Human root dentin microhardness and degradation by triple antibiotic paste and calcium hydroxide.

PURPOSE: To investigate and compare the effects of the two widely used regenerative endodontics medicaments: Triple antibiotic paste (ciprofloxacine-metronidazole-clindamycin) and calcium hydroxide on the microhardness and degradation of human root dentin. METHODS: Following ethical approval and subject consent to use teeth in this research study, 60 singled-rooted permanent human teeth were randomly divided into six groups:(1) Tri-antibiotic paste with distilled water, or with (2) propylene glycol, (3) calcium hydroxide with distilled water, (4) calcium hydroxide propylene glycol, (5) untreated extracted teeth as negative controls, or (6) teeth instrumented and filled with calcium hydroxide or tri-antibiotic paste as positive controls. The microhardness tests were conducted after 1 and 2 months of exposure to the medicaments using a Vickers microhardness tester. Raman spectroscopy and energy dispersive x-ray spectroscopy were used to evaluate the chemistry and structure of the root dentin. RESULTS: There were differences in the dentin microhardness following treatment with the medicaments or controls (P< 0.05). The time of root dentin exposure to the medicaments was similar (P> 0.05). The root dentin microhardness was lower in the teeth treated with the triple antibiotic paste or calcium hydroxide when combined with propylene glycol. The root dentin collagen in these treated teeth were also significantly degraded when viewed with Raman spectroscopy and energy dispersive x-ray spectroscopy, whereas the inorganic phase (dentin) remained unaltered. Samples exposed to the antimicrobial agents with water as a vehicle exhibited stronger microhardness and less degradation. CLINICAL SIGNIFICANCE: These ex vivo results suggest that the triple antibiotic paste and calcium hydroxide should be used with propylene glycol if a fast diffusion is desired or with water to avoid degrading the collagen and weakening the microhardness of the teeth. Clinical trials are needed of new formulations of medicaments with propylene glycol to disinfect teeth for regenerative endodontic procedures, to help strengthen the teeth to prevent the loss of children's permanent immature teeth by fracture following caries or trauma.

Key Parameters in the Manufacture of SiC-Based Composite Materials by Reactive Melt Infiltration.

The manufacture of SiC-based composites is quite widespread, and currently different methods are employed to produce them. The most efficient method, taking into account the cost/performance ratio, is reactive melt infiltration. It consists in infiltrating liquid silicon into a porous preform that must contain carbon, so that SiC is produced during infiltration. In the present work, the synthesis of two SiC-based composite materials with very different applications and microstructures has been studied and optimized. In both cases, materials have been obtained with suitable properties for the selected applications. One of the materials studied is silicon carbide particles/silicon (SiCp/Si) for protection systems such as armor jackets, and the other one is carbon fiber/silicon carbide (Cf/SiC) for use in braking systems. For the optimization, the dwell time and the atmosphere (Ar or primary vacuum) were used as variables. It has been found that in both preforms, the optimum conditions are 1 h dwell time and a vacuum atmosphere at 1450 °C. The effect of these parameters on microstructure and infiltration kinetics are discussed.

Graphene Translucency and Interfacial Interactions in the Gold/Graphene/SiC System.

Integration of graphene into electronic circuits through its joining with conventional metal electrodes (i.e., gold) appears to be one of the main technological challenges nowadays. To gain insight into this junction, we have studied the physicochemical interactions between SiC-supported graphene and a drop of molten gold. Using appropriate high-temperature experimental conditions, we perform wetting experiments and determine contact angles for gold drops supported on graphene epitaxially grown on 4H-SiC. The properties of the metal/graphene interface are analyzed using a wide variety of characterization techniques, along with computational simulations based on density functional theory. In contrast with the established literature, our outcomes clearly show that graphene is translucent in the gold/graphene/SiC interface, and therefore its integration into electronic circuits primarily depends on the right choice of the support to produce favorable wetting interactions with liquid gold.