published_or_final_version / abstract / Dentistry / Doctoral / Doctor of Philosophy

published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

published_or_final_version / Dentistry / Master / Master of Dental Surgery

The demand for posterior aesthetic restorations has dramatically increased in recent years. Several new materials have been developed with improved aesthetic, adhesive and mechanical properties. However, microleakage elimination, especially if the margins are on dentine or cementum, and attainment of optimum mechanical properties for posterior use, are still questionable. The aim of this study was to investigate microleakage and surface microhardness of a nanofilled, a nanohybrid and an ormocer based nano-ceramic composite restorative material.

<p>Amalgam bonding agents have been shown to enhance retention of amalgam restorations by mechanical means. However, recent studies showed that the use o glass ionomer cements and resin cements as lining and bonding materials to amalgam restorations will increase the retentive strength of the amalgam restorations, hence reducing the micro leakage and secondary caries. The purpose of this study was to compare the relative retentive strength of conventional amalgam restorations and bonded amalgam restorations using resin adhesive, glass ionomer cements and resin cements.</p>

<p>The use of provisional acrylic crowns is common practice with prosthodontic treatment. Provisional crowns are prone to marginal leakage and poor retention due to weak interim cements. The aim of this study was to assess the effect of the application of two different dentine-bonding agents on the microleakage of provisional crowns.</p>

Dissertation submitted in compliance with the requirements for the Master's Degree in Technology: Dental Technology, Technikon Natal, 1997. / Globally, difficulties are being experienced by the dental world to match manufactured prosthetic restorations with natural tooth colour. The primary objective of this study was therefore to evaluate the colour of five different metalceramic base metal alloy oxide layers, and the effects of each oxide layer on the shade of the porcelain applied to its surface. The increase in the cost of gold alloys in the dental industry has influenced manufacturers to provide alloys which are cost effective and have adequate mechanical properties for the manufacture of metal ceramic restorations. Five base metal alloys used in the fabrication of metal-ceramic restorations were selected. The selection of the base metal alloys was based on popularity in the industry, availability and cost. The following five base metal alloys were selected for the investigation: Wiron 99 (nickel-chrome) Ceradium V (nickel-chrome-beryllium) Remanium CD (nickel-chrome) \x95 Wirobond (cobalt-chrome) Heranium (nickel-chrome) Bond-on-4 (low noble content alloy {control group; which was gilded}) II Thirty specimens for each alloy group (180 in all) were cast, using the lost wax technique. Three ceramic layers (notably the opaque, dentine and a glaze layer) were applied to the 20mm in diameter surface of each specimen. .\xB7t Finally both sample groups were tested against a custom shade guide the colour being compared specifically with the Vita A 1 shade. The reason for the inclusion of the shade guide was that, clinically, most shade selections are made by comparing the patient's tooth shade with a manufactured shade guide. A wide selection of shades are available to the ceramist. A certain school of thought that recommends that the metal surfaces of semi-precious metals be gilded with a gold gilding paste before the application of ceramics. in order to block out the dark oxide colour and enhance the colour of the ceramic to a more aesthetic and warmer colour. Therefore, prior to the opaque firing of the control group (Bond-on-4), a gilding layer of Spectra Seal Paste was applied to the surface of each specimen. Following each application of ceramic, the appropriate firing cycles were used to fire the ceramic. The following factors affected the selection of the shade of ceramic used in this study: the shade which is most influenced by the dark oxide layer the more popular shades of ceramic ( the A class of shades). It was established, through a review of the literature (Crispen, 1991), that the most objective form of testing colour at the time of the study, was the use of a reflectance spectrophotometer. This form of testing had been proved to be cost effective and was consequently used in this investigation. III Thesurve / M

Dissertation submitted in compliance with the requirements for the Master's Degree in Technology: Dental Technology, Technikon Natal, 2000. / The greatest problem in maximizing strength and aesthetic characteristics of metal ceramic restorations arises when there is a lack of available space to allow sufficient thickness of metal alloy and porcelain. This generally results in the metal alloy being reduced to its minimum to allow adequate porcelain thickness. The minimum thickness to which noble metal alloys can safely be reduced, is generally accepted to be 0.3 mm due to previous clinical time-dependent trial and error. Agreement regarding the minimum thickness to which base metal alloys can safely be reduced is still under dispute possibly because base metal alloys have not had the same duration of clinical exposure. The objectives of the present study were: 1. To determine the influence thickness variations of the base metal alloy would have on strength characteristics of metal ceramic restorations and thereby establishing the minimum thickness to which base metal alloys can safely be reduced. 2. To determine the influence thickness variations of porcelain would have on strength and aesthetic characteristics of metal ceramic restorations and thereby establish the minimum thickness to which the porcelain thickness can safely be reduced. 3. To determine which base metal alloy to porcelain thickness ratios would be most suited in order to maximize strength and aesthetic characteristics in metal ceramic restorations where the amounts of available space for the alloy and porcelain are varied. For objective (1) Tensile strength tests to determine and compare the ability of various alloy thickness to resist porcelain fracture were performed in Newtons. For objective (2) Tensile tests to determine and compare the ability of various porcelain thickness to resist porcelain fracture were performed in Newtons. / M

O objetivo deste trabalho foi avaliar a resistência às uniões bráquete-resina-esmalte, bráquete-resina-níquel-cromo, bráquete-resina-cobre-alumínio e bráquete-resina-porcelana utilizando o Sistema Adesivo Universal EnForce e a resina Concise Ortodôntico, através de ensaios de cisalhamento. Para tanto, foram confeccionados corpos de prova nas ligas de níquel-cromo, cobre-alumínio, porcelana, e como grupo controle foram utilizados 20 pré-molares. Estes receberam condicionamento com ácido fosfórico a 35%, enquanto os corpos de prova de Ni-Cr, Cu-Al e porcelana receberam condicionamento de superfície com jateamento; logo após bráquetes metálicos foram cimentados utilizando os Sistemas Adesivos Concise Ortodôntico e o Sistema Adesivo EnForce. Em seguida à colagem de todos os acessórios, os corpos de prova foram armazenados em ambiente úmido a uma temperatura de \'37GRAUS\' durante 1 hora. Concluído este tempo, todos os grupos foram submetidos aos respectivos ensaios de cisalhamento na máquina de ensaios Kratos, a uma velocidade de 5 mm/min, aplicada por meio de uma haste metálica. Os resultados obtidos permitiram as seguintes conclusões: O sistema adesivo EnForce apresentou uma força de união superior ao sistema adesivo Concise, para todos os substratos e condições empregados neste estudo, entretanto sem evidenciar significância estatística. Nos grupos ligas metálicas níquel-cromo, cobre-alumínio e porcelana, o jateamento com partículas de óxido de alumínio de 50\'mü\'m proporcionou um condicionamento mecânico eficiente, produzindo resultados similares em relação aos obtidos nos grupos esmalte onde foi efetuado condicionamento de superfície com ataque ácido. / The aim of this in vitro study was to assess the shear bond strength of bracket-resin-enamel, bracket-resin-Ni-Cr, bracket-resin-Cu-Al, and bracket-resin-porcelain using EnForce Universal Adhesive System and Concise Orthodontic Resin. Ni-Cr, Cu-Al alloys and Porcelain surfaces were sandblasted with 50m aluminium oxide and surfaces of enamel group were etched with phosforic acid, and brackets were immediately bonded with Orthodontic Concise Resin, and EnForce Universal Adhesive System. All specimens were stored under humidity at 37º C for one hour. The shear bond strentgh was performed with a kratos testing machine at a cross-head speed of 0,5mm per minute. The results showed that the sanblasting produced stronger bonds to Porcelain, and Ni -Cr, Cu-Al alloys. EnForce Universal Adhesive System provided stronger bonds than Concise Orthodontic Resin, for all specimens and conditions used in this study. The bond strengths obtained with sandblasting, intermediate application of silano or primer to porcelain and alloys were comparable to those obtained with conventionally etched human teeth with Concise Orthodontic Resin.

A hiperestesia dentinária é uma das mais antigas queixas de desconforto dos pacientes e, devido à sua alta incidência e diversidade de tratamentos sugeridos na literatura, novos produtos devem ser avaliados quanto ao efeito e aplicabilidade. O propósito deste estudo foi avaliar as respostas imediata e mediata de 94 dentes (caninos e pré-molares), que apresentavam algum grau de sensibilidade dentinária (1, 2 ou 3) de acordo com a Escala de Medida Verbal (EMV) aos estímulos sonda e ar, após a aplicação de três formulações à base de oxalato de potássio: Oxa-Gel®, Solução Experimental 1 e Solução Experimental 2, tendo um placebo como controle. Cada formulação de oxalato de potássio e o placebo foram aplicados passivamente por 3 minutos na superfície da dentina úmida, sendo o excesso de material removido posteriormente. O grau de sensibilidade foi avaliado antes (baseline) e imediatamente após a aplicação de cada formulação com um intervalo de 7 dias. Os resultados obtidos após a quarta aplicação foram denominados resultados imediatos e, após 6 meses, resultados mediatos. Os escores foram submetidos à análise estatística através dos testes de Kruskal-Wallis e de Friedman two-way ANOVA (p< 0,05). A aplicação de todos os materiais, inclusive o placebo, independente do tempo avaliado e dos estímulos utilizados, resultou em uma redução estatisticamente significante na hiperestesia dentinária podendo essa redução prolongar-se até seis meses. Houve uma tendência de respostas mais severas ao estímulo ar quando comparado ao estímulo sonda antes do tratamento, sendo que a hiperestesia provocada pela sonda se mostrou mais persistente ao longo do tratamento. O tratamento da hiperestesia dentinária está sujeito a variáveis clínicas que podem aumentar ou diminuir o efeito anti-hiperestésico dos agentes estudados.