Programa de Pós-Graduação em Odontologia
Tese
Influência da formulação e translucidez na estabilidade de cor e eficiência de polimerização de compósitos odontológicos
Vinícius Esteves Salgado
Vinícius Esteves Salgado
Influência da formulação e translucidez na estabilidade de cor e eficiência de polimerização de compósitos odontológicos
Tese apresentada ao Programa de Pós-Graduação em Odontologia da Faculdade de Odontologia da Universidade Federal de Pelotas, como requisito para obtenção do título de Doutor em Odontologia, área de concentração Materiais Odontológicos.
Orientador: Prof. Dr. Luis Felipe Jochims Schneider Co-orientador: Prof. Dr. Rafael Ratto de Moraes
S164i Salgado, Vinícius Esteves
SalInfluência da formulação e translucidez na estabilidade de cor e eficiência de polimerização de compósitos
odontológicos / Vinícius Esteves Salgado ; Luis Felipe Jochims Schneider, orientador ; Rafael Ratto de Moraes, coorientador. — Pelotas, 2016.
Sal64 f. : il.
SalTese (Doutorado) — Programa de Pós-Graduação em Materiais Odontológicos, Faculdade de Odontologia, Universidade Federal de Pelotas, 2016.
Sal1. Propriedades ópticas. 2. Envelhecimento. 3. Descoloração. 4. Pigmentação. 5. Materiais dentários. I. Schneider, Luis Felipe Jochims, orient. II. Moraes, Rafael Ratto de, coorient. III. Título.
Black : D151 Elaborada por Fabiano Domingues Malheiro CRB: 10/1955
Influência da formulação e translucidez na estabilidade de cor e eficiência de polimerização de compósitos odontológicos
Tese apresentada, como requisito parcial, para obtenção do grau de Doutor em Odontologia, Programa de Pós-Graduação em Odontologia, na área de concentração em Materiais Odontológicos, Faculdade de Odontologia, Universidade Federal de Pelotas.
Data da defesa: 23 de junho de 2016.
Banca examinadora:
Prof. Dr. Luis Felipe Jochims Schneider (Orientador)
Doutor em Materiais Dentários pela Universidade Estadual de Campinas Prof. Dr. Flávio Fernando Demarco
Doutor em Odontologia (Dentística) pela Universidade de São Paulo Prof. Dr. Fabrício Aulo Ogliari
Doutor em Odontologia (Dentística) pela Universidade Federal de Pelotas Prof. Dra. Cristina Pereira Isolan
Doutora em Odontologia (Materiais Odontológicos) pela Universidade Federal de Pelotas
Prof. Dra. Lisia Lorea Valente
Doutora em Odontologia (Dentística) pela Universidade Federal de Pelotas Prof. Dr. Evandro Piva (Suplente)
Doutor em Materiais Dentários pela Universidade Estadual de Campinas Prof. Dra. Gabriela Romanini Basso (Suplente)
Doutora em Odontologia (Materiais Odontológicos) pela Universidade Federal de Pelotas
Dedico este trabalho aos meus pais Luiz Carlos e Selma e à minha irmã Vitoria por todo amor e incentivo.
Agradecimentos
À Universidade Federal de Pelotas, através do magnífico reitor Prof. Dr. Mauro Augusto Burkert Del Pino, por possibilitar o meu crescimento acadêmico.
À Faculdade de Odontologia, em nome da diretora Profa. Dra. Adriana Etges, pela acolhida e contribuição na minha formação acadêmica e profissional.
Ao Programa de Pós-Graduação em Odontologia, através do coordenador Prof. Dr. Rafael Ratto de Moraes, pela sua excelência e por toda a contribuição na minha formação acadêmica como docente e pesquisador.
Ao orientador deste projeto, Prof. Dr. Luis Felipe Jochims Schneider, por toda a ajuda no planejamento e na execução deste, por todo auxílio fora do meio acadêmico, por toda a confiança em mim depositada, por ser um dos meus exemplos profissionais, por compartilhar e incentivar tantos outros projetos. Por ser um grande mentor profissional, ajudando e guiando o meu crescimento.
Ao co-orientador deste projeto, Prof. Dr. Rafael Ratto de Moraes, por toda a ajuda dada dentro e fora deste, pela acolhida em Pelotas, pelas intensas revisões nos textos científicos, por elevar o meu padrão de qualidade, por ser um dos meus exemplos profissionais e por todos os incentivos nos meus projetos científicos.
À Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, através do coordenador da área Odontologia Prof. Dr. Carlos José Soares, pela bolsa de estudos concedida.
Ao secretário do Programa de Pós-graduação em Odontologia, Celaniro Borges de Farias Junior, por todo o apoio durante o período do doutorado, principalmente nos momentos de ausência em Pelotas.
Ao N-PBO, Núcleo de Pesquisa em Biomateriais Odontológicos da Universidade Veiga de Almeida em nome do coordenador Luis Felipe Jochims Schneider, por possibilitar o desenvolvimento laboratorial dos estudos deste projeto.
Aos amigos Guilherme Ferreira Rego e Pedro Paulo Albuquerque Cavalcanti de Albuquerque por toda a ajuda na execução das etapas laboratoriais deste projeto e por toda a cumplicidade.
Aos demais colaboradores deste projeto, Prof. Dra. Carmem Silvia Costa Pfeifer, Prof. Dr. Jack L. Ferracane e Prof. Dra. Larissa Maria Assad Cavalcante, por toda a ajuda.
À amiga Ana Paula Rodrigues Gonçalves por toda a ajuda dada na fase final do período do doutorado, por toda a cumplicidade e por todos os bons momentos de convivência em Pelotas.
Ao Prof. Dr. Flávio Fernando Demarco e ao Prof. Dr. Maximiliano Sérgio Cenci por todo o conhecimento transmitido, por serem exemplos profissionais, por todo o estímulo ao pensamento crítico e por me mostrarem a significância da aplicação da pesquisa científica em benefício da sociedade.
À Prof. Dra. Patricia dos Santos Jardim por toda a amizade, convívio, acolhida, incentivo e por ser um dos meus exemplos profissionais.
Ao Prof. Dr. Fabrício Aulo Ogliari e ao Prof. Dr. Evandro Piva por todo o conhecimento transmitido e por me mostrarem a importância da pesquisa científica fora do meio acadêmico.
Aos demais professores do PPGO por contribuírem na minha formação acadêmica.
Aos colegas discentes do PPGO Aline Oliveira Ogliari, Andrea Soares Quirino da Silva Fonseca, Bruna Vetromila, Cristina Pereira Isolan, Gabriela Romanini Basso, Lisia Lorea Valente, Manuel Tomás Borges Radaelli, Marina da Rosa Kaizer, Quéren Ferreira da Rosa, Tharsis Christini de Almeida Rossato e Sonia Luque Peralta, pela amizade, convívio e trocas de experiências neste período.
Aos meus pais Luiz Carlos Marques Salgado e Selma Esteves Salgado pela minha criação, por toda a educação dada, por todo incentivo no meu crescimento como pessoa e como profissional e por todo amor.
Notas Preliminares
A presente Tese foi redigida segundo o Manual de Normas para Dissertações, Teses e Trabalhos Científicos da Universidade Federal de Pelotas de 2013, adotando o Nível de Descrição 3 – estrutura em Capítulos não convencionais. <http://sisbi.ufpel.edu.br/?p=documentos&i=7> Acesso em: 01 de junho de 2016.
A qualificação do projeto de Tese foi realizada em 19 de novembro de 2015 e aprovada pela Banca Examinadora composta pelos Professores Doutores Rafael Ratto de Moraes, Marina da Rosa Kaizer e Gabriela Romanini Basso.
Resumo
SALGADO, Vinícius Esteves. Influência da formulação e da translucidez na estabilidade de cor e eficiência de polimerização de compósitos odontológicos. 2016. 64f. Tese (Doutorado em Odontologia) - Programa de Pós Graduação em Odontologia, Faculdade de Odontologia, Universidade Federal de Pelotas, Pelotas, 2016.
O objetivo deste estudo, dividido em duas etapas, foi investigar a influência da composição e da translucidez de compósitos odontológicos na estabilidade de cor e eficiência de polimerização. A primeira etapa envolveu a formulação de compósitos experimentais com a proposição de determinar a relação entre o sistema fotoiniciador e o conteúdo inorgânico sobre a estabilidade de cor e a eficiência de polimerização. Três sistemas fotoiniciadores foram empregados (canforquinona/amina – CQ/amina; óxido mono-alquil fosfínico - TPO e óxido bis-alquil fosfínico - BAPO) e dois tamanhos médios de partículas de sílica como carga (7nm ou 16nm). A eficiência de polimerização foi analisada pela dureza Knoop a 25kgf/mm2 por 15s utilizando microdurômetro. A estabilidade de cor foi calculada pela fórmula de diferença de cor CIELAB, mensurada com espectrofotômetro. Os materiais foram submetidos ao envelhecimento pela imersão em água e em solução de café. Os dados foram submetidos à Análise de Variância, seguidos pelo teste de
Student-Newman-Keuls (α=0,05). Os materiais formulados com TPO apresentaram
maior estabilidade de cor. O tamanho da partícula não influenciou os resultados da estabilidade de cor. A eficiência de polimerização não foi influenciada pelo sistema fotoiniciador ou pelo tamanho da partícula de carga. A segunda etapa deste projeto envolveu a avaliação de quatro compósitos comerciais (IPS Empress Direct, Estelite ∑ Quick, Filtek Z350 XT e Opallis), com diferentes níveis de translucidez, com a proposição de verificar a relação entre o nível de translucidez e a estabilidade de cor, assim como entre o nível de translucidez e a eficiência de polimerização. A eficiência de polimerização foi analisada pelo grau de conversão de C=C utilizando espectroscopia no infravermelho transformada de Fourier, enquanto a estabilidade de cor foi avaliada pela fórmula de diferença de cor CIEDE2000. Os dados foram submetidos à Análise de Variância e teste de Student-Newman-Keuls (α=0,05). Foi observado que quanto maior a translucidez, menor a estabilidade de cor dos compósitos odontológicos, apesar de não ter sido observada diferença significativa em relação à eficiência de polimerização. De acordo com os resultados dos estudos pode ser concluído que o sistema fotoiniciador, o tamanho das partículas de carga e a translucidez afetaram a estabilidade de cor dos compósitos odontológicos apesar de não ter sido observada influência destes sobre a eficiência de polimerização.
Palavras-chave: propriedades ópticas; envelhecimento; descoloração; pigmentação; materiais dentários
Abstract
SALGADO, Vinícius Esteves. Influence of formulation and translucency on color stability and cure efficiency of dental composites. 2016. 64p. Thesis (PhD in Dentistry) - Programa de Pós Graduação em Odontologia, Faculdade de Odontologia, Universidade Federal de Pelotas, Pelotas, 2016.
The objective of this study, separated in two phases, was to investigate the process related to resin-based composites’ formulation and translucency over the color stability and cure efficiency. The first phase involved experimental resin-based composite formulations with the purpose to determine the relationship between the photoinitiator system and inorganic content over the color stability and cure efficiency. Three different photoinitiator systems were used (camphorquinone/amine – CQ/amine, monoalquil oxide – TPO, and bisalquil oxide – BAPO) and two average silica nanofiller sizes (7 nm or 16 nm). The cure efficiency was analyzed by Knoop hardness reading under 25kgf/mm² for 15s using a microindenter. The color stability was measured by CIELAB color difference formula measured with a spectrophotometer. The materials were aged by immersion in water and coffee solution. Data were submitted to Analysis of Variance followed by Student-Newman-Keuls’ test (α=0.05). TPO-based materials presented the higher color stability. The filler size did not influence the color stability results. The cure efficiency was not influenced by photoinitiator system or filler size. The second phase involved four commercial resin-based composites (IPS Empress Direct, Estelite ∑ Quick, Filtek Z350 XT and Opallis) tested in different translucent degrees with the purpose to determine the relationship between translucency and color stability and between translucency and cure efficiency. The cure efficiency was analyzed by degree of C=C conversion using Fourier-transformed infrared spectroscopy. The color stability was measured by CIEDE2000 color difference formula. Data were submitted to Analysis of Variance and Student-Newman-Keuls’ test (α=0.05). It was observed that the higher the translucency, the lower the color stability, despite no significant difference in cure efficiency results. Based on the results from both studies, it can be concluded that the photoinitiator system, filler-particle size and translucency affect the color stability of resin-based composites although no significant influence on the cure efficiency was observed.
Sumário
1 Introdução ... 10
2 Capítulo 1 – Influence of photoinitiator system and nanofiller size on the optical properties and cure potential of model composites …………. 14
3 Capítulo 2 – Does translucency influence the color stability and the cure efficiency of resin-based composites? ………..……….. 32
4 Considerações finais ... 52
Referências ... 54
1 Introdução
Atualmente os compósitos odontológicos são considerados materiais de escolha para restaurações dentárias diretas. Estes materiais têm sido amplamente utilizados na prática clínica nos últimos 30 anos e, desde a sua introdução, sofrem modificações na composição com o objetivo de melhorar o desempenho clínico. O sucesso estético das restaurações dentárias é dependente da combinação entre material restaurador e tecido dentário adjacente, assim como da estabilidade das propriedades ópticas do material. Entre as principais falhas das restaurações com compósitos odontológicos na região anterior estão aquelas por motivos estéticos (BALDISSERA et al, 2013). Entre estas, falhas na combinação da cor e/ou translucidez são frequentes.
A alteração de cor dos compósitos odontológicos pode ter origem em fatores extrínsecos, relacionados à absorção de pigmentos das diversas soluções com as quais o material entra em contato durante o consumo pelo paciente, como produtos oriundos da dieta (ERTAS et al, 2006) e em fatores intrínsecos, relacionados às reações químicas que ocorrem no corpo do material associadas à captação de água pela interface entre partícula de carga e matriz (KALACHANDRA; WILSON, 1992), formação de peróxidos cromáticos pelas reações de oxidação dos monômeros não-reagidos, (FERRACANE, 1995), degradação do agente silano de união (SÖDERHOLM, 1981; KARABELA; SIDERIDOU, 2008), lixiviação de componentes do sistema fotoiniciador ou outros componentes que não foram consumidos durante a fotoativação (ALBUQUERQUE et al, 2013) e à oxidação dos produtos formados pelo co-iniciador (SCHNEIDER et al, 2009).
O sistema fotoiniciador, presente nos materiais poliméricos ativados por luz, compreende um grupo de moléculas capazes de absorver luz e, direta ou indiretamente, gerar espécies reativas que possibilitam a iniciação da reação de polimerização (STANSBURY, 2000). A associação da canforquinona (CQ) com uma amina terciária tem sido amplamente utilizada como sistema fotoiniciador desde a introdução dos compósitos odontológicos ativados por luz visível. A CQ é um sólido
cromóforo cuja estrutura molecular inclui um grupo cromático que possibilita que o material seja ativado por luz, porém confere intensa coloração amarela ao material. Por motivos estéticos, a utilização de sistemas fotoiniciadores alternativos à CQ/amina tem sido investigada (NEUMANN et al, 2005; ARIKAWA et al, 2009; ALBUQUERQUE et al, 2013).
O uso de sistemas fotoiniciadores menos cromáticos, com menor coloração amarela, como os derivados do óxido fosfínico – óxido mono-alquil fosfínico (MAPO ou TPO) ou o óxido bis-alquil fosfínico (BAPO) – pode minimizar os problemas da instabilidade de cor dos materiais baseados no sistema CQ/amina. De forma distinta à CQ, que possui pico de absorção máxima (λmax) na luz visível a 470nm, TPO e BAPO possuem os picos de absorção máxima próximos à radiação ultravioleta (381nm e 370nm, respectivamente), embora seu perfil de absorção se estenda à região da luz visível dentro do espectro eletromagnético (NEUMANN et al, 2005). Como TPO e BAPO absorvem luz em menor comprimento de onda que a CQ, apresentam coloração amarela pálida ou coloração branca. São considerados iniciadores Norrish Tipo I, o que significa que geram radicais livres por processo de fotoclivagem que não necessita de co-iniciador. Sistemas Norrish Tipo II, como a CQ, necessitam de molécula co-iniciadora para gerar efetivamente radicais livres, que são formados pela mudança do hidrogênio da molécula do fotoiniciador (STANSBURY, 2000). As aminas terciárias são conhecidas por gerarem subprodutos durante a fotoativação, o que pode a causar descoloração do amarelo ao marrom, dependendo do tipo e quantidade de amina no sistema (SCHNEIDER et al, 2009). Além disso, há potencial efeito citotóxico da CQ não-reagida e moléculas de amina liberadas pelo material (NOMURA et al, 2006; VOLK et al, 2009).
A translucidez é uma das propriedades ópticas mais importantes nos compósitos odontológicos. Para reprodução das características ópticas de cada terço dentário, o uso de materiais com elevada translucidez pode ser necessário. Resulta da relação entre os índices de refração entre partículas de carga e matriz resinosa. Quanto maior esta diferença, menor a translucidez (KIM et al, 2007). Sabe-se que a composição dos compósitos odontológicos afeta diretamente a translucidez (LEE, 2008; ARIKAWA et al, 2009; AZZOPARDI et al, 2009; SALGADO et al, 2013; SALGADO et al, 2014), porém não há informação na literatura sobre a estabilidade de cor dos compósitos com diferentes níveis translúcidos.
Entre as formas de obtenção de compósitos com maior translucidez, alguns fabricantes podem reduzir a concentração de CQ e/ou adicionar sistemas fotoiniciadores alternativos, de menor croma em comparação à CQ. Entretanto, a quantidade desses componentes não é informada precisamente nos materiais comerciais (PALIN et al, 2008). Além do uso de sistemas fotoiniciadores alternativos para substituição parcial ou total da CQ, a tecnologia de fotopolimerização de radical amplificado (“radical amplified photopolymerization - R.A.P. technologyTM”) é descrita como nova tentativa de redução da quantidade de CQ utilizando co-iniciador inovador. Segundo o fabricante (Tokuyama Dental, Tóquio, Japão), enquanto consumida durante a polimerização nos materiais baseados no sistema CQ/amina, a CQ é dita como reciclada dentro da reação da geração de iniciador nos materiais baseados na tecnologia RAP. Assim, uma única molécula de CQ pode produzir múltiplos radicais de iniciação. Essa tecnologia leva à maior profundidade de polimerização de materiais baseados no sistema CQ/amina (ILIE; KREPPEL; DURNER, 2014).
As propriedades ópticas dos compósitos odontológicos são dependentes do grau de conversão de C=C (FERRACANE, 2006), assim como da sua formulação (ARIKAWA et al, 2007; SABATINI, 2015). Tipo, tamanho e distribuição das partículas de carga do conteúdo inorgânico (ARIKAWA et al, 2007; SALGADO et al, 2013), composição da matriz resinosa e tipo e concentração do sistema fotoiniciador (ARIKAWA et al, 2009; ALBUQUERQUE et al, 2013) são fatores que influenciam a estabilidade das propriedades ópticas. A reação de polimerização nesses materiais é limitada à profundidade da penetração da luz e, por isso, é dependente da distribuição do conteúdo inorgânico, da translucidez do material, da absorção e do espalhamento da luz pelo material (LEE, 2008). A polimerização é mais efetiva na superfície próxima à fonte de luz e gradualmente menos efetiva em direção às porções mais profundas, gerando gradiente de polimerização dentro do material (FAN et al, 2002). Entretanto não há informação na literatura sobre a eficiência de polimerização dos diferentes níveis translúcidos de sistemas restauradores utilizados na prática clínica. Complicações relacionadas à polimerização ineficaz incluem aumento do risco de fratura das margens da restauração ou do corpo do material (FERRACANE, 1995), baixa resistência ao desgaste (CONDON; FERRACANE, 1997) e baixa estabilidade de cor (JANDA et al, 2007). Em estudo prévio (SALGADO
et al, 2013), foi observado que quanto menor o tamanho médio da partícula de carga em um compósito experimental formulado com sistema CQ/amina, menor a coloração amarela (CIE b*) e a maior tendência à estabilidade de cor (menor ∆E*). Porém, não há relato na literatura de relação entre sistemas fotoiniciadores alternativos e o tamanho do conteúdo inorgânico na estabilidade das propriedades ópticas e eficiência de polimerização.
Dessa forma, o objetivo geral do presente estudo é determinar a influência da composição e da translucidez nas propriedades ópticas e eficiência de polimerização de compósitos odontológicos restauradores. Os objetivos específicos do presente estudo incluem:
1. determinar a influência do sistema fotoiniciador e do conteúdo inorgânico nas propriedades ópticas e eficiência de polimerização de compósitos odontológicos experimentais;
2. determinar a relação entre translucidez e eficiência de polimerização e entre translucidez e estabilidade de cor de diferentes sistemas restauradores comerciais.
2 Capítulo 11
Influence of photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites
2.1 Abstract
Objective: To establish the relationship between photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites.
Methods: Model composites based on BisGMA/TEGDMA (60:40 mol%) were loaded with 40 wt% of 7 nm or 16 nm-sized filler particles. One of the following photoinitiator systems was added: camphorquinone (CQ) associated with an amine (EDMAB), monoacylphosphine oxide (TPO), or bysacylphosphine oxide (BAPO). The optical properties of disc-shaped specimens were measured 24 h after curing and repeated after storage in water for 90 days and coffee for 15 days. A large spectrum LED unit (Bluephase G2, Ivoclar Vivadent) was used for photoactivation. CIEL*a*b* parameters, color difference (ΔE), and translucency parameter (TP) were calculated. Knoop hardness readings were taken at top and bottom composite surfaces. Cure efficiency was determined by bottom/top hardness ratio. Data were statistically analyzed at α=0.05 significance level.
Results: Composites formulated with 16 nm particles had higher CIE L* than those with 7 nm particles in all storage conditions. BAPO-based composites generally had lower CIE a* than the other composites. The group TPO+16nm before storage and all groups with 16 nm-sized particles after storage had lower CIE b* (i.e. lower degree of yellowing). TPO-based materials had higher color stability. The cure efficiency was not significantly affected by photoinitiator system or particle size. CQ+7 nm had the lowest and BAPO+16 nm the highest hardness values.
Significance: Combination of photoinitiator system and filler particle size might affect the optical properties of composites, with low influence on cure efficiency.
1
Keywords: alternative photoinitiators; BAPO; camphorquinone; CIELAB; fumed silica; storage; TPO.
2.2 Introduction
The photoinitiator system in dental composites is a group of molecules capable of absorbing light and as a result, directly or indirectly, giving rise to reactive species that can initiate polymerization. Photoinitiator molecules usually have in their structure a carbonyl group, which presents one electron capable of being transformed in anti-bonding orbital when exposed to light at appropriate wavelengths (STANSBURRY, 2000). Association of camphorquinone (CQ) with a tertiary amine has been largely used as the photoinitiator system since the introduction of visible-light activated dental composites. CQ is a solid chromophore, meaning that the molecular structure includes a chromatic group that makes the material photoactive, in turn bringing a strong yellow color for the material. For esthetic reasons, the use photoinitiator systems alternative CQ/amine has been suggested.
The use of less yellow photoinitiators such as the phosphine oxide derivatives monoacylphosphine oxide (MAPO, also known as TPO) or bysacylphosphine oxide (BAPO) could minimize problems related to the color instability of CQ-based materials. TPO and BAPO absorb light at shorter wavelengths than CQ and, as a consequence, present a very pale yellow color or no color at all. BAPO and TPO are Norrish Type 1 photoinitiators, which means that they generate free-radicals by a photocleavage process that does not require co-initiator. Type 2 photoinitiators such as CQ need a co-initiator to effectively generate free-radicals, which are formed from displacement of hydrogen from the photoinitiator molecule (ALBUQUERQUE et al, 2013). Amines are known to generate by-products during photoreaction, which tend to cause discoloration from yellow to brown, depending on the type and fraction of amine in the system (JANDA et al, 2004; SCHNEIDER et al, 2009). In addition, there is a potential cytotoxicity of unreacted CQ (VOLK et al, 2009) and amine molecules (NOMURA et al, 2006) eluted from the composite.
Previous studies have demonstrated the polymerization efficiency of TPO and BAPO (SUN; CHAE, 2000; NEUMANN et al, 2005; NEUMANN et al, 2006; LEPRINCE et al, 2011). These photonitiators require a modification of the existing dental lights to extend the emission profile beyond blue light wavelengths for better curing. To accommodate that, several companies have developed new LED curing
units that are capable of activating resin composites containing other photoinitiators, which highlights the commercial potential of these alternative systems. TPO and BAPO both have maximum absorption peaks (λmax) close to UV radiation, although their absorption profile extends towards the visible light region of the electromagnetic spectrum.
Despite the several benefits derived from photoreaction, the polymerization of composites is limited to the depth of light penetration. In composites, high filler loading causes light to be absorbed and scattered, and thus attenuated as it passes through the material. Polymerization is usually far more efficient on the surface close to the light source, and that efficiency decreases at deeper portions. This creates a gradient of polymerization within the material, and may result in undercured layers at the bottom areas (FAN et al, 2002). It is known that the quantity, size, and shape of particles all affect the scattering of light through the composites (LEE, 2008). A previous study reported that use of larger nanoparticles increased lightness and reduced the yellowing effect of composites, whereas materials with smaller particles tended to have increased color stability (SALGADO et al, 2013). However, to our knowledge, no data is available about the relationship between alternative photoinitiator systems and particle size in nanostructured composites and their influence on optical properties.
The aim of this study was establish a relationship between photoinitiator system and nanoparticle size on the optical properties and curing efficiency of model dental composites. The hypotheses of this study were: i) composites formulated with CQ would present higher yellowing effect and higher color difference during storage than composites with BAPO or TPO; ii) composites formulated with higher nanoparticle size would have lower yellowing effect and higher lightness than composites with lower nanoparticles; iii) composites formulated with TPO and BAPO would present higher curing efficiency than composites formulated with CQ.
2.3 Materials and methods
2.3.1 Formulation of the model composites
Experimental composites were formulated by a 60:40 mol% mixture of BisGMA and TEGDMA (Esstech, Essington, PA, USA). Composites were prepared by incorporating 40 wt% of nanoparticles with either 7 nm (Aerosil® R 812, Evonik, Germany) or 16 nm (Aerosil® R 972) in average size. Fillers consist in hydrophobic
fumed silica particles treated with hexamethyldisilazane (Aerosil® R 812) or dimethyldichlorosilane (Aerosil® R 972). Composites with three different photoinitiator systems added at 1 mol% were tested: CQ associated with ethyl 4-dimethylaminobenzoate (EDMAB), TPO, or BAPO, all from Sigma-Aldrich (Chemie, Steinheim, Germany). The photoinitiators were diluted in TEGDMA and then BisGMA was added. Fillers were gradually incorporated initially by hand-mixing, then the materials were mechanically mixed using a centrifugal mixer (SpeedMixer DAC150; FlackTek, Landrum, SC, USA) to produce a homogeneous paste. Six composites were formulated based on distinct filler size–photoinitiator system combinations.
Disc-shaped specimens were made in a circular steel mold (8 mm in diameter, 2 mm in thickness). After composite insertion, the top surface was covered with a Mylar strip and made flat by pressure with a glass slide. For each group, 12 specimens were obtained: six were used for optical properties analysis, and the other six for cure efficiency analysis. The specimens were light cured from the top surfaces for 40 s with a large spectrum LED curing unit (Bluephase G2; Ivoclar Vivadent, Schaan, Liechtenstein) with irradiance of 1200 mW/cm2. All specimens were mechanically polished in both surfaces in a grinding/polishing machine (Buehler, Lake Bluff, IL, USA) with a sequence of 2000- and 4000-grit SiC papers under continuous water cooling.
2.3.2 Optical properties analysis
Twenty-four hours after dry storage in the dark, the specimens were submitted to baseline optical properties analyses. Color was measured according to the CIELAB parameters in the reflectance mode, with the SCI mode, over a zero calibrating box (CIE L*=0.0, a*=0.0, and b*=0.0), a white background (CIE L*=93.2,
a*=-0.3, and b*=1.6), and a black background (CIE L*=0.5, a*=0.7, and b*=-0.6)
using a spectrophotometer (CM-2600d, Konica Minolta, Ramsey, NJ, USA) with a circular, 6 mm diameter aperture. The SCI mode is the recommended operational mode of spectrophotometer with an integrate sphere for color measurement of resin composites. The specular component is the reflected light from the surface such that the angle of reflection equals the angle of incidence (HOSOYA et al, 2009). Illuminating and viewing configurations complied with CIE 10º observer geometry and D65 illuminant. An average of three readings in the center of the top surface for each specimen was calculated.
CIE L*, a*, and b* values were automatically calculated by the equipment. The CIE L* is the lightness, with 100 for white and 0 for black. The axes CIE a* and CIE
b* are the red-green and yellow-blue chromatic coordinates respectively. A positive
CIE a* or CIE b* value represents a red or yellow shade, and a negative CIE a* or CIE b*, represents green or blue respectively. Measurements were obtained after dry storage at 37ºC for 24 h after polymerization (baseline) and after immersion in distilled water at 37º C for 90 days. After water storage, the specimens were immersed in coffee solution for 15 days at 37ºC in order to subject the specimens to staining. The solution was made with 3.6 g of coffee powder dissolved in 300 mL of boiling distilled water. After 10 minutes of stirring, the solution was filtered through a filter paper (ERTAS et al, 2006). The CIELAB color difference (ΔE) was calculated from the average of L*a*b* values of each specimen using the formula (CIE, 2004):
ΔE = [(ΔL*)² + (Δa*)² + (Δb*)²]1/2
where ΔL*, Δa* and Δb* are the mathematical differences between L*a*b* of the different evaluated periods and baseline. The translucency parameter (TP) was calculated using the formula (JOHNSTON; MA; KIENLE, 1995):
TP = [(L*w – L*b)² + (a*w – a*b)² + (b*w – b*w)²]1/2
where the subscript “w” refers to CIELAB values for each specimen on the white background and the subscript “b” refers to values for specimen on the black background.
2.3.3 Cure efficiency analysis
Twenty-four hours after dry storage in the dark, hardness readings were taken using a microhardness tester (Micromet 5104; Buehler) under a load of 25 kgf/mm2 for 15 s. Readings were taken at five locations on both top and bottom composite surfaces. The Knoop hardness number (KHN, kgf/mm2) for each surface was calculated as the average of five readings. To check the curing efficiency, the ratio of bottom and top hardness values was calculated. The closer to one is the ratio value the more efficient is the curing process. KHN readings were taken again at top surfaces after four days of storage in absolute ethanol (Synth, Diadema, SP, Brazil).
2.3.4 Statistical analysis
Statistical analysis was conducted using SigmaSTAT® 3.5 software (Systat Software, San Jose, CA, USA). Data for CIELAB individual parameters, ΔE, TP, and top KHN as a function of ethanol storage were submitted to two-way repeated measures analysis of variance (one factor repetition), with photoinitiator/filler size combination and storage condition as factors. KHN ratio data were analyzed using one-way analysis of variance. Heteroscedastic data sets were rank-transformed before statistical analysis. All pairwise multiple comparisons procedures were performed using the Student-Newman-Keuls’ method (α=0.05).
2.4 Results
Values of CIE L* (lightness), are shown in Figure 2.1. For CIE L*, the factors ‘photoinitiator/filler size combination’ (p=0.001) and ‘storage condition’ (p<0.001) as well as the interaction between factors (p=0.04) were significant. In all storage conditions, composites formulated with 16 nm particles showed significantly higher CIE L* than those with 7 nm particles, for all photoinitiator systems. No significant differences in CIE L* were observed between photoinitiators with same filler size in any storage condition. For each photoinitiator/filler size combination, storage in water significantly increased CIE L*, whereas storage in coffee significantly reduced CIE L* for all groups but CQ+16nm and BAPO+16nm.
Figure 2.1. Results for CIE L* at baseline and after storage in water (WS) and coffee (CS). Bars are means + standard deviations (n=6). Distinct letters indicate statistical differences between storage conditions for each photoinitiator/filler size combination. Statistically similar groups in each storage condition are indicated by connected dots above bars.
Values of CIE a* (green and red coordinates), and b* (blue and yellow coordinates) are shown in Figure 2.2. For CIE a*, the factors ‘photoinitiator/filler size combination’ and ‘storage condition’ were both significant (p<0.001), whereas the interaction between factors was not significant (p=0.081). Composites formulated with BAPO showed significantly lower CIE a* than the other composites, except after storage in coffee. TPO-based materials generally had higher CIE a* than the other composites in the baseline analysis, but this difference was not observed after storage. No significant differences in CIE a* were observed between photoinitiators with same filler size in any storage condition. The filler size had no significant impact in CIE a* values. For each photoinitiator/filler size combination, storage in water and then in coffee significantly increased CIE a*.
Figure 2.2. Results of CIE a* and CIE b* at baseline and after storage in water (WS) and coffee (CS). Bars are means + standard deviations (n=6). Distinct letters indicate statistical differences between storage conditions for each photoinitiator/filler size combination. Statistically similar groups in each storage condition are indicated by connected dots above bars.
For CIE b*, both statistical factors and their interaction were significant (p<0.001). In the baseline analysis, the group TPO+16nm was significantly less yellow (lower CIE b*) than the other groups. After storage in water and then coffee, all composites formulated with 16 nm particles had significantly lower CIE b* than composites with 7 nm particles. For each photoinitiator/filler size combination,
storage in water significantly decreased the CIE b* values, which receded slightly after storage in coffee for all groups except TPO+16nm.
Results for ΔE are shown in Figure 2.3. Both statistical factors were significant (p<0.001), whereas their interaction was not significant (p=0.634). After water storage, TPO-based composites presented significantly lower ΔE, and there was no significant difference between CQ and BAPO. After the additional 15 days of coffee storage, ΔE values of all groups were significantly reduced, but the results for TPO-based materials were still significantly lower than the other photoinitiators. After storage in coffee, CQ- and BAPO-based composites with 7 nm particles had significantly lower ΔE values than composites with 16 nm particles
Figure 2.3. Results for ΔE after storage in water (WS) and coffee (CS) compared with baseline. Bars are means + standard deviations (n=6). Distinct letters indicate statistical differences between storage conditions for each photoinitiator/filler size combination. Statistically similar groups in each storage condition are indicated by connected dots above bars.
TP results are presented in Figure 2.4. CQ+7 nm presented the highest values, irrespective of the storage condition, while the other groups had no significant differences. Water storage significantly decreased TP values of composites with 16 nm-sized particles, while storage in coffee significantly decreased TP of TPO+7 nm, TPO+16 nm and BAPO+7 nm groups.
Figure 2.4. Results for translucency parameter after storage in water (WS) and coffee (CS). Bars are means + standard deviations (n=6). Distinct letters indicate statistical differences between storage conditions for each photoinitiator/filler size combination. Statistically similar groups in each storage condition are indicated by connected dots above bars.
Results of the cure efficiency analysis are shown in Table 2.1. For CQ, composites with 16 nm particles showed significantly higher top and bottom hardness than composites with 7 nm particles, while the other photoinitiators had no significant differences. The bottom/top KHN ratios were similar among groups. After ethanol storage all composites showed significantly lower top hardness, with CQ+7 nm composite still showing the lowest hardness results among photoinitiator/filler size groups.
Table 2.1 - Results of the cure efficiency analysis (n=6). Values are Knoop hardness number (KHN, kgf/mm2) means ± standard deviations
Photoinitiator /
filler size Top hardness
Bottom hardness Bottom/Top ratio Top KHN as a function of ethanol storage Before After CQ + 7 nm 28.5 ± 0.8 A,d 21.5 ± 3.2 B,c 0.75 ± 0.10 a 28.5 ± 0.8 A,d 14.9 ± 1.3 B,c CQ + 16 nm 33.7 ± 0.7 A,bc 24.0 ± 0.1 B,b 0.71 ± 0.03 a 33.7 ± 0.7 A,bc 18.5 ± 1.2 B,b TPO + 7 nm 30.7 ± 3.4 A,cd 24.6 ± 3.4 B,b 0.80 ± 0.03 a 30.7 ± 3.4 A,cd 18.0 ± 0.6 B,b TPO + 16 nm 33.4 ± 1.2 A,c 23.1 ± 2.6 B,b 0.69 ± 0.06 a 33.4 ± 1.2 A,c 19.3 ± 1.7 B,b BAPO + 7 nm 36.5 ± 1.4 A,ab 28.0 ± 3.2 B,a 0.77 ± 0.12 a 36.5 ± 1.4 A,ab 21.9 ± 1.7 B,b BAPO + 16 nm 40.8 ± 1.1 A,a 32.3 ± 1.9 B,a 0.79 ± 0.06 a 40.8 ± 1.1 A,a 28.2 ± 2.0 B,a In the first two columns, distinct capital letters in each row indicate significant differences between top and bottom
hardness, while distinct lowercase letters in each column indicate significant differences between photoinitiator/filler size groups. No significant differences in bottom/top ratios were observed. In the last two columns, distinct capital letters in each row indicate significant differences before and after ethanol storage, while distinct lowercase letters in each column indicate significant differences between photoinitiator/filler size groups (α=0.05).
2.5 Discussion
The first hypothesis of this study was rejected because composites formulated with BAPO and CQ had similar degree of yellowing. After 90 days of water storage, the specimens of all groups showed a decrease in the CIE b* and increase in CIE a* axes. This could be related to leaching of unreacted monomers and photoinitiators by water dissolution (ALBUQUERQUE et al, 2013). The increased CIE b* values in all groups after storage in coffee might be associated with the surface staining caused by coffee molecules (ERTAS et al, 2006). The color change resulting from contact with the coffee solution originates, in most cases, from extrinsic staining, but internal material discoloration may also occur. Pigmentation caused by coffee might occur by surface absorption of dark pigments and absorption of pigments at the subsurface layer (DIETSCHI et al, 1994).
At baseline color evaluation, BAPO showed the highest yellowing effect. Similar results were also found by Arikawa et al. (ARIKAWA et al, 2009), who observed that BAPO presented degree of yellowing close to CQ. Although the λmax for BAPO lies near 370 nm, its absorption activity extends toward the visible region of the electromagnetic spectrum, above 400 nm. This factor makes the perception and absorption in the yellow region more evident, affecting both the color stability of
composites and their final aesthetics (NEUMANN et al, 2005). By comparison, TPO presented the lowest degree of yellowing irrespective of the evaluation period, particularly when 16 nm-sized particles were used. This finding are associated with the low color saturation and high reactivity of TPO (SCHNEIDER et al, 2012; ALBUQUERQUE et al, 2013).
Regarding filler size and its influence on optical properties of the composites, it was observed that composites with 16 nm particles generally had higher lightness and were less yellow than composites with 7 nm particles. Thus, the second hypothesis is accepted. A recent study has shown that nanofilled composites usually have similar surface roughness and gloss than submicron and microhybrid composites even after surface challenges (KAIZER et al, 2014). It is interesting to note, however, that composites with 16 nm-sized particles generally had lower poorer results for color stability. The color stability of dental composites is influenced by extrinsic factors, such as the absorption of coloring solutions (e.g., coffee), or even by adsorption of plaque, or by intrinsic factors leading to chemical changes occurring in the resin matrix and, therefore, in all volume of the restoration. The involvement of deeper composite layers makes the removal of staining by polishing difficult, if not impossible. Intrinsic discoloration is caused mainly by the photoinitiator system (SCHNEIDER et al, 2008). Changes in CIE L*, a*, and b* parameters during storage may also be explained by hydrolysis reactions. Color stability is related to water sorption and solubility, which cause polymer matrices to swell and reduce the frictional forces between polymer chains (FERRACANE; BERGE; CONDON, 1998). Since water has a much different refractive index than the polymer network and filler particles, light transmission is impaired by refraction at the polymer-filler-water interfaces. Ultimately, that leads to increased light scattering and changes in the perception of color (IKEDA et al, 2005).
ΔE values lower than 1.0 are regarded as not appreciable by the human eye as well as ΔE values between 1.0 and 3.3 are considered appreciable by skilled operators, but still in a clinically acceptable range. ΔE values greater than 3.3 are perceivable even by untrained observers, and for that reason are regarded as not clinically acceptable (VICHI et al, 2011). The ΔE values in this study ranged between 3.5 and 10.1, indicating that all experimental groups presented unacceptable color changes during storage. A potential explanation for this result is that the inorganic loading of the model composites tested here are much lower than commercial
composites. In that scenario, the color changes occurring due to leaching and/or degradation of the resin matrix and photoinitiator components are more evident.
Translucency and opacity are fundamental factors in achieving esthetic restorations with composites, since they are indicators of the quality and quantity of reflected light (KIM; ONG; OKUNO, 2002). The main component of a dental composite that significantly affects its translucency is the inorganic content (AZZOPARDI et al, 2009). It is known that the quantity, size, and shape of particles all affect the light scattering in dental composites (LEE, 2008). When particle size is below the wavelength of visible light, it will not scatter that particular wavelength. If particle size is far below the wavelength of light, it will not scatter or absorb the light, resulting in inability of the human eye to visualize the particles (KIM et al, 2007). Both particle sizes used here are far below the wavelength of light, so that was unlikely a factor affecting the results. It should not be disregarded, however, that filler agglomeration could also interfere with the optical properties. Another factor effecting translucency is the mismatch in refractive indices between filler and matrix. The filler increases light scattering at the resin-filler interfaces, tending to produce opaque materials. The opacity of the composite is raised as the refractive index difference between filler and resin matrix increases (KIM et al, 2007). As the degree of C=C conversion increases, the mismatch between refractive indices decreases, which means that composites that achieved lower conversion are likely to have more light scattering (HOWARD et al, 2010).
It has been reported that the TP is altered after immersion in water at 37°C for 24 h due to the increased surface energy and interposition of two media with distinct refractive indices (LEE et al, 2005). Composites may absorb water at the matrix-particle interface and undergo hydrolytic degradation, altering the pattern of light diffusion (LEE et al, 2005). Results of TP in this study showed that the group CQ+7 nm presented the highest TP, and that some groups had reduced TP after storage. These results could be related to different polymerization extents and difference in refractive index when monomers are converted into polymer. The lower the degree of C=C conversion the higher the difference between the refractive indices between filler particles and resin matrix (AZZOPARDI et al, 2009).
Hardness was significantly higher at the top than bottom composite surfaces in all groups. Light excites the top composite surface easily, with minimum attenuation, consequently more efficiently reaching and exciting the photoinitiator
molecules (RUEGGEBERG, 1999). Softer bottom surfaces are a result of reduced irradiance as light travels through the material, i.e. the quantity of photons that reaches the bottom surface is not the same that reaches the top surface (TSAI; MEYERS; WALSH, 2004). Usually, larger particles generate composites with higher hardness due to the higher resistance of surface to indention (MORAES et al, 2009). However, in this study, larger particles led to higher hardness only for materials with CQ-amine, probably due to lower polymerization efficiency of this binary system. BAPO-based composites were generally harder at top and bottom surfaces than CQ and TPO-based materials. BAPO is more efficient in initiating the polymerization reaction, with formation of four potentially active radicals for each molecule. As a result, more active centers for radical formation and chain extension are formed, also favoring crosslinking, which makes the polymer less susceptible to softening.
In this study, hardness values of TPO-based composites were similar to CQ-based materials. Using the differential scanning calorimetry, Schneider et al. (SCHNEIDER et al, 2012) evaluated the kinetics of polymerization of model resin composites containing different photoinitiator systems. The authors observed that TPO was capable of promoting higher C=C conversion than CQ using a halogen curing unit. However, a recent studie diverges as regards the feasibility of polymerization of materials formulated with TPO, since its absorption in wavelengths lower than CQ may cause lower values of conversion in deeper composite portions (LEPRINCE et al, 2011). A possible reduction in depth of cure, however, is irrelevant when composite increments no thicker than 3 mm are used (SCHNEIDER et al, 2012).
After evaluating the hardness of dry surfaces, all groups were stored for 4 days in absolute ethanol for subsequent measurement. The results were that all groups showed a decrease in KHN values, as expected. Due to the large amount of [-OH] terminations present in ethanol, higher absorption occurs by the polar portion of the matrix, causing swelling. This dimensional change in the matrix causes stress at the matrix-silane-filler particle interfaces, resulting in degradation of the bonds. As a consequence, inorganic particles may detach from the surface, causing an increase in surface roughness and contributing to make the surfaces softer (MORAES et al, 2009). The results of top hardness after ethanol storage were basically the same as before storage as regards the influence of photoinitiator system and filler particle size.
2.6 Conclusions
Combination of photoinitiator system and filler particle size might affect the optical properties of dental resin composites, with minor influence on cure efficiency. Composites formulated with 16 nm-sized particles had higher lightness and were generally less yellow than composites with 7 nm-sized particles. The color stability of TPO-based materials was higher compared with the other photoinitiator systems.
2.7 References
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3 Capítulo 22
Does translucency influence the color stability and the cure efficiency of resin-based composites?
3.1 Abstract
Objective: To determine if the material's translucency influences the cure efficiency and color stability of resin-based composites.
Methods: Four distinct commercial resin-based composites indicated for aesthetic restorations were selected for this study in their available translucency degrees on A3 shade (IPS Empress Direct - IED: A3 Dentin, A3 Enamel, Trans 20, and Trans 30 / Filtek Z350 XT - FZX: A3D, A3B, A3E, and T-Clear / Estelite ∑ Quick - EQ: OA3, A3, and CE / Opallis - OP: DA3, EA3, and T-Neutral). For color measurement, disk-shaped specimens (8 mm X 2 mm) were made by photoactivation with a large spectrum L.E.D. source for 30 s and 1.200 mW/cm² irradiance. Color data (n=6) was obtained by CIEDE2000 individual parameters (L*, a*, b*, C* and h-) in three different periods: 24 h after photoactivation (baseline), after water storage for 30 days at 37 ºC, and after coffee solution storage for 30 days at 37 ºC. The translucency parameter (TP), lightness (L’), chroma (C’), hue (h’), and the CIEDE2000 color difference (∆E00) were calculated. The cure efficiency (n=6) was obtained directly by the degree of C=C conversion (DC), determined by Fourier-transformed infrared spectroscopy in two thicknesses: 0.05 mm and 2 mm, corresponding to top and bottom surfaces. Then, the bottom/top ratio was calculated. Data was submitted to two-way ANOVA and Tukey’s post hoc test at α=0.05 significance level. Pearson’s correlation tests were used to analyze the correlation between TP and DC, and between TP and ∆E00.
Results: With the exception of IED A3 Enamel and Trans 20, the TP was statistically different among the different shades for all the other materials. It was observed that the higher the TP, the higher the DC for FZX and EQ, but the lower the DC for IED
2
and OP. However, no differences were observed among the cure efficiency results. For all RBCs, the higher the TP, the higher the ∆E00 (higher after CS than after WS, except for EQ A3).
Significance: The translucency did not influence the cure efficiency but affected the color stability for all materials. High-translucent materials presented lower color stability. The degree of C=C conversion was material dependent.
Keywords: staining, photoinitiator, hydrolysis.
3.2 Introduction
The major cause for replacement of resin-based composite restorations in the anterior teeth is aesthetic reasons (BALDISSERA et al, 2013). The mismatch between the tooth structure and material may occur due to technical failure or the material’s discoloration during its clinical lifetime. In the direct restorative technique, to reproduce properly all tooth characteristics, it is important to distinguish the different features of teeth three thirds and translucency is one of the most important optical properties to take in consideration when evaluating esthetics. Therefore, in a single restoration, one might need to use several translucency/opacity shades of a restorative material to achieve the match between the material and dental tissues.
The translucency of resin-based composites results from the relationship between the refractive indices of the filler-particles and resin matrix and the greater the difference, the lower the translucency (KIM et al, 2007). It is known that the inorganic filler-particles content and type (ARIKAWA et al, 2007; LEE, 2008; SALGADO et al, 2013; DE OLIVEIRA et al, 2016), organic matrix type and fraction (LEE, 2008; AZZOPARDI et al, 2009), as well as the photoinitiator system (ARIKAWA et al, 2009; SALGADO et al, 2014), may all affect the material’s translucency.
Another component that might dictates the materials' aesthetics over the time is the photoinitiator system used in the formulation. The association of camphorquinone (CQ) with a tertiary amine remains the most common photoinitiator system in commercial resin-based composites. CQ has an intense yellow, which gives the material a high potential of discoloration (SALGADO et al, 2014; SALGADO et al, 2015). To overcome the aesthetic problems of this system, alternative photosensitizer molecules were tested, such as phosphine oxide derivatives. The
diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide, also known as TPO, is already component of some commercial resin-based composites (PALIN et al, 2008; ARIKAWA et al, 2009; SANTINI et al, 2012) and has demonstrated higher color stability (ARIKAWA et al, 2009; SALGADO et al, 2014) and higher curing efficiency than CQ (NEUMANN et al, 2005; SALGADO et al, 2014), albeit having decreased depth of cure (SCHNEIDER et al, 2012). Recently a new attempt to reduce the CQ content, based on a radical amplified photopolymerization (R.A.P. technologyTM) was proposed. Results available for materials formulated with this technology indicate increased degree of C=C conversion, with no reported data regarding color stability (ILIE; KREPPEL; DURNER, 2014).
In a previous study involving model composites, improved color stability was observed when alternative photoinitiators were associated with the CQ/amine system, particularly TPO (SALGADO et al, 2015). In commercial resin-based composites, manufacturers usually do not disclose or specify the type and/or amount of components presented, including the photoinitiator system. To achieve different translucent shades, the manufactures may decrease the amount of CQ/amine and/or use alternative photosensitizer molecules (PALIN et al, 2008), or even change the inorganic content amount (LEE, 2008). However, there is a lack of information regarding the specific components of different translucent shades for the same resin-based composite brand and no available data about their optical properties, including their color stability. Besides, there is no information regarding the cure efficiency of these materials.
To supply such data, the objective of this study was to determine the cure efficiency and the color stability of four distinct commercial restorative resin-based composite systems, with different compositions including organic matrix, inorganic content, and photoinitiator system, in their different translucent shades. The research hypotheses were that for all resin-based composites, the material’s translucency would affect (1) the cure efficiency and (2) the color stability.
3.3 Materials and methods
3.3.1 Study design and materials tested
This in vitro study (14 groups) involved four resin-based composites (Filtek Z350 XT, IPS Empress Direct, Estelite ∑ Quick, and Opallis). The sample size calculation was based in previous studies (SALGADO et al, 2014; SALGADO et al,
2015). For the color measurements (n=6) two factors were evaluated: translucency (four/three levels) and ageing condition (baseline, after water storage, and after coffee solution storage). The cure efficiency (n=5) was determined by the bottom/top ratio of the degree of C=C conversion data, performed at two different material’s thickness: 0.05 mm (top) and 2 mm (bottom).
Four distinct commercially-available resin-based composites indicated for aesthetic restorations were selected for this study (Table 3.1) in its different available translucency levels: the microhybrid (stated as “nanohybrid” by manufacturer) IPS Empress Direct (Ivoclar-Vivadent, Schann, Liechtenstein), the nanofilled Filtek Z350 XT (3M-ESPE, St Paul, MN, USA), the submicron filled Estelite ∑ Quick (Tokuyama Dental, Tokyo, Japan), and the microhybrid Opallis (FGM Produtos Odontológicos, Joinville, SC, Brazil).
Table 3.1 - Commercially available resin-based composites systems selected for this study
Translucent
shade Lot
Filler size range (mean) Inorganic content fraction Photoinitiator system IPS Empress Direct (Ivoclar Vivadent) A3 Dentin S50879 40 nm-3.0 µm (57 nm -1.8 µm)* 75-79 wt% / 52-59 vol%* CQ/amine + Lucirin TPO** A3 Enamel T34990 Trans 20 S35613 Trans 30 S23109 Filtek Z350 XT (3M ESPE) A3D 147906 0.6-1.4 µm (20 nm) † 78.5 wt% / 59.5 vol% † 72.5 wt% / 55.5 vol% Y (translucent shades) CQ/amine** A3B 280018 A3E 247867 CT N636853 Estelite ∑ Quick (Tokuyama) OA3 W925 0.1-0.3 µm (0.2 µm)* 82 wt% / 71 vol% † CQ/amine - R.A.P. † A3 E838 CE W4781 Opallis (FGM) DA3 151214 40 nm-3.0 µm (0.5 µm) † † 79.8 wt% / 57 vol% † † CQ/amine § EA3 291014 T-Neutral 271014
* KIM; PARK, 2013; ** PRICE et al, 2014; † SABATINI, 2015; Y 3M ESPE Ind.; †† RODRIGUES-JUNIOR et al, 2015; § COUTINHO et al, 2013.
The materials’ classification was according to their inorganic content (FERRACANE, 2011). For this study, it was selected translucency variations within A3 shade due A3 shade Vita classical represents the most common human teeth color (ELAMIN et al, 2015), besides the more translucent variety in this shade.
3.3.2 Optical data and translucency parameter
Six disc-shaped specimens were made for each group using a cylindrical metal mold of 8-mm inner diameter and 2-mm thickness. After the composite insertion, the top surface was covered with a Mylar strip and made flat by pressing down with a glass slab. The specimens were light-activated for 40 s from the top surface using a LED curing unit (Bluephase, Ivoclar-Vivadent) operated in high mode with irradiance of 1200 mW/cm², as measured with a hand-held radiometer (LED radiometer, Demetron – Kerr, Middleton, WI, USA). Then, all specimens were mechanically polished on both surfaces in a grinding/polishing machine (Buehler, Lake Bluff, IL, USA) with 2000- and then 4000-grit SiC papers under continuous water cooling (SALGADO et al, 2014). After this, the thickness of each specimen was checked with a digital caliper with resolution of 0.01 (Digimatic Caliper 0.01-150 mm, Mitutoyo, Tokyo, Japan).
Optical data (n=6) was obtained according to the CIEDE2000 individual parameters (L*, a*, b*, C*, and h-) in the SCI mode (HOSOYA et al, 2009), over a zero calibrating box (L* = 0.0, a* = 0.0, b* = 0.0, C* = 0.0, and h- = 0.0), using a spectrophotometer (CM-2600d, Konica Minolta Inc., Tokyo, Japan). The measuring aperture used was 6 mm in diameter. Illuminating and viewing configurations complied with CIE 10º observer geometry and D65 illuminant (CIE, 2004).
The translucency of each material was measured at baseline by the CIE translucency parameter (TP) formula (JOHNSTON; MA; KIENLE, 1995):
TP = [(L*w – L*b)² + (a*w – a*b)² + (b*w – b*b)²]1/2
where “w” refers to the color values for each specimen measured over the white background and “b” over the black background. The analyses were carried out with the specimens placed over a black background (Ceramic Colour Standard, Ceram Research Ltd., StrokeonTrent, Staffordshire, United Kingdom) / L* = 38.2, a* = -0.6, and b* = -2.5, C* = 2.6 , and h- = 257.7 ) and a white background (Ceramic Colour Standard, Ceram Research Ltd. / L* = 123.2, a* = -1.2, and b* = 0.8, C* = 1.4,
