Mechanical characterization of the enamel microstructure treated with non alcoholic drinks

In previous studies, it has been shown that the microstructure of prismatic dental enamel presents differences between the external and internal zone. Radial enamel is found in the outer third of enamel and has higher microhardness values than enamel with Hunter- Schreger Bands (HSB) that occupies the inner 2/3. Our aim was to evaluate the mechanical behavior of radial enamel and HSB due the action of a non-alcoholic beverage in vitro. Longitudinal sections of dental crowns were embedded in polymer, worn and polished with sandpapers of decreasing granulation. The samples were immersed in a flavoured natural water for 12 minutes. Nanohardness tests (Triboindenter Hysitron) were performed on the radial and HSB enamel before and after the exposure to the drink. Hardness determinations "H", reduced modulus "Er" and contact depth "hc" were obtained. The percentage of reduction of hardness was determined. The values found in healthy radial enamel were H: 5.48±0.23 GPa; Er: 86.97±8.11 GPa; hc: 149.73±4.25 nm and in HSB H: 4.24±0.43 GPa; Er: 75.24±7.09 GPa; hc: 176.36±11.29 nm. After exposure to beverage, it was found in the radial enamel H: 2.22±0.31 GPa; Er: 58.73±10.79 GPa; hc: 270.29±21.22 nm, and in HSB H: 1.54±0.42 GPa; Er: 48.11±6.54 GPa; hc: 350.10±63.33 nm. After the drink action, the values of hardness of the radial enamel and HSB decreased and the trend observed in healthy enamel remained, where the highest values corresponded to the radial enamel. The percentage reduction of H in the radial enamel was 59.48% and in the HSB enamel it was 63.67%. The contact depth increased by about 50%.The decrease in hardness is related to the mineral loss produced by the acids contained in the drink. We conclude that the action of the non-alcoholic beverage produces a decrease in the mechanical properties in both the radial enamel and the HSB. The lower values in the reduced module Er indicate the formation of a superficial softened layer, the enamel with HSB being more vulnerable.

The ultrastructure of the tooth enamel of small Equus of the “tarpan” group and their possible phylogenetic connections

The paper presents the results of a comparative analysis of the ultrastructure of tooth enamel (incisors, premolars and molars) in representatives of morphologically (and possibly phylogenetically) similar forms of small horses. These are both extinct forms of tarpan – Equus gmelini from various sites of the early Holocene of Ukraine (Myrne, Kamiana Mohyla and Hirzhevo) and modern forms – konik polski and E. przewalskii, and European wild ass – E. hydruntinus. Morphology of prisms in different layers of tooth enamel and its relative relationships in various taxa were thoroughly described. The data obtained in the form of tables and graphs, with the appropriate statistical processing thereof, show the morphological similarity of tarpan remains from different sites, and their similarity to the konik polski and Przewalski’s horse. However, the European wild ass differs significantly from the other groups studied. In equines, the radial enamel varieties (types І, ІІ and ІІІ) have evolutionary tendencies to strengthen the first and second types of hydroxyapatite prisms, while reducing the share of the IPM matrix in the enamel structure. In turn, the enamel of the incisors is characterized by lamellar enamel of the HSB uniserial type.

Tooth Enamel Microstructure in Megasorex gigas (Merriam, 1897) and Cryptotis magna (Merriam, 1895) from Mexico – In Comparison to the Schmelzmuster in other Shrews

The enamel microstructure of molars in Mexican soricines Megasorex and Cryptotis is described and compared to the six types of schmelzmuster found in fossil and recent Soricidae. These types of schmelzmuster show a high correlation to the current systematics of Soricidae. In Megasorex, the relatively simple schmelzmuster is dominated by radial enamel. However, a very thin innermost layer of differentiated enamel indicates the beginning of a two-layered schmelzmuster. This corresponds to the Notiosorex-schmelzmuster. The teeth of Megasorex lack pigmentation, which is not reflected in its schmelzmuster. Similarities to the white-toothed Crocidura-schmelzmuster are superficial. Cryptotis has the typical two-layered enamel of derived Soricinae. The specific enamel type of the inner layer and the strong lateral inclination of its prisms represent a new modification of the highly derived Blarina-schmelzmuster.