Relevant Aspects in the Mechanical and Aging Degradation of NiTi Alloy with R-Phase in Endodontic Files.

One of the most important challenges in endodontics is to have files that have excellent flexibility, toughness, and high fatigue life. Superelastic NiTi alloys have been a breakthrough and the new R-phase NiTi alloys promise to further optimize the good properties of NiTi alloys. In this work, two austenitic phase endodontic files with superelastic properties (Protaper and F6) and two austenitic phase files with the R-phase (M-wire and Reciproc) have been studied. The transformation temperatures were studied by calorimetry. Molds reproducing root canals at different angles (30, 45, and 70°) were obtained with cooling and loads simulating those used in the clinic. Mechanical cycles of different files were realized to fracture. Transformation temperatures were determined at different number of cycles. The different files were heat treated at 300 and 500 °C as the aging process, and the transformation temperatures were also determined. Scanning and transmission electron microscopy was used to observe the fractography and precipitates of the files. The results show that files with the R-phase have higher fracture cycles than files with only the austenitic phase. The fracture cycles depend on the angle of insertion in the root canal, with the angle of 70° being the one with the lowest fracture cycles in all cases. The R-Phase transformation increases the energy absorbed by the NiTi to produce the austenitic to R-phase and to produce the martensitic transformation causing the increase in the fracture cycles. Mechanical cycling leads to significant increases in the transformation temperatures Ms and Af as well as Rs and Rf. No changes in the transformation temperatures were observed for aging at 300 °C, but the appearance of Ni4Ti3 precipitates was observed in the aging treatments to the Nickel-rich files that correspond to those with the R transition. These results should be considered by endodontists to optimize the type of files for clinical therapy.

Limas rotatorias de uso en Odontopediatría: revisión de la literatura / Rotary files for use in pediatric dentistry: Literature review

Introducción: Los dientes primarios juegan un importante papel en el crecimiento y desarrollo general de los niños, por lo que es necesario conservarlos hasta el momento de su recambio fisiológico. Cuando existe una afectación pulpar que compromete la vitalidad del diente, la pulpectomía se convierte en un reto para el odontopediatra debido a la compleja anatomía radicular de los dientes primarios. En esta revisión bibliográfica se darán a conocer diferentes sistemas de limas usados en odontopediatría, y así brindar una mirada actualizada de la instrumentación rotatoria al realizar pulpectomías en los molares primarios. Material y Método: se realizó una búsqueda bibliográfica en Pubmed y Web of Science de acuerdo con criterios de inclusión y exclusión previamente establecidos. Resultados: tras aplicar los criterios de inclusión y exclusión fueron seleccionados un total de 30 referencias bibliográficas de los últimos 15 años. Conclusión: las limas rotatorias pediátricas pueden considerarse alternativas seguras y más eficientes en la realización de pulpectomías en molares primarios, ya que se reduce el tiempo de tratamiento, se produce desbridamiento completo de los conductos y se mantiene la función del diente hasta su exfoliación. (AU)

Introduction: Primary teeth play an important role in the growth and development of children, so it is necessary to keep them until the moment of their physiological replacement. When there is a pulp involvement that compromises the vitality of the tooth, pulpectomy treatment becomes a challenge for the pediatric dentist due to the complex root anatomy of primary teeth. This review of the literature will present different file systems used in primary teeth and provide an updated look at rotary instrumentation when performing pulpectomies on primary molars. Material and Method: a bibliographic search was carried out in Pubmed and Web of Science according to previously established inclusion and exclusion criteria. Results: after applying the inclusion and exclusion criteria, a total of 30 bibliographic references from the last 15 years were selected. Conclusion: pediatric rotary files can be considered safe and more efficient alternatives in performing pulpectomies on primary molars, due to treatment time is reduced, complete debridement of the root canals is produced, and tooth function is maintained until exfoliation. (AU)

Limas rotatorias de uso en Odontopediatría: revisión de la literatura / Rotary files for use in pediatric dentistry: Literature review

Introducción: Los dientes primarios juegan un importante papel en el crecimiento y desarrollo general de los niños, por lo que es necesario conservarlos hasta el momento de su recambio fisiológico. Cuando existe una afectación pulpar que compromete la vitalidad del diente, la pulpectomía se convierte en un reto para el odontopediatra debido a la compleja anatomía radicular de los dientes primarios. En esta revisión bibliográfica se darán a conocer diferentes sistemas de limas usados en odontopediatría, y así brindar una mirada actualizada de la instrumentación rotatoria al realizar pulpectomías en los molares primarios. Material y Método: se realizó una búsqueda bibliográfica en Pubmed y Web of Science de acuerdo con criterios de inclusión y exclusión previamente establecidos. Resultados: tras aplicar los criterios de inclusión y exclusión fueron seleccionados un total de 30 referencias bibliográficas de los últimos 15 años. Conclusión: las limas rotatorias pediátricas pueden considerarse alternativas seguras y más eficientes en la realización de pulpectomías en molares primarios, ya que se reduce el tiempo de tratamiento, se produce desbridamiento completo de los conductos y se mantiene la función del diente hasta su exfoliación. (AU)

Introduction: Primary teeth play an important role in the growth and development of children, so it is necessary to keep them until the moment of their physiological replacement. When there is a pulp involvement that compromises the vitality of the tooth, pulpectomy treatment becomes a challenge for the pediatric dentist due to the complex root anatomy of primary teeth. This review of the literature will present different file systems used in primary teeth and provide an updated look at rotary instrumentation when performing pulpectomies on primary molars. Material and Method: a bibliographic search was carried out in Pubmed and Web of Science according to previously established inclusion and exclusion criteria. Results: after applying the inclusion and exclusion criteria, a total of 30 bibliographic references from the last 15 years were selected. Conclusion: pediatric rotary files can be considered safe and more efficient alternatives in performing pulpectomies on primary molars, due to treatment time is reduced, complete debridement of the root canals is produced, and tooth function is maintained until exfoliation. (AU)

Effect of Stabilized Martensite on the Long-Term Performance of Superelastic NiTi Endodontic Files.

One of the most used rotary files in endodontics is NiTi files due to their superelastic properties. This property means that this instrument has extraordinary flexion that can adapt to large angles inside the tooth canals. However, these files lose their superelasticity and fracture during use. The aim of this work is to determine the cause of fracture of the endodontic rotary files. For this purpose, 30 NiTi F6 SkyTaper® files (Komet, Germany) were used. Their chemical composition was determined by X-ray microanalysis, and their microstructure was determined by optical microscopy. Successive drillings were carried out with artificial tooth molds at 30, 45, and 70°. These tests were carried out at a temperature of 37 °C with a constant load controlled by a high sensitivity dynamometer of 5.5 N, and every five cycles were lubricated with an aqueous solution of sodium hypochlorite. The cycles to fracture were determined, and the surfaces were observed by scanning electron microscopy. Transformation (austenite to martensite) and retransformation (martensite to austenite) temperatures and enthalpies were determined by Differential Scanning Calorimeter at different endodontic cycles. The results showed an original austenitic phase with a Ms temperature of 15 °C and Af of 7 °C. Both temperatures increase with endodontic cycling, indicating that martensite forms at higher temperatures, and the temperature must be increased with cycling to retransform it to austenite. This fact indicates the stabilization of martensite with cycling, which is confirmed by the decrease in both transformation and retransformation enthalpies. The martensite is stabilized in the structure due to defects and does not retransform. This stabilized martensite has no superelasticity and, therefore, fractures prematurely. It has been possible to observe the stabilized martensite by studying the fractography, observing that the mechanism is by fatigue. The results showed that the files fracture earlier the greater the angle applied (for the tests at 70° at 280 s, at 45° at 385 s, and at 30° at 1200 s). As the angle increases, there is an increase in mechanical stress, and, therefore, the martensite stabilizes at lower cycles. To destabilize the martensite, a heat treatment can be carried out at 500 °C for 20 min, and the files recovers all its superelasticity.