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En este estudio se midió la microdureza Vickers del esmalte dental después de la exposición a tres bebidas industrializadas más consumidas en la ciudad de Lima y una bebida control, para evaluar el efecto erosivo de esta bebidas ácidas y su relación con la acidez titulable, el nivel de pH y el efecto buffer de las mismas. Se elaboraron 60 bloques de esmalte superficial de 2mm de espesor por 2-4mm de longitud; se colocaron en acrílico de curado rápido en moldes circunferenciales de 10mm de diámetro y 5mm de altura en diferentes colores (azul para la bebida carbonatada, anaranjado para la bebida refrescante, verde para la bebida isotónica y blanco para la bebida control; para poder diferenciarlos) los cuales se les dieron el paralelismo ente la superficie libre y la base del molde; luego se les dio un pulido tipo espejo para después ser llevados al microdurómetro Buehler donde se les midió la microdureza. Los datos obtenidos fueron analizados a través de la prueba estadística de TSTUDENT, ANALISIS DE VARIANZA ANOVA, TUKEY HSD, KRUSKAL WALLIS Y U DE MANN WHITNEY. Se concluyó que la microdureza superficial del esmalte disminuye significativamente luego de ser sometido a la acción de las bebidas ácidas estudiadas y que el efecto erosivo es inmediato y se incrementa con cada exposición. Se obtuvo como resultado que la bebida isotónica es más erosiva que las otras bebidas; y se concluyó que no hay una relación entre el efecto erosivo y los valores de pH, acidez titulable y efecto buffer las bebidas. / In this study we measured the Vickers microhardness of enamel after exposure to three industrialized beverages more consumed in the city of Lima, and a control beverage; we want to evaluate the erosive effect of the acidic beverages and their relation with the titratable acidity, the level of pH and buffer effect of this beverages. 60 blocks of surface enamel were made of 2mm thickness, and 2-4mm in length, were placed in fast curing acrylic circumferential mold of 10mm in diameter and 5mm in height, in different colors (blue for the carbonated drink, orange for the drink refreshing, green for the drink isotonic and white for the control beverage; to be differentiated); we gave them that the free surface being parallel with the base of the mold, then they were given a mirrorpolished for microhardness after that, they were being taken to Buehler where microhardness was measured. The data were analyzed by the statistical test T-STUDENT, ANALYSIS OF VARIANCE ANOVA, HSD TUKEY, YU WALLIS KRUSKAL WHITNEY MANN. It was concluded that the enamel surface microhardness decreases significantly after being subjected to the action of acidic drinks and the erosive effect is immediate and increases with each exposure. The result was that the isotonic beverage is more erosive than other drinks, and it was concluded that there is not a relationship between the erosive effect of pH values, titratable acidity and buffer effect of the beverages.

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A thesis submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2015. / It is recognised that tooth loss as a consequence of oral diseases affects quality of life in humans. This has directed studies towards biological tooth replacement in vivo. In humans and other mammals, tooth replacement occurs only once (diphyodonty) as opposed to non-mammalian vertebrates where tooth replacement continues throughout life (polyphyodonty). Detailed knowledge of tooth initiation, development and morphology amongst vertebrates and especially amniotes, is necessary to understand the tooth replacement process. Crocodilians provide an interesting model for tooth replacement studies as they also exhibit thecodonty. Regulation of polyphyodonty has not been genetically defined, and it is uncertain whether the molecular mechanisms of continuous tooth replacement are similar to those involved in the primary dentition. The aim of this study was therefore to analyse crocodilian odontogenesis in detail, with the aid of light microscopy and CT scans, in order to provide a structural framework for molecular processes regulating polyphyodonty. Crocodile probes to bmp4 and pitx2 were designed, generated and labelled for use in in situ hybridisation. The expression patterns of pitx2 and bmp4 in embryos and hatchlings of the polyphyodont Nile crocodile (Crocodylus niloticus) were examined at different stages of tooth development. Histologically crocodilian tooth development appears similar to mammals. Interesting variations include the initiation of odontogenesis in the ectomesenchyme, the presence of dental placodes, the ‘null generation teeth’, the two different bell-stage tooth germs and the tooth-family organisation. A direct 1:1 relationship between the status of the erupted tooth and the developmental phase of the replacement tooth was not seen. However in more mature teeth, the replacement tooth germs were at a more advanced developmental stage than those associated with less mature teeth. Molecular data revealed that pitx2 was expressed in the oral epithelium and the dental placode. Bmp4 expression was not evident in the dental placode, but was localised in the odontoblasts of early bell stage tooth germs. Pitx2 and bmp4 were expressed in both the odontoblast and ameloblast layers in late bell stage tooth germs. Expression of pitx2 and bmp4 is conserved across vertebrates and pitx2 may play a role in initiation of primary and successional teeth.