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Influência da biodegradação por biofilme cariogênico de S. mutans nas propriedades fisicos mecânicas de compósitos Bulk Fill : Biodegradation influence by S. mutans cariogenic biofilm in thephysico mechanical properties of Bulk Fill composites

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Faculdade de Odontologia de Piracicaba

Jessica Rodrigues Camassari

Influência da biodegradação por biofilme cariogênico de S.

mutans nas propriedades fisicos mecânicas de compósitos

Bulk Fill

Biodegradation influence by S. mutans cariogenic biofilm in

the physico mechanical properties of Bulk Fill composites

Piracicaba 2018

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Jessica Rodrigues Camassari

Influência da biodegradação por biofilme cariogênico de S.

mutans nas propriedades fisicos mecânicas de compósitos

Bulk Fill

Biodegradation influence by S. mutans cariogenic biofilm in

the physico mechanical properties of Bulk Fill composites

Dissertação apresentada a Faculdade de

Odontologia de Piracicaba da Universidade

Estadual de Campinas como parte dos requisitos

exigidos para a obtenção do título de Mestra em Materiais Dentários

Dissertation presented to the Piracicaba Dental School of the University of Campinas in partial fulfillment of the requirements for the degree of Master in Dental Materials.

Orientadora: Profa. Dra. Andreia Bolzan de Paula

Coorientadora: Profa. Dra. Regina Maria Puppin Rontani

ESTE EXEMPLAR CORRESPONDE À VERSÃO FINAL DA DISSERTAÇÃO DEFENDIDA PELA ALUNA JESSICA

RODRIGUES CAMASSARI E ORIENTADA PELA PROFA. DRA. ANDREIA BOLZAN DE PAULA.

Piracicaba 2018

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Ficha catalográfica

Universidade Estadual de Campinas

Biblioteca da Faculdade de Odontologia de Piracicaba Marilene Girello - CRB 8/6159

Camassari, Jessica Rodrigues,

C14i CamInfluência da biodegradação por biofilme cariogênico de S. mutans nas propriedades fisicos mecânicas de compósitos Bulk Fill / Jessica Rodrigues Camassari. – Piracicaba, SP : [s.n.], 2018.

CamOrientador: Andreia Bolzan de Paula.

CamCoorientador: Regina Maria Puppin Rontani.

CamDissertação (mestrado) – Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba.

Cam1. Biodegradação. 2. Resinas compostas. 3. Streptococcus mutans. I. Paula, Andreia Bolzan de. II. Puppin-Rontani, Regina Maria, 1959-. III.

Universidade Estadual de Campinas. Faculdade de Odontologia de Piracicaba. IV. Título.

Informações para Biblioteca Digital

Título em outro idioma: Biodegradation influence by S. mutans cariogenic biofilm in the physico mechanical properties of Bulk Fill composites

Palavras-chave em inglês: Biodegradation

Composite resins

Streptococcus mutans

Área de concentração: Materiais Dentários Titulação: Mestra em Materiais Dentários Banca examinadora:

Andreia Bolzan de Paula [Orientador] Giovana Spagnolo Albamonte de Araújo Mário Alexandre Coelho Sinhoreti Data de defesa: 07-06-2018

Programa de Pós-Graduação: Materiais Dentários

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UNIVERSIDADE ESTADUAL DE CAMPINAS

Faculdade de Odontologia de Piracicaba

A Comissão Julgadora dos trabalhos de Defesa de Dissertação de Mestrado, em sessão pública realizada em 07 de Junho de 2018, considerou a candidata JESSICA RODRIGUES CAMASSARI aprovada.

PROFª. DRª. ANDREIA BOLZAN DE PAULA

PROFª. DRª. GIOVANA SPAGNOLO ALBAMONTE DE ARAÚJO

PROF. DR. MÁRIO ALEXANDRE COELHO SINHORETI

A Ata da defesa com as respectivas assinaturas dos membros encontra-se no processo de vida acadêmica do aluno.

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A Deus

Ele que sempre me amparou nos momentos mais difíceis da minha vida e me permitiu concluir mais essa etapa.

À minha mãe Ana Kátia

Que diante de todas as dificuldades sempre esteve ao meu lado, oferecendo todo o seu amor e carinho de mãe, fundamental nessa jornada.

Ao meu pai Luiz Sérgio (In Memorian)

Toda a minha gratidão por ser meu pai. Me deu a vida, meus estudos e tantos outros momentos inesquecíveis que levo no coração.

Aos meus avós Geraldo e Ivete

Por todo o apoio que sempre dedicaram a mim, mesmo não sabendo o que eu faço, estiveram presentes me apoiando e sendo os melhores avós que alguém poderia ter em vida

Aos padrinhos e tios José e Cristina

Por valorizarem o meu esforço e incentivarem a continuar estudando além do suporte emocional e financeiro que recebi durante todo esse ano.

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Agradecimento Especial

Às professoras,

Andreia Bolzan de Paula, por acreditar em mim e no meu trabalho, pela confiança e sobretudo por me incentivar a continuar lutando pelos meus objetivos.

Regina Maria Puppin Rontani, por tudo que proporcionou à minha vida acadêmica e pelos ensinamentos que levo como inspiração pessoal.

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Agradecimentos

À Faculdade de Odontologia de Piracicaba, em nome do diretor Professor Doutor Guilherme Elias Pessanha Henriques e diretor associado Professor Doutor Haiter Neto.

Ao Prof. Dr. Simonides Consani, Titular da Área de Materiais Dentários da Faculdade de Odontologia de Piracicaba da Universidade Estadual de Campinas por ter me dado a honra de tê-lo como banca avaliadora na qualificação desse trabalho, bem como todas as sugestões construtivas deferidas brilhantemente ao mesmo.

Ao Prof. Dr. Mário Alexandre Coelho Sinhoreti, Titular da Área de Materiais Dentários da Faculdade de Odontologia de Piracicaba da Universidade Estadual de Campinas, pelos ensinamentos durante as aulas e toda a paciência para com os alunos.

Ao Prof. Dr. Mário Fernando de Goés, Titular da Área de Materiais Dentários da Faculdade de Odontologia de Piracicaba da Universidade Estadual de Campinas, por todos os ensinamentos científicos durante o curso e sobretudo por sempre me tratar com gentileza.

Ao Prof. Dr. Marcelo Giannini, Titular da Área de Dentística da Faculdade de Odontologia de Piracicaba da Universidade Estadual de Campinas, pela oportunidade de participar de um grande congresso junto a grandes nomes da Odontologia e por sempre nos incentivar a dar o nosso melhor e sobretudo por ser um exemplo de profissional a ser seguido.

Ao Prof. Dr Américo Bortolazzo Correr, Titular da Área de Materiais Dentários da Faculdade de Odontologia de Piracicaba da Universidade Estadual de Campinas, por toda a orientação em todas as vezes que lhe foi solicitada e pela contribuição dada durante a qualificação com sugestões extremamente construtivas.

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Ao Prof. Dr. Lourenço Correr Sobrinho, Titular da Área de Materiais Dentários da Faculdade de Odontologia de Piracicaba da Universidade Estadual de Campinas por todo conhecimento transmitido durante as aulas.

À Prof. Dra. Ana Rosa Rosa Costa Correr por todo o conhecimento transmitido durantes as aulas.

Ao Prof. Dr. Roberto Bragga pelas sugestões construtivas e reconhecimento do projeto.

À Prof. Dra. Janaína de Cássia Orlandi Sardi por todas as sugestões dadas a este trabalho durante a qualificação, sobretudo na parte microbiológica, a qual foi minuciosamente detalhada e imprescíndivel.

À Agência de fomento FAPESP e CAPES, processo n° 2016/18720-8, Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP).

A todos os amigos da pós graduação mas em especial à Aline, Lincoln, Eduardo, Paulo, Gabriel Abuna, Cristian, Júlia, Marina, Jamille , Maurício e Renally que sempre estiveram dispostos a me ajudar nos momentos de alguma dificuldade.

Audrey Foster por ser uma amiga fiel e que mesmo longe está sempre torcendo pelo meu crescimento como profissional.

As amigas que o GBMD me proporcionou: Kamila Rosamilia Kantovitz e Potira Meirelles, muito obrigada pela amizade e bons momentos compartilhados.

Aos funcionários da área de materiais dentários Selma Segalla e Marcos Blanco Cangiani e ao funcionário da Odontopediatria Marcelo por sempre estarem dispostos a ajudar e orientar em atividades de laboratório.

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custo.

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Onde estiver o seu tesouro, lá também estará seu coração.

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O objetivo neste estudo foi avaliar a influência do biofilme por Streptococcus mutans na rugosidade (Ra), brilho (GU), dureza de superfície (KHN) e resistência à flexão (RF) de compósitos Bulk Fill de alta viscosidade. Os compósitos utilizados foram: Filtek Bulk Fill (FBF), Tetric N Ceram (TNC), X-tra fil (XF) e Filtek Z350 (FZ-controle). Foram confeccionados 10 discos de cada compósito com dimensões de 5 mm de diâmetro x 2 mm de espessura para os ensaios de Ra e KHN, e 10 discos com dimensões de 10 mm de diâmetro x 2 mm de espessura para o ensaio de GU. Para RF, 20 amostras de cada compósito (10 para análise inicial e 10 para análise final) foram confeccionadas com dimensões de 25 mm de comprimento x 2 mm de largura x 2 mm de espessura. Após 24 horas de armazenagem em estufa a 37ºC, todas as amostras foram polidas e submetidas às análises iniciais de Ra, GU, KHN, e RF. Todas amostras foram esterilizadas com óxido de etileno e submetidas à degradação por S. mutans durante 7 dias e a Ra, GU, KHN e RF reavaliados. Três amostras representativas de cada grupo foram avaliadas em Microscópio Eletrônico de Varredura (MEV). Após o teste de normalidade, os dados de Ra, GU e KHN foram submetidos à ANOVA dois fatores para medidas repetidas e os dados de RF à ANOVA dois fatores e teste de Tukey (α=0,05). Para Ra houve interação significativa entre os fatores. Antes da biodegradação, o XF (0,1251) apresentou maiores valores de Ra quando comparado aos demais materiais, os quais mostraram valores similares. Após a biodegradação, XF (0,3100) apresentou maiores valores de Ra e FZ (0,1443) os menores, enquanto TNC e FBF foram similares. O biofilme aumentou a Ra de todos os materiais. Não houve interação entre os fatores para GU. Maiores valores de GU foram observados para FZ (inicial 71,7 e final 62,0) e FBF (inicial 69,0 e final 64,6) e os menores para TNC (inicial 61,4 e final 53,3) e XF (inicial 58,5 e final 53,5), tanto antes quanto após a biodegradação. A degradação diminuiu o GU para todos os materiais.

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Houve interação significativa entre os fatores material x biodegradação nos valores de KHN. Maiores valores foram obtidos pelo XF (inicial 151,7 e final 106,0) e os menores para TNC (62,2 e 51,8, respectivamente), tanto antes quanto após a biodegradação, enquanto FBF e FZ foram similares. A biodegradação reduziu a KHN em todos os materiais. Houve interação entre os fatores nos valores de RF. Maiores valores iniciais de RF foram observados para FZ quando comparado ao TNC. Após a biodegradação, XF apresentou maiores valores quando comparados aos TNC e FBF. A biodegradação reduziu os valores de RF apenas para o FZ. Concluiu-se que a degradação por biofilme de S. mutans afetou negativamente as propriedades de superfície dos compósitos Bulk Fill, no entanto, não foi capaz de alterar a resistência à flexão desses materiais, diferentemente do compósito controle.

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The aim of this study was to evaluate the influence of biofilm by Streptococcus mutans on the roughness (Ra), gloss (GU), surface hardness (KHN) and flexural strength (FS) of high viscosity bulk fill composites. Methods: Filtek Bulk Fill (FBF), Tetric N Ceram (TNC), X-tra fil (XF) and Filtek Z350 (FZ- control) were used in this study. Ten discs of each composite were prepared with 5 mm diameter x 2 mm thickness for the Ra and KHN tests, and 10 discs with dimensions of 10 mm in diameter x 2 mm in thickness for the GU assay. For RF, 20 samples of each composite (10 for initial analysis and 10 for final analysis) were made with dimensions 25 mm long x 2 mm wide x 2 mm thick. After 24 hours of incubation at 37ºC, all samples were polished and submitted to the initial assays of Ra, GU, KNH and RF. All the samples were sterilized with ethylene oxide and subjected to degradation by S.mutans for 7 days and Ra, GU, KHN and RF reassessed. Three representative samples of each group were evaluated in Scanning Electron Microscope (SEM). After normality testing, data from Ra, GU and KHN were subjected to two-way ANOVA for repeated measures and the data from RF to ANOVA two factors and Tukey's test (p <0.05). For Ra there was a significant interaction between factors. Before the biodegradation, the XF (0.1251) presented higher values of Ra when compared to the other materials, which showed similar values. After biodegradation, XF (0.3100) presented higher values of Ra and FZ (0.1443) the smaller, while TNC and FBF were similar. Biofilm increased of Ra in all materials. There was no interaction between the factors for GU. Higher GU values were observed for FZ (71.7 initial and 62.0 final) and FBF (69.0 initial and 64.6 final) and the lowest for TNC (61.4 initial 53.3, final) and XF (58.5 initial and 53.5 final), both before and after biodegradation. Degradation promoted a decrease in GU for all materials. There was significant interaction between the material x biodegradation factors in KHN values. Higher values were obtained by XF (151.7 and

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106.0, respectively) and the lower values for TNC (62.2 and 51.8, respectively), both before and after biodegradation, while FBF and FZ were similar. Biodegradation reduced KHN in all materials. There was interaction between the factors in the RF values. Higher initial RF values were observed for FZ when compared to TNC. After biodegradation, XF presented higher values when compared to TNC and FBF. Biodegradation promoted reduction in RF values only for FZ. It was concluded that biodegradation negatively affected the surface properties of Bulk Fill composites; however, did not affect the flexural strength of these materials, unlike control composite.

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1 INTRODUÇÃO ... 16

2 ARTIGO: Physical properties of Bulk Fill composites submitted to the cariogenic challenge ... 21

3 CONCLUSÃO ... 46

REFERÊNCIAS ... 47

APÊNDICE 1 - Confecção das amostras ... 54

APÊNDICE 2 - Polimento e análises iniciais. ... 55

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INTRODUÇÃO

Considerando a grande demanda pela estética, compósitos resinosos têm substituído o amálgama de prata como material para restaurar dentes posteriores. Além de serem ativados pela luz, esteticamente da cor do dente e reparáveis, os preparos cavitários para restaurações de compósito também são mais conservadores quando comparados aos para restaurações de amálgama. No entanto, restaurações em dentes posteriores realizadas com compósito constituem um desafio técnico e de execução demorada, pois são necessários preenchimento incremental e fotoativação graduais devido à contração de polimerização e limitada profundidade de polimerização do material (Versluis et al., 1996; Roulet et al., 1997).

A técnica restauradora com compósitos envolve a inserção de incrementos de até 2 mm, adaptação e fotoativação dos materiais sendo uma desvantagem devido ao tempo de execução prolongado (Yap et al., 2016). Mesmo com a evolução dos compósitos, a técnica restauradora foi pouco modificada. A inserção em pequenos incrementos tem sido ainda largamente preconizada com a intenção de minimizar as tensões de contração como mostrado na literatura (Ferracane, 2008), promover maior grau de conversão e obter adequada adaptação marginal (Roggendorfet al., 2011). Na tentativa de facilitar o procedimento clínico, diminuir o tempo restaurador e reduzir as tensões de contração, uma nova geração de compósitos resinosos, denominados de Bulk Fill, foi desenvolvida e, segundo os fabricantes, podem ser inseridos na cavidade em incrementos de 4 mm de espessura, reduzindo o tempo clínico, minimizando incorporação de ar e melhorando a qualidade da restauração. (Roggendorf et al., 2011; Moorthy et al.,2012; El-Damanhoury et al., 2014). Os fabricantes também alegam que esses materiais causam menor flexão das cúspides e permitem melhor transmissão da luz. Essa última vantagem tornou-se viável devido ao aumento da translucidez pelos compósitos Bulk Fill.(Finan et al.,2013).

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Essa categoria de compósitos resinosos pode ser de baixa viscosidade (flow) ou alta viscosidade. Afim de se obter bom sucesso clínico, várias condições devem ser cumpridas como: incrementos espessos devem ser polimerizados adequadamente, enquanto que a contração e a tensão de polimerização devem ser mantidas baixas para não romper a união deste material restaurador (Tarle et al.,2015).

Grande parte das pesquisas tem focado nos compósitos Bulk Fill de baixa viscosidade que revelaram dados muito promissores em relação à baixa contração e tensão de polimerização quando comparados aos compósitos resinosos convencionais (Tauböck et al., 2014). No entanto, compósitos Bulk Fill de baixa viscosidade possuem baixa dureza e baixo módulo de elasticidade (Ilie et al.,2011; Van Ende et al., 2017) e por consequência necessitam de uma camada de cobertura feita com um compósito convencional na espessura de até 4 mm. Ao contrário, os compósitos Bulk Fill de alta viscosidade são indicados para uso sem a necessidade de recobrimento (Van Ende et al; 2017), e podem ser assim aplicados como material de restaurador de passo único.

Geralmente os compósitos Bulk Fill de alta viscosidade possuem maior quantidade de partículas em porcentagem e algumas vezes um sistema iniciador modificado para garantir melhor polimerização em profundidade quando comparados às compósitos convencionais (Abouellei et al., 2015), além de apresentarem componentes que permitem a modulação na polimerização, pelo uso de monômeros que aliviam a tensão, o uso de fotoiniciadores mais reativos e a incorporação de diferentes tipos de partículas, como as pré polimerizadas (Fronza et al., 2015).

No entanto, alguns fabricantes recomendam tempo mínimo de fotoativação para os compósitos Bulk Fill (Chesterman et al., 2017). De acordo com Tarle et al. (2014), o tempo sugerido pode não ser suficiente para obtenção de grau de conversão adequado, necessitando maior tempo de exposição a luz. Ainda, há relatos na literatura de que com

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menor intensidade de luz as propriedades dos compósitos Bulk Fill podem ser afetadas negativamente. Além disso, compósitos Bulk Fill apresentam elevado grau de conversão comparado aos compósitos convencionais, em virtude de sua alta translucidez, o que poderia comprometer a estética do material. (Van ende et al 2017).

Apesar do desenvolvimento de novos materiais e técnicas restauradoras, todos os materiais restauradores devem ter adequado desempenho frente ao ambiente desafiador, o qual está relacionado a diversos fatores, como: forças mastigatórias, hábitos oclusais, ingestão de alimentos ácidos, variações da temperatura e produtos bacterianos. Esses fatores, separados ou associados determinam a longevidade da restauração (Levartovsky et al., 1994; Sarrett, 2005). Além disso, o desempenho do compósito resinoso está relacionado aos tipos de monômero e partícula de carga de cada material, além do grau de conversão (Ferracane et al.,1994). Menor longevidade das restaurações têm sido atribuída, em parte, à degradação do material ocasionada pela adesão bacteriana (Khalichi et al., 2009; Santerre et al., 2001).

O biofilme dentário é definido como uma comunidade de diferentes espécies microbianas envoltas por uma matriz polimérica de origem bacteriana e película adquirida (Marsh, 2005). Esta estrutura organizada se forma rapidamente na cavidade bucal, ambiente composto por diferentes superfícies não descamativas, como os tecidos dentários e os variados materiais utilizados nos tratamentos reabilitadores (Busscher et al., 2010).

Um dos principais agentes etiológicos responsável pela cárie dentária é o S. mutans, sendo um dos habitantes primários presente na interface marginal das restaurações. Desta forma, grandes biomassas e metabólitos podem ser acumulados em áreas de retenção, como na superfície oclusal (sulcos, fóssulas e fissuras), cervical (próximas ao sulco gengival) e mesmo em espaços marginais da interface dente-

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restauração (Carvalho et al., 1996). Protegido das forças mecânicas de remoção (escovação, língua, fluxo salivar e mastigação), o biofilme torna-se estável e maduro, capaz de produzir primariamente cárie dentária e doença periodontal, além de cárie recorrente e inflamação/necrose pulpar quando presente nas interfaces (Al-Naimi et al., 2008; Sousa et al., 2009).

S. mutans tem maior afinidade pelos compósitos em comparação ao esmalte dental e outros materiais restauradores, tais como metais e cerâmicas (Svanberg et al.,1990; Fúcio et al., 2009 He et al., 2011; Padovani et al.,2014;). Segundo (Beyth et al., 2008), este microrganismo apresenta crescimento acelerado sobre compósitos quando avaliado in vitro. No entanto, não está claro se o crescimento ocorre devido à lixiviação dos monômeros que não reagiram fato que facilita o crescimento dessa bactéria cariogênica, ou se é pela característica da rugosidade da superfície do material que permite melhor adesão bacteriana (Kawai et al., 2000;Beyth et al., 2008). Todavia, ambos os fatores promovem acúmulo de bactérias em materiais resinosos. Além disso, Bourbia et al. (2013) sugerem que S. mutans apresenta atividade de esterase em níveis capazes de degradar materiais poliméricos. Consequentemente, a formação do biofilme pode resultar na degradação contínua dos compósitos, comprometendo a durabilidade clínica destes materiais devido à alterações das propriedades físico-mecânicas.

A diminuição da dureza (Asmussen, 1984; Yap et al., 2000) e o aumento da rugosidade de materiais restauradores resinosos (Yap et al., 2000; Turssi et al., 2002; Jung et al., 2007) são as alterações mais evidentes na degradação ocasionada por ácidos (Paula et al., 2011). Além disso, o brilho do material, propriedade extremamente importante pelo efeito sobre a percepção da cor e aparência comparável à de dentes naturais (O´Brien et al., 1964), e sobre a lisura da superfície (Kakaboura et al., 2007) poderá ser reduzido devido ao processo de degradação.

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Consequentemente, fatores que interferem na difusão dos solventes ácidos, como por exemplo, composição da matriz, grau de conversão e densidade de ligações cruzadas apresentam grande importância na resistência do material à degradação química (Aguiar et al., 2005; Gonçalves et al., 2007; Ferracane, 2008). Dessa forma, a superfície das restaurações fica mais susceptível ao desgaste e, consequentemente, à perda de componentes que resulta na alteração da forma anatômica e afeta o desempenho clínico da restauração (De Paula et al., 2014).

Nesse contexto, considerando a disponibilidade de novos compósitos que propõem inovações significativas nas técnicas restauradoras como os compósitos Bulk Fill de alta viscosidade, o objetivo da presente dissertação de capítulo único foi avaliar a influência da degradação por biofilme de S. mutans na rugosidade, dureza, brilho de superfície e resistência à flexão de compósitos Bulk Fill de alta viscosidade.

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Physical properties of Bulk Fill composites submitted to the cariogenic challenge

Abstract: The aim of this study was to evaluate the influence of biofilm by Streptococcus

mutans on the roughness (Ra), gloss (GU), surface hardness (KHN) and flexural strength (FS) of high viscosity bulk fill composites. Methods: Filtek Bulk Fill (FBF), Tetric N Ceram Bulk Fill (TNC), X-tra fil (XF) and Filtek Z350 (FZ- control) were used in this study. Ten discs of each composite were prepared for Ra, KHN and UG assays and 20 bars for the RF assay. After 24 h, all specimens were polished and the initial analyzes of Ra, GU, KHN and RF were performed. All samples were sterilized in ethylene oxide and subjected to degradation by S. mutans for 7 days. The final analyzes of Ra, GU, KHN and RF were performed. Samples representative of each group were evaluated in Scanning Electron Microscope (SEM). Data for Ra, GU and KHN were submitted to repeated measures two-way analysis of variance, and data for FS to two-way analysis of variance and Tukey´s test (p<0.05). Results: XF presented the highest values of Ra (µm) before and after biodegradation (0.1251; 0.3100), and Z350 (0.1443) the lowest only after biodegradation, while there were no significant difference between TNC and FBF. The highest GU values were observed for FZ (71.7; 62) and FBF (69.0; 64.6), and the lowest for TNC (61.4; 53.3) and XF (58.5; 53.5) both before and after biodegradation. For KNH the highest values were obtained by XF (151.7; 106, respectively), and the lowest values for TNC (62.2; 51.8) both before and after biodegradation, while no significant difference were found between FBF and FZ. Initially, the highest values of FS were observed for FZ (127.6) and the lowest values for TNC (86.9), while FBF and XF presented intermediate values. After biodegradation, XF (117.7) presented the highest values compared to TNC and FZ. Biodegradation promoted increase of Ra and reduction of GU and KHN for all materials, and reduction of FS values only for FZ. Conclusion: Biodegradation negatively

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affected the surface properties of Bulk Fill composites; however, did not affect the flexural strength of these materials, unlike the control composite.

Keywords: Biodegradation, Composite resin, Streptococcus mutans.

CLINICAL SIGNIFICANCE: Biodegradation negatively affects mechanical properties

of Bulk Fill composites, being indispensable knowledge of the composition of materials associated with the use of oral hygiene techniques to obtain clinical longevity of the restorations.

Introduction

Due to greater demand for aesthetics, the composite resin has been the material of choice for direct restorative treatment. In order to simplify the restorative procedure, reduce clinical time, and decrease polymerization shrinkage stresses and cusp deflection, Bulk Fill composites were introduced into dental market with the proposal of simplifying the restorative procedure by single increment insertion of up to 4 mm depth with an adequate polymerization (1,2).

According to the manufacturers, these composites require a short activation time due to the modification of the initiation system that includes higher concentrations of conventional photoinitiators. In addition, larger filler particles are used to reduce light scattering (3) and the translucency of the material adjusted to increase light transmission (4), providing satisfactory material polymerization. Although yet there is no consensus about the classification of this materials , Bulk Fill composites can be classified as low or high viscosity depending on the quantity of inorganic fillers (5).

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Although new materials and restorative techniques are constantly developed, dental materials in the oral cavity are subject to thermal, mechanical, and chemical challenges (6). The chemical challenges can be caused by acids produced by cariogenic biofilm, (7), acid diet (8) and salivary enzymes (9) causing destructive effect on the polymers and negatively affecting the materials properties in short or long term (10).

The biofilm that attaches the dental surface is defined as a diverse community of microorganisms embedded in an extracellular matrix of polymers of host and bacterial origin (11). S. mutans is considered one of the main etiological agent responsible for dental caries (12) and shows fast growth in composites resins surface (13). Thus, the damage caused by the acids produced by the bacteria of the cariogenic biofilm affects the surface of the composite by the softening of the resin matrix (13), increasing surface roughness and reducing hardness and gloss (14). Moreover, the flexural strength is considered an indicative factor about the performance and longevity of the composites when subjected to biological degradation and masticatory forces, influencing the material performance (15).

Although there are several studies in the literature in relation to Bulk Fill composites related mainly to mechanical performance (16-18), there are still no reports on the influence of cariogenic biofilm on the properties of materials. Considering this lack of information in the literature and due to the routine use of composites resins to restore posterior teeth, it would be essential to evaluate the material performance under cariogenic challenge. Therefore, the aim of this study was to evaluate the biodegradation influence by S. mutans biofilm on the roughness, hardness, surface gloss and flexural strength of high viscosity Bulk Fill composites.

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Three commercial high viscosity Bulk Fill composites: Filtek Bulk Fill, Tetric N Ceram, X-tra fil and a conventional Filtek Z350 composite were used in this study. The composition, lot number and manufacturer information of these products are presented in Table 1.

Table 1. Material, composition, size of fillers and manufactures of the materials used in

the study.

Material Composition Shade

Size, filler fraction (%), volume (%) e shape

particles

Manufacter # Lote number

Filtek Z350

Sílica Zirconia Clusters, silica nanoaglomerates, Bis-GMA, Bis-

A2 EMA, UDMA e TEGDMA, CQ.

5-20nm (nanopartículas) 0.6- 1.4 µm (clusters) 72.5w%, 55.6v% spherical 3M/ESPE, St Paul, MN, USA (90284830233)

Filtek Bulk Fill Bis-GMA, Bis-EMA, UDMA, TEGDMA EBPADMA, Zirconia

Silica, Ytterbium, EDMAB, CQ

0.01 – 3.5 µm (average 0.6 µm) A2 76.5%w 58.4v% 3M ESPE, St. Paul, MN, USA (N867072)

Bis-EMA= Ethoxylated bisphenol-A-glycidyl methacrylate. Bis-GMA= Bisphenol-A glycidyl methacrylate. UDMA= Urethane dimethacrylate. EBPADMA: ethoxylated bisphenol-A dimethacrylate; TEGDMA= Triethylene glycol dimethacrylate; CQ= Canphorquinone;TPO=2,4,6-tri-methylbenzoyl-

diphenylphosphineoxide, EDMAB = ethyl-4-N,N-dimethylaminobenzoate.

Spherical

Bis-GMA, UDMA, BIS-EMA,

Tetric N Ceram Barium glass, ytterbium 0.4 – 0.6 µm IvoclarVivadent,

Bulk Fill trifluoride, oxides and IVA 77%w 55v% Inc, NY, USA

prepolymers. Irregular (V19409)

TPO, Ivocerim, CQ

Bis-GMA, UDMA,TEGDMA, X-tra fil

Barium glass, Borium, Alumina,

Silica Universal 2 - 3µm 86 %w 70.1%v VOCO,Cuxhave n,Germany N/A Irregular (1702532)

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Each material was light-activated using a polywave light-emitting diode curing unit (BluePhase 20i; Ivoclar Vivadent, Schaan, Liechtenstein) with 10 seconds of exposure time for Bulk Fill and 20 seconds for conventional composite in high power mode with irradiance of 1,200 mW/cm2. The irradiance of the LCU was determined using a laboratory-grade spectral radiometer (Hilux Dental Curing Light Meter; Benilioglu Dental, Demetron, Ankara, Turkey).

For all the tests, samples were randomly distributed in 4 experimental groups (n =10) according to each material, with evaluations before and after 7 days of biodegradation, regarding to properties of surface: roughness, hardness, gloss and flexural strength.

2.1 Roughness

Roughness test was carried out in discs (5 mm in diameter, 2 mm in thickness for all composites) using a silicone mold (Aquasil LV; Dentsply DeTrey, Maquira, Maringa, PR, Brazil) pressed between two glass slides covered by polystyrene strips (n=10). The composites were placed in a single increment and the photoactivation procedure was performed following the manufacturers’ instructions. After storage for 24 h at 37ºC in relative humidity, discs were polished (400 rpm under 2N) using #1000, #1200, and #2000 grit silicon carbide sandpaper (Norton Abrasives, Vinhedo, SP, Brazil) and finished with diamond pastes 3, 2, 1, and 0.5 µm (Diamond Excel; Buehler) applied with felt discs, according to protocol previously described in the literature (Fronza et al., 2016). Surface roughness was measured using Surfcorder 1700 SE rugosimeter (Kosaka; Tokyo, Japan), whose system is based on a diamond tip driven at a constant speed over a distance of 1.250 mm with 0.25 mm cut-off and 0.1 mm/s speed. Three measurements

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were taken at different surface sites rotating the sample 90, 135 and 180 degrees to obtain the mean roughness (Ra-µm).

2.2Knoop Hardness

Ten samples for each composite were prepared following the same procedures described for the roughness test. After 24 h in relative humidity, the top surface was indented using a load of 50 gf for 15s with a Knoop Hardness Indenter (Shimadzu; Tokyo, Japan) at five different locations and the average mean calculated for each sample.

2.3 Surface Gloss

Ten samples for each composite (10 mm in diameter and 2 mm in thickness) were prepared following the same procedures described for item 2.1. The surface gloss of the composites was measured with the gloss meter (ZGM 1120 glossmeter; Zehntner GmbH Testing Instruments; Switzerland). The values of gloss resulting from the incidence and reflection of the light beam on the composite surface at a 60 degrees angle (20) were evaluated. The device was calibrated against highly polished black glass provided by the manufacturer. For measurements, each sample was placed in the center of the aperture of a device developed, providing contact of the gloss gauge with the surface of the sample. Four measurements were performed in each sample and the average of the readings was considered as Gloss values and expressed as gloss units (GU). The data obtained was recorded by the software Zehntner Glosstools 1.0.0023.

2.4 Flexural Strength

The samples were perfomed according to ISO 4049. Twenty bar shaped samples were made for each composite with dimensions of 25 mm x 2 mm x 2 mm. After

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polymerization, the excess of the material was removed and the dimensions of the bars measured with a digital caliper (Mitutoyo 293-821; Neuss, Germany) with an accuracy of 0.01 mm. Ten samples were submitted to the flexural strength test after 24 h of storage (Fanem, Sao Paulo, SP, Brazil) in relative humidity at 37ºC, and the remaining samples after biodegradation for 7 days. The three-point bending flexural strength test was performed in an universal testing machine (Instron, Model 4411; Corona, CA, USA) with 500N load performed in the central part of the bar length, and crosshead speed of 0.5 mm/min until sample fracture. The flexural strength was calculated in megapascal (MPa) with Bluehill 2 software (Illinois Tool Works; IL, USA) interconnected to test machine.

2.5 Biodegradation

All the samples subjected to initial tests of roughness, Knoop hardness and surface gloss, as well as those subjected to the flexural strength test after biodegradation were sterilized with ethylene oxide in ACECIL (Sterilization Center, Campinas, SP, Brazil). S. mutans strain UA159 was obtained from a culture of the Department of Microbiology and Immunology,Piracicaba Dental School, University of Campinas. To prepare the inoculum, S mutans was first grown on Mitis Salivarius Agar (Difco Laboratories, Sparks MD, MI, USA) plates at 37oC for 48 h in an environment supplemented with 10% CO2.

Subsequently, single colonies were inoculated into 5 mL of brain heart infusion (BHI) broth (Difco Laboratories) and incubated at 37oC for 18 h. Discs samples were exposed

under static conditions to 25 µL of S mutans and bars shaped samples to 150 µL inoculum adjusted to an optical density of 0.6 at 550 nm (approximately 8 x 1011 CFU/mL) (6).

After 2 h at room temperature, the non-adhering cells were removed by washing two times with 0.9% NaCl solution (saline). After, a single material disk was placed in each well of polystyrene plates (Nunce multidish 96-well, Sigma, Saint Louis, MO, USA)

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with 2 mL of sterile, fresh, BHI broth containing 1% of sucrose (wt/vol). Samples for flexural strength test were stored in test tubes with 4 mL of sterile BHI solution containing 1% of sucrose. The bacterial accumulation occurred at 37°C in an environment supplemented with 10% CO2, developing 7-day-old biofilm (21). The medium was renewed at 24-hour intervals. At the end of the experimental period, samples were ultrasonically washed for 10 min and the finals tests for surface roughness,hardness,gloss and flexural strength were performed as described for the initial period. Representative samples of each material (n = 3), before and after biodegradation, were sputter-coated with gold under vacuum (Balzers-SCD 050 sputter coater, Balzers, Liechtenstein) and examined using scanning electron microscope (Model JEOL JSM 5600 LV, Tokyo, Japan) operating at 1000x magnification.

2.6 Statistical Analysis

Data were assessed for normality by the Kolmogorov-Smirnov test. Data for roughness, Knoop hardness and surface gloss were submitted to repeated measures two- way analysis of variance (ANOVA) and Tukey’s test with 5% significance level. Data of the flexural strength were submitted to two-way analysis of variance and Tukey’s test with significance of 5% using SPSS software 22.

2. Results

The averages and standard deviations of surface roughness, gloss, Knoop hardness and flexural strength of each material, before and after biodegradation, are presented in Tables 2, 3, 4 and 5, respectively.

Table 2 shows the surface roughness of the composites before and after the biodegradation. There was a significant difference for materials (p = 0.000) and

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biodegradation (p = 0.000). The interaction between material and biodegradation was significant (p = 0.003). Surface roughness increased for all materials after S.mutans biodegradation. Comparing different composites before the biodegradation, it was observed that the X-tra fil composite presented higher roughness value, while other composites did not differ statistically and presented the lowest values of surface roughness. After biodegradation, the highest roughness value was observed for X-tra fil and the lowest for Filtek Z350, while Tetric and Filtek Bulk Fill were intermediate, and did not differ statistically for each other.

Table 2. Means and standard deviations of the surface roughness (μm) before and after

biodegradation by S. mutans.

Biodegradation

Composites Before After

Filtek Z 350 0.0944 (0.037) b B 0.1443 (0.044) c A

Filtek Bulk Fill 0.0787 (0.007) b B 0.1673 (0.066) b A

X-tra fil 0.1251 (0.042) a B 0.3100 (0.118) a A

Tetric N Ceram 0.0861 (0.010) b B 0.1766 (0.048) b A

Different lower case letters in each column and capital letters in each row show significant difference by the Tukey’s test (p <0.05).

Table 3 shows the gloss results before and after biodegradation.There was significant difference between the materials (p = 0.008) and biodegradation (p = 0.001). However, there was no interaction between the material x biodegradation factors (p = 0.845). It was observed that Filtek Z350 and Filtek Bulk Fill showed higher gloss values both before and after the biodegradation when compared to other materials. Tetric N

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Ceram Bulk Fill and X-tra fil showed similar lower gloss values. It was observed reduction of gloss values for all the composites after biodegradation.

Table 3. Means and standard deviations of gloss (GU), before and after biodegradation

by S. mutans. Composites Biodegradation Before After Filtek Z350 71.7 (11.2) a A 62.0 (9.6) a B

Filtek Bulk Fill

69.0 (9.9) a A 64.6 (8.4) a B

X-tra fil

58.5 (13.4) b A 53.5 (11.6) b B

Tetric N Ceran

61.4 (5.7) b A 53.3 (9.2) b B

Different Lower case letters in each column and capital letters in each row show significant difference by the Tukey’s test (p <0.05).

Table 4 shows the Knoop hardness results of the composites before and after biodegradation. There was significant difference between the materials (p = 0.000) and biodegradation (p = 0.000). The interaction between the material and biodegradation factors was significant (p = 0.024). The surface hardness values for all materials decreased after biodegradation. It was observed that for both before and after biodegradation, the X-tra fil composite presented the highest values for hardness when compared to other materials, and the lowest value was shown by Tetric N Ceram Bulk Fill, while Filtek Bulk Fill and Filtek Z350 presented similar intermediate values.

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Table 4. Means and standard deviation of Knoop hardness (KHN), before and after

biodegradation by S. mutans.

Biodegradation

Composites Before After

Filtek Z350

97.0 (23,8) b A 77.2 (12.0) b B

Filtek Bulk Fill

86.6 (12,6) b A 66.7 (10.4) b B

X-tra fil

151.7 (27,8) a A 106.0 (27.2) a B

Tetric N Ceram

62.2 (5.6) c A 51.8 (8.6) c B

Different lower case letters in each column and capital letters in each row show significant difference by the Tukey’s test (p <0.05).

Table 5 shows the results of the flexural strength of the composites before and after the biodegradation by S. mutans. There was a significant difference between the materials (p = 0.000), biodegradation (p = 0.03) and interaction between the factors material x biodegradation (p=0.004). Filtek Z350 composite showed higher flexural strength when compared to Filtek Bulk Fill and Tetric N Ceram composites, the latter with lower value. The flexural strength values showed statistical similarity between Filtek Bulk Fill and X-tra fil, as well as between Filtek Bulk Fill and Tetric N Ceram. After biodegradation, X-tra fil showed higher value when compared to Filtek Z350 and Tetric N Ceram composites, the latter with lower value. The flexural strength values showed statistical similarity between Filtek Z350 and Filtek Bulk Fill, and between Filtek Bulk Fill and X-tra fil, as well as between Filtek Z350 and Tetric N Ceram. When the times before and after the biodegradation were compared for each composite, there was a reduction in the flexural strength value only for the Filtek Z350 composite.

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Table 5. Means and standard deviations of flexural strength (MPa), before and after

biodegradation by S. mutans.

Biodegradation

Composites Before After

Filtek Z350 127.6 (15.3) a A 99.0 (12.1) bc B

Filtek Bulk Fill 105.6 (14.8) bc A 104.2 (15.8) ab A

X-tra fil 117.7 (5.6) ab A 117.7 (16.1) a A

Tetric N Ceram 86.9 (9.0) c A 81.9 (5.4) c A

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Figure 1. Representative scanning electron microscopy of Filtek Z350 (A,E), Filtek Bulk

(B,F), Tetric N Ceram (C,G) and Fill X-tra fil (D,H) composites before and after degradation of S. Mutans, respectively. Magnification of 1000x.

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Representative Scanning electron microscopy images presented in Figure 1 show initial aspect of composite surfaces and the changes that occurred on the composites surface after degradation by S. mutans biofilm. After biodegradation, it is possible observe to a smoother surface with uniform distribution of filler particles for the Filtek Z350 composite (E). For X-tra fil composite (H), is possible to notice the presence of larger sized particles with irregular shape and distribution. Tetric N Ceram (G) presented a slightly corroded surface and on the surface of Filtek Bulk Fill composite (F) may be observed the exposure of intermediate sized filler particles.

3. Discussion

In order to obtain aesthetics and longevity in resin composite restorations, surface smoothness is required considering that surfaces with roughness greater than 0.2 μm allow an increase in biofilm accumulation (19, 20). According to the results obtained in this study, before biodegradation the composite X-tra fil showed the highest roughness when compared to other composites. Previous study showed that this result is related to highest percentage in volume (70.1%) and size (2-3 μm) of the filler (21). Furthermore, Marghalani (22) has shown that the shape of the filler particles also influence the surface roughness, suggesting that irregular fillers, such as X-tra fil composite, promote rougher surfaces.

Filtek Z350, Filtek Bulk Fill and Tetric N Ceram Bulk Fill composites showed similar roughness values before biodegradation. As it can be seen in Table 1, these composites have in the composition filler particles with reduced size and similar or lower percentage in volume when compared to X-tra fil composite, factor that allows better polishing and, consequently, higher surface smoothness.

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After biodegradation, higher roughness value was observed for X-tra fil. According to Montanaro et al (23), the adhesion of S. mutans to surface of the composites is related to size, shape and distribution of the charge particles, besides the composition of the organic matrix. As it can be seen in Figure 1, the X-tra fil composite showed irregular filler particles, allowing greater adhesion of S. mutans. In addition, the material presents an organic matrix with hydrophilic characteristics when compared to other materials due to the presence of higher percentage of TEGDMA monomer, being probably more susceptible to chemical degradation (24).

Adversely, in the conventional composite Filtek Z350 there is a fillers combination involving nanosilic and nanoglomerates (clusters) particles. The reduced size and wide distribution of the filler particles in this composite (Figure 1) resulted in lower S. mutans adhesion, similar to previous study (23). It is also known that in this nanocomposite there is lower interstitial space among the filler particles and, consequently, less exposure of the organic matrix (25), making it more resistant to biodegradation. According to literature, degradation of the organic matrix occurs because it is more stable and chemically inert (26). Therefore, these factors are responsible for the lower surface roughness of Filtek Z350 after biodegradation. Tetric N Ceram Bulk Fill and Filtek Bulk Fill composites showed intermediaries and did not differ statistically in roughness after biodegradation. This result was attributed to similarity of size and volume percentage of the filler particles of these materials (27). However, all the composites presented increase in roughness values after the biodegradation by S.mutans. According to Beyth et al (13), S. mutans shows fast growth in resin composites. Still, it is unclear whether this fact occurs due to the leaching of unreacted monomers that may alter bacterial growth, or whether it occurs due to surface characteristics that allow higher bacterial adhesion. Bourbia et al. (28) suggest that S. mutans also shows esterase activity

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at levels capable of degrading resinous materials. In addition, the penetration of water or solvents into the polymer allows the chemical degradation process to begin, resulting in changes in the microstructure of polymers. As consequence, oligomers, monomers, degradation products and additives are released causing erosion and decrease in the mass of the polymer surface (26), leading to increased composite roughness.

It is claimed that the surface gloss of the composites shows an inverse relation with roughness (29), corroborating with the results obtained in the current study. Gloss is an optical phenomenon defined by the amount of light beams reflected on the surface of materials and is significative for the aesthetic of composite restorations (30). It can be observed in this study that after biodegradation, besides the increase of surface roughness, all composites presented reduction in the brightness values. This result is due to surface changes that occurred in the materials exposed to the cariogenic biofilm and by the acids and water that affect the incidence and reflection of the light, promoting reduction of the surface gloss of the composites (31). According to Münchow et al (32), any factor that changes the organic matrix and the interaction between matrix and filler particles may promote significant reduction of the surface gloss of composites.

However, when the materials were compared before and after biodegradation may be observed that higher gloss values were obtained for Filtek Z350 and Filtek Bulk Fill composites. The surface gloss is dependent on the size and shape of the filler particles and the diffusive light reflection may increase proportionally with the particle size (33). Thus, when the filler particles are small, diffusive reflection decreases and the surface appears glossier (34). According to Takanashi et al. (35), spherical fillers present higher refractive index when compared to irregular fillers due to reduced surface area. These factors are related to the higher gloss values obtained by these composites.

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Furthermore, the light reflection may be related to homogeneity of the matrix- filler complex. According to Lefever et al. (36), the larger the particle size, the lower the homogeneity of the matrix-filler complex, resulting in low light reflection which may explain the lower gloss values obtained by X-tra fil and Tetric N Ceram Bulk Fill composites, that are composed by irregular shape particles (37).

Surface hardness is directly related to mechanical performance and depends on the degree of polymerization of the material (38). The hardness is also dependent on the size and the amount inorganic fillers as well as the composition of the composite matrix (39-40).

It can observe that for both before and after biodegradation, the performance was similar among the composites resins. The X-tra fil composite presented higher hardness value, which may be attributed to higher percentage of filler in volume (70%), being one of the factors responsible for increasing the performance of the mechanical properties (41). According to Ilie et al. (42), increasing the size of the inorganic fillers reduces the amount incorporated into the material and, consequently, the matrix-filler interface. Thus, light scattering is reduced during photo-activation due to higher absorption, increasing the degree of conversion and resulting in higher hardness values.

However, lower hardness value was observed for Tetric N Ceram Bulk Fill. Even though the photoinitiator is part of the composition, which according to manufacturer would provide increase at the polymerization depth, it also contains prepolymers that may be related to lower hardness values (35,42) because pre polymers are calculated together with the volume percentage of the inorganic matrix (43). The Filtek Z350 and Filtek Bulk Fill composites presented intermediaries Knoop hardness values and this may be attributed to the similar size of the inorganic fillers.

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Biofilm degradation by S.mutans caused a significant decrease in hardness of all materials. Bacteria from the dental biofilm produce high concentrations of lactic, acetic and propionic acid (44) and it has been reported that low pH of the medium may affect the surface hardness of resinous composites (45). There is a great possibility that the functional groups -OH and -CHOO of the acids produced by the bacteria form hydrogen bonds with the polar side of the methacrylate monomer of the composites, causing greater water absorption and softening of the resin matrix. This fact induces tension at the matrix- silane-filler interface separating the inorganic fillers from the organic matrix, causing a decrease in hardness (46, 47).

Before biodegradation, the Filtek Z350 composite presented higher value of flexural strength when compared to the Tetric N Ceram Bulk Fill and Filtek Bulk Fill composites. The values suggest that higher inorganic particle content does not necessarily result in higher flexural strength values (48). In addition to the filler content, other factors such as tension between fillers and resin matrix, as well as the bond between the components and the composition of the organic matrix (41) may be relevant on the flexural strength of these materials. According to Fronza et al. (49), better mechanical properties indicate a higher degree of monomeric conversion, which was also observed in previous study for Filtek Z350 (50).

However, Tetric N Ceram Bulk Fill showed lower value when compared to X-tra fil and Filtek Z350 composites. As previously discussed, despite the incorporation of the Ivocerim photoinitiator in an attempt to improve the polymerization depth, the presence of prepolymers in the composite may have negative influence on the mechanical properties, reflecting the lower value of flexural strength for this material (51). When comparing the composites after biodegradation, it may be observed that the X-tra fil presented a higher value of flexural strength when compared to the Tetric N Ceram Bulk

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Fill and Filtek Bulk Fill composites. Probably, this result would be related to the larger size and volume of the filler particles (52).

Despite the differences found in flexural strength values when comparing the different composites, the degradation by S. mutans biofilm was able to reduce only the resistance of the Filtek Z350 composite. This result may be related to different compositions of the organic matrices of these materials. In addition, the Filtek Z350 composite exhibits the highest amount of zirconia-silica clusters, responsible for increasing the water absorption by the material due to the higher volume of silane, which makes it more susceptible to hydrolytic degradation (47,51)

In this context, it is evident that the biodegradation by S. mutans negatively affected the mechanical properties of the materials, which are related to the composition not totally informed by the manufacturer (53). Thus, the selection of the restorative material and the knowledge of the patient about the importance of the continuous use of oral hygiene techniques is essential for maintaining aesthetics and longevity of composite resin restorations.

4. Conclusion

In conclusion, the biodegradation by biofilm promoted:

1- Increased roughness and decreased hardness and gloss of all composites evaluated; 2- No effect on the flexural strength occurred for the Bulk Fill composites;

3- Reduction of flexural strength occurred only for the conventional Filtek Z350 composite.

Acknowledgements

The author acknowledge FAPESP and CAPES grant# 2016/18720-8, São Paulo Research Foundation (FAPESP) for financial support of this study.

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38. Ferracane JL (1985) Correlation between hardness and degree of conversion during the setting reaction of unfilled dental restorative resins Dental Materials 1:11–4.

39. Scougall-Vilchis RJ, Hotta Y, Hotta M, Idono T, & Yamamoto K (2009) Examination of composite resins with electron microscopy, microhardness tester and energy dispersive X-ray microanalyzer Dental Materials Journal 28(1) 102-112.

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49. Fronza BM, Ayres APA, Pacheco RR, Rueggeberg FA, Dias CTS, Giannini M (2017) Characterization of Inorganic Filler Content, Mechanical Properties, and Light

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CONCLUSÃO

Dentro das limitações deste estudo in vitro, pode-se concluir que a degradação por biofilme de S. mutans ocasionou:

1- Aumento da rugosidade e diminuição da dureza e brilho de superfície de todos os compósitos avaliados;

2- Nenhum efeito na resistência à flexão dos compósitos Bulk Fill;

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REFERÊNCIAS*

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3. Al-Naimi OT, Itota T, Hobson RS, McCabe JF. Fluoride release for restorative materials and its effect on biofilm formation un natural saliva. J MaterSciMater. 2008;19(3):1243-1248.

4. Alrahlah A, Silikas N, Watts DC. Post-cure depth of cure of bulk fill dental resin composites. Dent Mater. 2014;30(2):149–154.

5. Asmussen E. Softening of Bis-GMA-based polymers by ethanol and by organic acids of plaque. Scand J Dent Res. 1984;92(3):257-61.

6. Asmussen E, Peutzfeldt A. Influence of pulse-delay curing on softening of polymer structures. J Dent Res. 2001;80(6):1570-3.

7. Asghar S, Ali A, Rashid S, HussainT. Replacement of resin-based composite restorations in permanent teeth. J Coll Physicians Surg Pak. 2010;20(10):639–43.

8. Beyth N, Bahir R, Matalon S, Domb AJ, Weiss EI. Streptococcus mutans biofilm changes surface-topography of resin composites. Dent Mater. 2008;24(6):732–736.

*De acordo com a norma da UNICAMP/FOP, baseadas na norma do International Committee of Medical Journal Editors – Grupo de Vancouver. Abreviatura dos periódicos em conformidade com o Medline

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9. Bollen CM, Lambrechts P, QuirynenM .Comparison of surface roughness of oral hard materials to the threshold surface roughness for bacterial plaque retention: a review of the literature. Dent Mater. 1997;13(4):258-69.

10. Bourbia M, Ma D, Cvitkovitch DG, Santerre JP, Finer Y. Biodegradation of dental resin composites and adhesives by cariogenic bacteria. J Dent Res. 2013;92(11):989-94.

11. Breschi L, Mazzoni A, Ruggeri A, Cadenaro M, Di Lenarda R, & De Stefano DorigoE .Dental adhesion review: Aging and stability of the bonded interface. Dent Mater. 2008;24(1):90-101.

12. Bucuta S, Ilie N Light transmittance and micro-mechanical properties of bulk fill vs. conventional resin based composites. Clin Oral Investig. 2014;18(8):1991-2000.

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Referências

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