published_or_final_version / abstract / Dental Surgery / Master / Master of Dental Surgery

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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O estudo objetivou avaliar a resistência da união de sistemas adesivos aplicados ao esmalte, bem como a morfologia do substrato condicionado e a qualidade da interface de união formada. Após o esmalte das superfícies lisas de molares receberem profilaxia com pedrapomes, abrasão por lixa ou desgaste por ponta de diamante, foram aplicados Scotchbond Multi-Purpose Plus (SBMP), Single Bond (SB), Clearfil SE Bond (CSE); OptiBond Solo Plus Self-Etch (OP) e Tyrian Self Priming Etching (TY). Os semidentes ?restaurados? com resina Filtek Z250 foram armazenados em água deionizada (24h/37°C), secionados no formato de paralelogramo (área transversal aproximada de 0,8 mm2), aleatorizados em grupos (24h, 6 e 12 meses de armazenagem), e testados em microtração (0,5mm/min). Os valores médios de resistência da união (MPa) foram tratados por métodos de ANOVA e Tukey. Os resultados não mostraram diferenças significativas para os fatores Tratamento, Armazenagem, nem para as interações..Porém, houve diferença significante para o fator Adesivo (p<0,05). Os padrões morfológicos do esmalte obtidos após o uso do agente condicionante dos sistemas SBMP e SB não foram influenciados pelo Tratamento. Os fatores Adesivo e Tratamento influenciaram no padrão dos sistemas CSE, OP e TY. Não foram observadas fendas nas interfaces dos sistemas SBMP e SB, independente dos outros fatores. .Os sistemas OP e TY mostraram fendas em todas as condições, e o CSE após 12 meses no esmalte abrasionado por lixa. Com base nos resultados, conclui-se que o desempenho dos sistemas adesivos estudados está vinculado mais às características dos produtos do que ao tratamento realizado no esmalte ou armazenagem. / This study aimed to evaluate the resin-enamel bond strength, the etching pattern and the bonded interfaces provided by self-etch systems by means of scanning electron microscopy. The following adhesives systems (Scotchbond Multi-Purpose Plus [SBMP], Single Bond [SB], Clearfil SE Bond [CSE]; OptiBond Solo Plus Self-Etch [OP] or Tyrian Self Priming Etching [TY] were applied to sound enamel (after tooth prophylaxis), SiC paper or diamond bur-treated enamel. Resin composite buil-dups (Filtek Z250) were bonded to the enamel surfaces. After storage in water (24h/37°C), the bonded samples were sectioned into beams (0.8mm2), randomly assigned into subgroups (24h, 6 and 12 months) and subjected to microtensile bond strength test (0.5 mm/min). The data was analyzed by ANOVA and Tukey?s test. The main factors enamel Treatment and Storage as well as the interactions were not statistically significant. Significant differences were observed only for the main factor Adhesive (p<0.05). The Treatment did not affect the etching pattern of SBMP and SB; for CSE, OP and TY the morphology varied with the Treatment and Adhesive system. Gaps were not observed in the interfaces bonded with SBMP and SB, regardless of the Storage and Treatment. The adhesive CSE showed gaps after 12 months of storage for SiC paper, while this finding was observed for OP and TY in all conditions. Based on the results of the present investigation, it was concluded that the performance of some adhesive systems is influenced by the material´s composition instead of surface treatment or storage.

Zinc has been investigated extensively as an anti-plaque and calculus agent. However, its interaction with enamel and its putative role in demineralisation and remineralisation are considerably less understood. In comparison to zinc, the interactions between fluoride and enamel have been extensively reported in the literature. The overall aim was to understand the effects of zinc ions [Zn2+] on enamel demineralisation (relevant to dental caries), whilst the effect of fluoride ions [F–] were similarly studied and used as a benchmark for the zinc investigations. The independent effects of varying concentrations of [Zn2+] and [F–] on enamel demineralisation kinetics were investigated during in vitro caries-simulating conditions. Human enamel blocks were exposed to series of in vitro demineralising solutions consisting of 0.1 M acetic acid adjusted to pH 4.0, with increasing concentrations of [Zn2+] or [F–]. Scanning Microradiography (SMR) obtained accurate, real-time quantitative measurements of changes in enamel mineral mass, as they were exposed to [Zn2+] or [F–]-containing acid solutions. Further, amongst other characterisation techniques, ultralow Energy Secondary Ion Mass Spectrometry (uleSIMS) and 19F MAS-NMR were used for determination of possible surface physical-chemical mechanisms of [Zn2+] and [F–] on the enamel dissolution processes respectively. This study confirmed that zinc reduces enamel demineralisation during in vitro caries-simulating conditions. An overall log-linear relationship was observed between the reduction in demineralisation and increasing [Zn2+] up to 3565 ppm. Fluoride showed this log-linear relationship up to 135 ppm, however, further reductions in demineralisation were minimal above this concentration. 19F MAS-NMR established that fluorite (CaF2) predominantly formed above 135 ppm [F–], whereas fluorohydroxyapatite (FHAp) largely formed below 135 ppm. uleSIMS indicated that zinc was largely concentrated at the near-surface region of enamel, which suggested that zinc acts predominantly at the enamel crystal surface in its mechanism of reducing demineralisation. Thus, at low concentrations, zinc appeared to act at PO43– sites on enamel surfaces, possibly via an adsorption-type process and was confirmed to form an α-hopeite-like phase, once surface adsorption was complete at higher concentrations. These results have significant implications on the understanding of the fundamental chemical aspects of zinc in toothpastes and demonstrate its therapeutic potential in preventing tooth mineral loss.

Magister Chirurgiae Dentium - MChD / To compare the efficacy of two fluoride containing materials, namely, FluorSure and Duraphat, in protecting the enamel around and underneath the orthodontic brackets against decalcification. / South Africa

Doctor of Philosophy / This work was digitised and made available on open access by the University of Sydney, Faculty of Dentistry and Sydney eScholarship . It may only be used for the purposes of research and study. Where possible, the Faculty will try to notify the author of this work. If you have any inquiries or issues regarding this work being made available please contact the Sydney eScholarship Repository Coordinator - ses@library.usyd.edu.au

Doctor of Philosophy(PhD) / Objectives As the outer cover of teeth structure, enamel is the hardest, stiffest and one of the most durable load-bearing tissues of the human body. Also, enamel is an elegantly designed natural biocomposite. From a material science point of view, scientists are interested in the structure and function of the nature material. How does nature design the material to meet its functional needs? From a dental clinic point of view, dental practitioners are keen to know the properties of enamel and compare it with different dental materials. What kind of dental materials can best simulate enamel as a restoration in the oral cavity? The research presented in this thesis on the mechanical behaviour of enamel in respect of its structural and compositional characteristics will attempt to provide answers or indications to the above questions. Theoretical analysis, as well as experimental investigations of both man-made and natural composites materials, has shown that hierarchical microstructure and organic matrix glues the inorganic particles together and plays an important role in regulating the mechanical properties of the composite. Bearing this finding in mind, in the current investigations, we assume the hierarchical microstructure and trace protein remnants in enamel regulate the mechanical behaviour of the natural biocomposite to meet its functional needs as a load bearing tissue with superb anti-fatigue and wear resistant properties. One of the important reasons that dental hard tissues haven’t been thoroughly investigated is due to the limited sample volume. Fortunately, with the development of nanoindentation technique and equipment, it is now possible to explore the mechanical properties of small volume samples. The application of nanoindentation on dental hard tissues has been documented. However, most investigations have concentrated on only reporting the basic mechanical properties such as elastic modulus and hardness. Very few of them have taken the role of microstructure and composition of these natural biocomposites into their considerations. The main aim of this investigation is to interpret how microstructural and compositional features of enamel regulate its mechanical behaviour. To achieve this goal, the analytical methods considering nanoindentation data need to be expanded so that more information not only elastic modulus and hardness but also stress-strain relationship, energy absorption ability, and creep behaviour may be evaluated with this technique. These new methods will also be of benefit to dental material evaluation and selection. Materials and methods Based on the Oliver-Pharr method1 for the analysis of nanoindentation data, Hertzian contact theory2 and Tabor’s theory3, a spherical nanoindentation method for measuring the stress-strain relationship was developed. Furthermore, nanoindentation energy absorption analysis method and nanoindentation creep test were developed to measure the inelastic property of enamel. With the above methods, sound enamel samples were investigated and compared with various dental materials, including dental ceramics and dental alloys. • Firstly, using a Berkovich indenter and three spherical indenters with 5, 10 and 20 µm nominal radius, the elastic modulus, hardness and stress-strain relationship of different samples were investigated and compared. • Secondly, mechanical properties of enamel in respect to its microstructure were investigated intensively using different indenters by sectioning teeth at different angles. • Thirdly, inelastic behaviour of enamel such as energy absorption and creep deformation were observed and compared with a fully sintered dense hydroxyapatite (HAP) disk to illustrate the roles of protein remnants in regulating the mechanical behaviour of enamel. • Fourthly, to confirm the functions of protein remnants in controlling mechanical behaviour of enamel, enamel samples were treated under different environments such as burning (300°C exposure for 5 min), alcohol dehydration and rehydration to change the properties of proteins before the nanoindentation tests. • Lastly, micro-Raman spectroscopy was employed to measure and compare the indentation residual stresses in enamel and HAP disk to evaluate the role of both hierarchical microstructure and protein remnants in redistributing the stresses and reinforcing the mechanical response of enamel to deformation. Results and significance Nanoindentation is an attractive method for measuring the mechanical behaviour of small specimen volumes. Using this technique, the mechanical properties of enamel were investigated at different orientations and compared with dental restorative materials. From the present study, the following results were found and conclusions were drawn.  Although some newly developed dental ceramics have similar elastic modulus to enamel, the hardness of these ceramic products is still much higher than enamel; in contrast, despite the higher elastic modulus, dental metallic alloys have very similar hardness as enamel. Furthermore, enamel has similar stress-strain relationships and creep behaviour to that of dental metallic alloys. SEM also showed enamel has an inelastic deformation pattern around indentation impressions. All of these responses indicated that enamel behaves more like a metallic material rather than a ceramic.  Elastic modulus of enamel is influenced by highly oriented rod units and HAP crystallites. As a result, it was found to be a function of contact area. This provides a basis to understand the different results reported in the literature from macro-scale and micro-scale tests. Anisotropic properties of enamel, which arise from the rod units, are well reflected in the stress-strain curves. The top surface (perpendicular to the rod axis) is stiffer and has higher stress-strain response than an adjacent cross section surface because of the greater influence of the prism sheaths in the latter behaviour.  Enamel showed much higher energy absorption capacity and considerably more creep deformation behaviour than HAP, a ceramic material with similar mineral composition. This is argued to be due to the existence of minor protein remnants in enamel. Possible mechanisms include fluid flow within the sheath structure, protein “sacrificial bond” theory, and nano-scale friction within sheaths associated with the degustation of enamel rods.  A simple model with respect of hierarchical microstructure of enamel was developed to illustrate the structural related contact deformation mechanisms of human enamel. Within the contact indentation area, thin protein layers between HAP crystallites bear most of the deformation in the form of shear strain, which is approximately 16 times bigger than contact strain in the case of a Vickers indenter. By replotting energy absorption against mean strain value of a protein layer, data from different indenters on enamel superimposed, validating the model. This model partially explained the non-linear indentation stress-strain relationship, inelastic contact response and large energy absorption ability of enamel and indicated the inelastic characteristics of enamel were related to the thin protein layers between crystallites.  Following different treatments, mechanical properties of enamel changed significantly. By denaturing or destroying the protein remnants, mechanical behaviour, especially inelastic abilities of enamel decreased dramatically, which indicates matrix proteins endow enamel better performance as a load bearing calcified tissue.  Comparison of Raman derived residual maps about indentations in enamel and a sintered homogeneous HAP showed the hierarchical structure influenced the residual stress distribution within enamel. Moreover, less residual stresses were found in enamel and were a consequence of the protein remnants. These are evidence as to how the microstructure meets the functional needs of the enamel tissue. In general, evidence from different approaches indicated that the hierarchical microstructure and small protein remnants regulated the mechanical behaviour of enamel significantly at various hierarchical levels utilising different mechanisms. This investigation has provided some basis for understanding natural biocomposites and assisting with dental clinic materials selection and treatment evaluation procedures. References 1. Oliver WC, Pharr GM. An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments. J Mater Res. 1992;7(6):1564-83. 2. Hertz H. Miscellaneous Papers. London: Jones and Schott, Macmillan; 1863. 3. Tabor D. Hardness of Metals. Oxford: Clarendon Press; 1951.

<p>To compare the efficacy of two fluoride containing materials, namely, FluorSure and Duraphat, in protecting the enamel around and underneath the orthodontic brackets against decalcification.</p>

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 96-105).