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Initial enamel crystals are not spatially associated with mineralized dentine (1994)

Diekwisch, Thomas G. H. ; Berman, Brett J. ; Gentner, Steven ; [et al.]

Springer

Cell & tissue research 279 (1994), S. 149-167

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ISSN: 1432-0878

Keywords: Key words: Enamel ; Tooth development ; High-voltage electron-microscopy ; 3-D reconstruction ; Mouse

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine

Notes: Abstract. During epithelial-mesenchymal interactions associated with mammalian tooth development, epithelially-derived and mesenchymally-derived extracellular matrix molecules form a discrete dentine-enamel junction. The developmental and molecular processes required to form this junction are not known. To address this problem we designed studies to test the hypothesis that ectodermally-derived epithelial cells synthesize and secrete enamel proteins which function to nucleate and regulate the growth of enamel calcium phosphate crystals. Initial enamel crystals were detected separate from the adjacent dentine. Electron-microprobe analyses revealed that early enamel crystals were octacalciumphosphate or tricalciumphosphate rather than hydroxyapatite. Thereafter, enamel crystals became confluent with the adjacent, albeit significantly smaller hydroxyapatite crystals associated with mineralized dentine. Therefore, we interpret our data to indicate that de novo enamel crystal nucleation and growth are independent from the mineralization processes characterized for dentine. We further argue that gene expression of enamel protein appears to have a constitutive function during early enamel formation and that supramolecular aggregates of amelogenin and enamelin provide the microenvironment for the nucleation and crystal growth of the initial enamel matrix.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004410050271

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Determination of the Enthalpies of Formation of DyI2 and DyI3 and estimation of the Dy3+/Dy2+ standard aqueous electrode potentialDedicated to Professor Rudolf Hoppe on his 70th Birthday (1992)

Morss, Lester R. ; Spence, Thomas G.

Weinheim : Wiley-Blackwell

Zeitschrift für anorganische Chemie 616 (1992), S. 162-168

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ISSN: 0044-2313

Keywords: Dysprosiumdiiodide ; dysprosium triiodide ; enthalpy ; electrode potential ; Chemistry ; Inorganic Chemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Description / Table of Contents: Bestimmung der Bildungsenthalpien von DyI2 und DyI3 sowie Abschätzung des Dy3+/Dy2+-Standardelektrodenpotentials in wäßrigem MediumDyI2 and DyI3 wurden nach Literaturmethoden hergestellt. Ihre Lösungsenthalpien wurden bestimmt und die Bildungsenthalpien zu ΔfH°(DyI3, s, 298 K) = -(394 ± 16) kJ · mol-1 und ΔfH°(DyI2, s, 298 K) = -(616 ± 10) kJ· mol-1 berechnet. Entsprechenden Literaturangaben sowie geschätzten Lösungsenthalpien und Standardentropien wurde E°(Dy3+/Dy2+, aq.) zu -(2.6 ± 0.2) V berechnet. Ein Vergleich der Enthalpien für die Reduktion von DyI3 zu DyI2 bzw. DyI zu DyI2 wird vorgenommen.

Notes: DyI2 and Dy3I were synthesized by literature techniques. Their enthalpies of solution were determined and their enthalpies of formation calculated to be ΔfH°(DyI2, s, 298 K) = -(394 ± 16) kJ· mol-1 and ΔfH°(DyI3, s, 298 K) = -(616 ± 10) kJ· mol-1. With appropriate literature and estimated enthalpies of solution and standard entropies, the E°(Dy3+/Dy2+, aq) was calculated to be -(2.6 ± 0.2) V. A comparison is made of the enthalpies of reduction of DyI3 to DyI2 and of DyCl3 to DyCl2.

Additional Material: 2 Tab.