IQR] 84.5-90.0 NN/m2), EIT (median 2670.5 MPa; IQR 2645.0-2726.0 MPa), ηIT (median 27.5%; IQR 25.9-28.1%), and RIT (mean 65.1%; SD 3.5%).

CONCLUSION

Printing direction seemed to have no effect on the mechanical properties of 3D-printed resin aligners, which are promising for orthodontic use.

Comparison of mechanical properties and color stability of various vacuum-formed orthodontic retainers: An in vitro study

Vacuum-formed retainer (VFR) is the most used retainer due to its higher aesthetic properties and lower cost, their mechanical properties of are important in determining the stability and long-term use of appliances made out of them.

AIM

This study aimed to evaluate and compare the flexural modulus, surface hardness, and color stability of three different VFR materials.

METHODS

Three different VFR materials, namely Duran, Keystone, and Zendura, of 1 mm thickness, were tested after thermoforming for flexural modulus, hardness, and color stability. They were formed over a stainless-steel model of 12 mm diameter and 6 mm height.

RESULTS

There were significant statistical differences (p = 0.000) in the flexural modulus and hardness of the three materials. Regarding color stability, Zendura exhibited significantly higher ΔE* values than Keystone and Duran (p < 0.05).

CONCLUSIONS

Zendura had the highest flexural modulus and hardness compared with Duran and Keystone; however, it is more susceptible to color change compared to the other tested materials.

Bisphenol-A release from thermoplastic clear aligner materials: A systematic review

AIM

The aim of the present study was to undertake a systematic review of the available evidence on the release of bisphenol-A (BPA) from thermoplastic materials used in the fabrication of clear aligners (CA).

METHODS

Electronic databases, such as MEDLINE (via PubMed), Google Scholar, Scopus, Cochrane Library, Web of Science, OpenGrey, and the U.S. National Institute of Heath-Clinical Trials, were searched up to 27 October 2022. In vivo/in vitro studies that assessed the release of BPA from different thermoplastic CA materials, with or without a control group, were selected. The risk of bias (RoB) in the randomised controlled trials (RCT) and in vitro studies was assessed using the Cochrane RoB tool and the guidelines for the reporting of pre-clinical studies, respectively. The quality of evidence was determined using the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) Pro tool.

RESULTS

Six studies were considered for review from a total of 1926 records. This included one RCT and five in vitro studies. Only two studies found leaching of BPA, while four did not report any traces. The RoB was found to be moderate to high. The GRADE evidence level ranged from low to very low. Five of the included studies were conducted in vitro. Significant heterogeneity among the included studies prevented a quantitative synthesis.

CONCLUSION

In light of the available conflicting evidence, BPA release from CAs can neither be confirmed nor denied. Safety remains questionable until high-quality in vivo trials prove otherwise.

REGISTRATION

PROSPERO CRD42022310434.

Predictability and Effectiveness of Nuvola® Aligners in Dentoalveolar Transverse Changes: A Retrospective Study

Nowadays, many people use clear aligners to address their dental issues. The efficacy of transparent dental aligners must be investigated even though they are more aesthetically pleasing, easy to use, and tidy than permanent tools. Thirty-five patients in this study's sample group who used Nuvola^® clear aligners for their orthodontic therapy were prospectively observed. Initial, simulated, and final digital scans were analysed with a digital calliper. The actual results were compared with the prescribed ending position to evaluate the efficacy of transversal dentoalveolar expansion. Aligner treatments in Groups A (12) and B (24), particularly in the dental tip measures, demonstrated high adherence to the prescription. On the other hand, the gingival measures exhibited a greater level of bias, and the differences were statistically significant. However, there was no difference in the outcomes between the two groups (12 vs. 24). Within specific parameters, the evaluated aligners were shown to be helpful in predicting movements in the transverse plane, particularly when considering movements linked to the vestibular-palatal inclination of the dental elements. This article compares the expansion effectiveness of Nuvola^® aligners compared with other work in the literature using competitor companies.

A Systematic Review and Network Meta-Analysis on the Impact of Various Aligner Materials and Attachments on Orthodontic Tooth Movement

The majority of patients strongly favor the use of aligners in the present time, especially with the advancement in esthetic dentistry. Today's market is flooded with aligner companies, many of which share the same therapeutic ethos. We therefore carried out a systematic review and network meta-analysis to evaluate research that had looked at various aligner materials and attachments and their effect on orthodontic tooth movement in relevant studies. A total of 634 papers were discovered after a thorough search of online journals using keywords such as "Aligners", "Orthodontics", "Orthodontic attachments", "Orthodontic tooth movement", and "Polyethylene" across databases such as PubMed, Web of Science, and Cochrane. The authors individually and in parallel carried out the database investigation, removal of duplicate studies, data extraction, and bias risk. The statistical analysis demonstrated that the type of aligner material had a significant impact on orthodontic tooth movement. The low level of heterogeneity and significant overall effect further support this finding. However, there was little effect of attachment size or shape on tooth mobility. The examined materials were primarily concerned with influencing the physical/physicochemical characteristics of the appliances and not tooth movement directly. Invisalign (Inv) had a higher mean value than the other types of materials that were analyzed, which suggested a potentially greater impact on orthodontic tooth movement. However, its variance value indicated that there was also greater uncertainty associated with the estimate compared to some of the other plastics. These findings could have important implications for orthodontic treatment planning and aligner material selection. Registration: This review protocol was registered on the International Prospective Register of Systematic Reviews (PROSPERO; registration number: CRD42022381466).

Farklı Şeffaf Plak Materyallerinin Mekanik Özelliklerinin Araştırılması

Amaç: Şeffaf plak tedavisinin başarılı olabilmesi için, plak materyalinin çevre periodontal dokulara zarar vermeden istenilen diş hareketlerini yaptırabilecek yeterli ortodontik kuvveti sağlaması gerekmektedir. Şeffaf plakların malzemesinin mekanik özellikleri üretilen ortodontik kuvvet için kritik bir role sahip olduğu bilinmektedir. Bu çalışmada, farklı şeffaf plak materyallerinin ortodontik kuvveti etkileyebilecek mekanik özelliklerinin değişimlerinin tespiti ve etkilerinin incelenmesi amaçlanmıştır. Bu çalışmanın sıfır hipotezi, termoplastik malzemelerden elde edilmiş farklı şeffaf plak materyallerinin farklı mekanik özellikler göstermesi sebebiyle CA Pro, GT Flex, Zendura Flex, Zendura, Taglus ve GT Pro plak materyallerinin mekanik özelliklerinin incelenmesidir.Yöntem: Çalışmada 6 farklı şeffaf plak materyalinin (CA Pro, GT Flex, Zendura Flex, Zendura, Taglus, GT Pro) mekanik özelliklerini belirlemek amacıyla ilgili standartlara uygun olarak çekme deneyleri yapılmıştır. Çekme deneyi sonuçlarından materyellerin gerilme uzama eğrilerinin yanında elastisite modülü, çekme dayanımı ve kopma uzaması parametreleri elde edilmiştir. Sonuçlar istastiksel olarak değerlendirilmiş ve materyallerin mekanik özellikleri yorumlanmıştır.Bulgular: Materyal türlerine göre elastisite modülü, çekme dayanımı ve kopma uzaması ölçümleri istatistiksel olarak anlamlı farklılık göstermiştir (p=0,001; p&lt;0,01). Yapılan ikili karşılaştırmalar değerlendirildiğinde en düşük elastisite modülü ve çekme dayanımı değerine Zendura Flex materyalinin sahip olmasının istatistiksel olarak anlamlı olduğu tespit edilmiştir.Sonuç: Çalışmanın sonuçlarına göre çok katmanlı yapıda olan Zendura Flex ve CA Pro materyalleri, en düşük elastisite modülü ve bu sonucu destekleyecek şekilde en düşük çekme dayanımı değerleri göstermiştir. Çalışmanın sonuçları farklı şeffaf plak materyallerinin farklı mekanik özellikler gösterdiğini desteklemiştir. Şeffaf plak tedavisinin başarısını arttırmak amacıyla plak materyalleri mekanik özelliklerinin iyi bilinmesi ile uygun plak materyallerinin belirlenebileceği öngörülmüştür.

Efficacy of Anterior Tooth Simulations with Clear Aligner Therapy - A Retrospective Cohort study of Invisalign and Flash Aligner Systems

Purpose:

The purpose of this study was to compare the efficacy of tooth movement between two clear aligner systems by comparing the predicted treatment outcomes versus actual outcomes achieved using a 3D best-fit algorithm.

Materials & Methods:

Clear aligner therapy (CAT) was used to treat 62 patients; n=38 Invisalign® and n=24 Flash®. The Invisalign group had a male to female distribution of 13:25 and a mean age of 35.5, while the Flash group had a male to female distribution of 6:18, with a mean age of 29.2. Differences in predicted versus achieved actual outcomes were compared using eModel Compare 8.1 software.

Results:

1) Intra-group differences between predicted and achieved tooth movements for angular movements were statistically (P<0.05) and clinically (>2°) significant with both treatment methods, except for tipping of maxillary and mandibular incisors for Flash® (<2◦). 2) Inter-group results demonstrated statistically significant differences in favor of Flash® for maxillary central incisor Tip (1.3°), BL movements for maxillary canines (0.1mm), and mandibular central incisor Rotations (1°). These did not exceed the threshold for the clinical relevance of 2° or 0.5mm.

Conclusions:

There were no differences in clinical accuracy and efficacy between Invisalign or Flash aligner systems in achieving predicted tooth movement.

Structural Conformation Comparison of Different Clear Aligner Systems: An In Vitro Study

The aim of this study was to evaluate the structural conformations of three clear aligner systems, Eon^®, SureSmile^®, and Clarity^®, and compare them with the most commonly used system, Invisalign^®. Clear aligner samples from Invisalign^®, Eon^®, SureSmile^®, and Clarity^® were cut into 5 × 5 mm squares and exposed to artificial saliva for 2 weeks. The specimens were then subjected to a Vickers hardness test by applying three separate indentations with a 25 gf load for 15 s. Hardness was calculated using the following formula: Vickers hardness number = 1.854 (F/D2). Fourier transform infrared spectroscopy (FTIR) analysis was performed, with a diamond hemisphere and infrared beam being allowed to pass through each specimen. A mid-infrared range from 4000 to 375 cm⁻¹ was recorded. The samples were also evaluated using scanning electron microscopy (SEM) combined with energy-dispersive X-ray microanalysis spectroscopy at different magnifications. No statistically significant differences were observed between the included systems with regard to hardness. All systems showed a polyurethane-based material, as illustrated by the FTIR analysis. Some structural variations were noted in the Invisalign^® system, which had a more homogeneous architecture. Statistically significant differences in the carbon weights were found among the systems. The four systems presented comparable hardness levels. Mild molecular composition differences were found, but all systems had the similarity of being composed of a polyurethane-based material. Carbon and oxygen were the main elements, as they were located in all studied clear aligners. The SEM analysis revealed that Invisalign^® had a smoother surface than the other three systems. All included clear aligners had similar characteristics with minimal differences, providing a wide variety of options for clinical orthodontic treatment according to patients’ demands.

In-house 3D-printed aligners: effect of in vivo ageing on mechanical properties

OBJECTIVE

To investigate alterations in the mechanical properties of in-house three-dimensional (3D) printed orthodontic aligners after intraoral ageing.

MATERIALS AND METHODS

Sixteen 3D-printed aligners (TC-85DAC resin, Graphy, Seoul, Korea) were used for the purpose of the study, which were divided into 10 control (not used) aligners and 6 materials retrieved from 4 patients after 1-week service (retrieved group). Samples from the control group were analysed by attenuated total reflectance-Fourier-transform infrared (ATR-FTIR) spectroscopy. Samples from control/retrieved groups were embedded resin and subjected to instrumented indentation testing (IIT) to record force-indentation depth curves, calculating the following (as per ISO 14577-1, 2002 standard): Martens hardness (HM), indentation modulus (EIT), and elastic index (ηIT), and the indentation relaxation index (RIT). Differences between control and retrieved 3D-printed aligners were checked with Mann-Whitney/t-tests at an alpha = 5%.

RESULTS

ATR-FTIR analysis showed that aligners were made of a vinyl ester-urethane material. The results of the IIT testing were: HM (control: median 91.5 N/mm2, interquartile range [IQR] 88.0-93.0/as-retrieved: median 90.5 N/mm2, IQR 89.0-93.0); EIT (control, mean 2616.3 MPa, standard deviation [SD] 107.0 MPa/retrieved, mean 2673.2 MPa, SD 149.4 MPa); ηIT (control: median 28.6%, IQR 28.2-30.9%/as-retrieved: median 29.0%, IQR 28.7-29.2%); and RIT (control: median 45.5%, IQR 43.0-47.0%/as-retrieved: median 45.1%, IQR 45.0-45.3%). No differences between as-retrieved and control aligners were found for any of the mechanical properties tested (P > 0.05 in all instances).

CONCLUSION

The mechanical properties of the in-house 3D-printed aligners tested were not affected after 1 week in service period.

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

Aim of this in vitro study was to analyze structural properties of two different polymeric orthodontic aligners, Exceed30 (EX30) and Smart Track (LD30), before and after use. Forty patterns of aligners were randomly selected: 20 LD30 and 20 EX30, worn intra-orally for 14±3 days, 22 h/day. From each aligner, 10 specimens were prepared from buccal surfaces of the incisor region by the cutting of samples 5×5 mm under a stereomicroscope. All samples were subjected to Fourier transform infrared spectroscopy, micro-Raman spectroscopy, X-ray diffraction, tensile and indentation strength test. LD30 appeared more homogeneous, with a crystalline fraction lower than EX30 and exhibited a higher elastic behavior and a lower tendency to warp after use than EX30. LD30 demonstrated better adaptability to the dental arch and greater consistency of application of orthodontic forces than produced with EX30. However, both materials showed structural modifications that resulted in increased sample hardness and hyper-plasticity.