Letícia Chaves de Souza

Influence of the Geometry of Curved Artificial Canals on the Fracture of Rotary Nickel-Titanium Instruments Subjected to Cyclic Fatigue Tests

INTRODUCTION This study evaluated the influence of different features of canal curvature geometry on the number of cycles to fracture of a rotary nickel-titanium endodontic instrument subjected to a cyclic fatigue test. METHODS BioRaCe BR4C instruments (FKG Dentaire, La Chaux-de Fonds, Switzerland) were tested in 4 grooves simulating curved metallic artificial canals, each one measuring 1.5 mm in width, 20 mm in total length, and 3.5 mm in depth with a U-shaped bottom. The parameters of curvature including the radius and arc lengths and the position of the arc differed in the 4 canal designs. Fractured surfaces and helical shafts of the separated instruments were analyzed by scanning electron microscopy. RESULTS The Students t test showed that a significantly lower number of cycles to fracture values were observed for instruments tested in canals with the smallest radius, the longest arc, and the arc located in the middle portion of the canal. Scanning electron microscopic analysis of the fracture surfaces revealed morphologic characteristics of ductile fracture. Plastic deformation was not observed in the helical shaft of the fractured instruments. CONCLUSIONS Curvature geometry including the radius and arc lengths and the position of the arc along the root canal influence the number of cycles to fracture of rotary nickel-titanium instruments subjected to flexural load.

Analysis of Multiple Cytokine Polymorphisms in Individuals with Untreated Deep Carious Lesions Reveals IL1B (rs1143643) as a Susceptibility Factor for Periapical Lesion Development

INTRODUCTION It has been proposed that individual genetic predisposition may contribute to persistent apical periodontitis. Cytokines are associated with levels of inflammation and are involved in caries, pulpal, and periapical tissue destruction. We hypothesized that polymorphisms in cytokine genes may contribute to an individuals increased susceptibility to apical tissue destruction in response to deep carious lesions. METHODS Subjects with deep carious lesions with or without periapical lesions (≥3 mm) were recruited at the University of Pittsburgh, Pittsburgh, PA, and the University of Texas at Houston, Houston, TX. Genomic DNA samples of 316 patients were sorted into 2 groups: 136 cases with deep carious lesions and periapical lesions (cases) and 180 cases with deep carious lesions but no periapical lesions (controls). Nine single-nucleotide polymorphisms in IL1B, IL6, TNF, RANK, RANKL, and OPG genes were selected for genotyping. Genotypes were generated by end point analysis using TaqMan chemistry (Invitrogen, Carlsbad, CA) in a real-time polymerase chain reaction instrument. Allele and genotype frequencies were compared among cases and controls using the PLINK program (http://pngu.mgh.harvard.edu/purcell/plink/). Ninety-three human periapical granulomas and 24 healthy periodontal ligament tissues collected postoperatively were used for messenger RNA expression analyses of IL1B. RESULTS A single-nucleotide polymorphism in IL1B (rs1143643) showed allelic (P = .02) and genotypic (P = .004) association with cases of deep caries and periapical lesions. We also observed altered transmission of IL1B marker haplotypes (P = .02) in these individuals. IL1B was highly expressed in granulomas (P < .001). CONCLUSIONS Variations in IL1B may be associated with periapical lesion formation in individuals with untreated deep carious lesions. Future studies could help predict host susceptibility to developing periapical lesions.

Buckling Resistance of Pathfinding Endodontic Instruments

INTRODUCTION This study compared the buckling resistance of the following endodontic pathfinding instruments: C-Pilot file (VDW, Munich, Germany), C+ file (Maillefer/Dentsply, Ballaigues, Switzerland), and PathFile (Maillefer/Dentsply). METHODS The test instruments were subjected to a devised buckling resistance test, which consisted of the application of an increasing load in the axial direction of the instrument by using a universal testing machine. The maximum load required to generate a lateral elastic displacement of 1 mm was recorded for each instrument. RESULTS The results indicated that the buckling resistance decreased in the following order: C+ file > C-Pilot file > PathFile. The difference was statistically significant (P < .05). CONCLUSIONS The stainless steel instruments (C+ and C-Pilot) were more resistant to buckling than the nickel-titanium instrument (PathFile). Considering that buckling resistance may influence the performance of instruments during the negotiation of constricted canals, the C+ files showed significantly better results than the other instruments tested.

Analysis of radiopacity, pH and cytotoxicity of a new bioceramic material.

Objective RetroMTA® is a new hydraulic bioceramic indicated for pulp capping, perforations or root resorption repair, apexification and apical surgery. The aim of this study was to compare the radiopacity, pH variation and cytotoxicity of this material to ProRoot® MTA. Material and Methods Mixed cements were exposed to a digital x-ray along with an aluminum stepwedge for the radiopacity assay. pH values were verified after incubation period of 3, 24, 48, 72 and 168 hours. The cytotoxicity of each cement was tested on human periodontal ligament fibroblasts using a multiparametric assay. Data analysis was performed using ANOVA and Tukey’s post hoc in GraphPad Prism. Results ProRoot® MTA had higher radiopacity than RetroMTA® (p<0.001). No significant differences were observed for the pH of the materials throughout experimental periods (p>0.05) although pH levels of both materials reduced over time. Both ProRoot® MTA and RetroMTA® allowed for significantly higher cell viability when compared with the positive control (p<0.001). No statistical difference was observed between ProRoot® MTA and RetroMTA® cytotoxicity level in all test parameters, except for the ProRoot® MTA 48-hour extract media in the NR assay (p<0.05). Conclusion The current study provides new data about the physicochemical and biological properties of Retro® MTA concerning radiopacity, pH and cytotoxic effects on human periodontal ligaments cells. Based on our findings, RetroMTA® meets the radiopacity requirements standardized by ANSI/ADA number 572, and similar pH values and biocompatibility to ProRoot® MTA. Further studies should be performed to evaluate additional properties of this new material.

Effect of autoclave cycles on cyclic fatigue resistance of control memory NiTi files observed by scanning electron microscopy.

Objective: Hyflex CM instruments were developed for debridement of the root canal system. The control-memory alloy recovers its shape on sterilization, thereby allowing instrument reuse. This study investigated the effect of shape recovery by sterilization on the fatigue life and crack formation of Hyflex CM NiTi instruments. Material and Methods: the cyclic fatigue test was performed in two groups: In the first, it was continuously performed to establish the fatigue life (group 1, n = 10); in the second, it was performed with outages of 30s to evaluate cracks’ nucleation and propagation (group 2, n = 10). The test was performed using a stainless steel canal that was 1.5mm in diameter and 3.5mm in depth, with an arc of 9.42mm and radius of curvature of 6mm. The instruments were driven at 300 rpm. The fatigue time was recorded using a digital stopwatch (Technos). An electronic microscope (Quanta 250) was used to observe the crack formation and growth during the cyclic fatigue. Results: the autoclaved instruments endured 1196.67+214.63 cycles, and the non-autoclaved endured 1000+199.42 cycles until the occurrence of fracture. The t-student test (α=5%) revealed a significant difference. The cyclic fatigue test with pauses demonstrated a significantly longer cyclic fatigue life than the continuous cyclic fatigue test (p<0.05). Conclusion: as revealed by SEM images, cracks grow with an increase in the number of cycles to fracture (NCF). It can be concluded that the shape of Hyflex CM instruments recovered by autoclaving withstood significantly more NCF than non-autoclaved instruments (p<0.05), demonstrating an improvement of approximately 16%.

Physico-chemical and Biological Properties of a New Portland Cement-based Root Repair Material

Published online: 21 December 2017 DOI 10.5152/eej.2017.17018 Objective: To propose bismuth carbonate, a radiopacifying agent, as a new endodontic root repair material that was added to Portland cement (PC) at 2 wt%, 5 wt%, 10 wt% and 15 wt%, and physicochemical and biological properties of each formulation were evaluated in comparison to MTA-Angelus. Methods: Mixed and powder samples were analysed by scanning electron microscopy (SEM) and X-ray power diffraction (XRD), and the semiquantitative constitution of the powder was determined by energy-dispersive spectrometer (EDS). Setting time was evaluated by Vicat needle and radiopacity analysed with digital X-ray. The pH of all tested materials was observed after immersion in water for 3, 24, 48, 72 and 168 h (or 7 days). Solubility and calcium release were measured after immersion in water for 24 h. A multiparametric assay XTT-NR-CVDE was used to evaluate the cytotoxicity of the materials in human periodontal ligament (HPDL) fibroblasts. HPDL fibroblasts were exposed to PC 15% and mineral trioxide aggregate (MTA), and the expression of proinflammatory cytokines (IL1A, IL6, IL8, TNF) and bone formation genes (ALP, COL1 , RUNX2) was evaluated by real-time PCR. Mineralisation of HPDL fibroblasts cocultured with PC, PC 15% and MTA was evaluated with Von Kossa staining. Results: PC-based groups presented more irregular and larger particles than MTA. PC and MTA showed similarities as observed by XRD and EDS. Setting time of PC-based groups was increased with the addition of bismuth carbonate. All tested materials were alkaline, and pH tended to reduce over time. All cements had solubility lower than recommended, with no difference between them (P>0.05) and showed calcium release. PC 15% had similar radiopacity when compared with MTA (P>0.05). Cell viability was higher for the tested materials than the positive control (P<0.001), but there was no difference when they were compared with negative control (P>0.05). Gene expression levels were similar for all tested groups (P>0.05). Analysed cements had positive Von Kossa staining. Conclusion: Overall, the addition of 15% of bismuth carbonate did not result in significant changes to its physicochemical and biological properties when compared with MTA, except for the setting time, and may be considered a potential substitute for MTA.

Influence of Different Manufacturing Methods on the Mechanical Behavior of Nickel-Titanium Endodontic Instruments

Objetivo: Avalir o comportamento mecânico de instrumentos endodonticos de NiTi K3 Sybron Endo,Orange, CA), fabricados convencionalmente e K3XF(Sybron Endo, Orange, CA), submetidos a tratamento termico na fabricacao. Metodos: Foram utilizados 20 instrumentos K3 e K3XF com D0 0,25 mm, conicidade 0,06 mm/mm e 25 mm de comprimento. Para estandardizacao, dez instrumentos de cada tipo foram examinados sob estereomicroscopio e dois instrumentos (K3 e K3XF) tiveram suas seccoes transversais analisadas em microscopio eletronico de varredura (MEV). A flexibilidade e resistencia a fratura foram avaliadas em ensaio de flexao em 45° e em teste estatico de fadiga, respectivamente. Dez instrumentos K3 e K3XF foram utilizados em cada teste, registrando-se os valores da carga flexural e o numero de ciclos para ocorrer a fratura (NCF). Para analise estatistica empregou-se o teste t de Student. Os instrumentos fraturados foram analisados em MEV. Resultados: A carga flexural foi significativamente maior para as limas K3 do que para as K3XF (p˂0,05), apresentando, respectivamente, os valores de 713,5 g e 536,4 g. O NCF foi significativamente maior para os instrumentos K3XF em comparacao com as limas K3 (p˂0,05). A analise das superficies fraturadas em MEV revelou caracteristicas morfologicas do tipo ductil para ambos os instrumentos e ausencia de deformacao plastica. Conclusao: Os instrumentos de NiTi submetidos a tratamento termico apresentaram os menores valores de forca para serem flexionados em 45° e os mais elevado valores de NCF. Desse modo, pode-se inferir que os instrumentos submetidos ao tratamento termico diferenciado (K3XF) sao mais flexiveis e mais resistentes a fratura por fadiga do que os instrumentos K3, fabricados convencionalmente.

Influência de Diferentes Métodos de Fabricação no Comportamento Mecânico de Instrumentos Endodônticos de Níquel-Titânio

Objective: To evaluate the mechanical behavior of K3 NiTi endodontic instruments (Sybron Endo, Orange, CA, USA) with conventional manufacturing or subjected ...