Magnetic Resonance Force Microscopy with a One-Dimensional Resolution of 0.9 Nanometers.

Magnetic resonance force microscopy (MRFM) is a scanning probe technique capable of detecting MRI signals from nanoscale sample volumes, providing a paradigm-changing potential for structural biology and medical research. Thus far, however, experiments have not reached sufficient spatial resolution for retrieving meaningful structural information from samples. In this work, we report MRFM imaging scans demonstrating a resolution of 0.9 nm and a localization precision of 0.6 nm in one dimension. Our progress is enabled by an improved spin excitation protocol furnishing us with sharp spatial control on the MRFM imaging slice, combined with overall advances in instrument stability. From a modeling of the slice function, we expect that our arrangement supports spatial resolutions down to 0.3 nm given sufficient signal-to-noise ratio. Our experiment demonstrates the feasibility of subnanometer MRI and realizes an important milestone toward the three-dimensional imaging of macromolecular structures.

Nanoladder Cantilevers Made from Diamond and Silicon.

We present a "nanoladder" geometry that minimizes the mechanical dissipation of ultrasensitive cantilevers. A nanoladder cantilever consists of a lithographically patterned scaffold of rails and rungs with feature size ∼100 nm. Compared to a rectangular beam of the same dimensions, the mass and spring constant of a nanoladder are each reduced by roughly 2 orders of magnitude. We demonstrate a low force noise of 158-42+62 zN and 190-33+42 zN in a 1 Hz bandwidth for devices made from silicon and diamond, respectively, measured at temperatures between 100-150 mK. As opposed to bottom-up mechanical resonators like nanowires or nanotubes, nanoladder cantilevers can be batch-fabricated using standard lithography, which is a critical factor for applications in scanning force microscopy.

Competing phases in the high field phase diagram of (TMTSF)(2)ClO(4).

A model is presented for the high field phase diagram of (TMTSF)(2)ClO(4), taking into account the anion ordering, which splits the Fermi surface into two bands. For strong enough field, the largest metal spin density wave critical temperature corresponds to the N=0 phase, which originates from two intraband nesting processes. At lower temperature, the competition between these processes puts at disadvantage the N=0 phase vs the N=1 phase, which is due to interband nesting. A first order transition then takes place from the N=0 to N=1 phase. We ascribe to this effect the experimentally observed phase diagrams.

Differentiation of odontoblasts in mouse dental papillae recombined with normal or chemically-treated dentinal matrices.

Separation and recombination experiments were made with manually or trypsin-dissociated dental papillae (day 15, 16, 17, 18 in utero and 2, 7, 14 postnatal) and manually isolated hard tissues of the third molar crown (14 postnatal days). Several series of hard tissues were further treated with citric acid, hyaluronidase or sodium hypochlorite. The recombinations were transplanted into the subcutaneous tissue of new-born mice. Grafts were removed 7, 14 and 21 days later and prepared for light and electron microscopy. Whatever the age of the papilla and whatever the treatment of the crowns, well-characterized odontoblasts differentiated and deposited new layers of tubular dentine, except when the recombined dental papilla was 15 days old. These findings indicate that odontoblasts are very early committed (since day 16 in utero) and that they may differentiate in dental papillae in contact with chemically altered dentinal matrices.

Ultrastructure of a new generation of odontoblasts in grafted coronal tissues of mouse molar tooth germs.

Third molar tooth germs were removed from 14-day-old mice and freed from the enamel organ and follicle. After section of the apical tissues, including Hertwig's sheath, they were transplanted in 1-day-old newborn mice of the same lineage. Electron microscopy of grafts removed 7, 14 and 21 days later showed that, following the disappearance of the initial layer of odontoblasts and a period of adaptation, 14 days after transplantation newly differentiated odontoblasts deposited tubular dentine. The dentine matrix production was increased over that of controls, demonstrating that synthesis was accelerated, possibly because of lack of nerves in the grafts. Numerous characteristic structures that might be involved in the transit of proteoglycans from the Golgi apparatus were seen, as far as the extremity of the odontoblast processes. The particular experimental conditions allowed the observation in the neck region of the odontoblast of a concentration of coated vesicles which might be involved in cellular lengthening. Thus, in the presence of a fine and regular vascular network, a new generation of odontoblasts may differentiate, even in the absence of epithelial and nervous elements, and so predentine may contain inductive factors that allow the odontoblastic differentiation of pulp cells in contact with it.

Cellular behaviour in epithelial root sheath following vinblastine administration in mouse.

After injection of vinblastine sulfate (VLB) cells of the epithelial root sheath (ERS) showed accumulation of phagosomes lysosomes and, in particular, of exocytosis vesicles facing the basal lamina. An unusual frequency of cell contacts was also noted between pulp mesenchyme and ERS. In the periradicular zone the cells showed accentuated signs of a squamous-like evolution. In addition, numerous mitotic figures were seen arrested at prometaphase all along the tissue: the mitotic arrest index was higher at the tip of the sheath and decreased more coronally. These findings strongly suggest that ERS participates actively to the formation of the basal lamina. They show that heterogenous cell relations frequently occur during root morphogenesis; however they put into question the role of ERS in cementogenesis. The existence of a high mitotic potential in ERS can explain its consistent morphology and might reflect a process of differential mitotic sequences involved in odontoblast differentiation.

Ultrastructural study of new connective tissue attachment following phosphoric acid application on human root dentin.

THE PRESENT STUDY was undertaken to verify whether acid conditioning of the root surface can promote new connective tissue attachment in man. A flap was raised over two maxillary central incisors, with 6-mm pockets, which had to be extracted in a 72-year-old woman. Following root planning, a rectangular area was delineated by a groove on the buccal surface of the teeth. Inside these limits, cementum was removed and the denuded dentin was etched with a 50% gelified phosphoric acid solution (pH, 1.3) for 1 minute and the flap was repositioned. Forty-two days later, the experimental teeth were extracted, and undecalcified specimens were prepared routinely for transmission electron microscopy. Results showed that new connective tissue attachment had occurred between healing connective tissues and acid-treated dentin surface, with functionally oriented Sharpey's fibers. The mechanism of new connective tissue attachment could be observed as a typical cementum crystallites deposition on a denuded dentin matrix coupled with an active collagen fibrils synthesis. This process resulted in the incorporation of fibers into the new superficial layer of cementoïd tissue.

[Scanning and transmission electron microscopy study of the effects of a citric acid solution on the human root dentine]. / Etude au microscope électronique à balayage et à transmission des effets d'une solution d'acide citrique sur la dentine radiculaire humaine.

After removal of the cementum layer, the buccal surface of human roots was been treated in vitro for 60, 120 and 180 seconds with a gel solution of 50% citric acid (pH 2.1). These surfaces were prepared for observation in the scanning electron microscope (SEM) and ultra-thin sections of the treated areas were studied in the transmission electron microscope (TEM). The SEM results showed that application of an acid solution revealed fibrous like structures on the dentinal surface after 60 and 180 seconds of treatment. A correlation between the results obtained in SEM and TEM is not always evident. The ultra-thin sections showed, in the superficial dentine, three distinct zones at the three time intervals chosen: from outside to inside, a very thin crust, a demineralized zone with collagen fibres and a deep dentine zone could be observed. After 120 seconds, the collagenous matrix seemed to be totally freed from the inorganic part.

Experimental induction of cementogenesis on the enamel of transplanted mouse tooth germs.

First and second maxillary molar tooth germs with their surrounding bone were removed from 9-day-old mice, freed of the reduced enamel epithelium, re-inserted crown downwards in their bony crypts and then transplanted in the subcutaneous tissue of hosts of the same age and litter. Grafts were removed 14 days later and prepared for light and electron microscopy. In the areas where the reduced enamel epithelium was missing, a layer of cementum-like tissue was present on the enamel surface, always associated with cells showing the typical features of cementoblasts. A thin electron-lucent layer of fine fibrillar material separated the enamel surface from the new hard tissue which was composed of densely-packed collagen mixed with a ground substance. Where the cementum-like tissue was thick, cells were trapped in a collagenous matrix. The cementogenesis on enamel was strictly dependent on the absence of the reduced enamel epithelium. Thus, when exposed to follicular tissue, the surface of immature enamel appears to exert an influence on follicular cells and stimulate cementogenesis. This hypothesis could explain the presence of overgrowths of cementum in the cervical region of tooth crowns where the reduced enamel epithelium may be particularly vulnerable.

[Microscopy and electron microscopy of the Hertwig sheath in the mouse]. / Etude en Microscopie photonique et électronique de la gaine de Hertwig chez la souris.

The structure and ultrastructure of Hertwig's sheath have been studied in the mice on molar tooth germs collected on day 16. On a morphological basis, two parts, a diaphragm portion and a sheath part could be described. The diaphragm portion consisted of two layers, one internal and one external with in between occasionally cells disposed in quincunx. Mitotic activity was noted in the external layer. This fact raised the possibility of the existence of a cellular flow from this layer towards the internal counterpulpal layer. The permanent existence of the sheath during root elaboration could thus be explained. In the internal layer structural modifications and cell axis variations seemed to be related to the odontoblast differentiation. In the "sheath" part electron microscopy revealed the existence of a fine layer of unmineralized collagen fibrils which remained under the internal epithelial layer. The observations related to the structure of the periradicular sheath cells questioned the hypothesis whether these cells assume secretory potentials.