RESUMEN
Reciprocating instruments made from M-wire alloy have been proposed to reduce the risk of fracture. No information is available on the surface alteration after single and multiple uses in root canals. Two reciprocating NiTi instruments were used on extracted teeth up to three times. ESEM/EDS analysis was conducted to determine defects, alterations, and wear features of the apical third of instruments and metallographic analysis was performed on the cross-section of new and used instruments to compare alloy properties. Topography of apical portion was evaluated by AFM before and after uses. Extracted single-rooted teeth were divided into two groups and instrumented according to the manufacturer's recommendations with: (A) WaveOne Primary and (B) Reciproc R25. Each group was divided into three subgroups according to the number of canals instrumented: 1, 2, and 3, respectively. Chi square test was performed to verify homogeneity of defects distribution and GLM to evaluate the differences of RMS at baseline and after use for both groups (α level 0.05). No instrument fractured and no spiral distortions were observed under optical microscope even when the number of uses increased. Not significant differences were found for WaveOne and Reciproc. Blades presented a wrapped portion in WaveOne group and a more symmetrical feature in Reciproc group. Metallographic analysis revealed in both groups the presence of twinned martensitic grains with isolated flat austenitic areas. Both instruments demonstrated limited alteration, such as tip deformation and wear. This study confirmed the safe clinical use of both instruments for shaping multi-rooted teeth.
Asunto(s)
Instrumentos Dentales , Preparación del Conducto Radicular/instrumentación , Ensayo de Materiales , Microscopía de Fuerza Atómica , Microscopía Electrónica de Rastreo , Espectrometría por Rayos X , Estrés Mecánico , Propiedades de SuperficieRESUMEN
The aim of the study was to evaluate cyclic fatigue resistance of two NiTi instruments and to analyse their surface, fractographic and matrix morphology under ESEM/EDS and optical microscopy. WaveOne Primary and ProTaper Universal F2 brand new instruments were subjected to fatigue testing in an artificial canal with 5.0 mm radius and 60° angle of curvature. Seventy-two instruments were divided into three groups (n = 24), according to the selected kinematics: WaveOne using reciprocation (A); ProTaper using reciprocation (B) or rotation (C). Time to fracture was recorded. Data were analysed with ANOVA and Tukey test. ESEM/EDS analysis was conducted on new files to examine surface characteristics and on fractured fragments to identify the fractographic features. Metallographic analysis was performed with optical microscope on new instruments to evaluate alloy properties. Significant differences were found with Group A, which was statistically more resistant to cyclic fatigue (P < 0.05) than the other groups. Surface analysis of new instruments showed both in WaveOne and ProTaper files the presence of deep milling marks. ESEM fractographic analysis of WaveOne showed multiple crack origins with an area of fatigue propagation wider than ProTaper instruments, in which a single crack origin could be detected. EDS analysis confirmed the equiatomic NiTi composition. Metallographic analysis under optical microscope revealed in WaveOne instruments the presence of nano-crystalline martensitic grains embedded in austenite matrix, presence which could not be found in ProTaper files. WaveOne NiTi files revealed higher resistance to fatigue stress, suggesting extended working time in clinical applications.
Asunto(s)
Instrumentos Dentales , Ensayo de Materiales , Níquel , Estrés Mecánico , Titanio , Microscopía Electrónica de Rastreo , Espectrometría por Rayos XRESUMEN
OBJECTIVES: The aim of this in vitro study was to evaluate the effectiveness of a fluoride-releasing bonding agent in inhibiting enamel demineralization around orthodontic brackets after the exposure to a demineralizing solution. MATERIALS AND METHODS: Twenty-six extracted upper molars were bonded with two different composites: Transbond XT (TXT) and Transbond Plus (TPlus), fluoride-releasing (both 3M Unitek, Monrovia, CA, USA). The samples were exposed to an acid lactic solution for three days and then subjected to Metallographic Optical Microscope (MOM) and Scanning Electron Microscope/Energy Dispersive X-Ray (SEM/EDX) analyses. Enamel surface was examined in different areas: un-treated, etched and primer-painted, un-treated area with no acid exposure, central area with bracket bonded. The maximum demineralization depths and the fluoride content at 100, 200 and 300 µm depth were evaluated. RESULTS: MOM analysis showed statistically significant (p<0.001) differences in demineralization depth for TPlus group compared to TXT group with lower values for the first one. EDX analysis confirmed the presence of fluoride in TPlus group. CONCLUSIONS: The fluoride content of TPlus appeared able to weakly reduce the enamel demineralization.
Asunto(s)
Cariostáticos/uso terapéutico , Resinas Compuestas/química , Esmalte Dental/efectos de los fármacos , Fluoruros/uso terapéutico , Soportes Ortodóncicos , Cementos de Resina/química , Desmineralización Dental/prevención & control , Grabado Ácido Dental/métodos , Calcio/análisis , Cariogénicos/efectos adversos , Cariostáticos/análisis , Cariostáticos/química , Recubrimiento Dental Adhesivo , Esmalte Dental/ultraestructura , Difusión , Microanálisis por Sonda Electrónica , Fluoruros/análisis , Fluoruros/química , Humanos , Concentración de Iones de Hidrógeno , Ácido Láctico/efectos adversos , Ensayo de Materiales , Microscopía Electrónica de Rastreo , Fósforo/análisis , Factores de Tiempo , Desmineralización Dental/patología , Agua/químicaRESUMEN
Metal-on-metal hip-bearing components with different percentages of carbon content (low and high carbon) were tested in 6 different configurations using a hip joint simulator. The aim of this study was to characterize metallurgical and tribological events occurring at the articulating surfaces of these articulations. Also, ion release was evaluated and correlated with wear. After the test, for the high-carbon components, carbides were observed below the matrix surface. In the low-carbon content components, most carbides were "carbide-free", while a minority were worn below the matrix surface with increased test cycles. In the cast alloy components, some carbides were pulled out resulting in micropits. Scanning microscope electron characterization of the tested specimens showed scratches and holes. The surface showed a dominant severe wear mechanism due to third-body particles. A greater amount of ions was released in the lubricant used during the wear test for the smaller diameter compared with the bigger one. This study showed that the metallurgical and tribological events taking place at the articulating surfaces of metal-metal hip implants are numerous and complex. The surface morphology after the test showed the effect of more critical working conditions with smaller diameters.
Asunto(s)
Artroplastia de Reemplazo de Cadera/instrumentación , Aleaciones de Cromo , Prótesis de Cadera , Vitalio , Artroplastia de Reemplazo de Cadera/efectos adversos , Fricción , Ensayo de Materiales , Microscopía Electrónica de Rastreo , Estrés Mecánico , Propiedades de SuperficieRESUMEN
INTRODUCTION: The aim of this study was to compare cyclic fatigue resistance of four nickel-titanium rotary systems and to evaluate their surface, fractographic, and matrix morphology. METHODS: Four models of endodontic rotary files (EasyShape [Komet/Gebr. Brasseler, Lemgo, Germany], ProTaper [Dentsply Maillefer, Ballaigues, Switzerland], NRT [MANI Inc, Toshigi-Ken, Japan], and AlphaKite [Komet/Gebr. Brasseler]) were subjected to fatigue testing in artificial canals with angle of curvature of 45° and 60° and a radius of curvature of 5 mm until fracture occurred. Nickel-titanium (NiTi) alloy properties were investigated by light microscopy, environmental scanning electron microscopy (ESEM), and energy dispersive x-ray spectrophotometry (EDS). ESEM analysis was conducted on new files to examine surface characteristics and on fractured samples to identify the crack origin and the fractographic features. RESULTS: Analysis of variance testing revealed significant differences (P < .001) among the groups. NRT files had the highest fatigue resistance followed by AlphaKite, EasyShape, and ProTaper. All the new files presented surface imperfections. Fractographic analysis found the crack initiation to originate at the level of surface irregularities. Optical microscope inspection of the NiTi alloy matrix disclosed different-sized nonmetallic inclusions among models. EDS analysis of these inclusions showed that they were composed of carbon and oxygen in addition to nickel and titanium. Under light microscopy, austenitic grains appeared larger near the handle and smaller near the tip in all instruments. CONCLUSIONS: NRT files presented the longest fatigue life. All samples showed surface irregularities and nonmetallic inclusions. Austenitic grains were smaller near the tip than near the handle. The angle of curvature was confirmed to influence the fatigue life of NiTi instruments.