Caries and ABO secretor status in a Hungarian population of children and adolescents: an exploratory study.

ABO blood group antigen (ABGA) secretion into the saliva and other body fluids is a well-known phenomenon, and there is evidence to suggest a link between secretor status and the appearance of caries. It has been proposed that secretion of these antigens into the saliva might be caries-preventive, however, this proposition is still a matter of debate. Our aim was to examine the relationship between caries experience and secretor status in a group of Hungarian children and adolescents in a cross-sectional study. Altogether 130 children and adolescents participated in the study (aged 6-18 years). Participants were divided into two groups according to dentition (i.e. mixed and permanent). ABGA were determined from saliva. The DMF-T and dmf-t (decayed, missing, and filled) indices were calculated, as well as the oral health hygiene index-simplified plaque index. Association of these indices with secretor status was examined. In mixed dentition, the mean dmf-t values were significantly lower in the secretor group (2.1 ± 0.52 SEM), as compared to the nonsecretor group (3.8 ± 0.93 SEM; p < 0.05, Mann-Whitney U test). The finding that children of mixed dentition are apparently better protected against caries suggests that the assumed protective effect might be associated with deciduous teeth, but given the general paucity of knowledge about this topic, further research is indicated.

Surface modifications induced by ns and sub-ps excimer laser pulses on titanium implant material.

Medical implants used in oral and orthopaedic surgery are mainly produced from titanium. Their biological behaviour, e.g. osseointegration, essentially depends on both the chemical composition and the morphology of the surface. Modifications achieved by excimer laser irradiation of titanium samples were investigated in order to improve their surface characteristics so as to facilitate biointegration. To enlarge the effective interfacial area of bone-implant contact, holes were ablated by laser pulses of ns or sub-ps length. During ns ablation, crown-like projecting rims formed around the borders of the holes. Ultra-short (0.5ps) KrF excimer laser pulses were successfully applied to avoid these undesirable formations. Since a smooth dental implant surface is necessary to maintain a healthy connection with the soft tissues, laser polishing of samples was investigated, too. Irradiation with a series of ns laser pulses resulted in effective smoothing, as measured with atomic force microscope. X-ray photoelectron spectroscopy analysis of the laser-polished titanium surface revealed that laser treatment led to a decrease of the surface contamination and in thickening of the oxide layer. X-ray diffraction measurements demonstrated that the original alpha-titanium crystal structure was preserved.

Isotopic scaling and the symmetry energy in spectator fragmentation.

Isotopic effects in the fragmentation of excited target residues following collisions of 12C on (112,124)Sn at incident energies of 300 and 600 MeV per nucleon were studied with the INDRA 4pi detector. The measured yield ratios for light particles and fragments with atomic number Z < or = 5 obey the exponential law of isotopic scaling. The deduced scaling parameters decrease strongly with increasing centrality to values smaller than 50% of those obtained for the peripheral event groups. Symmetry-term coefficients, deduced from these data within the statistical description of isotopic scaling, are near gamma = 25 MeV for peripheral and gamma < 15 MeV for central collisions.

Quinone-dependent delayed fluorescence from the reaction center of photosynthetic bacteria.

Millisecond delayed fluorescence from the isolated reaction center of photosynthetic bacteria Rhodobacter sphaeroides was measured after single saturating flash excitation and was explained by thermal repopulation of the excited bacteriochlorophyll dimer from lower lying charge separated states. Three exponential components (fastest, fast, and slow) were found with lifetimes of 1.5, 102, and 865 ms and quantum yields of 6.4 x 10(-9), 2.2 x 10(-9), and 2.6 x 10(-9) (pH 8.0), respectively. While the two latter phases could be related to transient absorption changes, the fastest one could not. The fastest component, dominating when the primary quinone was prereduced, might be due to a small fraction of long-lived triplet states of the radical pair and/or the dimer. The fast phase observed in the absence of the secondary quinone, was sensitive to pH, temperature, and the chemical nature of the primary quinone. The standard free energy of the primary stable charge pair relative to that of the excited dimer was -910 +/- 20 meV at pH 8 and with native ubiquinone, and it showed characteristic changes upon pH and quinone replacement. The interaction energy ( approximately 50 meV) between the cluster of the protonatable groups around GluL212 and the primary semiquinone provides evidence for functional linkage between the two quinone binding pockets. An empirical relationship was found between the in situ free energy of the primary quinone and the rate of charge recombination, with practical importance in the estimation of the free energy levels from the easily available lifetime of the charge recombination. The ratio of the slow and fast components could be used to determine the pH dependence of the free energy level of the secondary stable charge pair relative to that of the excited dimer.