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We present high angular resolution, near-infrared imaging, and spectroscopy of a low-mass companion to the lithium-depleted, double-line spectroscopic binary HBC 425 (St 34) obtained using NIRSPEC and the Keck II adaptive optics system. Positioned ?1.23? southeast of the primary pair, the companion, HBC 425C, is ?2.4 mag fainter at 2.2 ?m. Moderate-resolution (R? 2500) J- and K-band spectroscopy reveals HBC 425C to have an M5.5 (± 0.5) spectral type. Comparisons with pre-main-sequence evolutionary models imply a mass of ?0.09 M?and ages of 8-10 Myr, assuming the nominal distance of Taurus-Auriga (?140 pc), or ?25 Myr if placed at ?90 pc. We also present high-dispersion optical spectra of HBC 425 and HBC 425C obtained using the high-resolution echelle spectrometer (HIRES) on Keck I. We detect strong Li i?6708 absorption in the spectrum of HBC 425C. Using curves of growth for the Li i?6708 doublet, we estimate its abundance level to lie between log N(Li) = 1.9 and 3.1 dex. The spectrum of HBC 425 exhibits Ca iiH and K lines, He i??5876, 6678, and strong Balmer line emission, consistent with accretion. We place more restrictive upper limits on the surface abundance of lithium and find that HBC 425 retains less than ?0.1% of its primordial abundance. The presence of lithium in the photosphere of HBC 425C does not resolve the discrepancy between isochronal and lithium-depletion ages for the primary pair. However, if lithium were depleted relative to interstellar abundance levels, even minimally, considerable support would be gained for the more advanced age of this hierarchical triple system.

The purpose of the present work was to investigate the infrared (IR) spectrum of shark enameloid, especially with regard to hydroxide and carbonate bands. With thin sections placed directly in the IR beam it was possible to get high concentrations of ions without interfering effects from a dispersion medium (e.g., alkali halides). For comparison, spectra of shark dentin and a geo-apatite were also recorded. In spectra of shark enameloid and geo-apatite medium strong hydroxide absorption bands were found around 3535 cm−1, and in shark dentin and geo-apatite spectra weak shoulders were observed at about 3570 cm−1. Hydroxide libration bands at about 740 cm−1were found in shark enameloid and geo-apatite spectra; in the latter, also a band at 680 cm−1. Carbonate bands were found in shark enameloid spectra at 1480 (weak shoulder), 1453, 1423, and 868 cm−1. In shark dentin spectra there were carbonate bands at 1452, 1417, and 875 cm−1, and probably also a carbonate band at about 1530 cm−1overlapped by an amide II band. Weak carbonate bands were also found in the spectra of the geo-apatite at 1452 cm−1, and at about 1425 and 880 cm−1. The relative intensities of the bands at 1453 cm−1(contributed from A and B sites) and around 1420 cm−1(B sites) changed from shark enameloid to shark dentin, and also from shark enameloid to the geo-apatite. More A sites seem to be occupied by carbonate in shark dentin than in shark enameloid, supposedly owing to fluoride occupation of A sites in shark enameloid. In geo-apatite and shark enameloid there are hydroxide ions hydrogen bonded to fluoride. Both shark enameloid and the geo-apatite are fluoride rich, and geo-apatite seems to have the highest fluoride concentration. There are, however, indications that the hydroxide concentration is also higher in the geo-apatite than in shark enameloid. This can be explained by the much higher carbonate content, and partly also by the higher water content in shark enameloid. There are A sites in geo-apatite and probably also in shark enameloid which are occupied by carbonate, but the proportion of occupied A sites relative to occupied B sites is greater in geo-apatite than in shark enameloid. This difference can be explained by the preference of A sites when the carbonate concentration is very low. On the other hand, for greater amounts of carbonate such as we have in shark enameloid, B sites are preferred.

An in vitro test is described that simulates the in vivo fate of a denture adhesive, namely destruction, dilution, and dissolution of the adhesive, by repeated measurement of tensile bond strength for the adhesive in isotonic saline over time. The bond strengths were measured under two different settings of the testing machine. The main compositions of three denture adhesive pastes, Fittydent, Fixodent, and Super Poli-Grip and one powder adhesive, Super Wernet's, were determined by infrared spectroscopy. The tensile bond strengths of these adhesives and those of pure tragacanth gum were subjected to a three-way analysis of variance. The Fittydent and Super Poli-Grip adhesives exhibited the best results over time. The most appropriate of the described methods for testing denture adhesives seem useful; however, when seen in relation to the results of a published clinical study where the patients were asked to evaluate the retention and the duration of some of these adhesives, there are indications that the clinical validity of the method might be improved if paste adhesives are tested at temperatures above 35^oC.

The structure, the temperature dependence of the resistivity, thermopower, ESR-line-width and the spin susceptibility of a new series of organic metals (BEDT-TTF)2X·(TCE)0.5[X = BF4, FSO3and IO4] is presented and discussed.

Titanium tetrafluoride (TiF"4) was applied to acid-etched enamel surfaces to study the effect on surface structure and tensile bond strength of orthodontic brackets. Three groups of 20 premolars each were compared in debonding tests. Group l received a 1% and Group ll received a 4% topical TiF"4 treatment after acid etching. Group lIl served as control, that is, no fluoride solution was applied to the enamel after acid etching. Each treatment lasted 60 seconds followed by a thorough rinsing with water for 30 seconds. Brackets were bonded on all teeth with the same procedure. All premolars were then placed in a water bath at 37^o C. Ten teeth from each group were debonded after 24 hours, and the remaining teeth were debonded after 6 months. Results indicated that the application of 1% and 4% TiF"4 solutions on etched enamel surfaces did not alter the tensile bond strength significantly after 24 hours and 6 months. The scanning electron microscope (SEM) examination of the surface structure demonstrated the presence of extensive reaction products, which covered enamel surfaces and appeared to interfere with etch patterns. It was concluded that the application of TiF"4 solutions to etched enamel surfaces before bonding will not have an adverse effect on the tensile strength of orthodontic attachments. (AM J ORTHOD DENTOFAC ORTHOP 1995;108:256-61.)

Die zunehmende Verfeinerung der kieferorthopädischen Therapie stellt erhöhte technische Anforderungen sowohl an den Kliniker als auch an die Industrie. Seit wenigen Jahren sind sogenannte “superelastische” Drahtbögen auf dem Markt. Generell haben solche Bögen ein hervorragendes “Formgedächtnis”, das heißt, in bestimmten Bereichen bestehen ein “superelastisches” Kraftniveau und eine ausgesprochene Hysterese, wobei sie meist sehr temperaturempfindlich sind. Unter Temperaturkontrolle sind Belastungen aus dem klinischen Bereich in einem computergesteuerten “Lloyd 1000 R”-Testgerät simuliert und zahlenmäßig belegt. Für die klinische Arbeit ist das “Formgedächtnis” von Vorteil. Das “superelastische” Kraftniveau ist allerdings für Edgewisebögen weniger interessant, weil dieses bei herkömmlicher Aktivierung der Bögen nur selten erreicht wird. Durch die ausgeprägte Hysterese wird die mechanische Belastung der Zähne abgeschwächt, aber auch weniger kontrollierbar. Ein ähnlicher Effekt wird durch die gleichzeitig bestehende Temperaturempfindlichkeit erreicht. Aktive Bögen können durch Temperatursenkung entspannt werden mit dem Effekt einer Entlastung für empfindliche Zähne. Ob das möglicherweise auch zu einer Verbesserung der Durchblutung des parodontalen Gewebes führt und somit biologisch vorteilhaft ist, sollte Gegenstand künftiger Forschung sein.

A neutron activation method for the determination of rare earths in hard tissues was developed and the concentrations of some of these elements in human dentine and enamel were determined. The results obtained for La, Sm, Tb and Yb are very low, indicating a total rare-earth content of the order of 0.1 ppm or less in the samples investigated. The observed La/Sm ratios seem to indicate a slight enrichment of the lighter rare earths relative to the heavier, as compared to average geological abundances.