Pretratamiento y mejoría de la fuerza de unión de los cementos autoadhesivos de resina a los postes / Pretreatment and improvement of bonding strength of self-adhesive resin cements to posts

ABSTRACT Introduction: Posts and core are frequently used in endodontically treated teeth with excessive loss of coronal tooth structure. Objective: To evaluate the effectiveness of self-adhesive cements under different pre-treatments of dentin in the resistance to extrusion of fiberglass posts. Methods: An experimental in vitro study was conducted. The randomly selected sample was 56 extracted bovine incisors with mature apices and without root curvature. Before the cementing procedure, pretreatment of dentin was performed with 11.5 percent polyacrylic acid, 17 percent EDTA or sodium hypochlorite. The type of failure between the post/cement/dentin was evaluated by stereomicroscope. Two hundred and sixteen bovine dentin discs were used. The disks were approximately 1 mm thick, and were obtained from 72 bovine roots restored with intraradicular retentions. Data were analyzed for better comprehension in an SPSS database for Windows version 15. Results: The highest values were found in groups G3, G4 and G5, and there was no bond strength significant difference in group G2. Conclusions: The pre-treatment had no effect on dentin bond strength, and the self-adhesive cement RelyX U100 appears to be a viable option in the cementation of fiber posts(AU)

RESUMEN Introducción: Los postes y el núcleo se utilizan con frecuencia en los dientes tratados endodónticamente con una pérdida excesiva de la estructura dental coronal. Objetivo: Evaluar la efectividad de los cementos autoadhesivos bajo diferentes pretratamientos de dentina en la resistencia a la extrusión de postes de fibra de vidrio. Métodos: Se realizó una investigación experimental in vitro en 56 dientes de ganado seleccionados al azar con cierre apical maduro y sin curvaturas radiculares. Antes del procedimiento de cementación, se llevó a cabo el pretratamiento de la dentina con 11,5 por ciento de ácido poliacrílico, 17 por ciento de EDTA o hipoclorito de sodio. El estereomicroscopio evaluó el tipo de falla entre el poste / cemento / dentina. Se usaron 216 discos de dentina bovina. Los discos tenían aproximadamente 1 mm de espesor y se obtuvieron de 72 raíces bovinas restauradas con retenciones intrarradiculares. Los datos se analizaron para una mejor comprensión en una base de datos de SPSS para Windows versión 15. Resultados: Los valores más elevados fueron encontrados en los grupos G3, G4 y G5 y no fue significativa la prueba de resistencia en el grupo G2. Conclusiones: El pretratamiento no tuvo efecto sobre la fuerza de unión dentinaria, y el cemento autoadhesivo RelyX U100 parece ser una opción viable en la cementación postes de fibra(AU)

Suspensory Tethers and Critical Point Membrane Displacement in Endolymphatic Hydrops

Abstract Introduction Grossly displaced membranes are characteristic of endolymphatic hydrops. The process whereby physiological membrane displacement becomes pathological may be mediated by stress, but the membrane biomechanics underlying this transition are unclear. Objective This study seeks to determine the role of suspensory tethers during pressure-induced membrane displacement in the generation of the membranous lesions seen in this disease entity using a biomechanical model approach. Methods The location of membrane suspensory tethers was identified histologically. The influence of tethers on model membrane configuration during displacement was assessed graphically. The relationship of membrane configuration during displacement to curvature radius was quantified trigonometrically. The relationship of curvature radius to stress susceptibility was determined mathematically. The net effect of suspensory tethers on membrane stress levels for various degrees of membrane distention and displacement was then calculated numerically. Results In the inferior labyrinth, suspensory tethers are found to occur on the membranes' boundaries. Such tethering is found to impose a biphasic effect on membrane curvature with increasing degrees of displacement. As a consequence, tensile stress susceptibility is found to decline with initial membrane displacement to a critical point nadir beyond which stress then increases monotonically. No such effect was found for the superior labyrinth. Conclusion Boundary tethers in the inferior labyrinth are associated with significant tensile stress reductions until a critical point of membrane displacement is reached. Displacements short of the critical pointmay be physiological and even reversible,whereas such displacements beyond the critical point are apt to be overtly hydropic and irreversible.

Evaluation of tensile strength of tissue adhesives made of fibrin and cyanoacrylate used as reinforcement of colon suture in "ex vivo" swine

ABSTRACT Aim: To evaluate rupture pressures of tissue adhesives of cyanoacrylate (Omnex®) and fibrin (Evicel®), used as reinforcement in colonic suture from "ex vivo" swine. Methods: Surgical procedures were performed in the Surgical Technique Laboratory. From a division in segments of 10 cm of descending colon and sigmoid colon from three "ex vivo" female swine, Landrace breed, which were resected in less than six hours after the slaughter time, 30 segments were selected, 10 of each animal. They were stored in saline solution 0.9% at 36 °C, being randomly allocated in three groups (Control, Evicel and Omnex), each one containing 10 segments. Results: The lower and higher pressure values found in the groups Control, Evicel and Omnex were 36 mmHg and 41 mmHg, 70 mmHg and 90 mmHg, 90 mmHg and 120 mmHg, respectively. Containing statistical significance (p-value <0.0001) concerning the 2 to 2 comparisons (Control, Evicel and Omnex) with 95% trusting rate based on the application of the Turkey Method. Conclusion: One concludes that the use of tissue adhesives in anastomoses colonic in an experimental animal model of "ex vivo" swine increased the anastomoses rupture pressures. Among the tested adhesives, cyanoacrylate presented higher rupture pressure in relation to fibrin adhesive.

RESUMO Objetivo: Avaliar as pressões de ruptura dos adesivos teciduais de Cianoacrilato (Omnex®) e de Fibrina (Evicel®), usados como reforço em suturas colônicas de suínos "ex-vivo". Métodos: Os procedimentos cirúrgicos realizados foram realizados no Laboratório de Técnica Cirúrgica. A partir da divisão em segmentos de 10 cm do colo descendente e colo sigmoide de três suínas fêmeas ex-vivo, da raça Landrace, ressecados em tempo inferior a seis horas em relação ao momento do abate, foram selecionados 30 segmentos, 10 de cada animal. Foram armazenados em soro fisiológico 0,9% a 36 °C, alocando-se aleatoriamente esses segmentos em três grupos (Controle, Evicel e Omnex) com 10 segmentos cada. Resultados: Os menores e maiores valores pressóricos encontrados nos grupos Controle, Evicel e Omnex foram 36 mmHg e 41 mmHg, 70 mmHg e 90 mmHg, 90 mmHg e 120 mmHg, respectivamente. Com significância estatística (Valor-p < 0,0001) para as comparações 2 a 2 (Sutura, Evicel e Omnex) com um intervalo de confiança de 95% construído a partir da aplicação do método de Turkey. Conclusão: A partir desse estudo conclui-se que o uso de adesivos teciduais em anastomoses colônicas, em modelo experimental animal de suíno ex-vivo, aumentou as pressões de ruptura das anastomoses. Dentre os adesivos testados, o adesivo de Cianoacrilato apresentou maiores pressões de ruptura em relação ao adesivo de Fibrina.

Biomecánica de las fracturas por stress / Biomechanical features of stress fractures

Se define como estrés (stress) tanto la fuerza que una carga externa ejerce sobre un cuerpo sólido como la fuerza reactiva que acompaña a la primera (Ley de Newton), por unidad de área imaginaria transversal a su dirección. Las cargas internas reactivas inducen deformaciones proporcionales del cuerpo. La resistencia del cuerpo a deformarse se llama rigidez. La deformación puede resquebrajar el cuerpo y, eventualmente, producir una fractura por confluencia de trazos. La resistencia del cuerpo a separarse en fragmentos por esa causa se llama tenacidad. La resistencia del cuerpo a la fractura es proporcional al stress que puede soportar sin separarse en fragmentos por deformación (no hay fractura sin deformación y sin stress previo). El stress máximo que un cuerpo puede soportar sin fracturarse resulta de una combinación de ambas propiedades: rigidez y tenacidad, cada una con distintos determinantes biológicos. Una o varias deformaciones del cuerpo pueden provocarle resquebrajaduras sin fracturarlo. La acumulación de resquebrajaduras determina la "fatiga" del material constitutivo del cuerpo, que reduce su rigidez, tenacidad y resistencia a la fractura para la próxima ocasión ("fragilidad por fatiga"). En el caso de los huesos, en general, los términos stress y fatiga tienen las connotaciones amplias referidas, respecto de todas las fracturas posibles. La fatiga predispone a fracturas a cargas bajas, que se denominan (correctamente) "fracturas por fatiga" y también (incorrectamente) "fracturas por stress", para distinguirlas de las que ocurren corrientemente, sin resquebrajaduras previas al trauma, que se denominan (incorrectamente) "fracturas por fragilidad, o por insuficiencia". En realidad, todas las fracturas se producen por stress y por fragilidad o insuficiencia (en conjunto); pero la distinción grosera entre fracturas "por fatiga, o por stress", por un lado, y "por fragilidad" o "por insuficiencia", por otro, aceptando las amplias connotaciones referidas antes, tiene valor en la práctica clínica. Este artículo intenta explicar esas particularidades biomecánicas y describir las distintas condiciones que predisponen a las fracturas "por fatiga o por stress" en la clínica, distinguiéndolas de las fracturas "por fragilidad o por insuficiencia" (manteniendo estas denominaciones) y detallando las características de interés directo para su diagnóstico y tratamiento. (AU)

The term "stress" expresses the force exerted by an external load on a solid body and the accompanying, opposed force (Newton's Law), expressed per unit of an imaginary area perpendicular to the loading direction. The internal loads generated this way deform (strain) proportionally the body's structure. The resistance of the body to strain expresses its stiffness. Critical strain magnitudes may induce micro-fractures (microdamage), the confluence of which may fracture the body. The body's resistance to separation into fragments determines its toughness. Hence, the body's resistance to fracture is proportional to the stress the body can support (or give back) while it is not fractured by the loadinduced strain (no stress, no strain -> no fracture). Therefore, the maximal stress the body can stand prior to fracture is determined by a combination of both, its stiffness and its toughness; and each of those properties is differently determined biologically. One or more deformations of the body may induce some microdamage but not a fracture. Microdamage accumulation determines the fatigue of the material constitutive of the body and reduces body's toughness, leading to a "fatigue-induced fragility". In case of bones, in general, both stress and fatigue have the referred, wide connotations, regarding any kind of fractures. In particular, bone fatigue predisposes to low-stress fractures, which are named (correctly) "fatigue fractures" and also misnamed "stress fractures", to distinguish them from the current fractures that occur without any excess of microdamage, that are named (wrongly) "fragility" or "insufficiency" fractures. In fact, all fractures result from all stress and fragility or insufficiency as a whole; however, the gross distinction between "fatigue or stress fractures", on one side, and "fragility or insufficiency fractures", on the other, accepting the wide connotations of the corresponding terminology, is relevant to clinical practice. This article aims to explain the above biomechanical features and describe the different instances that predispose to "fatigue or stress fractures" in clinical practice, as a different entity from "insufficiency or fragility fractures" (maintaining this nomenclature), and describe their relevant features to their diagnosis and therapy. (AU)