Please use this identifier to cite or link to this item: http://hdl.handle.net/10316/20158
Title: Physical-Mechanical Characterization of Direct Restorative Dental Materials
Authors: Antunes, Pedro Alexandre de Almeida do Vale 
Orientador: Ramalho, Amílcar Lopes
Keywords: Compósitos dentários
Issue Date: 6-Jun-2012
Citation: ANTUNES, Pedro Alexandre de Almeida do Vale - Physical-mechanical characterization of direct restorative dental materials [em linha]. Coimbra : [s.n.], 2012. Tese de doutoramento. Disponível na WWW, em: http://hdl.handle.net/10316/20158.
Abstract: Materials dent´arios de restauro directo possuem caracter´ısticas muito especiais. Estes materiais operam num ambiente singular que ´e a boca. Os factores em jogo s˜ao diversos e a sua gama de varia¸c˜ao elevada, destes destacam-se; humidade, ciclos de carga, temperatura, bact´erias, agentes externos, meio ambiente, propriedades dos materiais, geometria de contacto, etc., s˜ao alguns exemplos. Os dentes e os materiais de restauro est˜ao, portanto, sujeitos a v´arios e numerosos factores. Durante as ´ultimas d´ecadas cl´ınicos e pacientes tˆem desenvolvido grande interesse pelas resinas para restauro de dentes posteriores. As exigˆencias por restauros com uma aparˆencia natural na regi˜ao posterior da boca al´em das controv´ersias relativamente `a amalgama e `a ac¸c˜ao do merc´urio, apesar das suas excelentes propriedades mecˆanicas, tem atra´ıdo a aten¸c˜ao dos investigadores na melhoria destes comp´ositos para a aplica¸c˜ao em dentes posteriores. Estas resinas comp´ositas tˆem sido certamente dos mais bem sucedidos materiais em aplica¸c˜oes dent´arias cumprindo requisitos rigorosos e dif´ıceis de alcan¸car com materiais homog´eneos tais como materiais cerˆamicos e ligas met´alicas. Quando a inten¸c˜ao ´e a repara¸c˜ao de cavidades tornase necess´ario combinar esteticamente a cor com a translucidez dos outros dentes e ao mesmo tempo mater o brilho. O material de restauro deve possuir a dureza do dente oposto e ser resistente ao desgaste ou `a fractura por fadiga. Deve, tamb´em,ser dimensionalmente est´avel e resistir `as tens˜oes, em grande parte devido `as varia¸c˜oes t´ermicas existentes na boca. As resinas “compact´aveis” foram denominadas por alternativas `a amalgama para o restauro de posteriores. Os crit´erios de selec¸c˜ao de comp´ositos bem como as poucas normas existentes n˜ao permitem estabelecer consenso relativamente a quais os testes a usar para determina¸c˜ao das propriedades ou para compara¸c˜ao de desepenho dos comp´ositos. A determina¸c˜ao das propriedades mecˆanicas e tribol´ogicas de materiais de restauro directo s˜ao cruciais verificar a semelhan¸ca destes materiais com o esmalte e a dentina, mas tamb´em para comparar comp´ositos entre si e determinar crit´erios objectivos para a sua correcta selec¸c˜ao. Este trabalhado ´e centrado na caracteriza¸c˜ao mecˆanica e tribol´ogica de materiais comerciais para restauro posterior. Devido `as caracter´ısticas, estes materiais n˜ao podem ser alterados (frac¸c˜ao em volume das part´ıculas, dimens˜ao da part´ıculas e composi¸c˜ao da matriz s˜ao parˆametros fixos) o que limitou os objectivos iniciais do estudo. Atrav´es da introdu¸c˜ao de um material comp´ositos produzido em laborat´oio este permitiu a varia¸c˜ao dos seus constituintes, sendo o trabalho complementado. A avalia¸c˜ao das propriedades mecˆanicas foi efectuada com a ajuda dos seguintes testes: dureza Vickers, teste dinˆamico do m´odulo de elasticidade e flex˜ao em quatro pontos. As propriedades mecˆanicas avaliadas foram: dureza, m´odulo de elasticidade (dinˆamico e est´atico), resistˆencia `a flex˜ao e trabalho de fractura. Para a determinar o comportamento tribol´ogico dos comp´ositos foi usado um teste de desgaste alternativo. O volume de desgaste do comp´osito e do antagonista (dente humano ou esfera de vidro) e os mecanismos envolvidos foram avaliados. Foram usadas abordagens; cl´assica e energ ´etica para perceber o comportamento dos comp´ositos e seus antagonistas. O uso da esfera de vidro como material antagonista foi submetido a valida¸c˜ao, sendo comparado com o desempenho do dente humano. Embora os volumes de desgaste sejam diferentes ´e poss´ıvel extrapolar os resultados dando aproxima¸c˜oes similares e aceit´aveis. Oito materiais comerciais de restauro directo foram ensaiados contra esferas de vidro por forma a determinar a sua resistˆencia ao desgaste e os diversos mecanismos envolvidos: abras˜ao e desgaste. A avalia¸c˜ao da influˆencia do meio ambiente nestes testes permitiu entender o comportamento dos comp´ositos em contacto de deslizamento alternativos atrav´es da medi¸c˜ao dos volumes de desgaste e coeficientes de atrito dos pares de materiais em contacto e analisar os mecanismos de desgaste envolvidos no processo. Nesta an´alise alguns pares de materiais mostraram alguma discrepˆancia em rela¸c˜ao ao desgaste e ao coeficiente de atrito, um estudo complementar foi efectuado para trˆes desses comp´ositos. Testes de “load-scanning” foram usados para perceber e explicar o regime de transi¸c˜ao destes materiais. Este teste permitiu perceber os mecanismos de desgaste/fractura provocados por diferentes valores de coeficiente de atrito. A influˆencia de factores externos no comportamento mecˆanico dos materiais comp´ositos tamb´em foi avaliada. Dois tipos de ambiente, nos testes de deslizamento alternativo foram introduzidos; saliva artificial/´agua destilada e solu¸c˜ao abrasiva. Os outros parˆametros externos introduzidos no estudo forma o efeito do; envelhecimento e pH. Dois lotes destes sete materiais comp´ositos foram envelhecidos em solu¸c˜oes de pH 3, 7 e 9, durante: 3, 6 e 22 meses. A avalia¸c˜ao tribol´ogica e mecˆanica destes comp´ositos foi realizada ap´os cada per´ıodo de envelhecimento. Do ponto de vista de aplica¸c˜ao foi poss´ıvel tirar conclus˜oes relativamente ao comportamento dos comp´ositos comerciais no que diz respeito ao desempenho mecˆanico e tribol´ogico. O efeito dos factores externos sobre o comportamento deste materiais comerciais foi avaliada sendo quantificada a varia¸c˜ao nas propriedades. Devido `a natureza da avalia¸c˜ao parameterizada dos comp´ositos produzidos o estudo trouxe progressos com conclus˜oes claras relativamente `a influˆencia da: frac¸c˜ao em volume de part´ıculas, dimens˜ao das part´ıculas de enchimento e matriz nas propriedades mecˆanicas e tribol´ogicas dos comp´ositos com material de enchimento. O comportamento tribol´ogico foi avaliado e os mecanismos de remo¸c˜ao envolvidos no processo de desgaste discutidos tendo em conta as observa¸c˜oes sistm´aticas dos modos de falha.
Direct restorative dental materials possess very special characteristics. These materials operate in a singular environment that is the mouth. The factors at play are numerous and their variation range is important. Humidity, load cycles, pH, temperature, bacteria, external agents, environment, material properties and contact geometry, etc., are some examples. Teeth and restorative materials are, therefore subjected to complex and numerous factors. During the past decade clinicians and patients have developed an interest in to posterior composite resins. The demand for restorations with a natural appearance in the posterior region and the controversy as to the mercury action of amalgam, although it’s excellent mechanical properties, has attracted researchers to focus on the improvement of the resin composites to be applied in posterior teeth. Resin composites have been by far the most successful in dental applications by meeting several stringent design requirements difficult to achieve with homogeneous materials such as ceramics and metal alloys. When the intention is to repair cavities, the product needs to be aesthetically matched in color and translucence with other teeth and retain its gloss. It must match the hardness of the opposing tooth and be resistant to wear or fatigue fracture. It must be dimensionally stable and withstand the largely varying thermal stresses in the mouth. “Packable” composites have been termed as alternative to amalgam, for usage in posterior restoration. Criteria to select a composite in detriment of another are very complex and the few existent standards do not allow for establishing a consensus as to which tests must be used to determine and compare composites properties. Mechanical and tribological properties of direct restorative filling materials are crucial not only to serve and allow similarity with human enamel and dentine but also to compare composites between them and determine objective criteria for their selection. This work is focused on the mechanical and tribological characterization of posterior direct commercial restorative materials. Due to their characteristics, commercial composites are materials which can not be altered (filler volume fraction, average particle dimension and matrix composition are pre-fixed parameters), thus limiting the objectives of the initial study. With the introduction of the production of a composite material which allowed variation of its constituents, the initial work was complemented. The mechanical properties assessment was done with the following tests: Vickers hardness, Impulse excitation of vibration and four point bending tests. The mechanical properties assessed were: hardness, elastic modulus (static and dynamic), flexural resistance and work-of-fracture. To determine the tribological behavior of composites reciprocating sliding tests was used. Wear and the mechanisms involved were evaluated on the composites as well as on the antagonist (human teeth and glass spheres). A classical and an energetic approach were used to understand the behavior of the composites and their antagonists. The use of glass sphere as antagonist material was subjected to validation, by comparison to the material pair composite natural tooth. Although difference in wear volumes of the distinct pairs does exist, extrapolation of results is possible with similar and acceptable results. Eight direct restorative commercial composites were tested against glass spheres, to determine wear resistance under different wear mechanisms: abrasion and attrition. The evaluation of environment influence in these tests allows us to understand composites behavior under reciprocating contact through the measuring of wear volumes and coefficients of friction of the contact pair and analyzing the removal mechanisms involved in the wear process. In this analysis, some composite-glass pair some materials showed some discrepancy regarding wear and the coefficient of friction, thus a complementary study involving, only, three commercial composite was done. A load-scanning test was used to understand and explain the wear regime transition of these. This test permitted the perception of the wear/fracture mechanisms induced by the different values of coefficient of friction. The influence of external factors on the mechanical behavior of composites was also evaluated. Two types of environment in the reciprocating wear tests were introduced: artificial saliva/distillate water and abrasive slurry. The other external parameters introduced in the study were aging time and pH. Two batches of seven commercial composites were aged in 3, 7 and 9 pH buffer solutions during three periods 3, 6 and 22 months. The tribological and mechanical evaluation of these composites was done after each aging period. Generally and from the point of view of application, it was possible to draw conclusions relatively to commercial composite mechanical and tribological behavior. The effect of external factors on the behavior of these commercial materials was also evaluated and the properties variation quantified. Due to the nature of the study, parameterized evaluation, of produced composites brought further progress, with clear conclusions as to volume content, filler dimension, matrix on the mechanical and tribological properties studied. The tribological behavior was evaluated and removal mechanisms enclosed in the wear process are discussed, taking into account the systematic SEMobservations to evaluate the failure modes.
Description: Tese de doutoramento em Engenharia Mecânica, na especialidade de Construção Mecânica
URI: http://hdl.handle.net/10316/20158
Rights: openAccess
Appears in Collections:FCTUC Eng.Mecânica - Teses de Doutoramento

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