Comparative analysis of passive play and torque expression in self-ligating and traditional lingual brackets.

INTRODUCTION: The aim of this study was to determine and compare the play and torque expression of self-ligating and conventionally ligated lingual brackets, with square and rectangular slots, when engaged with archwires of different size, cross section and material. METHODS: Passive play and torque expression of 3 types of archwires and 5 types of brackets from four different manufacturers were measured and compared using a dynamometer. Each archwire was tested five times in each bracket; passive play was compared to ideal values, while torque expression was tested at 5, 10 and 20 Nmm as clinically efficacious values. RESULTS: Regarding full thickness stainless steel archwires, the lowest passive play was found in STb brackets (2.66 ± 0.89°, Ormco, Glendora, CA, USA), which was statistically significantly lower than for ALIAS brackets (4.44 ± 0.75°, Ormco), In-Ovation L brackets (6.14 ± 3.22°, Dentsply GAC, Bohemia, NY, USA), Harmony brackets (7.76 ± 2.94°, American Orthodontics, Sheboygan, WI, USA) and eBrace brackets (9.46 ± 3.94°, Riton Biomaterial, Guangzhou, China). Increasing the torsional load to the greatest torsional load clinically applicable, there were no statistically significant differences between STb, ALIAS, In-Ovation L and Harmony brackets. CONCLUSIONS: STb and ALIAS brackets generated the lowest passive play; STb and In-Ovation L brackets showed the lowest angle of play at the greatest torque expression. These measurements allow to understand the accuracy of lingual systems and at the same time the amount of overcorrections to be applied in the setup in order to obtain high quality orthodontic treatments.

Stress Relaxation Properties of Five Orthodontic Aligner Materials: A 14-Day In-Vitro Study.

We aimed to investigate the stress relaxation properties of five different thermoplastic aligner materials subjected to 14 days of constant deflection. Five different thermoplastic aligner materials were selected, whose elastic properties varied: F22 Evoflex, F22 Aligner, Durasoft, Erkoloc-Pro and Duran. The static properties of these materials-in particular, stiffness, stress-strain curve and yield stress-were measured with a three-point bending test. For all the tests that were performed, a minimum of three samples per material were tested. The yield load, yield strength, deformation and particularly the stiffness of each material were found to be similar in the single-layer samples, while the double-layer samples showed far lower stiffness values and were similar one to another. F22 Evoflex and Erkoloc-Pro maintained the highest percentages of stress, 39.2% and 36.9%, respectively, during the 15-day period. Duran and Durasoft obtained the lowest final stress values, 0.5 MPa and 0.4 MPa, respectively, and the lowest percentage of normalized stress, 4.6% and 3.9%, respectively, during the 15-day period. All the materials that we tested showed a rapidity of stress decay during the first few hours of application, before reaching a plateau phase. The F22 Evoflex material showed the greatest level of final stress, with relatively constant stress release during the entire 15-day period. Further research after in vivo aging is necessary in order to study the real aligners' behavior during orthodontic treatment.

Glycolysis of semi-interpenetrated polymer network foam based on poly(vinyl chloride) for recovery and reuse of the individual components.

Rigid semi-Interpenetrated Polymer Network (semi-IPN) foam based on poly(vinyl chloride) (PVC) and crosslinked polyurea/isocyanurate are complex materials that at present are not recyclable. They are used in many fields, including wind blade cores. In this work we studied the depolymerization of the crosslinked portion of the foam under glycolysis conditions for the separation and reuse of the individual components. Reaction products were characterized by FT-IR, NMR, solvent solubility, DSC, elemental analysis, titration of amine and hydroxyl groups and rheology measurements. Triisocyanurates and urea moieties were synthesized and used as model compounds. Glycolysis conditions were optimized to maximize depolymerization while minimizing PVC degradation. The parameters studied were reaction time (8 min to 3 h), temperature (155 to 200 °C), catalyst (potassium acetate or dibutyl tin dilaurate (DBTL)), glycol (ethylene glycol, 1,4 butanediol, diethylene glycol, dipropylene glycol, polyethylene glycol), as well as the effect of PVC thermal stabilizers such as hindered phenols and organo-phosphites. The results showed that the optimal reaction condition for foam glycolysis is 165-175 °C for 20-30 min, using DBTL as catalyst and including thermal stabilizers. No drastic difference was noticed by the kind of glycol used, except for PEG that led to greater PVC degradation. The greatest part of the crosslinked portion (≥90 %) was depolymerized and the result were mainly hydroxyl- and in minor amount amine- terminated oligomers. The recovered PVC (purity roughly 90 %) had a low degree of degradation and a viscosity suitable for its processing as thermoplastic material, i.e. by injection moulding.

Tribological Behavior of a Rubber-Toughened Wood Polymer Composite.

Wood polymer composites or WPCs are increasingly used as substitutes for natural wood in outdoor applications due to their better environmental sustainability and the consequent reduction in carbon footprint. In this paper, the presence of an elastomer used as a toughening agent (Santoprene by Exxon Mobil) in a polypropylene-based WPC containing 50 wt % wood flour was investigated in terms of its tribological behavior by dry sliding wear tests. These were performed after two environmental pre-conditioning treatments, i.e., drying and water soaking. The ball-on-disk configuration under a constant load was chosen along two sliding distances. Dynamic mechanical thermal analyses were used to reveal the effect of the toughening agent on the storage modulus and damping factor of the composites. Results in terms of weight loss measurement and coefficient of friction were obtained, together with surface morphology analysis of the worn surfaces at the scanning electron microscope and 3D profilometer. An abrasive wear mechanism was identified, and it was shown that the toughening agent improved wear resistance after both pre-treatments. This beneficial effect can be explained by the increase in strain at break of the WPC containing the elastomer. On the other hand, the water soaking pre-treatment produced severe damage, and the loss of material cannot be completely compensated by the presence of the toughening agent.

Impact of the European Union on access to medicines in low- and middle-income countries: A scoping review.

This Scoping Review synthesises evidence of the impacts of European Union (EU) law, regulation, and policy on access to medicines in in non-EU low- and middle-income countries (LMICs), and the mechanisms and nature of those impacts. We searched eight scholarly databases and grey literature published between 1995-2021 in four languages. The EU exerts global influence on pharmaceuticals in LMICs in three ways: explicit agreements between EU-LMICs (ex. accession, trade, and economic agreements); LMICs' reliance on EU internal regulation, standards, or methods (ex. market authorisation); 'soft' forms of EU influence (ex. research funding, capacity building). This study illustrates that EU policy makers adopt measures with the potential to influence medicines in LMICs despite limited evidence of their positive and/or negative impact(s). The EU's fragmented internal and external actions in fields related to pharmaceuticals reveal the need for principles for global equitable access to medicines to guide EU policy.

Esta revisión exploratoria sintetiza la evidencia disponible sobre el impacto que ejercen las leyes, las políticas y las regulaciones de la Unión Europea (UE) sobre el acceso a los medicamentos en países de bajo y mediano ingreso (PBMI) que no pertenecen a la UE. La búsqueda se realizó en ocho bases de datos académicas, incluyendo literatura gris. Se incluyeron publicaciones en cuatro idiomas entre 1995 y 2021. Como resultado principal se encontró que la UE ejerce su influencia sobre los productos farmacéuticos en los PBMI a través de tres mecanismos principales: i) acuerdos explícitos entre la UE y los PBMI, por ejemplo, acuerdos de ascensión a la UE o tratados comerciales, ii) utilización de la normativa, estándares o métodos de la UE por parte de los PBMI (reliance) para, por ejemplo, autorizar el ingreso de nuevos medicamentos a partir de la autorización previa por parte de la UE) y, iii) formas blandas de influencia de la UE, por ejemplo, a través de financiación a la investigación o al desarrollo de capacidades locales. Esta revisión revela que los tomadores de decisión de la UE adoptan medidas que, a pesar de la escasa evidencia que sustenta su impacto, positivo o negativo, tienen el potencial de influir en el acceso a los medicamentos de los PBMI. El accionar fragmentado de la UE respecto a los productos farmacéuticos, tanto a nivel interno como externo, son una clara muestra de la necesidad de crear principios que guíen las políticas de la UE frente al acceso equitativo a los medicamentos a nivel global.

A Review of Wood Polymer Composites Rheology and Its Implications for Processing.

Despite the fact that wood polymer composites are interesting materials for many different reasons, they are quite difficult to shape through standard polymer processing techniques, such as extrusion or injection molding. Rheological characterization can be very helpful for understanding the role played by the many variables that are involved in manufacturing and to achieve a good quality final product through an optimized mix of formulation and processing parameters. The main methods that have been used for the rheological characterization of these materials are capillary and parallel plate rheometry. Both are very useful: rotational rheometry is particularly convenient to investigate the compounding phase and obtain structural information on the material, while capillary viscometry is well suited to understand final manufacturing. The results available in the literature at the moment are indeed very interesting and are mostly aimed at investigating the influence of the material formulation, the additives in particular, on the structural, mechanical, and morphological properties of the composite: despite a good number of papers, though, it is difficult to draw general conclusions, as many issues are still debated. The purpose of this article was to overview the state of the art and to highlight the issues that deserve further investigation.

Correlation between Mechanical Properties and Processing Conditions in Rubber-Toughened Wood Polymer Composites.

The use of wood fibers is a deeply investigated topic in current scientific research and one of their most common applications is as filler for thermoplastic polymers. The resulting material is a biocomposite, known as a Wood Polymer Composite (WPC). For increasing the sustainability and reducing the cost, it is convenient to increase the wood fiber content as much as possible, so that the polymeric fraction within the composite is thereby reduced. On the other hand, this is often thwarted by a sharp decrease in toughness and processability-a disadvantage that could be overcome by compounding the material with a toughening agent. This work deals with the mechanical properties in tension and impact of polypropylene filled with 50 wt.% wood flour, toughened with different amounts (0%, 10%, and 20%) of a polypropylene-based thermoplastic vulcanizate (TPV). Such properties are also investigated as a function of extrusion processing variables, such as the feeding mode (i.e., starve vs. flood feeding) and screw speed. It is found that the mechanical properties do depend on the processing conditions: the best properties are obtained either in starve feeding conditions, or in flood feeding conditions, but at a low screw speed. The toughening effect of TPV is significant when its content reaches 20 wt.%. For this percentage, the processing conditions are less relevant in governing the final properties of the composites in terms of the stiffness and strength.

Characterization and Vibro-Acoustic Modeling of Wood Composite Panels.

Natural fiber-filled polymers offer good mechanical properties and economic competitiveness compared to traditional materials. Wood flour is one of the most widely used fillers, and the resulting material, known as wood plastic composite (WPC), has already found a wide applicability in many industrial sectors including automotive and building construction. This paper, as a followup of a previous study on a numerical-based approach to optimize the sound transmission loss of WPC panels, presents an extensive numerical and experimental vibro-acoustic analysis of an orthotropic panel made out of WPC boards. Both structural and acoustical excitations were considered. The panel radiation efficiency and its transmission loss were modeled using analytic and semi-analytic approaches. The mechanical properties of the structure, required as input data in the prediction models, were numerically determined in terms of wavenumbers by means of finite element simulations, and experimentally verified. The accuracy of the predicted acoustic performances was assessed by comparing the numerical results with the measured data. The comparisons highlighted a significant influence of the junctions between the WPC boards, especially on the panel's transmission loss. The radiation efficiency results were mostly influenced by the boundary conditions of the plate-like structure. This latter aspect was further investigated through a finite element analysis.

Assessment of stiffness and load deflection of orthodontic miniscrews used for palatal anchorage: An in vitro biomechanical study.

OBJECTIVE: The purpose of this study was to evaluate the biomechanical properties of miniscrews of 5 different lengths, 2 different diameters, and different combinations of insertion used for palatal skeletal anchorage. MATERIALS AND METHODS: Twenty-four different combinations of a total of 120 miniscrews of two different diameters (2.0mm and 2.3mm) and five different lengths (9mm, 11mm, 13mm and 15mm) were tested at different angles of insertion (90° and 45°) and distances from a synthetic bone block (3mm, 5mm, 7mm). Samples were fixed in an Instron Universal Testing Machine and a load was applied in single cantilever mode to the neck of each miniscrew. The stiffness and maximum load before permanent deformation were recorded. Model-based recursive partitioning testing (CART) was used to evaluate differences between groups. RESULTS: Significantly higher forces were necessary to deform miniscrews of diameter 2.3mm than those of 2.0mm, those inserted at an angle of 45° with respect to 90°, and at smaller distances between the miniscrew neck and block; in addition, the maximum load and stiffness increased with increasing screw length. CONCLUSION: This in vitro experimental study showed strong correlations between deformation load and miniscrew geometry, insertion angle and distance from the synthetic block, results that should be considered when planning miniscrew insertion in order to reduce the risk of unwanted fracture.

FDM 3D Printing of Polymers Containing Natural Fillers: A Review of their Mechanical Properties.

As biodegradable thermoplastics are more and more penetrating the market of filaments for fused deposition modeling (FDM) 3D printing, fillers in the form of natural fibers are convenient: They have the clear advantage of reducing cost, yet retaining the filament biodegradability characteristics. In plastics that are processed through standard techniques (e.g., extrusion or injection molding), natural fibers have a mild reinforcing function, improving stiffness and strength, it is thus interesting to evaluate whether the same holds true also in the case of FDM produced components. The results analyzed in this review show that the mechanical properties of the most common materials, i.e., acrylonitrile-butadiene-styrene (ABS) and PLA, do not benefit from biofillers, while other less widely used polymers, such as the polyolefins, are found to become more performant. Much research has been devoted to studying the effect of additive formulation and processing parameters on the mechanical properties of biofilled 3D printed specimens. The results look promising due to the relevant number of articles published in this field in the last few years. This notwithstanding, not all aspects have been explored and more could potentially be obtained through modifications of the usual FDM techniques and the devices that have been used so far.

Mechanical properties of multi-force vs. conventional NiTi archwires.

AIMS: Mechanical properties along the length of latest generation "multi-force" archwires were measured and compare with commercially available thermally activated and non-thermally activated nickel-titanium (NiTi) archwires. MATERIALS AND METHODS: A modified deflection test was used to produce load/deflection curves for different positions along the lengths of a sample of 114 NiTi archwires composed by thermal NiTi, non-thermal NiTi, two types of multi-force NiTi and one type of multi-force copper archwires of various cross-sections (0.016â€¯× 0.016 inch, 0.016â€¯× 0.022 inch, 0.018â€¯× 0.025 inch and 0.019â€¯× 0.025 inch). The length, slope and mean force expressed were calculated from the resulting unloading plateaus, enabling comparison between types of archwire at different points along their lengths. RESULTS: Among conventional thermal, conventional nonthermal and multiforce archwires, all parameters investigated were statistically different, whereby the performance of the latter was superior. Multi-force archwires displayed 27% and 31% lighter mean forces in the upper and lower arches, respectively, in addition to 62% and 40% reductions in unloading plateau slope and length, respectively, as compared to conventional CuNiTi wires. Comparison of the different types of multi-force wires tested revealed statistically significant differences in the three parameters, depending on the testing position but irrespective of their cross-section. CONCLUSIONS: Although conventional archwires display identical behaviour along their lengths, as advertised the multi-force archwires do indeed exert a progressive force which differs between anterior, medial and posterior sections. The multi-force wires provide lighter, more prolonged and constant forces than conventional wires without cross-section-dependent variation.

The mechanical behavior of as received and retrieved nickel titanium orthodontic archwires.

OBJECTIVES: The aim of this study is to investigate and compare the characteristics of as received and retrieved NiTi archwires at a constant temperature by plotting their load/deflection graphs and quantifying three parameters describing the discharge plateau phase. MATERIALS AND METHODS: Two hundred four NiTi archwires, traditional and heat-activated, of various cross sections, were obtained from 5 different manufacturers. Specimens prepared from the selected wires were subjected to a three-point bending test where 92 were retrieved through an in vivo retrieval protocol (crowding group C1 and group C2), 56 went through an in vitro retrieval protocol, and 56 were as received. The in vitro retrieval protocol was performed by a gear motor connected to a stainless steel support that performed fatigue cycles to the bent wires in artificial saliva. The load/deflection graphs of as received and retrieved wires were described through three parameters and the results were analyzed with classification and regression trees (CART) and analysis of variance (ANOVA). RESULTS: Statistically significant differences between as received and retrieved wires were found only for the parameter plateau slope which represents the constancy of force expressed by the wire. CONCLUSIONS: The aging of NiTi archwires influences the force constancy expressed. The behavior of the wires changes depending on the size, brand, and type of retrieval protocol. In terms of performance, the poorest is represented by all wires retrieved in vitro and in vivo group C2 (moderate to severe crowding).

Stress relaxation properties of four orthodontic aligner materials: A 24-hour in vitro study.

OBJECTIVE: To investigate the stress release properties of four thermoplastic materials used to make orthodontic aligners when subjected to 24 consecutive hours of deflection. MATERIALS AND METHODS: Four types of aligner materials (two single and two double layered) were selected. After initial yield strength testing to characterize the materials, each sample was subjected to a constant load for 24 hours in a moist, temperature-regulated environment, and the stress release over time was measured. The test was performed three times on each type of material. RESULTS: All polymers analyzed released a significant amount of stress during the 24-hour period. Stress release was greater during the first 8 hours, reaching a plateau that generally remained constant. The single-layer materials, F22 Aligner polyurethane (Sweden & Martina, Due Carrare, Padova, Italy) and Duran polyethylene terephthalate glycol-modified (SCHEU, Iserlohn, Germany), exhibited the greatest values for both absolute stress and stress decay speed. The double-layer materials, Erkoloc-Pro (Erkodent, Pfalzgrafenweiler, Germany) and Durasoft (SCHEU), exhibited very constant stress release, but at absolute values up to four times lower than the single-layer samples tested. CONCLUSIONS: Orthodontic aligner performance is strongly influenced by the material of their construction. Stress release, which may exceed 50% of the initial stress value in the early hours of wear, may cause significant changes in the behavior of the polymers at 24 hours from the application of orthodontic loads, which may influence programmed tooth movement.

Cognitive load in academic clinical simulation activities. Cross-sectional study / Carga cognitiva en actividades académicas de simulación clínica. Estudio de corte transversal

Abstract Introduction: Cognitive load determines working memory ability to store and retain information in long-term memory, thus conditioning learning. Objective: To compare cognitive loads among different simulation activities, including anesthesia and surgery simulation workshops in medical students. Methods: Cross-sectional analytical observational study. Two cognitive load measurement scales (Paas and NASA-TLX) were given to the students after each simulation workshop. Comparisons were made based on the scores derived from the scales. Results: Relevant differences were found in terms of the mental effort assessed by means of the Paas scale, as relates to student rotation order in the airway management workshop, with a greater effort being found in the group that rotated initially in surgery (6.19 vs. 5.53; p = 0.029). The workshop with the highest associated rate of frustration was the airway management workshop. Higher scores were obtained for this workshop in all the items of the NASA-TLX scale, reflecting a higher cognitive load when compared to the others. Conclusions: It was not possible to determine whether higher scores in some of the activities were associated with the inherent difficulty of airway management or the specific workshop design. Consequently, further studies are required to distinguish between those components in order to improve the way learning activities are designed.

Resumen Introducción: La carga cognitiva determina la capacidad que tendrá la memoria de trabajo para almacenar y grabar información en la memoria a largo plazo, lo cual condiciona el aprendizaje. Objetivo: Comparar la carga cognitiva entre las distintas actividades de simulación, incluyendo talleres de simulación de anestesiología y cirugía en estudiantes de medicina. Métodos: Estudio observacional analítico tipo corte transversal. Se aplicaron dos escalas de medición de la carga cognitiva (Paas y NASA-TLX) a los estudiantes después de cada taller de simulación. Se realizaron comparaciones de los puntajes obtenidos mediante las escalas. Resultados: Se encontraron diferencias relevantes en cuanto al esfuerzo mental evaluado por la escala de Paas, en relación con el orden de rotación de los estudiantes en el taller de manejo de vía aérea; se encontró mayor esfuerzo en el grupo que rotó primero por cirugía (6,19 vs. 5,53; p = 0,029). El taller con mayores índices de frustración fue el de manejo de vía aérea. Este taller mostró los mayores puntajes en todos los ítems en la escala NASA-TLX, lo que indica una mayor carga cognitiva respecto a los demás. Conclusión: No fue posible diferenciar si los puntajes altos en algunas de las actividades se debieron a la dificultad natural del manejo de vía aérea, o al diseño específico del taller. Por lo que se requieren nuevos estudios que diferencien estos componentes para mejorar el diseño de actividades de aprendizaje.

Evaluation of the stiffness characteristics of rapid palatal expander screws.

BACKGROUND: The aim of this study is to evaluate the mechanical properties of the screws used for rapid expansion of the upper jaw. METHODS: Ten types of expansion screw were assessed, seven with four arms: Lancer Philosophy 1, Dentaurum Hyrax Click Medium, Forestadent Anatomic Expander type "S", Forestadent Anatomic Expander type "S" for narrow palates, Forestadent Memory, Leone A 2620-10 with telescopic guide, and Leone A 0630-10 with orthogonal arms; and three with two arms: Dentaurum Variety S.P., Target Baby REP Veltri, and Leone A 362113. A test expander with the mean dimensions taken from measurements on a sample of 100 expanders was constructed for each screw. The test expanders were connected to the supports of an Instron 4467 (Instron Corp., USA) mechanical testing machine equipped with a 500 N load cell, and the compression force exerted after each activation was measured. The mean forces expressed by the two- and four-arm expanders were then compared. RESULTS: After five activations, the forces expressed by the two-arm devices were double than those expressed by the four-arm devices on average (224 ± 59.9 N vs. 103 ± 32.9 N), and such values remained high after subsequent activations. CONCLUSIONS: The expanders tested demonstrated stiffness characteristics compatible with opening of the palatine sutures in pre-adolescent patients. The stiffness of such devices can be further increased during the construction phase.