Tooth morphology in function of selfprotective mechanism.

The degree of curvature of vestibular and oral tooth surfaces is determined by the shape sequence from the tooth crown to the epithelial attachment and the alveolar bone, and directly influences the health of gingiva and the entire tooth support system. The goal of this research was to determine vestibulo-oral planes of upper and lower permanent premolars and molars and the thickness of the associated alveolar osseous wall, and 2,727 measurings were processed using pertinent statistical procedures. The results have shown the degree of curvature of vestibular and oral tooth surfaces to be higher in upper teeth than in lower ones (p > 0.05); vestibular convexities higher than oral ones and especially noticeable at the junction from the meandle to the lower third of the crown. Higher vestibular curvature also entailed thicker osseous wall. All results were higher than the ones found in literature. We consider our results to be relevant for our population. The research on the relationship of teeth and the alveolar bone should be continued by using even more test points and more sophisticated research procedures.

Charge displacement by adhesion and spreading of a cell.

The potentiostatic control of surface charge density and interfacial tension of an electrode immersed in an aqueous electrolyte solution offers a possibility for direct studies of non-specific interactions in cell adhesion. Unicellular marine alga, Dunaliella tertiolecta (Chlorophyceae) of micrometer size and flexible cell envelope was used as a model cell and 0.1 M NaCl as supporting electrolyte. The dropping mercury electrode acted as in situ adhesion sensor and the electrochemical technique of chronoamperometry allowed measurement of the spread cell-electrode interface area and the distance of the closest approach of a cell. The adhesion and spreading of a single cell at the mercury electrode causes a displacement of counter-ions from the electrical double layer over a broad range of the positive and negative surface charge densities (from +16.0 to -8.2 microC/cm2). The flow of compensating current reflects the dynamics of adhesive contact formation and subsequent spreading of a cell. The adhesion and spreading rates are enhanced by the hydrodynamic regime of electrode's growing fluid interface. The distance of the closest approach of an adherent cell is smaller or equal to the distance of the outer Helmholz plane within the electrical double layer, i.e. 0.3-0.5 nm. There is a clear evidence of cell rupture for the potentials of maximum attraction as the area of the contact interface exceeded up to 100 times the cross-section area of a free cell.

Adhesion of acinetobacter venetianus to diesel fuel droplets studied with In situ electrochemical and molecular probes

The adhesion of a recently described species, Acinetobacter venetianus VE-C3 (F. Di Cello, M. Pepi, F. Baldi, and R. Fani, Res. Microbiol. 148:237-249, 1997), to diesel fuel (a mixture of C12 to C28 n-alkanes) and n-hexadecane was studied and compared to that of Acinetobacter sp. strain RAG-1, which is known to excrete the emulsifying lipopolysaccharide, emulsan. Oxygen consumption rates, biomass, cell hydrophobicity, electrophoretic mobility, and zeta potential were measured for the two strains. The dropping-mercury electrode (DME) was used as an in situ adhesion sensor. In seawater, RAG-1 was hydrophobic, with an electrophoretic mobility (&mgr;) of -0.38 x 10(-8) m2 V-1 s-1 and zeta potential (zeta) of -4.9 mV, while VE-C3 was hydrophilic, with &mgr; of -0.81 x 10(-8) m2 V-1 s-1 and zeta of -10.5 mV. The microbial adhesion to hydrocarbon (MATH) test showed that RAG-1 was always hydrophobic whereas the hydrophilic VE-C3 strain became hydrophobic only after exposure to n-alkanes. Adhesion of VE-C3 cells to diesel fuel was partly due to the production of capsular polysaccharides (CPS), which were stained with the lectin concanavalin A (ConA) conjugated to fluorescein isothiocyanate and observed in situ by confocal microscopy. The emulsan from RAG-1, which was negative to ConA, was stained with Nile Red fluorochrome instead. Confocal microscope observations at different times showed that VE-C3 underwent two types of adhesion: (i) cell-to-cell interactions, preceding the cell adhesion to the n-alkane, and (ii) incorporation of nanodroplets of n-alkane into the hydrophilic CPS to form a more hydrophobic polysaccharide-n-alkane matrix surrounding the cell wall. The incorporation of n-alkanes as nanodroplets into the CPS of VE-C3 cells might ensure the partitioning of the bulk apolar phase between the aqueous medium and the outer cell membrane and thus sustain a continuous growth rate over a prolonged period.