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.

Objetivo: Verificar a influência do nível de reaproveitamento e do tratamento de superfície sobre a resistência à flexão e microdureza Vickers de um sistema cerâmico prensado. Material e métodos: Foram utilizados sessenta corpos-de-prova do sistema cerâmico prensado IPS e.max (Ivoclar-Vivadent). Os corpos-de-prova (25X4X1,2mm) foram confeccionados seguindo a especificação ISO 6872, de acordo com o nível de reaproveitamento da cerâmica: GI 100% nova, GII 50% nova + 50% reaproveitada, GIII - 100% reaproveitada, GIV GI + ácido hidrofluorídrico, GV GII + ácido hidrofluorídrico e GVI GIII + ácido hidrofluorídrico. Foi realizado o teste de resistência à flexão de três pontos (n=10), conforme especificação ISO 10477 e ISO 6872. A microdureza Vickers foi mensurada em cinco corpos-de-prova de cada grupo, sob carga de quinhentos gramas por dez segundos. Os resultados foram submetidos ao teste de normalidade e posteriormente a ANOVA e post-hoc teste de Tukey, com nível de significância de 5%. Resultados: Os valores médios de microdureza variaram de 436,90 (GIV) a 605,97 (GII). Não foram observadas diferenças quanto ao nível de reaproveitamento, e o ácido reduziu estatísticamente os valores de dureza, para todos os grupos em estudo. Os valores médios de resistência a flexão variaram de 455,70 (GIV) a 500,56 (GIII). Não foram observadas diferenças estatísticas entre os grupos avaliados quanto ao nível de reaproveitamento e aplicação do ácido hidrofluorídrico. Conclusões: O reaproveitamento, total ou parcial, não exerceu influência sobre as propriedades mecânicas avaliadas. O condicionamento com ácido reduziu estatísticamente os valores de dureza, sem efeito sobre os resultados de resistência à flexão. / Objective: the aim of the present study was to observe the influence of the repressing level of ceramic and of the surface treatment on the flexural strength and Vickers microhardness of a pressable ceramic system. Material and methods: Sixty samples of a pressable ceramic system (IPS e.max - Ivoclar- Vivadent) were confectioned, with dimensions of 25X4X1.2mm, following specification ISO 6872, according to the level of repressing: GI - 100% new ceramic, GII - 50% new + 50% repressed, GIII - 100% repressed, GIV - GI + etching using hydrofluoric acid, GV - GII + etching using hydrofluoric acid and GVI - GIII + etching using hydrofluoric acid. Flexural strength test was accomplished by a three-point test, according to specification ISO 10477 and ISO 6872. Vickers microhardness was measured in five samples to each group, under load of five hundred grams for ten seconds. Results were submitted to ANOVA and Tukey post-hoc test, with level of significance of 5%. Results: Mean values of microhardness ranged between 436,90 (GIV) and 605,97 (GII). Statistical differences were not observed for the repressing level, but etching using hydrofluoric acid reduced statistically the mean values of hardness, for all groups. Mean values of flexural strength varied from 455,70 (GIV) to 500,56 (GIII). Statistical differences were not observed among the tested groups for repressing level and etching using hydrofluoric acid. Conclusions: Repressing the ceramic, totally or partially, did not influence the evaluated mechanical properties. Etching using hydrofluoric acid reduced statistically hardness values, with no effect on the flexural strength mean values.

This project explores the feasibility of the solid-state welding method direct-drive friction welding to be used as a joining method for the nitrogen alloyed steel Uddeholm Vanax SuperClean, produced via processes based on powder metallurgy. Vanax SuperClean cannot be welded using fusion welding methods where the base material melts, due to nitrogen escaping the material, resulting in inferior quality welds. The cost of the material motivates the use of Vanax SuperClean for critical parts in applications, combined with a less costly material for the remaining parts, causing alternative joining methods to be examined. Vanax SuperClean is friction welded to itself and to Uddeholm steel types Stavax ESR and UHB 11. Samples are prepared for a number of examinations. Microstructures of the samples are examined using microscopy, microhardness testing is carried out per the Vickers principle, retained austenite is measured using X-ray diffraction and tensile testing of the welded samples is performed. Defect-free welds are produced in all examined samples, showing that the method is suitable for Vanax SuperClean and that no preheating or slow cooling of workpieces are necessary. The possibility of using friction stir welding as a joining method for Vanax SuperClean is discussed. / Detta projekt undersöker möjligheten att använda trycksvetsningsmetoden friktionssvetsning som sammanfogningsmetod för det kvävelegerade pulvermetallurgiskt framställda stålet Uddeholm Vanax SuperClean. Vanax SuperClean kan inte svetsas med smältsvetsmetoder där grundmaterialet smälter, på grund av kvävgasbildning som resulterar i undermåliga svetsfogar. Kostnaden för materialet motiverar användandet av Vanax SuperClean för kritiska delar i applikationer, kombinerat med ett mindre kostsamt material till övriga delar, vilket föranleder undersökning av alternativa sammanfogningsmetoder. Vanax SuperClean friktionssvetsas mot sig själv, såväl som mot Uddeholmsstålen Stavax ESR och UHB 11. Prov tas fram för ett antal undersökningar. Mikrostruktur undersöks med mikroskopi, mikrohårdhetsprovning utförs enligt Vickersprincipen, restaustenitnivåer mäts med röntgendiffraktion och dragprovning utförs. Lyckade svetsfogar fås i alla undersökta prover, vilket visar att svetsmetoden är lämplig för Vanax SuperClean och att varken förvärmning eller långsamt svalnande av arbetsstycken krävs. Möjligheten att använda friktionsomrörningssvetsning som sammanfogningsmetod för Vanax SuperClean diskuteras.