MATEUS GARCIA ROCHA
DESENVOLVIMENTO E CARACTERIZAÇÃO DE COMPÓSITOS ODONTOLÓGICOS BULK FILL À BASE DE MONÔMERO ELASTOMÉRICO COM DIFERENTES FOTOINICIADORES
DEVELOPMENT AND CHARACTERIZATION OF BULK FILL DENTAL COMPOSITES CONTAINING ELASTOMERIC MONOMER
WITH DIFFERENT PHOTOINITATORS
PIRACICABA 2019
DESENVOLVIMENTO E CARACTERIZAÇÃO DE COMPÓSITOS ODONTOLÓGICOS BULK FILL À BASE DE MONÔMERO ELASTOMÉRICO COM DIFERENTES
FOTOINICIADORES
DEVELOPMENT AND CHARACTERIZATION OF BULK FILL DENTAL COMPOSITES CONTAINING ELASTOMERIC MONOMER WITH DIFFERENT
PHOTOINITIATORS
Tese apresentada à Faculdade de
Odontologia de Piracicaba da
Universidade Estadual de Campinas como parte dos requisitos exigidos para a obtenção do título de Doutor em Materiais Dentários.
Thesis presented to the Piracicaba
Dental School of the University of
Campinas in partial fulfillment of the
requirements for the degree of Doctor in
Dental Materials.
Orientador: Prof. Dr. Americo Bortolazzo Correr
ESTE EXEMPLAR CORRESPONDE À
VERSÃO FINAL DA TESE DEFENDIDA PELO ALUNO MATEUS GARCIA ROCHA, E ORIENTADA PELO PROF. DR. AMERICO BORTOLAZZO CORRER
PIRACICABA 2019
Marilene Girello - CRB 8/6159
Rocha, Mateus Garcia,
R582d RocDesenvolvimento e caracterização de compósitos odontológicos bulk fill à base de monômero elastomérico com diferentes fotoiniciadores / Mateus Garcia Rocha. – Piracicaba, SP : [s.n.], 2019.
RocOrientador: Americo Bortolazzo Correr.
RocTese (doutorado) – Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba.
Roc1. Resinas compostas. 2. Análise espectral. 3. Propriedades físicas. I. Correr, Americo Bortolazzo, 1981-. II. Universidade Estadual de Campinas. Faculdade de Odontologia de Piracicaba. III. Título.
Informações para Biblioteca Digital
Título em outro idioma: Development and characterization of bulk fill dental composite
containing elastomeric monomer with different photoinitiators
Palavras-chave em inglês:
Composite resins Spectrum analysis Physical properties
Área de concentração: Materiais Dentários Titulação: Doutor em Materiais Dentários Banca examinadora:
Americo Bortolazzo Correr [Orientador] Ivo Carlos Corrêa
Lucas Fernando Tabata Mario Fernando de Goes Regina Maria Puppin Rontani
Data de defesa: 29-07-2019
Programa de Pós-Graduação: Materiais Dentários Identificação e informações acadêmicas do(a) aluno(a)
- ORCID do autor: https://orcid.org/0000-0001-5658-5640 - Currículo Lattes do autor: http://lattes.cnpq.br/7205312023990155
Faculdade de Odontologia de Piracicaba
A Comissão Julgadora dos trabalhos de Defesa de Tese de Doutorado, em sessão pública realizada em 29 de Julho de 2019, considerou o candidato MATEUS GARCIA ROCHA aprovado.
PROF. DR. AMERICO BORTOLAZZO CORRER
PROF. DR. IVO CARLOS CORRÊA
PROF. DR. LUCAS FERNANDO TABATA
PROF. DR. MARIO FERNANDO DE GOES
PROFª. DRª. REGINA MARIA PUPPIN RONTANI
A Ata da defesa, assinada pelos membros da Comissão Examinadora, consta no SIGA/Sistema de Fluxo de Dissertação/Tese e na Secretaria do Programa da Unidade.
A Deus, pelas pessoas e caminhos que colocou em minha vida, que tornou
possível aprender tudo que sei e quem sou.
À minha família, mesmo distante, sempre tão perto e presente em minhas
decisões.
À minha esposa Dayane Carvalho Ramos Salles de Oliveira, por dividir
comigo toda alegria de ter alguém em quem confiar sempre.
À minha mãe Carla Simone Garcia de Almeida por me guiar em todos os
momentos da minha vida.
Ao meu irmão Marco Antonio Alves Rocha Jr., por ter sido sempre meu
AGRADECIMENTOS
Ao Prof. Dr. Americo Bortolazzo Correr, pelo exemplo profissional e
orientação acadêmica, sempre me guiando por todos os momentos da pós-graduação e carinhosamente me incentivando a buscar sempre grandes desafios.
O presente trabalho foi realizado com apoio da Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) - Código de Financiamento 001
O presente trabalho foi realizado com apoio da Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), processo nº 2016/06019 e 2017/22195-9
Ao Prof. Dr. Jean-François Roulet por auxiliar no desenvolvimento do projeto
de pesquisa de Doutorado.
Ao Prof Dr. Mário Alexandre Coelho Sinhoreti por sempre me instruir no
âmbito acadêmico e profissional.
Aos Professores do Programa de Pós-Graduação de Materiais Dentários da Faculdade de Odontologia de Piracicaba, Regina Maria Puppin Rontani, Lourenço Correr Sobrinho, Mário Alexandre Coelho Sinhoreti, Mário Fernando de Goes, Simonides Consani, Rafael Leonardo Consani, Ana Rosa Costa Correr, Andreia Bolzan de Paula, Luis Roberto Marcondes Martins, Marcelo Giannini, Fernanda Miori Pascon e Alan Roger Santos Silva por todo
aprendizado e apoio profissional durante minha formação durante o curso de pós-graduação.
Ao Prof. Dr. Ivo Carlos Correa, por sempre ter me apoiado durante minha
formação acadêmica e ter acreditado que eu poderia alcançar grandes objetivos na área de Materiais Dentários.
Ao Programa de Pós-Graduação da Faculdade de Odontologia de Piracicaba, Universidade Estadual de Campinas, nas pessoas da Profa. Dra. Karina Gonzales
Silvério Ruiz, coordenadora dos cursos de Pós-Graduação, e Prof. Dr. Americo Bortolazzo Correr, coordenador do curso de Pós-Graduação em Materiais
Dentários.
À Faculdade de Odontologia de Piracicaba (UNICAMP), na pessoa do seu diretor, o Prof. Dr. Francisco Haiter Neto e do seu Diretor Associado, o Prof. Dr.
Flávio Henrique Baggio Aguiar.
Aos meus amigos dos cursos de Pós-Graduação da Faculdade de Odontologia de Piracicaba.
Aos funcionários do Departamento de Odontologia Restauradora: Selma
Segalla e Marcos Cangiani pela amizade e profissionalismo.
À Universidade da Flórida e a todos os amigos que fiz durante o estágio de
pesquisa no Exterior. Lucas F. Tabata, Ana Paula Dias Ribeiro, Patrícia Pereira,
Saulo Geraldeli, Luisa Cassiano, André Reis, Panos Zoidis.
À Universidade Federal do Rio de Janeiro e aos Professores Kátia Regina Hostilio Cervantes Dias, Marcos Schroeder, Rafael Andreiuolo, Mária Cynésia Torres, Paulo Campos, Gisele Damiana, Lívia Menezes, Andrea Soares Quirino, Nanci Garden e José Carlos Netto-Ferreira.
E a todos meus amigos simplesmente por fazerem parte de momentos
RESUMO
O objetivo neste estudo foi desenvolver e caracterizar compósitos bulk fill (BF) contendo diferentes monômeros elastoméricos e sistemas fotoiniciadores. Para tanto, esse estudo foi realizado em duas partes. Na primeira parte, o monômero elastomérico Exothane 24 foi avaliado por análise elementar, espectroscopia de infra-vermelho e ressonância nuclear magnética para elucidação da formula química e estrutural do monômero. Em seguida, compósitos BF foram formulados contendo o monômero elastomérico (E), em concentrações de 10, 25, 50% em peso da matriz monomérica (E10, E25 e E50), e comparados com formulações controle contendo monômeros de uretano di-metacrilato (UDMA) (U) em concentrações similares (U10, U25 e U50). Os compósitos BF foram analisados quanto a dureza Vickers em profundidade, grau de conversão (GC), resistência à flexão (RF), módulo flexural (MF), tensão de polimerização (TP) e resistência ao desgaste. Os dados foram analisados estatisticamente considerando α=0,05 e β=0,2. Apenas o compósito E25 não apresentou diferença significativa entre o valor de dureza do topo até 4 mm de profundidade; entretanto, apresentou menor grau de conversão que U10, U25, U50 e E10. Não houve diferença estatística na RF entre os compósitos BF, exceto para E50 que apresentou menor RF. E25 e E50 apresentaram menor MF e TP. E25 apresentou a maior resistência ao desgaste com menor perda volumétrica e menor taxa de desgaste. Na segunda parte do estudo, a homogeneidade do feixe de luz do fotoativador LED multi-peak (Bluephase G2, Ivoclar Vivadent) foi avaliada utilizando espectrofotometria e análise do perfil do feixe de luz. O compósito bulk fill E25 foi formulado contendo dois diferentes sistemas de fotoiniciação em razões equimolares: o grupo CQ-amina contendo canforquinona (CQ) e amina (EDMAB); e o grupo CQ-amina/TPO contendo CQ, EDMAB e óxido trimetil fosfínico (TPO). Os compósitos BF foram analisados quanto ao GC em profundidade, transmissão de luz, módulo flexural, tensão de polimerização e contração volumétrica de polimerização. Os dados foram analisados estaticamente com α=0,05 e β=0,2. Não houve diferença estatística entre CQ-amina e CQ-amina/TPO no GC em 4mm de profundidade e na contração volumétrica de polimerização; entretanto CQ-amina/TPO apresentou maior MF, TP e GC no topo da restauração. Dessa forma, foi possível concluir que a utilização de monômeros elastoméricos em compósitos BF diminuiu a tensão de polimerização e aumentou a resistência ao desgaste. Entretanto, a utilização do sistema de fotoiniciação de CQ-amina associada ao TPO
ABSTRACT
The aim of this study was to develop and characterize a new bulk fill composite (BFC) containing elastomeric monomer with lower polymerization stress and higher wear resistance. Besides that, evaluate the influence of the beam profile of multi-peak LED light curing unit on the curing efficiency of BFC containing different photoinitiators systems. Therefore, this study was performed in two steps. First, the chemical structure of an elastomeric urethane methyl methacrylate monomer (Exothane 24, Esstech) was characterized using elemental analysis, infra-red spectroscopy and nuclear magnetic resonance. Six BFCs were made containing Exothane 24 (E) or UDMA (U) in three different concentrations (E10, E25 and E50 or U10, U25 and U50). The Vickers hardness as a function of depth was evaluated through each millimeter of each bulk fill increment up to 4 mm. The degree of conversion (DC) was assessed using ATR-FTIR spectroscopy. The flexural strength (FS) and flexural modulus (FM) were assessed by a three-point bending test. The polymerization stress was measured using the universal testing machine with a video extensometer method. Data were analyzed according to the different experimental designs (α=0.05 and β=0.2). E25 was the only BFC where no significant statistical difference was found in the VHN from the top up to 4 mm in depth. However, E25 had a lower degree of conversion than U10, U25, U50, and E10. All BFCs had similar flexural strength, except for E50. However, the composites E25 and E50 had lower flexural modulus and polymerization stress. E25 had the lowest volumetric wear loss and wear rate among all BFCs. In the second part, the multi-peak LED (Bluephase G2, Ivoclar Vivadent) was characterized using spectrophotometric and beam profiling analysis. The composite E25 was produced containing equal molar concentrations of either CQ-amine or CQ-amine/TPO. The degree of conversion in depth through, tight-transmittance, polymerization stress and volumetric shrinkage of the BFC were assessed. Data were analyzed according to the different experimental designs (α=0.05 and β=0.2). No statistical differences were found between CQ-amine and amine/TPO for the DC at 4mm in depth and volumetric shrinkage, however, CQ-amine/TPO had higher FM, PS and DC on the top part of the restoration. Thus, the use of elastomeric monomers reduced the PS increased the wear resistance of BFCs. However, the use of CQ-amine/TPO light cured using a multi-peak LED increased the DC only on the top part of the restoration and increased the PS without increasing the DC at 4mm in depth of the restoration.
SUMÁRIO 1. Introdução ... 13 2. Artigos ... 20 2.1 Artigo: Physical and chemical properties of bulk fill composites containing an elastomeric methacrylate monomer ... 20 2.2 Artigo: The Combination of CQ-amine and TPO Increases the Polymerization Shrinkage Stress and Does Not Improve the Depth of Cure of Bulk-fill Composites ... 46 3. Discussão ... 67 4. Conclusão ... 69 Referências ... 70 APÊNDICE – Beam profile of dental light curing units using digital single-lens reflex (DSLR) and smartphone cameras ... 76 ANEXO 1 – Carta de Submissão ... 121 ANEXO 2 – Relatório do Turnitin ... 122
restauradora de inserção incremental é fundamental devido a limitada profundidade de polimerização do material e para reduzir a tensão gerada durante a polimerização (Ferracane 2011). Sendo assim, o procedimento restaurador dos compósitos convencionais demanda grande tempo clínico (Bucuta and Ilie 2014; Ilie and Stark 2014; Leprince et al. 2014).
Com o objetivo de reduzir as etapas operatórias e o tempo necessário para confeccionar restaurações diretas foram desenvolvidos os compósitos bulk fill. Os compósitos bulk fill pertencem a uma classe de materiais restauradores indicados para restauração direta de dentes posteriores que permite a inserção e a fotoativação do material em incrementos de 4 a 5 mm de espessura (Bucuta and Ilie 2014; Ilie and Stark 2014; Tomaszewska et al. 2015). Essa nova classe de compósitos inclui materiais com menor viscosidade (flow) e maior viscosidade com propriedades mecânicas comparáveis às resinas compostas convencionais; porém, dependendo do material, com maior profundidade de polimerização e menor tensão de contração de polimerização que os compósitos convencionais (Leprince et al. 2014; van Dijken and Pallesen 2015; Zorzin et al. 2015).
A profundidade de polimerização dos compósitos fotoativáveis está relacionada com a capacidade de penetração de luz através do material para excitar os fotoiniciadores contidos na matriz orgânica e iniciar a polimerização (Flury et al. 2012; Jang et al. 2015; Leprince et al. 2012). A transmissão de luz pelo compósito é dependente da composição da matriz orgânica, como: espectro de absorção dos componentes da matriz (monômeros, fotoiniciadores, óxidos, etc.), índices de refração dos monômeros e do polímero formado na polimerização, como também do índice de refração, tipo e tamanho das partículas de carga (Shortall et al. 2008).
A polimerização de incrementos maiores nos compósitos bulk fill é possível em virtude do aumento da transmitância de luz pelo compósito, o que permite maior profundidade de polimerização (Lima et al. 2018). Compósitos bulk fill podem conter matriz de monômeros que formam polímeros com índice de refração mais próximo do índice de refração das partículas de carga, mas grandes diferenças dos materiais
comerciais são observadas no tipo e no tamanho das partículas de carga (Fronza et
al. 2017).
Alguns compósitos bulk fill contém partículas de carga com diâmetro médio entre 0,4 e 2 μm associadas a partículas de carga com diâmetro maior, de 8 até 40 μm (compósitos bulk fill híbridos) (Bucuta and Ilie 2014; Fronza et al. 2017; Leprince
et al. 2014). A utilização de partículas de carga maiores diminui o espalhamento de
luz devido à menor transição da radiação eletromagnética (luz) entre os dois meios com índices de refração diferentes (matriz orgânica e partícula de carga) (Lee 2007; Lim et al. 2008). Outros compósitos bulk fill contém partículas de cargas entre 0,4 e 2 μm associadas a nanopartículas de carga com tamanhos inferiores a 70 nm (compósitos bulk fill nanoparticulados) (Randolph et al. 2016). A utilização de nanopartículas com diâmetros menores que 1/6 do comprimento de onda de emissão da luz do fotoativador (495 nm), ou seja, partículas com diâmetro menor que 82,5 nm não são capazes de espalhar a luz; assim, ocorre maior transmissão da luz azul emitida pelo fotoativador através do compósito (Mitra et al. 2003).
Essas modificações na formulação dos compósitos odontológicos podem afetar significativamente as propriedades físico-químicas e, consequentemente, a longevidade clínica da restauração. O tamanho e a forma das partículas de carga são fatores que afetam o grau de conversão e a resistência ao desgaste dos compósitos odontológicos (Turssi et al. 2005). Em geral, o desgaste é menor quanto menor for o tamanho das partículas de carga com formas regulares, mas concomitantemente ocorre redução no grau de conversão. Para utilização de partículas irregulares, a combinação de partículas de diferentes tamanhos pode produzir resistência satisfatória ao desgaste sem afetar o grau de conversão. Em compósitos bulk fill com partículas de carga maiores e irregulares (Sonic Fill, Kerr; Tetric Evoceram Bulk fill, Ivoclar Vivadent), a resistência ao desgaste é inferior quando comparados a compósitos convencionais nanoparticulados (Filtek Z350XT, 3M ESPE) (Barkmeier et al. 2015), mas pouco se sabe sobre resistência ao desgaste de compósitos bulk fill que contenham nanopartículas (Filtek Bulk fill Posterior, 3M ESPE).
Além das modificações para aumentar a profundidade de polimerização, modificações na matriz orgânica são fundamentais para reduzir a tensão de contração de polimerização permitindo que o material restaurador possa ser inserido em maiores incrementos, reduzindo as falhas na interface adesiva e menor deflexão
elasticidade durante a transição do estado físico (Leprince et al. 2013). Essa tensão está relacionada a fatores como: tamanho e natureza dos monômeros, tempo de vitrificação do polímero e taxa de reação de polimerização. A fim de reduzir a tensão de contração de polimerização, os compósitos bulk fill podem conter monômeros com alto peso molecular e baixa viscosidade, e/ou monômeros com moduladores de tensão na cadeia espaçadora (Ferracane and Hilton 2016; Pitel 2013).
A utilização de monômeros de alto peso molecular e de baixa viscosidade altera a cinética de polimerização do material reduzindo a velocidade de conversão e o número de ligações duplas convertidas durante a polimerização. Além disso, altera a viscosidade do material durante a polimerização, facilitando o deslocamento das cadeias poliméricas em formação e, consequentemente, aliviando as tensões internas (Kalachandra et al. 1997; Sideridou et al. 2002). Monômeros com moduladores de tensão na cadeia espaçadora são capazes de se deformar (1,6-bis-(metacriloxi-2-etoxiaminocarbonila)-2,4,4-trimetilhexano, UDMA) sob tensão e assim promover a dissipação das tensões internas gerada pela polimerização (Asmussen and Peutzfeldt 1998; Barszczewska-Rybarek 2014).
Compósitos que contenham UDMA podem apresentar maior grau de conversão quando comparadas aqueles à base de BisGMA/TEGDMA. Durante a polimerização, o átomo de hidrogênio pendente, fracamente ligado ao nitrogênio, pode ser abstraído pelos radicais em propagação e funcionar como um agente de transferência de cadeia, otimizando a conversão no meio reacional (Sideridou et al. 2002). O alto grau de conversão deste monômero também está associado à sua estrutura molecular flexível, que ainda pode favorecer as propriedades mecânicas, como a tenacidade à fratura e a resistência à flexão, quando comparado à compósitos à base de BisGMA/TEGDMA (Asmussen and Peutzfeldt 1998; Sideridou
et al. 2002). Este comportamento é explicado pelo melhor desempenho da estrutura
alifática na cadeia espaçadora do UDMA, que permite a rotação e deformação da cadeia sob cargas compressivas e tensões de tração (Barszczewska-Rybarek 2014; Beatty et al. 1993).
Portanto, a substituição de monômeros como Bis-GMA por UDMA torna-se alternativa viável para obtenção de compósitos resinosos bulk fill. Monômeros de UDMA elastoméricos (Exothane™, Esstech) representam um dos mais recentes avanços na tecnologia dos monômeros à base de uretanos de dimetacrilatos. Modificações na molécula tornam esses monômeros versáteis, com ampla possibilidade de utilização em materiais resinosos odontológicos. Testes prévios, divulgados pelo fabricante, revelaram que as propriedades como a tenacidade à fratura, dureza, resistência à tração, alongamento e cor podem ser superiores ao UDMA convencional. Além disso, possuem baixa contração volumétrica, baixa tensão de contração e alta taxa de conversão (Esstech, 2016).
Apesar de tentativas prévias na utilização de monômeros de uretano elastomérico (Exothanes 8, 9, 10, 24 e 32) em formulações de sistemas adesivos odontológicos não terem sido promissoras (Münchow et al. 2014), as características químicas do monômero Exothane 24 anteriormente relatadas favorecem a utilização em matrizes monoméricas de compósitos bulk fill. Dentro do grupo de uretanos elastoméricos há 8 tipos que diferem principalmente nas cadeias espaçadoras e essas diferenças alteram as propriedades físico-mecânicas de formas distintas.
Para formulação de um compósito com componente elastomérico é fundamental que este não apresente elongação muito discrepante dos monômeros de metacrilatos porque essa discrepância altera a viscoelasticidade do compósito afetando a resiliência e módulo de elasticidade, tornando-o muito elástico, propriedade indesejável para materiais restauradores odontológicos (Asmussen and Peutzfeldt 1998; Sideridou et al. 2002).
O Exothane 24 é o monômero que apresenta elongação mais próxima dos monômeros de metacrilatos UDMA, Bis-EMA e Bis-GMA. O Exothane 24 apresenta dureza, superior aos outros Exothanes, mesmo com menor grau de conversão. Isso corrobora com os maiores valores de resistência de união para o Exothane 24 e 32, mesmo com menor grau de conversão (Münchow et al. 2014). Além disso, a viscosidade exerce papel importante na seleção da matriz monomérica e na cinética de polimerização.
Outro aspecto importante é o índice de refração do polímero de Exothane 24 que se apresenta mais próximo das partículas de carga utilizada na formulação do compósito e, portanto, pode apresentar maior profundidade de polimerização, propósito dos compósitos bulk fill.
mesmo índice de refração pode melhorar o desempenho ao desgaste de compósitos bulk fill com partículas de carga irregulares e de tamanhos diferentes. Desta forma, o monômero de Exothane 24 parece uma alternativa para compósitos bulk fill de forma a permitir a profundidade de polimerização em virtude do índice de refração próximo das partículas de carga, entretanto sem comprometer as propriedades físico-mecânicas, incluindo a resistência ao desgaste, em comparação ao monômero UDMA convencional.
Entretanto, é preciso salientar que a polimerização eficiente de espessuras maiores dos incrementos dos compósitos resinosos bulk fill também é possível pela alta eficiência dos sistemas fotoiniciadores atuais e alta irradiância dos aparelhos fotoativadores que associada ao aumento da transmitância de luz pelo material resinoso, permite maior profundidade de polimerização (AlQahtani et al. 2015).
A fotoativação de materiais restauradores resinosos é uma etapa essencial para a prática odontológica. A luz visível produzida pelos aparelhos fotoativadores é direcionada para a superfície do material a fim de iniciar a polimerização por adição para formação do polímero resinoso. Para isso, uma adequada exposição de emissão radiante é fundamental para resultar em restaurações biocompatíveis e com propriedades físicas adequadas para garantir maior longevidade clínica (Price
et al. 2015; Rueggeberg 2011). Durante a fotoativação, os compósitos resinosos
devem receber dose de energia luminosa adequada com comprimentos de onda que excitem os fotoiniciadores para que absorvam a energia luminosa e gerem radicais livres para iniciar a polimerização (Hadis et al. 2012).
A irradiância e o espectro de emissão dos aparelhos fotoativadores não são homogêneos. Assim, a emissão de um feixe de luz heterogêneo faz com que o recebimento de energia e a excitação de diferentes tipos de fotoiniciadores sejam dissimilares em diferentes regiões do material fotoativado. Como consequência disso, as extensões de polimerização, bem como a taxa de polimerização podem ser diferentes em cada região do material resinoso (Haenel et al. 2015; Michaud et al. 2014; Price et al. 2014).
Vários fatores, inerentes á composição dos compósitos, podem influenciar no grau de conversão e na taxa de polimerização dos materiais resinosos como: espessura, cor, translucidez, tipo do fotoiniciador, além de composição e quantidade de partícula de carga do material resinoso (Randolph et al. 2014). Outros fatores podem estar relacionados às características dos aparelhos fotoativadores: irradiância e espectro de emissão, ou ainda, com a técnica de fotoativação: tempo de exposição do material à luz e distância entre a ponta do aparelho fotoativador e a superfície do material resinoso a ser fotoativado (Price et al. 2015).
A necessidade do espectro de emissão no comprimento de onda específico para a excitação de fotoiniciadores não era um fato relevante quando as lâmpadas halógenas eram utilizadas, visto que esses aparelhos fotoativadores emitiam um largo espectro de emissão, numa faixa de ~375 nm a ~510 nm. Contudo, os diodos emissores de luz (LED) foram introduzidos no mercado odontológico e, rapidamente vêm substituindo as lâmpadas halógenas. A tecnologia dos LEDs permitiu a utilização mais eficiente dos aparelhos fotoativadores com melhor custo benefício, sendo também mais leves, portáteis e baterias recarregáveis (Rueggeberg 2011).
A 1ª e a 2ª geração de LEDs emitem espectro curto de comprimento de onda na região do azul (~ 440 a 485 nm). Esse espectro é eficiente na fotoativação de materiais resinosos que utilizam canforquinona (CQ) como fotoiniciador, pois a canforoquinona possui pico de absorção no espectro de luz azul, próximo a 470 nm (Jandt and Mills 2013).
Nos compósitos recentes, a CQ tem sido parcialmente substituída por fotoiniciadores alternativos como fenil 1,2 propanodiona (PPD), óxido mono-alquil fosfínico (TPO), óxido bis-alquil fosfínico (BAPO) e tioxantona (QTX), cujos picos de absorção de luz estão em comprimentos de onda menores que 420 nm. Deste modo, os LEDs de 1ª e 2ª geração não são capazes de promover a excitação desses fotoiniciadores de forma eficaz (Ely et al. 2012; Hadis et al. 2012; Schneider
et al. 2012).
Para compensar essa limitação, LEDs de 3ª geração, chamados de “polywaves”, “multi-peak” ou “multi-wave”, utilizam combinações de chips de LED com diferentes comprimentos de onda. Esses aparelhos fotoativadores emitem largo espectro que abrangem o comprimento de onda necessário para excitação da CQ, assim como de fotoiniciadores alternativos (Shortall et al. 2015).
definem a distribuição espacial e espectral do feixe de luz, e podem ter influência significativa nos materiais resinosos fotoativáveis (Li et al. 2015; Sampaio et al. 2017).
Estudos atuais demostram que o padrão de distribuição do feixe de luz tem influência significativa na microdureza de compósitos resinosos promovem diferentes zonas de polimerização de acordo com o padrão do feixe de luz (“Beam Profile”) (Michaud et al. 2014; Price et al. 2014). Por outro lado, pouco ainda se sabe sobre a influência da heterogeneidade do feixe em outras propriedades físico-químicas de materiais resinosos, principalmente em materiais que permitem a fotoativação em incrementos de 4 a 5 mm, como os compósitos restauradores bulk fill.
Portanto, o objetivo neste estudo foi desenvolver e caracterizar compósitos bulk
fill (BF) contendo diferentes monômeros elastoméricos e sistemas fotoiniciadores.
Na primeira parte do estudo o objetivo foi desenvolver e caracterizar um novo compósito bulk fill à base de monômero elastomérico. Na segunda parte o objetivo foi caracterizar a homogeneidade do feixe de luz de fotoativadores LED e avaliar a influência sobre propriedades físicas e químicas de compósitos bulk fill contendo diferentes sistemas de fotoiniciação.
2. Artigos
2.1 Artigo: Physical and chemical properties of bulk fill composites containing an elastomeric methacrylate monomer
Artigo a ser submetido ao periódico Dental Materials
Mateus Garcia Rochaab, Jean-François Rouletb, Dayane Carvalho Ramos Salles de
Oliveiraab, Mário Alexandre Coelho Sinhoretia, Americo Bortolazzo Correra
a Piracicaba Dental School, State University of Campinas, Piracicaba, SP, Brazil. b College of Dentistry, University of Florida, Gainesville, FL, USA.
Abstract
Purpose: Evaluate the microhardness in depth, degree of conversion, flexural
strength, flexural modulus, polymerization stress and two-body wear resistance of bulk fill composites (BFCs) containing elastomeric urethane methyl methacrylate monomer.
Methods: The chemical structure of an elastomeric urethane methyl methacrylate
monomer (Exothane 24, Esstech) was characterized using elemental analysis, infra-red spectroscopy and nuclear magnetic resonance. Six BFCs were made containing Exothane 24 (E) or UDMA (U) in three different concentrations: 10 wt% (E10 or U10), 25 wt% (E25 or U25) and 50 wt% (E50 or U50). The Vickers hardness as a function of depth was evaluated through each millimeter of each bulk fill increment up to 4 mm. The degree of conversion was assessed using ATR-FTIR spectroscopy. The flexural strength and flexural modulus were assessed by a three-point bending test. The polymerization stress was measured using the universal testing machine with video extensometer method. The BFCs were submitted to a two-body wear test using a chewing simulator machine (CS-4.8, SD Mechatronik) and the volumetric wear loss was evaluated using an optical scanner. Data were analyzed according to the different experimental designs (α=0.05 and b=0.2). Results: E25 was the only BFC where no significant statistical difference were found in the VHN from top up to 4 mm in depth, however E25 had lower degree of conversion than U10, U25, U50 and E10. All BFCs had the similar flexural strength, except for E50. However, the composites
1. Introduction
Bulk-fill composites (BFCs) are dental restorative materials indicated for direct restoration of posterior teeth. BFCs commercially available claim to have higher depth of cure, lower polymerization stress and mechanical properties comparable to conventional resin-based composites. However, several BFCs do not fulfill these characteristics and present lower mechanical properties than conventional resin-based composites (1, 2).
The polymerization stress is one major reasons for the incidence of marginal discrepancies, leakage, staining, reduced bond strengths and cuspal deflection in direct restorations using resin-based composites (3). These negative outcomes suggest the urge to develop low polymerization stress direct placed restorative materials without compromising the mechanical properties (4).
The urethane di-methyl methacrylate (UDMA) monomers are well known as an extensive family of monomers widely used in the formulation of dental BFCs. The urethane-based monomers have chemical structures that can easily be tailored through an appropriate choice of core and wing segments, resulting in diversity of monomers and corresponding polymers with a wide range of chemical and mechanical properties (5-7). Urethane methyl-methacrylate monomers are produced from the reaction between isocyanate (R-N=C=O) functional groups and methyl-methacrylate molecules with alcohol groups (R-OH), called polyols (8, 9).
Elastomeric urethane monomers are produced by specific isocyanates and polyols that co-polymerizes producing polymers with viscoelastic properties, lower elastic modulus, higher abrasion and chemical resistance when compared with other types of urethane monomers (10, 11). Elastomeric urethane methacrylate monomers
composites.
Thus, the aim of this study was to evaluate the influence of using an elastomeric urethane methyl methacrylate monomer in comparison to an UDMA monomer on the microhardness as a function of depth, flexural strength, flexural modulus, polymerization stress and two-body wear resistance of BFCs. The tested null hypotheses were that:
H1 – There will be no significant difference between UDMA and elastomeric
urethane methacrylate monomer in the microhardness in depth, flexural strength and flexural modulus of the BFCs.
H2 – There will be no significant difference between UDMA and elastomeric
urethane methacrylate monomer in the polymerization stress of the BFCs.
H3 – There will be no significant difference between UDMA and elastomeric
urethane methacrylate monomer in the two-body wear resistance of the BFCs.
2. Materials and Methods
2.1 Bulk fill composites (BFCs) formulation
The experimental design was developed to compare two different types of urethane monomers (UDMA or Exothane 24) in three different concentration (10 wt%, 25 wt% and 50 wt%). The monomers blend used in the BFCs formulation are listed in Table 1.
Table 1 – Formulation of the organic matrix of the bulk-fill composites containing Urethane or Exothane 24 monomers.
Urethane
U10 U25 U50
Bis-EMA 84 wt% 70 wt% 46 wt%
UDMA 10 wt% 25 wt% 50 wt%
TEGDMA 6 wt% 5 wt% 4 wt%
Exothane
E10 E25 E50
Bis-EMA 84 wt% 70 wt% 46 wt%
Exothane 24 10 wt% 25 wt% 50 wt%
TEGDMA 6 wt% 5 wt% 4 wt%
*Bis-EMA (Bisphenol A ethoxylate dimethcrylate), UDMA (Urethane Dimethacrylate), TEGDMA (Triethylene glicol dimethacrylate)
First, the monomers were blended using a centrifugal mixing device (SpeedMixer, DAC 150.1 FVZ- K, Hauschild Engineering, Hamm, North Rhine-Westphalia, Germany) for 60 s at 3000 rpm. To each monomer blend, 0.5 wt% of camphorquinone and 1 wt% of ethyl 4-(dimethylamino)benzoate was added as photoinitiator system. Then, 2 wt% of fumed silica filler (16 nm, R972, Evonik, Essen, Germany) was mixed with the monomer blend for 30 s at 3000 rpm followed by 75 wt% of BaBSiO2 (7.5 µm, Esstech Inc, Essington, PA, USA) filler for 1 min at 3500
rpm. The silanization of BaBSiO2 was performed using 3-MTPS
(3-Mercaptopropyl)trimethoxysilane) in a dichloromethane solution. Finally, each resin composite was mixed for 1 min at 3500 rpm under an 80 mmHg vacuum atmosphere.
2.2 Monomer Characterization
The elastomeric urethane methacrylate monomer was characterized by Fourier Transformed Infrared spectroscopy (FT-IR), Carbon, Hydrogen, Nitrogen (CHN) elemental analysis and nuclear magnetic resonance (NMR). For the FT-IR analysis,
composition of the monomer was determined using the Perkin Elmer 2400 series II CHN elemental analyzer (Perkin Elmer, Waltham, MA, United States). 13C and 1H
NMR experiments were carried out using a Varian Mercury (Palo Alto, CA, USA), operating at 75 MHz and 300 MHz, respectively. To obtain the spectra, 0.01 g of the monomer were dissolved in 0.7 mL of deuterated chloroform. The spectra were analyzed using the MestreLab Nova software and the molecular structure elucidation was carried out according to the signals obtained in each spectrum.
2.3 Microhardness as a function of depth
Microhardness as a function of depth was performed in a custom-made stainless-steel split mould with a semicircular notch of 15 mm in depth and 10 mm in internal diameter. Each bulk fill composite (n = 5) was inserted into a mould and covered with a Mylar strip. Then, the bulk fill composite was made flush with the top surface of the mould using a glass slide and the excess material was removed. Each bulk fill composite was light-cured on the top surface using the Bluephase G2 (Ivoclar Vivadent, Schaan, Lichtenstein) with 24 J/cm2 (1200 mW/cm2 for 20 s), keeping the
light tip centered and in contact with the Mylar strip. After light-curing, the split matrix was opened and the matrix including the bulk fill composite specimen was placed in the transversal position, with the bulk fill composite surface facing up, under a microhardness indentation tester (HMV 2000, Shimadzu, Tokyo, Japan). The test was performed using a Vickers diamond indenter that was used to apply a static load of 100 g (0.98 N) for 10 s to the composite surface at the pre-determined depths of 200 µm, 1 mm, 2 mm, 3 mm and 4 mm from the top surface of the specimen. For
each specimen, the averages of three indentations were used to calculate the Vickers Hardness number (VHN) of each bulk fill composite.
2.4 Degree of Conversion (%)
The degree of conversion for each bulk-fill composite was measured using Fourier transform infrared spectroscopy (FT-IR) in the mid-range. Each bulk-fill composite was placed on the diamond ATR detector of the FT-IR spectrometer (Frontier, Perking Elmer, Waltham, MA, United States). Unpolymerized blends were scanned and then photo-activated with 24 J/cm2 using the Bluephase G2 (Ivoclar Vivadent,
Schaan, Liechtenstein). After cure, unconverted carbon double bonds were quantified by calculating the ratio derived from the aliphatic C=C (vinyl) absorption (1638 cm-1) to the aromatic C=C absorption (1608 cm-1) signals for both polymerized
and unpolymerized samples (n = 3). Absorbance spectra included 50 scans at a resolution of 1 cm-1. The degree of conversion (DC) for bulk fill composite was
calculated, according to the following equation:
!" (%) = (1 − (+, -,⁄
(+/ -/⁄ 0 1 100
where, Xa (polymerized) and Xb (unpolymerized) represent the bands of the polymerizable aliphatic double bonds, and Ya (polymerized) and Yb (unpolymerized) represent the bands of the aromatic double bonds.
2.5 Flexural Strength (FS), Flexural Modulus (FM)
The flexural strength (FS) and flexural modulus (FM) were measured using a three-point bend test. Bar-shaped specimens (25 mm x 2 mm x 2 mm) (n=30) were made in a stainless steel split mould. After a 24 h storage in distilled water at 37 oC, the
3= = 7 × 8>
? × : × ;> × @ 1 10A5 where L = the maximum load at failure (N), D = distance
between the supports, w = the specimen width, h = the specimen height, and d = crosshead displacement.
2.6 Polymerization Stress
The polymerization stress was analyzed using the universal testing machine method(12). Glass rods (radius, 2 mm; 13 and 54 mm in length) had one of their flat surfaces roughened with #180-grit sandpaper, treated with a silane agent (Monobond S, Ivoclar Vivadent, Schaan, Liechtenstein). The 54-mm rod was attached to the upper fixture inside a 26-mm slot, connected to the load cell of a universal testing machine (Instron 4411, Instron, Canton, MA, USA). At the lower fixture, the 13-mm rod was fixed to a stainless-steel attachment with a slot allowing the positioning of the light guide in contact with its polished surface. The rods were aligned, leaving a vertical gap of 1 mm between the rods surface. A video extensometer was placed perpendicular to the gap in order to calculate the strain (in μm) between the two rods. The video extensometer consists in a camera (Nikon D3400, Nikon, Japan) attached to macro lens (Nikor 85mm, Nikon, Japan) and a software used to detect displacement in pictures (Trackmate, Fiji, ImageJ, National Institute of Health, Bethesda, MD, USA). The system compliance was calculated in 1.66 µm/N with a C-factor of 0.5. Also, the light transmittance through the 13-mm rod was 77 % of the total irradiance and the time of exposure was increased to achieve the same radiant exposure of 24 J/cm2 (924 mW/cm2 for 25s). The composite was inserted between
the treated surfaces and light cured while the video extensometer was used in order to record the specimen height. After 600 s, the strain from the video extensometer was assessed and it was manually input into the universal machine feedback system, in two different compliance situations: 0.4 µm/N (representing a Class I restoration) and 3 µm/N (representing a Class II restoration) (13, 14). The formula to calculate the sum of nominal and corrected polymerization stress forces was based on previous publications (15). Maximum stress was obtained by dividing maximal force by the cross-sectional area of the glass rod. Five specimens were tested for each experimental group.
2.7 Two-body Wear Test
The composites were submitted to a two-body wear test using a chewing simulator machine (Chewing Simulator CS-4.8, SD Mechatronik GMBH, Feldkirchen-Westerham, Germany) (n=10). Sixty aluminum sample holders (8 mm inner diameter and 1.5 mm depth) were prepared using a dental primer coating (Monobond Plus, Ivoclar Vivadent, Schaan, Liechtenstein) followed by dental adhesive application (Clear Fill SE, Kuraray, Tokyo, Japan) according to manufacturers’ instructions. The composites were filled into the sample holders in one increment and the top surface was flattened with a polyester sheet. The composites were light cured using the Bluephase G2 with 24J/cm2 and the specimens were stored in distilled water for 24 h
at 37 °C. Steatite balls (Ø 6 mm, SD Mechatronik) were fixed into aluminum sample holders with a flowable composite (Tetric Evoflow, Ivoclar Vivadent, Schaan, Liechtenstein) and these were used as antagonists.
All BFCs specimens and antagonist were randomized and allocated in six test trials, each trial, with eight composites and eight antagonists placed into the eight
simultaneously thermocycled (5/55 °C) every 90 s. The number of cycles were set at 10,000; 50,000; 100,000; 200,000; and 400,000 load cycles. After every pre-set cycle, impressions were made using polyvinylsiloxane (Virtual Extra Light Body, Ivoclar Vivadent, Schaan, Liechtenstein) with custom plastic trays. The impressions were scanned with an intraoral scanner (3M True Definition scanner, 3M ESPE, St. Paul, MN, USA) and using a geometric software (Geomagic control X, Rock Hill, SC, United States), the scanned data were used to measure the volumetric wear of the samples after each round. The flat surface of the samples was used as a reference plane and the wear was calculated as the volume of the wear facet relative to the reference plane.
2.8 Statistical Analysis
Data were entered into statistical analysis software (Stata/MP 13, StataCorp, College Station, TX, USA) and were checked for normality using Shapiro–Wilk’s test and for variance homoscedasticity using Lavene’s test. Statistical analyses were performed according to the different experimental designs with a level of significance of α = 0.05. A power analysis was conducted to determine the sample size for each experiment to provide a power of at least 0.8 at a significance level of 0.5 (b = 0.2). Vickers Hardness was analyzed using a repeated-measures analysis of variance (ANOVA) where the independent variables were set as between-subject groups for the experimental bulk fill composite (U10, U25, U50, E10, E25 or E50) and as within-subject groups for the depths (0, 1, 2, 3, and 4 mm). DC, FS, FM and PSS were analyzed independently using a one-way ANOVA where independent variables were
set as bulk fill composite (U10, U25, U50, E10, E25 or E50). The volumetric wear loss (mm3) was analyzed using a two-way repeated measures ANOVA where the
independent variables were set as between-subject groups for the experimental bulk fill composite (U10, U25, U50, E10, E25 or E50) and as within-subject groups for the number of cycles (10K, 50K, 100K, 200K, and 400K). Tukey’s test was applied for multiple comparisons between groups (α = 0.05). The wear rate (mm3/per cycle) was
analyzed using linear regression the BFCs where compared using the marginal analysis of the 95% confidence intervals. The data from the FS was also assessed using the Weibull distribution based on the 66% log-likelihood parameter.
3. Results
Table 2 shows the CHN elemental analysis results and the molecular formula of the Exothane 24. Figure 1 shows the molecular structure of the UDMA and Exothane 24. For the detailed information about the molecular structure elucidation of the Exothane 24 using the FTIR and the NMR (1H and 13C) analysis, refer to the supplementary
info.
Table 2 - Elemental Analysis of Carbon (C), Hydorgen (H), Nitrogen (N) and Oxigen (O) and molecular formulas of the Exothane 24 monomer.
Elemental Analysis C (%) H (%) N (%) O (%)
59.13 7.4 4.06 28.45
mols/g 4.93 7.30 0.29 1.78
Molecular Structures C H N O Chemical Formula Molecular Weight (g/mol)
Exothane 24 34 50 2 12 C34H50N2O12 682.65
Table 3 shows the depth of cure profile of each BFC according to the VHN. All BFCs presented statistical differences in VHN between top and bottom part of the composite, except for the E25. However, according to the top/bottom VHN ratio, the composites U25, E10 and E25 present values higher than 80%.
Table 4 shows the DC for each BFC according to the type and concentration of monomer used. For the BFCs using the Urethane monomer there is no statistical differences in the DC, however the use of Exothane 24 in the E25 and E50 concentrations reduced the DC in comparison to the E10, U10, U25 and U50.
Table 4 – Mean ± SD of the Degree of Conversion (DC, %) of the bulk fill
composites.
U10 U25 U50
Urethane 62.9 ± 2.4 Aa 66.3 ± 2.8 Aa 61.6 ± 3.9 Aa
E10 E25 E50
Exothane 60.0 ± 1.6 Aa 58.6 ± 3.8 Ab 48.3 ± 3.8 Bb
Capital Letters compare means between concentrations (U10, U25 and U50; E10, E25, and E50). Small case letters compare means between monomers (U10, U25 and U50; E10, E25, and E50).
Table 3 – Depth of Cure by Vickers Hardness Number (VHN) of the bulk fill composites in different depths and VHN top/bottom ratio (in %).
U10 U25 U50
depth (mm) VHN % VHN % VHN % Urethane 0 49.7 ± 2.4 A 100 40.3 ± 2.3 A 100 40.2 ± 2.9 A 100 1 43.7 ± 2.2 B 88 39.2 ± 1.6 A 97 36.6 ± 4.5 A 91 2 42.2 ± 1.2 BC 85 37.7 ± 1.3 AB 94 30.8 ± 4.5 B 77 3 40.3 ± 3.2 BC 81 37.5 ± 4.5 AB 93 29.6 ± 2.3 B 74 4 39.3 ± 2.1 C 79 34.1 ± 3.0 B 85 29.2 ± 4.4 B 73 Exothane
E10 E25 E50
0 49.8 ± 2.9 A 100 59.9 ± 3.4 A 100 43.3 ± 3.0 A 100 1 46.6 ± 2.9 AB 94 58.1 ± 3.0 A 97 37.4 ± 3.8 B 86 2 46.5 ± 2.9 AB 93 57.2 ± 3.8 A 95 37.6 ± 2.5 B 87 3 45.0 ± 5.3 B 90 53.7 ± 6.1 A 90 28.3 ± 3.1 C 65 4 44.1 ± 3.4 B 88 53.9 ± 6.2 A 90 20.4 ± 1.5 D 47 Capital Letters show differences between depths (mm).
Table 5 shows the mechanical properties of the BFCs according to the monomer based and concentration. For the urethane-based BFCs no statistical differences were found in the FS and FM, regardless the concentration used. For the exothane-based BFCs, E10 and E25 had similar FS than the urethane-exothane-based BFCs and higher than the E50. However, E25 had lower flexural modulus.
Table 6 shows the polymerization stress of the of the BFCs according to the monomer based and concentration. For the urethane-based BFCs, no statistical differences were found in the polymerization stress when the compliance system was a Class II, however in the Class I compliance system the composites U25 and U50 had lower PSS. For the exothane-based BFCs, the concentrations E10 had similar PSS to the urethane-based composites, however the exothane-based composites E25 and E50 had significantly lower polymerization stress than the other BFCs, in both systems with different compliances.
Table 5 - Mechanical Properties (mean ± standard deviation) — Flexural Strength (FS) with Weibull Statistic (m = Weibull parameter, σ =
Characteristic Strength, R² = Regression Coefficient) and Flexural Modulus (FM)
Monomer Concentration Flexural Strength (FS) Weibull Statistics Flexural Modulus (FM)
m σ, MPa R2 Urethane U10 89.2 ± 3.9 Aa 9.67 94.17 0.96 7.6 ± 0.1 Aa U25 88.0 ± 2.6 Aa 9.55 84.99 0.96 7.5 ± 0.1 Aa U50 80.4 ± 3.6 Aa 14.38 89.29 0.96 7.1 ± 0.1 Aa Exothane E10 92.0 ± 2.2 Aa 11.98 91.61 0.96 7.3 ± 0.2 Aa E25 86.4 ± 1.9 Aa 18.84 94.85 0.95 6.9 ± 0.1 Ba E50 65.7 ± 1.6 Bb 16.57 67.82 0.96 6.3 ± 0.1 Bb
Table 6 – Polymerization Stress (MPa) of the BFCs according to different compliances settings.
Monomer Concentration 0.4 µm/N (Class I) 3 µm/N (Class II)
Urethane U10 8.57 ± 0.19 Ab 2.86 ± 0.01 Aa U25 6.75 ± 0.24 Ba 2.32 ± 0.09 Aa U50 7.20 ± 0.22 Ba 2.76 ± 0.05 Aa Exothane E10 9.53 ± 0.72 Aa 3.23 ± 0.21 Aa E25 5.03 ± 0.23 Bb 1.80 ± 0.08 Ba E50 4.51 ± 0.21 Bb 2.01 ± 0.10 Ba
Capital Letters between concentration and Small Letters between monomers
Figure 2 and Figure 3 shows the volumetric wear loss (mm3) and wear rate
(mm3/cycle.103) of the bulk-fill composites. Up to 100 K cycles, no significant
differences were found between the composites, except for the E2 bulk fill composite that showed significantly lower volumetric wear than the other BFCs from 50K cycles.
Fi gur e 2 - Vo lu m et ri c W e a r L o s s (m m 3 ) fo r e a c h b u lk fi ll c o m p o s it e a c c o rd in g to di ff e re nt lo a d c y c le s .
Fi gur e 3 We a r R a te ( m m 3 /c y c le .1 0 3 ) o f e a c h b u lk fi ll c o m p o s ite a c c o rd in g to di ff e re nt loa d c y c le s .
the composite restorations (1, 16-18). For example, correlations between clinical and laboratory outcomes are moderately positive where fracture toughness is correlated with clinical fracture and flexural strength with clinical wear (16). The first null hypothesis tested in this study that there will be no significant difference between UDMA and elastomeric urethane methacrylate monomer in the microhardness in depth, flexural strength and flexural modulus of the BFCs was rejected.
Microhardness is a mechanical test to evaluate the materials’ surface resistance to penetration and is commonly used to determine the depth of cure of photopolymerizable dental composites (18-20). As long as the microhardness on the bottom part of the composite is at least 80% of the hardness on the top surface, the dental composite has proper depth of cure up to that thickness (19). In this study, the BFCs where design to achieve 80% of the top/bottom hardness up to 4mm in depth, but only U25, E10 and E25 achieved it. However, one major drawback of using the 80% top/bottom hardness ratio is to rely in an arbitrary value to ensure the quality of the composite in the bottom part of the restoration (21). Thus, based on the statistical analysis, it is certain to affirm that only the E25 had achieved proper polymerization from top to bottom.
The second null hypothesis tested in this study that there will be no significant difference between UDMA and elastomeric urethane methacrylate monomer in the polymerization stress of the BFCs was rejected.
There are two possible explanation for the polymerization stress reduction caused by the use of the elastomeric urethane methacrylate monomer. The first one is related to the molecular structure of the elastomeric monomer in comparison to the UDMA. As showed in the CHN elemental analysis the elastomeric methacrylate monomer is an organic molecule with 682.85 g/mol of molecular weight, while the UDMA used in this study has 470 g/mol of molecular weight. These differences in molecular weight between the two monomers are significant and thus are able to to induce differences in the total volumetric polymerization shrinkage, and as consequence, change the polymerization stress of the BFCs. Besides that, the elastomeric monomer has a cycloaliphatic core structure that makes the molecule more prone to strain and adapt in stress-developed scenarios, as well as, polyol structures that stretch and rotate reducing the internal stress development in addition to four polymerizable functional groups which create more possibilities to stress-strain dissipation, bind sites and crosslink during the polymerization process (4, 22, 23).
Furthermore, as showed in Table 5, the BFCs containing the elastomeric methacrylate monomer in the concentrations of E25 and E50 had lower FM. Since FM is equal to the ratio between stress and strain, it follows that the lower the FM, the lower the stress for a given strain, and this can lead to the assumption that composites with lower FM have lower polymerization stress (15, 24, 25). Thus, based on these statements and the results presented on table 6, it can therefore be implied that the lower polymerization shrinkage stress of the BFCs E25 and E50 is associated with the lower FM of these composites.
Besides that, the compliance of the system used to measure the polymerization shrinkage stress dictates the shrinkage-stress development in constrained situations
there is a strong possibility to expect a reduction in the mechanical properties of these composites (26). What is surprising is that the flexural strength and two-body wear resistance of the BFCs was not lower when the elastomeric methacrylate monomer was used, instead the E25 presented the higher wear resistance with significant lower volumetric wear loss and wear rate than the other BFCs tested. Therefore, the third research hypothesis that there will be no significant difference between UDMA and elastomeric urethane methacrylate monomer in the two-body wear resistance of the BFCs was rejected.
In most of the previous studies, the wear resistance of resin-based composites has been compared with the mechanical properties tests that have been obtained in static or low strain rate testing conditions (16, 17, 27). However, the mechanical response of elastomeric methacrylate monomers at high strain rates can be significantly different from that of loading with low strain rates. As showed in table 5, there is no statistical differences in the flexural strength of the BFCs, except for E50. However, the composites had completely different behavior in respect to wear and wear rate. The same is true for the FM, E25 and E50 had no statistical differences in the FM, however E25 had higher wear resistance. In this study, all composites tested had the same filler size, type and content and the differences in the wear resistance are strictly related to the monomer blend.
What is striking is that the composite with the higher FS and lower FM showed higher wear resistance which might lead us to a suggestion that the viscoelastic response of
elastomeric can provide a deeper understating of how the time depend properties of the elastomeric monomers may affect the mechanism of material removal and the final wear rate of the composite (28, 29). Besides that, further investigations should look into the polymer network and polymerization kinetics to understand if the elastomeric monomers with four polymerizable groups can produce polymers with higher crosslink density.
5. Conclusion
The use of an elastomeric urethane methyl methacrylate monomer in the concentration of 25 wt% of the organic matrix reduced the polymerization stress and increased the wear resistance of BFCs.
6. Acknowledgment
This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) – (AUX CAPES-PROEX 0878/2018) and Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP) (grant #2016/06019-3 and #2017/22195-9). DO is a Post-Doctoral Researcher at FAPESP (grant #2016/05823-3 and #2017/22161-7).
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Figure S1 - FT-IR spectra of Exothane 24. The following characteristic peaks are
observed: B = 3386 cm−1 (N-H stretching peak); B = 2958 cm−1 (C–H stretching peak); B = 1715 cm−1 (C=O stretching peak); B = 1637 cm−1 (C=C stretching peak); B = 1525 cm−1 (N-H bend peak); = 1146 cm−1 (C-O-C stretching peak).
Figure S2 - The molecular structure of the monomer Exothane 24 and the following
peak characteristics: 13C NMR (75 MHZ, cdcl3) C 166.95, 155.46, 136.02, 126.29,
69.97, 63.05, 62.73, 51.79, 48.81, 47.97, 46.37, 42.26, 39.49, 37.55, 35.24, 33.05, 29.69, 27.51, 26.47, 25.24, 22.42, 20.58, 18.32.
Figure S3 - The molecular structure of the monomer Exothane 24 and the following
peak characteristics: 1H NMR (300 MHz, cdcl3) C 6.12, 5.58, 5.27, 4.36, 3.16, 1.94,
2.2 Artigo: The Combination of CQ-amine and TPO Increases the Polymerization Shrinkage Stress and Does Not Improve the Depth of Cure of Bulk-fill Composites
Artigo aceito para publicação no Operative Dentistry (2019) in press
doi.org/10.2341/18-234-L
Abstract
Objectives: To evaluate the effect of combining camphorquinone (CQ) and
diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) on the depth of cure and polymerization shrinkage stress of bulk fill composites. Materials and Methods: Experimental bulk fill composites were produced containing equal molar concentrations of either CQ-amine or CQ-amine/TPO. The degree of in-depth conversion through each millimeter of a 4 mm thick bulk fill increment was evaluated by FT-NIR micro-spectroscopy using a central longitudinal cross-section of the increment of each bulk fill composite (n=3). Light-transmittance of the multi-wave LED emittance used for photoactivation (Bluephase G2, Ivoclar Vivadent) was recorded through every millimeter of each bulk fill composite using spectrophotometry. The volumetric shrinkage and polymerization shrinkage stress were assessed using a mercury dilatometer and the Bioman, respectively. The flexural modulus was also assessed by a three-point bend test as a complementary test. Data were analyzed according to the different experimental designs (α=0.05 and b=0.2). Results: Up to 1 mm in depth, TPO addition to CQ-based bulk fill composites increased the degree of conversion, but beyond 1 mm no differences were found. The light-transmittance of either wavelengths emitted from the multi-wave LED (blue or violet) through the bulk fill composites were only different up to 1 mm in depth, regardless of the photoinitiator system. The addition of TPO to CQ-based bulk fill composites did not affect volumetric shrinkage, but did increase the flexural modulus and polymerization shrinkage stress. Conclusion: The addition of TPO to CQ-based bulk fill composites did not increase the depth of cure. However, it did increase the degree of conversion on the top of the restoration, increasing the polymerization shrinkage stress.
