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Objective: The aim of this study was to compare the mechanical properties of orthodontic aligners among different commercially available 3D printing devices. Materials and Methods: Five 3D printers (Ka:rv LP 550, Swinwon; "KAR"), (L120, Dazz 3D; "L12"), (MiiCraft 125, Miicraft Jena; "MIC"), (Slash 2, Uniz; "SLS") and (Pro 95, SprintRay; "PRO") were used to prepare orthodontic aligners with dental resin (Tera Harz TC‐85DAW, Graphy). The central incisors of each aligner were cut, prepared and evaluated in terms of Martens‐Hardness (HM), indentation‐modulus (EIT) and elastic‐index (ηIT) as per ISO14577‐1:2002. Force‐indentation curves were recorded and differences among printers were checked with generalized linear regressions (alpha=5%). Results: Statistically significant differences were seen for all mechanical properties (P <.05), which were in descending order: HM (N/mm2) as median (Interquartile Range [IQR]): SLS 108.5 (106.0‐112.0), L12 103.0 (102.0‐107.0), KAR 101.5 (97.5‐103.0), MIC 100.0 (97.5‐101.5) and PRO 94.0 (93.0‐96.0); EIT (MPa) as mean (Standard Deviation [SD]): SLS 2696.3 (124.7), L12 2627.8 (73.5), MIC 2566.2 (125.1), KAR 2565.0 (130.2) and PRO 2491.2 (53.3); and ηIT (%) as median (IQR): SLS 32.8 (32.3‐33.1), L12 31.6 (30.8‐32.3), KAR 31.3 (30.9‐31.9), MIC 30.5 (29.9‐31.2) and PRO 29.5 (29.1‐30.0). Additionally, significant differences existed between liquid crystal display (LCD) and digital light processing (DLP) printers for HM (P <.001), EIT (P =.002) and ηIT (P <.001), with aligners from the former having higher values than aligners from the latter printer. Conclusion: Under the limitations of this study, it may be concluded that the mechanical properties of 3D‐printed orthodontic aligners are dependent on the 3D printer used, and thus, differences in their clinical efficacy are anticipated. [ABSTRACT FROM AUTHOR]

Background Although ceramic brackets have been extensively used for decades in orthodontics there is not till today any study focusing on the possible deterioration of mechanical properties after in vivo ageing. Objectives To determine whether the mechanical properties of alumina orthodontic brackets change after intraoral ageing thereby assessing the validity of a theoretical model established for the performance of ceramics in wet environments. Materials and methods Two alumina brackets, one single crystal (Radiance, American Orthodontics, Sheboygan, WI) and one polycrystalline (Clarity, 3M, St. Paul, MN) were included in this study. Ten brackets for each group were collected from different patients after a minimum of 3-month intraoral exposure, whereas as-received brackets of the same manufacturers were used as controls. The specimens were subjected to Raman spectroscopy and were then embedded in epoxy resin and metallographic ground and polished. The mechanical properties of four groups (radiance control: RAC, radiance-retrieved RAR, clarity control: CLC and clarity-retrieved CLR) were determined using instrumented indentation testing according to ISO 14577-2002. The mechanical properties tested were Martens hardness (HM), indentation modulus (E IT), the ratio of elastic to total work, commonly known as elastic index (η IT), and fracture toughness (K IC). The numerical results were statistically analysed employing two-way analysis of variance (ANOVA) and Tukey multiple comparison test at a = 0.05. Results Raman analysis revealed that both brackets are made of a-Al2O3 (corundum). No statistically significant differences were found for HM (N/mm2): RAC = 7249 (1507), RAR = 6926 (1144), CLC = 8052 (1360), CLR = 7390 (2393), or for E IT (GPa): RAC = 141 (27), RAR = 139 (23), CLC = 139 (28), CLR = 131 (47). However, significant differences were identified between the two alumina brackets tested for η IT (%): RAC = 55.7 (4.2), RAR = 54.0 (3.5), CLC = 62.5 (4.4), CLR = 61.8 (4.7), while K IC was measured only for the polycrystalline bracket (Clarity) because of the complicated fractured pattern of the single-crystal bracket. Both brackets share equal HM and E IT before and after orthodontic intraoral ageing. Limitations Whereas the study assessed the changes after intraoral exposure per theoretical model, which describes the reduction of critical stress to induce fracture after wetting, long-term intraoral ageing could have induced more pronounced effects. Conclusions/Implications The results of this study indicate that 3 months of intraoral ageing do not change the mechanical properties of single-crystal and polycrystalline orthodontic brackets tested, thus indicating that the Griffith theory may not be applied to the case of manufactured ceramic brackets owing possibly to internal defects. [ABSTRACT FROM AUTHOR]

To characterize the effect of elemental composition and manufacturing process on the electrochemical properties of Co-Cr-Mo, Co-Cr-W and Co-Cr-Mo-W alloys. Six Co-Cr based alloys were included in this study. All alloys are Co-Cr based alloys, classified in three different types according to their elemental composition. The first group has Mo as the third alloying element while the second one has W instead of Mo. The third one has both alloying elements. The groups are further divided by the manufacturing process (casting or Selective Laser Melting(SLM)). All groups were subjected to static immersion, open circuit potential, anodic scan, SEM/EDX analysis, static and cyclic tarnish testing according to ISO 10271 requirements. The ionic release was evaluated by inductively coupled plasma mass spectrometry and the results were statistically analyzed by two way ANOVA and Tukey test (a=0.05). No statistical differences were identified for Co-Cr-Mo alloy for all elements and their total ionic release between casting and SLM manufacturing processes, in contrast to significantly lower values for SLM groups for the other two groups. All groups tested demonstrated similar performance in OCP and AS testing while no gross elemental changes before and after AS were identified following EDX analysis. All alloys fulfilled the requirements of tarnish resistance The ionic release is dependent on alloy type and manufacturing process while all groups were found to fulfill the requirements of international standards for ionic release, corrosion and tarnish resistance and thus an acceptable clinical performance is anticipated. [ABSTRACT FROM AUTHOR]

Objective: The objective of this study was to examine the impact of intraoral aging on the mechanical properties of directly printed aligners (DPA) compared to thermoformed aligners (TA)., Materials and Methods: This prospective in vivo experiment included three types of aligners: DPAs (group DP) fabricated from Tera Harz TC-85 DAC resin (Graphy, Korea), TA (group INV) made from a polyurethane-based polymer (Align Technology, Inc., CA, USA), and TA (group DUR) made from polyethylene glycol terephthalate based polymer (Scheu-Dental, Germany). Each group was categorized into retrieved (Clin) and unused aligners (Ctr). Thirty patients (10 per group) wore the aligners for 7 days, thereby generating the retrieved samples. Thirty unused aligners were employed as control samples. The following mechanical properties were determined: Martens Hardness (HM), indentation modulus (EIT), elastic index (ηIT), and indentation relaxation (RIT). Intergroup comparisons were conducted using ANOVA/Kruskal-Wallis test. Comparisons between retrieved and control samples were done using Wilcoxon-Mann-Whitney-U/Student's t-test/Welch's test., Results: Statistically significant differences between the groups were found for both control and used samples (P < .001). Pairwise comparisons also revealed significant differences between the samples. The mechanical properties did not differ significantly between unused and retrieved INV- and DUR-aligners, whereas for DP-aligners significant differences for ηIT and RIT were found following intraoral service (P-values .012 and .002, respectively)., Conclusions: Group DUR showed generally more favorable mechanical properties compared to DP and INV. The much higher RIT and EIT in DP aligners suggest their higher rigidity and force decay, which could compromise their clinical efficacy., (© The Author(s) 2023. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Objectives: Three-dimensional (3D)-printed aligners present a promising orthodontic treatment modality, whose clinical success largely depends on the material's mechanical properties. The aim of this study was to evaluate the mechanical properties of resin-made 3D-printed aligners and assess the effect of two different post-curing conditions., Materials and Methods: Forty dumbbell-shaped specimens and 40 resin aligners were 3D-printed and divided into four equal groups according to post-curing conditions: presence or absence of oxygen during post-curing and water heat treatment at 85°C for 15 s or none. Samples from the central incisor of the aligner (n = 5/group) were studied by Attenuated Total Reflection Fourier-transform infrared spectroscopy (ATR-FTIR). The dumbbell-shaped specimens were loaded up to fracture under tensile mode and yield strength, ultimate tensile strength, elastic and plastic strain were calculated. The first mandibular molar area from 3D-printed aligners (n = 10/group) was cut and embedded in acrylic resin and then underwent metallographic grinding and polishing followed by instrumented indentation testing to determine the following mechanical properties: Martens hardness, indentation modulus, elastic index, and indentation relaxation. After descriptive statistics, differences according to each post-curing protocol, as well as their combination, were analyzed with linear regression modeling at a 5% significance level., Results: All groups showed identical ATR-FTIR spectra, while no statistically significant effects were seen for either post-curing protocol (N2 presence and heat treatment) or their combination (P > .05 in all instances)., Conclusions: The mechanical properties of 3D-printed resin aligners were not considerably affected either by post-curing in N2 atmosphere or heat treatment., (© The Author(s) 2023. Published by Oxford University Press on behalf of the European Orthodontic Society.)

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., (© The Author(s) 2021. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

The aim of this study was to estimate the possible changes of surface roughness and the mechanical properties of Invisalign ® appliances over one- and two-week of service. Forty appliances with attachments were retrieved after the end of orthodontic treatment from different patients. Half of them had been used for one week (1W), and the rest for two weeks (2W). Ten unused Invisalign ® appliances were used as the control (CON). An equal number of teeth possessing attachments were cut of aligners deriving from all groups (1W, 2W, and CON), and the Sa, Sq, Sz, Sc, and Sv roughness parameters of the internal surface of the aligner attachment area and the opposite lingual side (which was in contact to enamel) were determined by optical profilometry. Then, ten first molars originating from all groups were embedded in acrylic resin, and were ground and polished. Instrumented indentation testing (IIT) was performed in order to determine the Martens hardness (HM), indentation modulus (E IT ), and relaxation index (R IT ), according to ISO 14577-2002. The produced data were statistically processed by one- or two-way analysis of variance (ANOVA) and multiple comparison post-hoc tests (a = 0.05). Both the surface roughness and mechanical properties of the retrieved groups (1W and 2W) showed statistically significant differences compared with CON, but without statistically significant differences between each other. The roughness variables of the as-received material were shown to be reduced after intraoral service demonstrating a wear effect. Ageing has a detrimental effect on the surface roughness and mechanical properties of Invisalign ® appliances, although this effect is restricted to the first week of clinical usage.