Marginal adaptation and fracture resistance of feldspathic and polymer-infiltrated ceramic network CAD/CAM endocrowns for maxillary premolars.

OBJECTIVE: The aim of this study was to evaluate the marginal adaptation and fracture resistance of feldspathic and Polymer-Infiltrated Ceramic Network (PICN) CAD/CAM endocrowns for maxillary premolars. MATERIALS AND METHODS: Twenty extracted human permanent maxillary premolars were randomly divided into two groups (n = 10); Group CEREC (GC), which was produced by feldspathic ceramic and the Group Enamic (GE), which was produced by PICN. All teeth were endodontically treated and decoronated horizontally at 2 mm above the cemento-enamel junction. Endocrown preparations were done with 4 mm depth into the pulp chamber. Endocrowns were manufactured using CAD/CAM from ceramic blocks. Following adhesive cementation, all specimens were subjected to thermocycling. Marginal adaptation evaluated under SEM at 200 × magnification. Each specimen was fixed in a universal testing machine and a compressive load was applied at 45° to long axis of the teeth until failure. Failure load was recorded and failure modes were evaluated. Statistical analyses were performed with SPSS 19.0 software and data were compared using Mann-Whitney U test. RESULTS: There were no significant differences in the marginal adaptation between two groups (P > 0.05). GE presented significantly higher fracture resistance when compared to GC (P < 0.05). Failure pattern was similar and characterized by the tooth-ceramic fracture on the force-applied side. CONCLUSIONS: CAD/CAM fabricated feldspathic ceramic and PICN endocrowns provide sufficient marginal adaptation, but the PICN endocrowns shows higher fracture resistance than the feldspathic ceramic endocrowns.

Evaluation of Mechanical Properties of Various Nanofibre Reinforced Bis-GMA/TEGDMA Based Dental Composite Resins / Evaluación de las propiedades mecánicas de varias resinas compuestas dentales basadas en Bis-GMA/TEGDMA reforzadas con nanofibras

ABSTRACT Objective: To investigate the mechanical properties of various mass fractions of Nylon 6 (N6), polymethyl-metacrylate (PMMA) and polyvinylidene-difluoride (PVDF) nanofibres reinforced bisphenol A-glycidyl methacrylate (Bis-GMA) and tri-ethylene glycol dimethacrylate (TEGDMA) based dental composite resins and to evaluate the penetration characteristics of the nanofibres into the resin. Methods: Nylon 6, PMMA and PVDF nanofibres were produced using the electrospinning method. The morphologies of the fabricated nanofibres were evaluated with a scanning electron microscope (SEM). The nanofibres were placed into the resin matrix at different mass fractions (3%, 5% and 7%). The three-point bending test was applied to nanofibre-reinforced dental composite resins and neat resin specimens. The flexural strength (Fs), flexural modulus (EY) and work of fracture (WOF) of the groups were found. The analysis of variance was used for the statistical analysis of the acquired data. Tukey 's multiple test was performed to compare the Fs, EY and WOF means. Fractured surfaces of the samples were observed by SEM, and fracture morphologies were evaluated. Results: Polymethyl-metacrylate nanofibres dissolved in the matrix, and a polymer alloy took place in the matrix. Fibre pull-out and fibre bridging mechanisms were observed by SEM images of the N6 and PVDF nanofibre-reinforced dental composites. The produced nanofibres enhanced the mechanical properties of the dental composite resins. Conclusion: Fibre pull-out and fibre bridging mechanisms on the fractured surfaces of samples may play a key role in the reinforcement of dental composite resins. However, polymer alloy of PMMA nanofibres increased the mechanical properties of the resin matrix.

RESUMEN Objetivo: Investigar las propiedades mecánicas de resinas compuestas dentales basadas en bisfenol A-diglicidildimetacrilato (Bis-GMA) y dimetacrilato trietilen-glicol (TEGDMA) reforzadas con nanofibras de fracciones de masa de Nylon 6 (N6), polimetilmetacrilato (PMMA) y fluoruro de polivinilideno (PVDF), y evaluar las características de la penetración de las nanofibras en la resina. Métodos: Se produjeron nanofibras de Nylon 6, PMMA y PVDF utilizando el método de electrohilado (electrospinning). Las morfologías de las nanofibras fabricadas fueron evaluadas con un microscopio electrónico de barrido (MEB). Las nanofibras fueron introducidas en la matriz de resina en diferentes fracciones de masa (3%, 5% y 7%). La prueba de flexión de tres puntos fue aplicada a las resinas compuestas dentales reforzadas por nanofibras y a las muestras de resina pura. La resistencia a la flexión (Rf), el módulo de flexión (EY) y el trabajo de fractura (WOF) de los grupos fueron halladas. El análisis de varianza se usó para el análisis estadístico de los datos adquiridos. Se realizó la prueba de comparaciones múltiples de Tukey con el propósito de comparar las medidas de Rf, EY y WOF. Las superficies fracturadas de las muestras fueron observadas mediante un MEB, y se evaluaron las morfologías de fractura. Resultados: Las nanofibras de polimetilmetacrilato se disolvieron en la matriz, y tuvo lugar una aleación de polímeros en la matriz. Los mecanismos de desprendimiento de fibras y puenteo de fibras fueron observados mediante imágenes de MEB de los compuestos dentales reforzados con nanofibras de N6 y PVDF. Las nanofibras producidas realzaron las propiedades mecánicas de las resinas compuestas dentales. Conclusión: Los mecanismos de desprendimiento de fibras y puenteo de fibras en las superficies fracturadas de las muestras pueden desempeñar un papel clave en el reforzamiento de las resinas de los compuestos dentales. Sin embargo, la aleación polimérica de las nanofibras de PMMA aumentó las propiedades mecánicas de la matriz de resina.

Reinforcement of maxillary dentures with silane-treated ultra high modulus polyethylene fibers.

Midline fractures appear to be the most common problem in maxillary complete dentures, and they can be prevented by reinforcement of the base material. In this clinical trial, complete upper dentures made, for patients having a history of midline fractures, that were reinforced with ultra-high modulus polyethylene fiber in woven form. This fiber was treated with a silane-coupling agent and sandwiched between acrylic dough. Laboratory procedures were conducted easily and conventionally, without any special equipment. At the end of 18 months, all of the dentures were well accepted and did not show any signs of fracture.