Resistance to fracture due to cyclic fatigue of stainless steel manual files and its association to surface roughness.

The aim of this study was to evaluate the possible association between the roughness of 5 brands of stainless steel endodontic files and their resistance to fracture due to cyclic fatigue. The study included five different brands of stainless steel endodontic files: SybroEndo Triple-Flex Files (Kerr, Glendora, USA), Ready Steel K-Flexofile (Dentsply Sirona, Ballaigues, Switzerland), Mani Flexile Files (Mani, Tochigi- Ken, Japan), FKG K-Files (FKG, La Chaux-de-Fonds, Switzerland) and Zipperer Flexicut Files (VDW, Munich, Germany). Twelve files per brand (total 60 files) were evaluated. File surface roughness over an area (Sa) was quantified using a focus variation microscope. Then the files were subject to a cyclical fatigue test to determine the number cycles to fracture due to fatigue and length of fractured fragment. Finally, fractographic analysis was performed using a scanning electron microscope. The electropolished Ready Steel K-Flexofile® files had the highest roughness according to Sa parameters, though they also had the highest resistance to fracture due to cyclic fatigue and the longest fractured fragment. Moderate positive correlation was found between fractured fragment length and roughness. The fractured surface showed characteristics of ductile fracture with cracks and plastic deformation. The electropolished stainless steel Ready Steel K-Flexofile® files were the most resistant to fracture due to cyclic fatigue even though they had highest surface roughness.

El objetivo del presente estudio fue evaluar la posible asociación entre la rugosidad de 5 marcas de limas endodónticas de acero inoxidable y su resistencia a la fractura por fatiga cíclica. Se incluyeron cinco grupos diferentes de limas endodónticas de acero inoxidable: SybroEndo Triple-Flex Files (Kerr, Glendora, EE. UU.), Ready Steel K-Flexofile (Dentsply Sirona, Ballaigues, Suiza), Mani Flexile Files (Mani, Tochigi- Ken, Japón), FKG K-Files (FKG, La Chaux-de-Fonds, Suiza) y Zipperer Flexicut Files (VDW, Munich, Alemania); se evaluaron doce instrumentos por grupo para un total de 60 limas. Mediante un microscopio de variación focal se cuantificó la rugosidad superficial por área (Sa) de los instrumentos, posteriormente fueron sometidos a una prueba de fatiga cíclica donde se determinó el número de ciclos de fractura por fatiga y la longitud del fragmento fracturado. Finalmente, se realizó un análisis fractográfico mediante microscopía electrónica de barrido. Las limas Ready Steel K-Flexofile® con electropulido mostraron el mayor valor de rugosidad en los parámetros Sa; sin embargo, también tenían la mayor resistencia a la fractura por fatiga cíclica y la mayor longitud del fragmento fracturado del instrumento. Además, se encontró una correlación moderada positiva entre la longitud del fragmento fracturado y la rugosidad. La superficie fracturada mostró características de fractura dúctil con grietas y deformación plástica. Las limas Ready Steel K-Flexofile® fabricadas en acero inoxidable con electropulido, fueron más resistentes a la fractura por fatiga cíclica a pesar de tener la mayor rugosidad superficial.

Resistance to fracture due to cyclic fatigue of stainless steel manual files and its association to surface roughness / Resistencia a la fractura por fatiga cíclica de las limas manuales de acero inoxidable y su relación con la rugosidad superficial

ABSTRACT The aim of this study was to evaluate the possible association between the roughness of 5 brands of stainless steel endodontic files and their resistance to fracture due to cyclic fatigue. The study includedfive different brands of stainless steel endodontic files: SybroEndo Triple-Flex Files (Kerr, Glendora, USA), Ready Steel K-Flexofile (Dentsply Sirona, Ballaigues, Switzerland), Mani Flexile Files (Mani, Tochigi- Ken, Japan), FKG K-Files (FKG, La Chaux-de-Fonds, Switzerland) and Zipperer Flexicut Files (VDW, Munich, Germany). Twelve files per brand (total 60 files) were evaluated. File surface roughness over an area (Sa) was quantified using a focus variation microscope. Then the files were subject to a cyclical fatigue test to determine the number cycles to fracture due to fatigue and length of fractured fragment. Finally, fractographic analysis was performed using a scanning electron microscope. The electropolished Ready Steel K-Flexofile® files had the highest roughness according to Sa parameters, though they also had the highest resistance to fracture due to cyclic fatigue and the longest fractured fragment. Moderate positive correlation was found between fractured fragment length and roughness. The fractured surface showed characteristics of ductile fracture with cracks and plastic deformation. The electropolished stainless steel Ready Steel K-Flexofile® files werethe most resistant to fracture due to cyclic fatigue even though they had highest surface roughness.

RESUMEN El objetivo del presente estudio fue evaluar la posible asociación entre la rugosidad de 5 marcas de limas endodónticas de acero inoxidable y su resistencia a la fractura por fatiga cíclica. Se incluyeron cinco grupos diferentes de limas endo-dónticas de acero inoxidable: SybroEndo Triple-Flex Files (Kerr, Glendora, EE. UU.), Ready Steel K-Flexofile (Dentsply Sirona, Ballaigues, Suiza), Mani Flexile Files (Mani, Tochigi-Ken, Japón), FKG K-Files (FKG, La Chaux-de-Fonds, Suiza) y Zipperer Flexicut Files (VDW, Munich, Alemania); se evaluaron doce instrumentos por grupo para un total de 60 limas. Mediante un microscopio de variación focal se cuantificó la rugosidad superficial por área (Sa) de los instrumentos, posteriormente fueron sometidos a una prueba de fatiga cíclica donde se determinó el número de ciclos de fractura por fatiga y la longitud del fragmento fracturado. Finalmente, se realizó un análisis fractográfico mediante microscopía electrónica de barrido. Las limas Ready Steel K-Flexofile® con electropulido mostraron el mayor valor de rugosidad en los parámetros Sa; sin embargo, también tenían la mayor resistencia a la fractura por fatiga cíclica y la mayor longitud del fragmento fracturado del instrumento. Además, se encontró una correlación moderada positiva entre la longitud del fragmento fracturado y la rugosidad. La superficie fracturada mostró características de fractura dúctil con grietas y deformación plástica. Las limas Ready Steel K-Flexofile® fabricadas en acero inoxidable con electropulido, fueron más resistentes a la fractura por fatiga cíclica a pesar de tener la mayor rugosidad superficial.

Factors associated to apical overfilling after a thermoplastic obturation technique - Calamus® or Guttacore®: a randomized clinical experiment.

The aims of this study were to analyze whether age, tooth type and sex are related to radiographically visible extrusion of filling material as an unintended outcome in teeth undergoing endodontic treatment with a thermoplastic obturation technique (Calamus® or GuttaCore®) and to determine whether the presence of such overfilling is associated to postoperative pain. We selected 120 teeth with diagnoses involving vital pulp and indication for endodontic treatment. Biomechanical preparation was performed using the Protaper Next® system with X2 or X3 master apical file. Teeth were randomly divided into 2 groups (n=60). Teeth in Group 1 were filled with the Guttacore® system and teeth in Group 2 were filled with single cone technique and Calamus® obturation system. Thermoplastic obturation techniques were found to cause overfilling in 53. 33% of the total cases (64 teeth) (56. 66% in Guttacore® group and 50% in the Calamus® group). Anterior teeth were found to be associated to presence of overfilling (p= 0. 024) (OR = 4. 35). Of the 120 teeth treated, 10 (8. 33%) presented postoperative pain and radiographically visible overfilling. The association between presence of extruded filling material and mild/moderate pain was statistically significant withp = 0. 002. To conclude, endodontic thermoplastic obturation with Guttacore® and Calamus® systems are significantly associated with the probability of filling material extrusion, and overfilling is associated to postoperative pain. Anterior teeth are 4 times more likely to be overfilled with the obturation techniques tested.

Los objetivos de esta investigación fueron: Analizar si factores como la edad, el tipo de diente y el género están asociados con la extrusión de material obturador radiográficamente visible como desenlace imprevisto en dientes sometidos a tratamiento endodóntico con una técnica de obturación termoplástica (Calamus® o GuttaCore®) y determinar si la presencia de esta sobreobturación está asociada con dolor posoperatorio. Se seleccionaron 120 dientes con diagnósticos que implicaban pulpa vital y con indicación de tratamiento de endodoncia. La preparación biomecánica se llevó a cabo con el sistema ProtaperNext® con lima apical principal X2 o X3. Los dientes se dividieron aleatoriamente de la siguiente forma (n=60): El grupo 1 se obturó con el sistema Guttacore® y el grupo 2 se obturó con una técnica de obturación de cono único y el sistema de obturación Calamus®. Se observó quelas técnicas de obturación termoplástica generaron sobreobturación en 53. 33% del total (64 dientes), 56. 66% se presentaron en el grupo de obturación con Guttacore® y 50% en el grupo de la técnica con el sistema Calamus®. Se encontró que los dientes anteriores presentaron asociación con la presencia de sobreobturación (p= 0. 024) (OR=4. 35). De los 120 dientes tratados, 10 (8. 33 %) presentaron dolor posoperatorio y sobreobturación radiográficamente visible. La asociación entre la presencia de extrusión de material de obturación y dolor leve-moderado fue estadísticamente significativa con un valorp= 0. 002. Como conclusión las técnicas de obturación termoplástica en endodoncia Guttacore® y el sistema Calamus® están asociadas significativamente con la probabilidad de extrusión de material obturador y dicha sobreobturación está asociada con dolor posoperatorio, los dientes anteriores presentan 4 veces más riesgo de sobreobturación con las técnicas de obturación utilizadas.

Factors associated to apical overfilling after a thermoplastic obturation technique - Calamus(R) or Guttacore(R): a randomized clinical experiment / Factores asociados con la presencia de sobreobturación apical posterior a una técnica de obturación termoplástica Calamus® o Guttacore®: experimento clínico aleatorizado

The aims of this study were to analyze whether age, tooth type and sex are related to radiographically visible extrusion of filling material as an unintended outcome in teeth undergoing endodontic treatment with a thermoplastic obturation technique (Calamus® or GuttaCore®) and to determine whether the presence of such overfilling is associated to postoperative pain. We selected 120 teeth with diagnoses involving vital pulp and indication for endodontic treatment. Biomechanical preparation was performed using the Protaper Next® system with X2 or X3 master apical file. Teeth were randomly divided into 2 groups (n=60). Teeth in Group 1 were filled with the Guttacore® system and teeth in Group 2 were filled with single cone technique and Calamus® obturation system. Thermoplastic obturation techniques were found to cause overfilling in 53.33% of the total cases (64 teeth) (56.66% in Guttacore® group and 50% in the Calamus® group). Anterior teeth were found to be associated to presence of overfilling (p= 0.024) (OR = 4.35). Of the 120 teeth treated, 10 (8.33%) presented postoperative pain and radiographically visible overfilling. The association between presence of extruded filling material and mild/moderate pain was statistically significant with p = 0.002. To conclude, endodontic thermoplastic obturation with Guttacore® and Calamus® systems are significantly associated with the probability of filling material extrusion, and overfilling is associated to postoperative pain. Anterior teeth are 4 times more likely to be overfilled with the obturation techniques tested (AU)

Los objetivos de esta investigación fueron: Analizar si factores como la edad, el tipo de diente y el género están asociados con la extrusión de material obturador radiográficamente visible como desenlace imprevisto en dientes sometidos a tratamiento endodóntico con una técnica de obturación termoplástica (Calamus® o GuttaCore®) y determinar si la presencia de esta sobreobturación está asociada con dolor posoperatorio. Se seleccionaron 120 dientes con diagnósticos que implicaban pulpa vital y con indicación de tratamiento de endodoncia. La preparación biomecánica se llevó a cabo con el sistema ProtaperNext® con lima apical principal X2 o X3. Los dientes se dividieron aleatoriamente de la siguiente forma (n=60): El grupo 1 se obturó con el sistema Guttacore® y el grupo 2 se obturó con una técnica de obturación de cono único y el sistema de obturación Calamus®. Se observó quelas técnicas de obturación termoplástica generaron sobreobturación en 53.33% del total (64 dientes), 56.66% se presentaron en el grupo de obturación con Guttacore® y 50% en el grupo de la técnica con el sistema Calamus®. Se encontró que los dientes anteriores presentaron asociación con la presencia de sobreobturación (p= 0.024) (OR=4.35). De los 120 dientes tratados, 10 (8.33 %) presentaron dolor posoperatorio y sobreobturación radiográficamente visible. La asociación entre la presencia de extrusión de material de obturación y dolor levemoderado fue estadísticamente significativa con un valor p= 0.002. Como conclusión las técnicas de obturación termoplástica en endodoncia Guttacore® y el sistema Calamus® están asociadas significativamente con la probabilidad de extrusión de material obturador y dicha sobreobturación está asociada con dolor posoperatorio, los dientes anteriores presentan 4 veces más riesgo de sobreobturación con las técnicas de obturación utilizadas (AU)

Theoretical evaluation of Nickel-Titanium Mtwo series rotary files.

Nickel-Titanium rotary files are a technological development that enables dentists to prepare irregularly shaped root canals without altering them. Unfortunately, these files may fracture without any prior visible warning signs. The aim of this study was to perform a theoretical evaluation of the mechanical behaviour of Mtwo Nickel-Titanium rotary files for endodontics, in order to determine which of the files in the basic series are most likely to fracture. Mathematical models of the Mtwo basic file series were analyzed using the finite elements method. Bending and torsion loads were applied to the files both under normal conditions and under extreme conditions, to determine which of them had the highest Von Mises stresses. When the approximation was similar to normal use none of the file models reached the maximum limit of failure by fracture. When used inadequately, file models 10/0.04 and 25/0.06 had the highest Von Mises stresses for bending and torsion, respectively. Thus, it is recommended that Mtwo files 10/0.04 and 25/0.06 should be used once only, to prevent fractures.

A theoretical model of dentinogenesis: dentin and dentinal tubule formation.

INTRODUCTION: Dentinogenesis, odontoblast dentin formation, includes dentinal growth, mineralization and dentinal tubule formation. Odontoblasts synthesize collagen resulting in collagen apposition contributing to dentinogenesis. Furthermore, within the tubule, they express non-collagenous proteins, such as dentin phosphoprotein (DPP), associated with hydroxyapatite crystal formation and growth. The aim of this work was to determine patterns of growth and dentin formation and quantification of its mineralization. Findings from our work are relevant to endodontics for future regenerative treatment. METHODS: We formulated a 3D domain mathematical model, which recreates the events that lead to dentinal tubule mineralization. As reference we used collagen apposition and DPP activity. RESULTS: We obtained a model depicting predentin's mineralization distribution during dentin development. Furthermore, we verified different DPP diffusion coefficients to test the model's sensitivity. CONCLUSIONS: We present a model to shed light on the process of dentin and dentinal tubule formation, and its relation to diffusion and mineralization processes.

Theoretical evaluation of nickel-titanium MTWO series rotary files

Las limas rotatorias de níquel-titanio son un avance tecnológico que permite al odontólogo llevar a cabo tratamientos en conductos con morfologías irregulares Lamentablemente, estos instrumentos pueden fracturarse sin presentar señales visibles que permitan prevenir este accidente. Por lo tantoel objetivo del presente estudio fue evaluar teóricamente el comportamientomecánico de las limas rotatorias de Níquel-Titanio para uso en endodoncia Mtwo® para determinar cuál de losinstrumentos de la serie básica es el que presenta mayor probabilidad de fractura. Con este fin se realizó un análisis por medio del método de los elementos finitos utilizando modelos matemáticos de los instrumentos de la serie básica de las limas Mtwo®. Aestos instrumentos se les aplicaron cargas de flexión y torsión en condiciones normales y en condiciones extremas, para determinar cuáles presentaban los esfuerzos de Von Mises más altos. En una aproximación similar al uso normal, ninguno de los modelosde las limas alcanzó el limite máximo de falla por fractura. Ante un uso inadecuado, los modelos de las limas 10/0.04 y 25/0.06 mostraron los esfuerzos de Von Mises más altos tanto a flexión como a torsión respectivamente, por lo tanto se recomienda dar un solo uso a la lima 10/0.04 y a la lima 25/0.06 de Mtwo® para prevenir la fractura de estos instrumentos.

Nickel-Titanium rotary files are a technological development thatenables dentists to prepare irregularly shaped root canals withoutaltering them. Unfortunately, these files may fracture without anyprior visible warning signs. The aim of this study was to perform atheoretical evaluation of the mechanical behaviour of Mtwo®Nick-el-Titanium rotary files for endodontics, in order to determinewhich of the files in the basic series are most likely to fracture.Mathematical models of the Mtwo®basic file series were analyzedusing the finite elements method. Bending and torsion loads wereapplied to the files both under normal conditions and under extremeconditions, to determine which of them had the highest Von Misesstresses. When the approximation was similar to normal use, noneof the file models reached the maximum limit of failure by fracture.When used inadequately, file models 10/0.04 and 25/0.06 had thehighest Von Mises stresses for bending and torsion, respectively.Thus, it is recommended that Mtwo®files10/0.04 and 25/0.06should be used once only, to prevent fractures.

Theoretical evaluation of Nickel-Titanium Mtwo series rotary files. / Theoretical evaluation of Nickel-Titanium Mtwo series rotary files.

Nickel-Titanium rotary files are a technological development that enables dentists to prepare irregularly shaped root canals without altering them. Unfortunately, these files may fracture without any prior visible warning signs. The aim of this study was to perform a theoretical evaluation of the mechanical behaviour of Mtwo Nickel-Titanium rotary files for endodontics, in order to determine which of the files in the basic series are most likely to fracture. Mathematical models of the Mtwo basic file series were analyzed using the finite elements method. Bending and torsion loads were applied to the files both under normal conditions and under extreme conditions, to determine which of them had the highest Von Mises stresses. When the approximation was similar to normal use none of the file models reached the maximum limit of failure by fracture. When used inadequately, file models 10/0.04 and 25/0.06 had the highest Von Mises stresses for bending and torsion, respectively. Thus, it is recommended that Mtwo files 10/0.04 and 25/0.06 should be used once only, to prevent fractures.

Theoretical evaluation of nickel-titanium MTWO series rotary files

Las limas rotatorias de níquel-titanio son un avance tecnológico que permite al odontólogo llevar a cabo tratamientos en conductos con morfologías irregulares Lamentablemente, estos instrumentos pueden fracturarse sin presentar señales visibles que permitan prevenir este accidente. Por lo tantoel objetivo del presente estudio fue evaluar teóricamente el comportamientomecánico de las limas rotatorias de Níquel-Titanio para uso en endodoncia Mtwo« para determinar cuál de losinstrumentos de la serie básica es el que presenta mayor probabilidad de fractura. Con este fin se realizó un análisis por medio del método de los elementos finitos utilizando modelos matemáticos de los instrumentos de la serie básica de las limas Mtwo«. Aestos instrumentos se les aplicaron cargas de flexión y torsión en condiciones normales y en condiciones extremas, para determinar cuáles presentaban los esfuerzos de Von Mises más altos. En una aproximación similar al uso normal, ninguno de los modelosde las limas alcanzó el limite máximo de falla por fractura. Ante un uso inadecuado, los modelos de las limas 10/0.04 y 25/0.06 mostraron los esfuerzos de Von Mises más altos tanto a flexión como a torsión respectivamente, por lo tanto se recomienda dar un solo uso a la lima 10/0.04 y a la lima 25/0.06 de Mtwo« para prevenir la fractura de estos instrumentos.(AU)

Nickel-Titanium rotary files are a technological development thatenables dentists to prepare irregularly shaped root canals withoutaltering them. Unfortunately, these files may fracture without anyprior visible warning signs. The aim of this study was to perform atheoretical evaluation of the mechanical behaviour of Mtwo«Nick-el-Titanium rotary files for endodontics, in order to determinewhich of the files in the basic series are most likely to fracture.Mathematical models of the Mtwo«basic file series were analyzedusing the finite elements method. Bending and torsion loads wereapplied to the files both under normal conditions and under extremeconditions, to determine which of them had the highest Von Misesstresses. When the approximation was similar to normal use, noneof the file models reached the maximum limit of failure by fracture.When used inadequately, file models 10/0.04 and 25/0.06 had thehighest Von Mises stresses for bending and torsion, respectively.Thus, it is recommended that Mtwo«files10/0.04 and 25/0.06should be used once only, to prevent fractures.(AU)

Does the geometric location of odontoblast differentiation and dentinal tubules depend on a reaction-diffusion system between BMP2 and Noggin? A mathematical model.

INTRODUCTION: The mesenchymal differentiation to odontoblasts is a complex process that determines the formation of dentinal tubules. This process involves a carefully regulated sequence of changes in the behavior of mesenchymal cells coordinated by the expression of different molecular factors that includes mainly the Noggin and bone morphogenetic protein type 2 (BMP2). METHODS: We investigated a bioregulatory mathematic model based on a set of equations of reaction-diffusion to predict the geometry of the formation of the dentinal tubules. RESULTS: We found that odontoblast location and the dentinal tubules formation are determined by the spatial distribution of a set of molecular signals that compete among themselves to maintain places of the greatest concentration of BMP2, which determines the step from mesenchymal cells to odontoblasts and the formation of the dentinal tubules. CONCLUSIONS: This mathematic model suggests a regulatory loop between BMP2 and Noggin, which is highly stable and repeatable and determines the right location patterns of the odontoblasts and the formation of dentinal tubules. This mathematic approach allows us to understand biological phenomena and biochemical activity during the period of pulp differentiation.