ANIELE CARVALHO LACERDA
“ INFLUÊNCIA DE IRRIGANTES ENDODÔNTICOS, AGENTES
ANTIOXIDANTES E ENVELHECIMENTO NA RESISTÊNCIA DE
UNIÃO DE UM CIMENTO RESINOSO AUTOADESIVO À DENTINA
RADICULAR”
"ENDODONTIC IRRIGANTS, ANTIOXIDANT AGENTS AND AGING
INFLUENCE ON BOND STRENGTH OF A SELF-ADHESIVE RESIN
CEMENT TO ROOT DENTIN"
“ INFLUÊNCIA DE IRRIGANTES ENDODÔNTICOS, AGENTES
ANTIOXIDANTES E ENVELHECIMENTO NA RESISTÊNCIA DE
UNIÃO DE UM CIMENTO RESINOSO AUTOADESIVO À DENTINA
RADICULAR”
"ENDODONTIC IRRIGANTS, ANTIOXIDANT AGENTS AND AGING
INFLUENCE ON BOND STRENGTH OF A SELF-ADHESIVE RESIN
CEMENT TO ROOT DENTIN"
Tese apresentada à Faculdade de Odontologia de Piracicaba da Universidade Estadual de Campinas como parte dos requisitos exigidos para a obtenção do título de Doutora em Clínica Odontológica, na Área de Endodontia.
Thesis presented to the Piracicaba Dental School of the University of Campinas in partial fulfillment of the requirements for the degree of Doctor in Clinical Dentistry, in Endodontics Area.
Orientador: Prof. Dr. Caio Cezar Randi Ferraz
Coorientador: Prof. Dr. José Flávio Affonso de Almeida
ESTE EXEMPLAR CORRESPONDE À VERSÃO FINAL DA TESE DEFENDIDA PELA ALUNA ANIELE CARVALHO LACERDA E ORIENTADA PELO PROF. DR. CAIO CEZAR RANDI FERRAZ.
Piracicaba 2017
A Deus, por manter viva a minha fé e me fortalecer nos momentos difíceis.
Ao meu pai, Dorvilê, por ter me feito a criança, a menina mais feliz do mundo. Deu-me tudo o que eu queria e até o pouco que eu desejava. A você, Pai, que Deu-me faz sentir orgulho de quem você é, todo o meu amor.
À minha mãe, Diana, por toda a sua sabedoria, autoconfiança, por me ensinar a ter força, perseverança e o caminho de tudo. Essa conquista é nossa, mas principalmente sua. Foi por você que trilhei este caminho e continuarei seguindo em frente.
Aos meus irmãos, Juliana e Nilo Neto, pelo companheirismo e por dividirem comigo todos os seus momentos. Obrigada pelo apoio de vocês!
A toda minha família, por ser tão especial na minha vida.
Ao meu orientador, Prof. Caio Ferraz, por tudo que me ensinou e por todas as oportunidades que me proporcionou. Continuo admirando-o pela competência profissional, por sua inteligência com raciocínio e respostas rápidas. A minha gratidão é eterna e sinto muito orgulho por ser meu orientador.
Ao meu coorientador, Prof. José Flávio, por ter aceitado “tocar o barco” nesta reta final. O meu muito obrigada pela sua orientação, disponibilidade e paciência, pois reconheço que a minha força e entusiasmo já não são os mesmos de antes. Agradeço também por ter contado sempre com sua ajuda durante todos esses anos de pós-graduação.
À minha orientadora do doutorado sanduíche, Profa. Juliana Santos, por toda orientação e ensinamentos. Você não tem ideia do quanto fui feliz e o quanto aprendi por ter me aceitado no seu laboratório. Obrigada pela receptividade e pela maravilhosa convivência que tivemos. Admiro muito sua simpatia, competência, determinação e a profissional que você é.
À Profa. Brenda Gomes por quem tenho enorme carinho, admiração e gratidão. A sua dedicação incansável à Endodontia e ao conhecimento em geral me inspira. E toda vez que desanimo, lembro da sua vivacidade e do ensinamento que me deixou em Quebec: mesmo no topo, nunca desistir de conhecer e seguir em frente para descobrir o novo. Obrigada por todas as dicas e conselhos ao longo desses anos.
Andréa, Amanda, Ana Carolina, Ana Pimentel, Augusto, Aline, Carlos
Meloni, Daniel, Daniela, Darklilson, Diogo, Eloá, Érika, Fabrício, Felipe,
Flávia, Jaqueline, Maicon, Marlos, Priscila, Rafaela, Rodrigo
Não tenho palavras para expressar o tamanho da gratidão que sinto por ter a amizade de vocês!!!
Obrigada por tudo que vivemos. Obrigada pelos ensinamentos.
Obrigada pelas experiências compartilhadas. Obrigada por dividirem comigo suas casas.
Obrigada pelos telefonemas, pelas alegrias no fim do dia,
pelas caronas, pelas viagens e congressos,
pelo aperto de mão, por estenderem suas mãos,
pelo abraço apertado, pelos sorrisos e churrascos,
por sermos irmãos. Obrigada por serem quem são.
Obrigada, obrigada, obrigada...
À Faculdade de Odontologia de Piracicaba da UNICAMP – FOP/UNICAMP, na pessoa do seu Diretor, Prof. Dr. Guilherme Elias Pessanha Henriques e Diretor Associado Prof. Dr. Francisco Haiter Neto.
À Profa. Dra. Cínthia Pereira Machado Tabchoury, coordenadora geral dos cursos de Pós-Graduação e a Profa. Dra Karina Gonzales Silvério Ruiz, coordenadora do curso de Pós-Graduação em Clínica Odontológica da FOP – UNICAMP.
Ao Prof. Dr. Alexandre Augusto Zaia, responsável pela área de Endodontia da FOP/UNICAMP.
A todos da secretaria de Pós-Graduação, Ana Paula Carone, Claudinéia Prata Pradella, Érica A. Pinho Sinhoreti, Leandro Viganó, Raquel Q. Marcondes Cesar, pela competência e atenção dispensada a todos os pós-graduandos. Vocês merecem todos os aplausos!
Aos docentes da área de Endodontia da FOP/UNICAMP, Profa. Dra. Adriana de Jesus Soares, Prof. Dr. Alexandre Augusto Zaia, Profa. Dra. Brenda Paula Figueiredo de Almeida Gomes, Prof. Dr. Caio Cezar Randi Ferraz, Prof. Dr. Francisco José de Souza-Filho (in memoriam), Prof. Dr. José Flávio Affonso de Almeida, por compartilharem seus conhecimentos e serem minha referência na Endodontia.
Aos professores: Profa. Dra. Vanessa Cavalli Gobbo, Prof. Dr. Américo Bortolazzo Correr, Prof. Dr. Daniel Rodrigo Herrera Morante e Profa. Dra. Adriana de Jesus Soares por terem aceitado o convite de participar do meu Exame de Qualificação e contribuírem para minha tese.
Aos professores membros da banca de defesa, Prof. Dr. José Flávio Affonso de Almeida, Profa. Dra. Juliana Nascimento Santos, Profa. Dra. Maraisa Greggio Delboni, Profa. Dra. Brenda Paula Figueiredo de Almeida Gomes, Prof. Dr. Flávio Henrique Baggio Aguiar, Profa. Dra. Daniela Cristina Miyagaki, Prof. Dr. Raimundo Rosendo Prado Júnior e Profa. Dra. Maria Tereza Pedrosa de Albuquerque. É uma honra para mim tê-los como mestre e contar com o apoio e os ensinamentos valiosos de vocês.
Herrera, Emmanuel Nogueira, Fernanda Signoretti, Frederico Martinho, Giselle Abi Rached, Jefferson Marion, Juliana Nagata, Karine Schell, Letícia Nóbrega, Maíra do Prado, Marcos Endo, Maria Rachel Monteiro. Meu muito obrigada!
À minha amiga Tereza Pedrosa, pelo carinho e amizade. Sou imensamente grata a você, orgulhosa das suas conquistas e saiba que estarei sempre na torcida! Meu padrão ouro!
Ao Doglas Cechin, pelas orientações e disponibilidade sempre quando preciso.
Ao Carlos Augusto Pantoja, pela amizade e apoio desde o início do mestrado.
A Priscilla Lazari, pela sua amizade, apoio e companhia em Piracicaba. Aprendi muito com você! A minha admiração e aplausos sempre!
A Muriel Rodrigues, minha coorientada de iniciação científica, por ter me suportado e ensinado que se pode relaxar nos estudos e ainda assim ganhar prêmios. Nunca vi ninguém ter tanta sorte na vida! Obrigada Muri por sua dedicação e amizade!
A Ana Cristina Godoy, Maicon Passini e Maria Helídia pela amizade e os bons momentos de convívio no laboratório.
Aos funcionários do laboratório de Materiais Dentários, Odontopediatria e do CeMI, Marcos Blanco, Marcelo e Adriano Martins. O meu muito obrigada por toda atenção, paciência e ensinamentos. Vocês foram fundamentais para a concretização deste trabalho.
A todos os Funcionários da Clínica de Graduação, Especialização, Almoxarifado, Portaria, Serviço Geral e etc. Obrigada pela amizade, pelos “bom-dia” e o sorriso no rosto.
Ao Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) pela concessão da bolsa de estudos e adicional de bancada, que permitiu o desenvolvimento de parte desta pesquisa, processo n° 141129/2014-0.
O objetivo neste estudo foi investigar o efeito de irrigantes endodônticos, agentes antioxidantes e o envelhecimento na resistência de união (RU) de um cimento resinoso autoadesivo à dentina radicular. No artigo 1, avaliou-se a RU imediata e após 1 ano, em armazenamento em água, de pinos anatômicos cimentados com um cimento resinoso autoadesivo à dentina radicular bovina após protocolos com irrigantes endodônticos e um agente antioxidante, durante a terapia endodôntica, como segue: G1(controle negativo): cloreto de sódio 0,9% (NaCl); G2: hipoclorito de sódio 5,25% (NaOCl) + ácido etilenodiaminotetracético 17% (EDTA) + NaOCl; G3 e G4: similar ao G2 seguido por tiossulfato de sódio (Na2S2O3) 5% por 1 ou 10 minutos, respectivamente; G5: clorexidina 2% gel (CHX) + EDTA; G6: NaOCl; G7: EDTA; G8: Na2S2O3; G9: CHX. No artigo 2, investigou-se a RU imediata e após ciclagem termomecânica (TMC) de pinos de fibra de vidro cimentados com um cimento autoadesivo à dentina radicular de pré-molares humanos após o pré-tratamento do espaço para pinos com irrigantes endodônticos e agentes antioxidantes: G1 (controle negativo): água destilada (AD); G2: NaOCl; G3 e G4, similar ao G2 seguido por Na2S2O3 10% ou ascorbato de sódio 10% (SA) por 1 minuto, respectivamente; G5, CHX. Nos dois artigos, os pinos foram cimentados com RelyX U200®(3M ESPE, St Paul, MN, USA). Após cimentação, metade dos espécimes de cada grupo (n = 5) foi testado após 24 horas e o outra metade submetida ao envelhecimento por 1 ano em água (Artigo 1) ou TMC (Artigo 2). Quatro secções transversais, de 2 mm de espessura, foram obtidas de cada raiz (Artigo 1). No artigo 2, de cada terço radicular, coronal e médio, foram obtidas 3 secções transversais com 1 mm de espessura, e os valores de RU avaliados por terço. Todas as secções foram submetidas ao teste de cisalhamento por extrusão. Os dados, em MPa, foram analisados por ANOVA e teste de Tukey-Kramer (α = 0.05). Os padrões de fratura foram classificados em falhas coesiva, adesiva ou mista. Os resultados indicaram que não houve diferença dos protocolos de irrigação comparado ao controle negativo (P > 0,05) na adesão imediata e após envelhecimento do cimento resinoso autoadesivo à dentina radicular nos dois estudos. No artigo 1, a irrigação com CHX (G9) diminuiu significativamente a RU após 1 ano (P < 0,05). No artigo 2, o terço médio da dentina radicular apresentou valores significativamente maiores (P < 0,05) na adesão que o terço coronal para os grupos G1, G3 e G4 do teste imediato; e para o G4 do teste após TMC. Após TMC, a RU do terço coronal do G1 e G2 aumentou
cimento resinoso autoadesivo de acordo com o terço radicular testado.
and aging on the bond strength of a self-adhesive resin cement to root dentin. In the first article of this work, it was evaluated the immediate and after 1 year storage in water bond strength of anatomic posts luted with a self-adhesive resin cement to bovine root dentin after irrigation protocols with endodontic irrigants and an antioxidant agent, during the endodontic therapy, as follows: G1 (negative control), 0.9% sodium chloride (NaCl); G2, 5.25% sodium hyplochlorite (NaOCl) + 17% ethylenediaminetetraacetic acid (EDTA) + NaOCl; G3 and G4, similar to G2 followed by 5% sodium thiosulfate (Na2S2O3) for 1 or 10 minutes, respectively; G5, 2% chlorhexidine gel (CHX) + EDTA; G6, NaOCl; G7, EDTA; G8, Na2S2O3; G9, CHX. In the second article, it was investigate the immediate and after thermemecanical cycling (TMC) bond strength of fiber posts luted with a self-adhesive resin cement to root dentin of human premolars after post space pretreatment with endodontic irrigants and antioxidant agents: G1 (negative control), distilled water (DW); G2, 5.25% NaOCl; G3 and G4, similar to G2 followed by 10% Na2S2O3 or 10% sodium ascorbate (SA) for 1 minute, respectively; G5, 2% CHX. In both articles, fiberglass posts were then luted with RelyX U200®(3M ESPE, St Paul, MN, USA). After cementation, half of the specimens from each group (n = 5) was tested after 24 hours and the other half submitted to aging for 1 year in water in the article 1 or TMC in the article 2. Four slices of 2 mm thickness were obtained from each root in article 1. In article 2, from each root third, coronal and middle, three slices with 1 mm thickness were obtained, and the bond strength values evaluated by third. All slices were submitted to the push-out test. Data in MPa were analyzed by ANOVA and Tukey-Kramer test (α = 0.05). The fracture patterns were classified into cohesive, adhesive and mixed failures. The results indicated that there was no difference of the irrigation protocols compared to negative control (P > 0.05) in the immediate adhesion and after aging of the self-adhesive resin cement in the two studies. In article 1, the irrigation with CHX (9) decreased the bond strength after 1 year (P < 0.05). In article 2, the middle third of the root dentin presented significant higher mean
values (P < 0.05) on the adhesion than the coronal third for groups G1, G3 and G4 of the
immediate test, and for the G4 of the test after TMC. After TMC, the bond strength of the
coronal third of G1 and G2 increased significantly (P < 0.05). In general, it was concluded that irrigation protocols with endodontic irrigants and antioxidant agents did not affect the immediate and after aging bond strength of the self-adhesive resin cement to root dentin.
Key words: Root canal irrigants. Antioxidants. Dental bonding. Dentin.
1 INTRODUÇÃO ... 16
2 ARTIGOS ... 20
2.1 Artigo: Effect of Endodontic Irrigants and Sodium Thiosulfate on the Bond Strength Longevity of a Self-Adhesive Resin Cement to Root Dentin ... 21
2.2 Artigo: Effect of Endodontic Irrigants, Antioxidant Agents, and Artificial Aging on Bond Strength of a Self-Adhesive Resin Cement to Root Dentin ... 36
3 DISCUSSÃO ... 49
4 CONCLUSÃO ... 54
REFERÊNCIAS ... 55
APÊNDICE 1- Detalhamento das Metodologias ... 61
ANEXOS ... 73
Anexo 1 - Comprovação de Submissão do Artigo ... 73
Anexo 2- Aprovação do Comitê de Ética em Pesquisa ... 74
INTRODUÇÃO
O uso de procedimentos adesivos tem se tornado uma opção comum para restaurar dentes tratados endodonticamente (Stevens, 2014), restabelecendo a função, a estética e contribuindo para permanência em longo prazo dos dentes envolvidos. Avanços nas técnicas e materiais adesivos têm permitido que restaurações com pinos e núcleos de preenchimento ou com resina composta direta sejam realizadas imediatamente após o tratamento endodôntico, blindando aberturas de acesso, sem a necessidade das tradicionais formas de retenção do passado. Porém, são exigidas boas propriedades física e mecânica dos sistemas adesivos e/ou cimentos resinosos para as técnicas adesivas serem bem sucedidas (Schawartz e Robbins, 2004; Schwatz e Fransman, 2005; Stevens, 2014).
Os pinos pré-fabricados de fibra de vidro foram os grandes responsáveis por aumentar a taxa de sucesso e a previsibilidade das restaurações com retentores intrarradiculares, pois suas propriedades mecânicas, como elevada resistência flexural e módulo de elasticidade próximo ao da dentina, permitiram minimizar a transmissão de tensões sobre as paredes radiculares e reduzir a possibilidade de fraturas das raízes (Cheung, 2005; Goracci e Ferrari, 2011). Além disso, a composição química dos pinos de fibra, compatível com os cimentos e adesivos resinosos, possibilitou a formação de um complexo biomecânico (pino, cimento e material de preenchimento coronário) com união adesiva à dentina, apresentando propriedades semelhantes à estrutura dentária remanescente(Duret et al., 1996).
Cimentos resinosos são recomendados para unir os pinos de fibra de vidro à dentina radicular e são classificados em dois grupos dependendo da estratégia de cimentação, em cimentos resinosos convencionais ou autoadesivos (Radovic et al., 2008). Os cimentos autoadesivos foram desenvolvidos em 2002, objetivando simplificar o processo de cimentação (Ferracane et al., 2011). Estes cimentos têm a propriedade de autoaderir-se à dentina, são utilizados em passo único e não necessitam do pré-tratamento da superfície dentinária com ácido fosfórico ou sistema adesivo autocondicionante (De Munck et al., 2004; Radovic et al., 2008). Dessa forma, suas características vantajosas e resistência de união similar ou maior que os cimentos resinosos convencionais possibilitaram-no ser de grande interesse aos clínicos (Bitter et al., 2014; Simões et al., 2016).
Por outro lado, durante o tratamento endodôntico, o uso de substâncias químicas auxiliares pode afetar a adesão dentinária. Vários são os estudos que mostram que o tratamento da dentina com hipoclorito de sódio reduz significativamente a sua resistência de
união à materiais resinosos (Lai et al., 2001; Vongphan et al., 2005; Santos et al., 2006; Moreira et al., 2009; Stevens, 2014; Pimentel Corrêa et al., 2016). Este fato é decorrente do hipoclorito de sódio ser um forte agente oxidante, induzindo a fragmentação das longas cadeias peptídicas e a cloração de grupos terminais amino, o que resulta na polimerização incompleta da resina (Nikaido et al., 1999; Lai et al., 2001). Causa também a degradação e desorganização estrutural das fibrilas colágenas (Moreira et al., 2009) e afeta negativamente as propriedades mecânicas da dentina, como módulo de elasticidade, resistência flexural, microdureza (Sim et al., 2001; Marending et al., 2007) comprometendo a interação micromecânica entre a dentina e os diversos materiais adesivos.
A clorexidina, no entanto, tem demonstrado não causar alteração estrutural nas fibrilas colágenas (Moreira et al., 2009), não influenciar negativamente a resistência de união da dentina à materiais resinosos (Santos et al., 2006, Bitter et al., 2014) e possui ação antiproteolítica, inibindo de forma inespecífica a atividade das enzimas endógenas metaloproteinases da matriz, as MMP’s (Gendron et al., 1999; Pashley et al., 2004; Carrilho et al., 2007, Breschi et al., 2010, Bitter et al., 2014). Assim, sua utilização poderia contribuir para a longevidade das restaurações adesivas.
Como o hipoclorito de sódio e a clorexidina não são capazes de remover a smear
layer, é recomendado o uso de um agente quelante como o EDTA associado à substância
antimicrobiana auxiliar da terapia endodôntica para promover limpeza efetiva das paredes instrumentadas. A remoção da smear layer permite uma maior penetração da medicação intracanal, quando utilizada, e de cimentos obturadores e restauradores no interior dos túbulos dentinários. Por outro lado, EDTA pode alterar a proporção dos íons cálcio e fósforo da dentina, modificando o módulo de elasticidade, a resistência flexural e aumentando a permeabilidade da dentina (Ari e Erdemir, 2005; Marending et al., 2007; Zhang et al., 2010, Simões et al., 2016), comprometendo, dessa forma, a adesão dos materiais resinosos (Santos et al., 2006; Pimentel Corrêa et al, 2016). Entretanto, os efeitos da exposição de substâncias auxiliares do tratamento endodôntico à superfície da dentina promovem diferentes interações de acordo com o material resinoso utilizado (Lai et al., 2001; Santos et al., 2006; Stevens, 2014), o qual apresenta comportamento específico dependendo da sua composição e características (Stevens, 2014).
Sabendo-se que o bom prognóstico da terapia endodôntica depende do selamento coronário efetivo e imediato após o tratamento dos canais radiculares, impedindo a recontaminaçāo do sistema de canais por fluidos, saliva e microrganismos da cavidade bucal
(Saunders e Saunders, 1994; Vârlan et al., 2009), pesquisadores têm buscado alternativas para aumentar a adesão de materiais resinosos à dentes submetidos ao tratamento com substâncias oxidantes (Lai et al., 2001; Vongphan et al., 2005; Weston et al., 2007; Stevens, 2014; Pimentel Corrêa et al., 2016). O ácido ascórbico e o seu sal, o ascorbato de sódio, vêm sendo largamente estudados na Odontologia Restauradora com o objetivo de reduzir os componentes oxidados das estruturas dentinárias após o uso do hipoclorito de sódio e, assim, aumentar os valores adesivos da dentina (Lai et al., 2001; Vongphan et al., 2005; Weston et al., 2007; Stevens, 2014). O efeito benéfico do ácido ascórbico e ascorbato, na concentração de 10%, em restabelecer a resistência de união dos materiais resinosos à dentina radicular imediatamente após o tratamento com hipoclorito de sódio é relatado em estudos prévios (Morris et al., 2001; Weston et al., 2007, Stevens, 2014). Por outro lado, estes antioxidantes possuem alguns aspectos negativos como a sua instabilidade química, pequena vida útil, dificuldade de armazenamento (Muraguchi et al., 2007), tempo de aplicação prolongado (Lai et al., 2001; Vongphan et al., 2005; Weston et al., 2007), elevado custo e difícil acesso comercial.
Dessa forma, outras substâncias antioxidantes vêm sendo estudadas com a finalidade de superar as características limitantes do ácido ascórbico e o seu sal, como, por exemplo, o tiossulfato de sódio. Este último é bastante utilizado em estudos in vivo de coletas microbiológica na Endodontia para neutralizar os efeitos do hipoclorito de sódio (Jacinto et al., 2005; Vianna et al., 2007; Martinho et al., 2010). Resultados favoráveis foram obtidos por Pimentel Corrêa et al. (2016), ao avaliar o efeito do tiossulfato de sódio na resistência de união à dentina da câmara pulpar bovina tratada com hipoclorito de sódio. Baseando-se nestes resultados e na premissa de que não há dados literários sobre o efeito desta substância à dentina radicular, que apresenta características peculiares na raiz dentária em relação a densidade e orientação dos túbulos dentinários, existe a necessidade de pesquisas avaliando sua habilidade antioxidante nesta superfície, uma vez que permitirá a análise da reversão dos efeitos oxidantes do hipoclorito neste substrato e a restauração imediata com materiais resinosos.
Além da avaliação dos efeitos de soluções irrigantes e agentes antioxidantes, o presente estudo avaliou a resistência de união imediata e após envelhecimento de pinos de fibra de vidro cimentados com cimento resinoso autoadesivo. As investigações deste trabalho poderão, ainda, fornecer importantes subsídios sobre a realização de protocolos de irrigação dentinária na clínica endodôntica quando do uso do cimento avaliado.
O presente estudo tem como objetivo geral avaliar o efeito de irrigantes endodônticos, agentes antioxidantes e o envelhecimento na resistência de união de um cimento resinoso autoadesivo à dentina radicular. No primeiro artigo, investigou-se o efeito de substâncias químicas auxiliares (hipoclorito de sódio 5,25%, clorexidina 2% gel e EDTA 17%) e um agente antioxidante (tiossulfato de sódio 5%) durante o tratamento endodôntico na resistência de união imediata e mediata de um cimento resinoso autoadesivo à dentina radicular. No segundo artigo avaliou-se o efeito do pré-tratamento do espaço para pinos com clorexidina 2% gel e hipoclorito de sódio 5,25% associado ou não a agentes antioxidantes (tiossulfato de sódio 10% e ascorbato de sodio 10%) na resistência de união imediata e após ciclagem termomecânica de um cimento resinoso autoadesivo à dentina radicular.
2 ARTIGOS
2.1 Artigo: Effect of Endodontic Irrigants and Sodium Thiosulfate on the Bond Strength Longevity of a Self-Adhesive Resin Cement to Root Dentin
Artigo submetido ao periódico Journal of Endodontics (Anexo 1)
Aniele Carvalho Lacerda, MSc, José Flávio Affonso de Almeida, PhD, Alexandre Augusto Zaia, PhD, Brenda Paula Figueiredo de Almeida Gomes, PhD, and Caio Cezar Randi Ferraz, PhD.
2.2 Artigo: Effect of Endodontic Irrigants, Antioxidant Agents, and Artificial Aging on Bond Strength of a Self-Adhesive Resin Cement to Root Dentin
Artigo será submetido ao periódico Journal of Endodontics.
Aniele Carvalho Lacerda, MSc, Juliana Santos, PhD, José Flávio Affonso de Almeida, PhD, Adriana de Jesus Soares, PhD, Alexandre Augusto Zaia, PhD, Brenda Paula Figueiredo de Almeida Gomes, PhD, and Caio Cezar Randi Ferraz, PhD.
2.1 Artigo: Effect of Endodontic Irrigants and Sodium Thiosulfate on the Bond Strength Longevity of the Bond Strength of a Self-Adhesive Resin to Root Canal Dentin
ABSTRACT
Introduction: This study investigated the effects of endodontic irrigants and sodium thiosulfate (Na2S2O3) on the bond strength of a self-adhesive resin cement to root dentin after 24 hours or 1 year of storage in water. Methods: Ninety roots of bovine incisors were prepared and divided into nine groups according to the following irrigation protocols: G1 (negative control), 0.9% sodium chloride (NaCl); G2, 5.25% sodium hypochlorite (NaOCl) + 17% ethylenediaminetetraacetic acid (EDTA) + NaOCl; G3 and G4, similar to G2 followed by 5% Na2S2O3 for 1 and 10 minutes, respectively; G5, 2% chlorhexidine gel (CHX) + EDTA; G6, NaOCl; G7, EDTA; G8, Na2S2O3; and G9, CHX. Next, fiberglass posts relined with composite resin were cemented with RelyX U200 (3M ESPE St Paul, MN, USA). After cementation, half of the specimens (n=5) was tested after 24 hours and the other half after 1 year. Four slices were obtained from each specimen and submitted to the push-out test. The data (MPa) were analyzed by ANOVA and Tukey-Kramer tests (α = 0.05). Results: The results indicated that after 24 hours, G8 and G9 presented higher bond strength (P < 0.05) than G5 and G6. Single irrigation with CHX (G9) also had significantly higher bond strength (P < 0.05) compared to G2, G3 and G7. After one year, G9 showed lower bond strength compared to their immediate group (P < 0.05). Conclusions: The irrigation protocols did not influence the immediate and mediate bond strengths of the self-adhesive resin cement and Na2S2O3 did not increase the bond strength of NaOCl-treated root dentin.
INTRODUCTION
Teeth with extensive loss of tooth structure require intra-radicular posts (1). Intracanal posts provide retention of the final restoration, thus allowing recovery of esthetics and function as well as long-term survival of the restored tooth (2). Fiber posts with biomechanical advantages, such as high flexural strength and modulus of elasticity similar to those of dentin, are preferred nowadays (3) because they minimize the transmission of stresses to the root walls and thus reduce the risk of root fracture (3, 4, 5). Furthermore, an individualized fiber post relined with composite resin allows better adaptation to the root canal shape (5), higher frictional retention and higher bond strength compared to non-relined fiberglass posts (6).
The application of irrigants to root canal during endodontic treatment may affect the dentin bonding, and these effects on dentin are not equal regarding all bonding systems (7, 8, 9). Sodium hypochlorite (NaOCl) has a long history of success as root canal irrigant in endodontics (10). Chlorhexidine gel 2% (CHX) has also been used an endodontic irrigant during root canal therapy and is reported to be as effective as sodium hypochlorite against microorganisms (9, 11). In addition, chlorhexidine has substantivity and relative absence of cytotoxicity (12, 13). As sodium hypochlorite and chlorhexidine are not capable of removing the smear layer, which may hamper the penetration of filling materials into the dentinal tubules, the use of chelating agents like EDTA is recommended (7, 14).
The immediate sealing of endodontically treated teeth right after treatment has been already established as a successful protocol in preventing early coronal leakage (9, 15, 16). Having in mind that NaOCl is a potent oxidizing agent resulting in oxidation of some components in the dentin matrix, which affects negatively the polymerization of adhesive materials (9, 15, 16, 17, 18) and therefore reduces the resin-dentin bond strength, studies have shown that the application of an antioxidant agent can revert the effect of NaOCl and increase the bond strength (16, 18, 19).
A previous study (16) evaluated sodium thiosulfate (Na2S2O3), a chemical agent with antioxidant properties, in an attempt to overcome the limitations of the sodium ascorbate, the most studied antioxidant but which presents short shelf life (16, 18, 19). The new alternative was effective in increasing the bond strength of a total etching adhesive system to coronal dentin treated with NaOCl. However, no study has yet evaluated the effect of
Na2S2O3 on resin cements to root dentin.
As self-adhesive cements have been shown to be a promising option to restore endodontically-treated teeth due to their technical simplicity and similar bond strength to dentin compared to conventional cements (7), the aim of this in vitro study was to investigate the effects of auxiliary chemical substances (i.e. 5,25% NaOCl, 2% CHX gel and 17% EDTA) and an antioxidant agent (i.e. 5% Na2S2O3) on immediate and mediate bond strengths of a self-adhesive resin cement to root dentin. The null hypotheses tested were: 1) immediate and mediate bond strengths of fiber posts would not be affected by endodontic irrigants and 2) sodium thiosulfate would not increase the bond strength of self-adhesive cement after irrigation protocol with NaOCl.
MATERIALS AND METHODS
Specimen Preparation
Ninety freshly extracted bovine incisors with similar root anatomy and fully developed apices were selected. Teeth were stored in 0.02% thymol solution for a maximum period of 1 month. Each tooth was decoronated 4 mm below the cemento-enamel junction perpendicularly to the longitudinal axis by using a double sided diamond disc (KG Sorensen, Barueri, SP, Brazil) under running water to obtain a uniform length of 14 mm. The pulp tissue was removed and the root canals were instrumented by using Largo burs # 6 (Maillefer, Ballaigues, VD, Switzerland). The apexes of the teeth were sealed with a temporary filling material (Coltosol®, Vigodent, Rio de Janeiro, RJ, Brazil). Roots were rinsed with 5 mL of saline solution to remove remaining debris before being randomly divided into nine groups (n = 10) according to the irrigation regimen, as described in Table 1. The substances used were 0.9% sodium chlorite (NaCl, pH=6.3), 5.25% NaOCl (pH = 12), 2% CHX gel (pH = 8. 0), 17% EDTA (pH = 7.3) and 5% Na2S2O3 (pH = 8.2), all being prepared by Drogal Pharmacy (Piracicaba, SP, Brazil).
Table 1. Irrigation Protocols According to the Experimental Groups
NaCl, 0.9% sodium chloride; NaOCl, 5.25% sodium hypochlorite; EDTA, 17% ethylenediaminetetraacetic acid; Na2S2O3, 5% sodium thiosulfate; CHX, 2% chlorhexidine. NaOCl and CHX used for 30 minutes were renewed every 5 minutes. EDTA was renewed every 1 minute and Na2S2O3 every 5 minutes when used for 10 minutes.
Intracanal Restoration with Anatomical Posts
The intracanal restoration with fiber post relined with resin composite was made with fiberglass post (Reforpost® #3, Angelus, Londrina, PR, Brazil) and composite resin (Filtek Z250®, B1, 3M ESPE, St Paul, MN, USA). After the irrigation protocols, the root canal walls were rinsed with 0.9% NaCl, dried with with Capillary Tips® (Ultradent, South Jordan, UT, USA) and lubricated with water soluble gel (Natrosol, Drogal Pharmacy, Piracicaba, SP, Brazil). The post was etched with 37% phosphoric acid (Condac 37®, FGM, Joinville, SC, Brazil) for 10 seconds in order to clean its surface and then rinsed and air-dried before application of a thin layer of bond (Adper Scotchbond Multi-purpose®, 3M). The adhesive was light-cured for 10 seconds per facet (i.e. buccal, palatal, mesial and distal) and the post was covered with resin composite and carefully inserted into the root canal. The excess of resin was removed before being light-cured for 5 seconds and the polymerization of the anatomical posts was completed outside the root canal, that is, 10 seconds per facet at 1200 mW/cm2 (Optilight Max, Gnatus, Ribeirão Preto, SP, Brazil). After copious water rinse Groups Irrigation protocols
1 NaCl (30 mL) for 30 minutes
2 NaOCl (30 mL) for 30 minutes followed by EDTA (1 mL) for 3 minutes and NaOCl (5 mL) for 1 minute
3 Similar to G2 followed by Na2S2O3 (1 mL) for 1 minute 4 Similar to G2 followed by Na2S2O3 (1 mL) for 10 minutes
5 CHX (3 mL) for 30 minutes, rinsing with NaCl followed by EDTA (1 mL) for 3 minutes
6 NaOCl (30 mL) for 30 minutes 7 EDTA (1 mL) for 3 minutes 8 Na2S2O3 (1 mL) for 10 minutes 9 CHX (3 mL) for 30 minutes
to remove the water soluble gel from the root canal, the specimens were dried with capillary tips (Ultradent) and paper points (Endopoints, Paraíba do Sul, RJ, Brazil). The self-adhesive resin cement (RelyX U200®, 3M ESPE) was mixed according to the manufacturer’s instructions and injected into the root canal with a syringe (Centrix®, DFL, Rio de Janeiro, RJ, Brazil). Next, the anatomical posts were placed inside the root canal, kept under finger pressure for 20 seconds and light-cured for 40 seconds (Optilight Max, Gnatus) on the occlusal facet.
The specimens of each group were randomly divided into two subgroups (n=5) according to their storage regime: 24 hours or 1 year of water storage.
Push-Out Test and Failure Pattern Analysis
Each root was horizontally sectioned by using water-cooled diamond saw (Isomet 2000, Buehler, Lake Buff, IL, USA) at slow-speed (i.e. 300 rpm) to produce slices of approximately 2 mm thickness. Four slices from each root canal were evaluated. The apical side of each slice was marked with an indelible marker. The push-out test was performed by using a universal testing machine (Emic, São José dos Campos, SP, Brazil) operating at a cross-speed of 1 mm/min. Loads were applied in an apical-to-cervical direction until a segment of the relined post was dislodged from the root slide. To express the bond strength in megapascals (MPa), the load causing failure was recorded in Newton (N) and divided by the area (mm2) of the post-dentin interface. The bonding area was calculated by using the formula π(R+r)[(h2+(R-r)2]0.5, where “R” represents the root canal radius in the coronal portion, “r” the root canal radius in the apical portion and “h” the thickness of the slice. These values were measured by using Leica Image Manager 50 software associated with a stereomicroscopic magnifying glass under 25x magnification (Leica MZ7.5, Meyer instruments, Houston, TX, USA), whereas the thickness of the slices were measured by using a digital caliper (Vonder, Curitiba, PR, Brazil).
After the push-out test, the failure modes of all specimens were evaluated under a stereomicroscope (Leica MZ7.5) at 40x magnification and two slices with representative failure were selected from each group and prepared for evaluation with scanning electron microscopy (SEM). The specimens were sputter-coated with gold by using a sputtering device
(Denton Vacuum Desk II, Cherry Hill, NJ, USA) before being observed by SEM (JSM-5600LV, JEOL Ltd., Akishima, Tk, Japan). The failure modes were classified as Bitter et al. (2009): 1) cohesive in post; 2) adhesive failure between post and resin; 3) adhesive failure between cement and dentin, and 4) mixed failure.
The mean and standard deviation values of bond strength were calculated, and data were analyzed by using two-way ANOVA (irrigation protocol, time) and Tukey-Kramer test for post-hoc comparisons (α=0.05). Statistical analysis was performed by using the SAS software (SAS Institute, Cary, NC, 2010, USA).
RESULTS
Table 2 shows the mean and standard deviation of the bond strength values for the experimental groups, with two-way ANOVA revealing significant differences between the groups (P < 0.05). As for the groups of the immediate test, single irrigations of Na2S2O3 (G8) and CHX (G9) produced significant higher bond strength (P < 0.05) compared to groups G5 and G6 as well as to groups G2, G3, G5, G6 and G7, respectively. After 1-year storage, there was no statistical difference between the groups (P > 0.05). By comparing the immediate results to mediate ones, only G9 had a significant decrease (P < 0.05) in the long-term bond strength. As for immediate and mediate groups, no statistical difference (P > 0.05) was found in the experimental groups in relation to the negative control. Na2S2O3 did not increase the bond strength of self-adhesive cement after irrigation protocols with NaOCl.
Figure 1 shows the failure modes observed in each group. Adhesive failure between cement and dentin and mixed failure were frequently observed in the groups of the immediate test, whereas adhesive failure between dentin and resin cement was predominant in the groups of the mediate test.
Table 2. Mean (Standard Deviation) Values of Bond Strength (Mpa) to Dentin According to Experimental Conditions
NaCl, 0.9% sodium chloride; NaOCl, 5.25% sodium hypochlorite; EDTA, 17% ethylenediaminetetraacetic acid; Na2S2O3, 5% sodium thiosulfate; CHX, 2% chlorhexidine. Different uppercase letters in columns and lowercase letters in rows indicate statistical significant difference (P < 0.05).
Figure 1. Failure Mode Distribution in the Experimental Groups
Groups Irrigation Protocols 24 hours 1 year
1 NaCl 7.97(1.50)A,B,C,a 8.08(1.0) A,a
2 NaOCl + EDTA + NaOCl 6.73(2.41)B,C,a 8.03(2.40)A,a
3 Group 2 + Na2S2O3 1 min 6.41(0.92) B,C,a 7.49(0.95)A,a 4 Group 2 + Na2S2O3 10 min 8.14(2.23)A,B,C,a 7.00(0.90)A,a
5 CHX + EDTA 4.55(1.34)C,a 5.05(2.13)A,a
6 NaOCl 5.27(1.78)C,a 6.63(1.01) A,a
7 EDTA 6.70(1.47)C,B,a 6.46(1.21) A,a
8 Na2S2O3 9.70(1.34)B,A,a 8.58(0.77)A,a 9 CHX 10.93(1.19)A,a 5.44(2.12)A,b 0 20 40 60 80 100
24 h 1 year 24 h 1 year 24 h 1 year 24 h 1 year 24 h 1 year 24 h 1 year 24 h 1 year 24 h 1 year 24 h 1 year G1 G2 G3 G4 G5 G6 G7 G8 G9 P er ce n ta ge s Experimental groups
DISCUSSION
The immediate results indicated that, when self-adhesive resin cement was used, irrigation with CHX alone (G9) produced mean values significantly higher than those observed in the other groups, except negative control (G1), group with Na2S2O3 for 10 minutes after use of NaOCl/EDTA (G4) and positive control with Na2S2O3 (G8). However, G9 was the only group showing significant reduction in the bond strength over time. Na2S2O3 did not affect the mediate and immediate bond strengths of NaOCl-treated dentin.
The reason why the bond strength of self-adhesive resin cement after single irrigation with CHX was higher than that of the groups with NaOCl, whether associated or not with EDTA, is that NaOCl and EDTA are able to promote structural alterations in the dentin. Reductions in both calcium and phosphorus levels (20) and in the mechanical properties of dentin, such as elastic modulus, flexural strength and microhardness (21), were reported after irrigation of root canals with NaOCl and/or EDTA (22, 23), which can contribute to a decrease in the micromechanical interaction between resins and dentin (9, 16, 18, 24). In addition, the irrigation regimen of NaOCl/EDTA/NaOCl can interact synergistically (25) and cause a progressive dissolution of peritubular and intertubular dentin, thus increasing the negative effects on adhesion (18, 26). Besides, NaOCl causes degradation and structural disorganization of collagen (27) and forms protein-derived radicals (28), which reduces the bond strength due to the inhibition of interfacial polymerization of methacrylate-based resin cements (9, 16, 18, 19).
Similarly, the irrigation protocol of G5 using EDTA after CHX produced a significant decrease in the immediate bond strength compared to G9. These lower mean values may also be related to the removal of calcium ions from dentin by the chelating agent, thus compromising the chemical interactions between hydroxyapatite, functional monomers and phosphoric acid esters of the self-adhesive resin cement used (7, 29). Secondary retention promoted by chemical interactions at the bond interface of this cement has been described and confirmed as being more crucial than the ability to hybridize the dentin (29). On the other hand, combining the use of CHX/EDTA with the capacity to clean and demineralize dentin surfaces was effective in maintaining the mediate adhesion values by retention mechanisms of resin-based sealers to root canal walls (30, 31).
In contrast, CHX alone does not cause changes in the organic and inorganic matrices of dentin and it is not an oxidizing agent (9, 24), which contributed to a better
immediate adhesion. However, the single irrigation with CHX failed to maintain the high values of mediate bond strength over time. Our results are in accordance with a study reporting no effect on the shear bond strength of self-adhesive resin cement after 24 hours, but a decrease after 1-year storage in water (32). It is known that chlorhexidine is a non-specific inhibitor of the matrix metalloproteinase (MMP) activity in dentin, thus being useful in preventing collagen deterioration of the bonding interface in the long-term (24, 33). Nevertheless, in the current study, it is believed that the effect of CHX on MMP has not occurred as the RelyX U200 cement was applied directly on the smear layer-covered dentin. It was suggested that there was only an interaction between CHX and dentin surface rather than an exposure to collagen in the underlying layer.
Additionally, CHX has hydrophilic characteristics and binds to hydroxyapatite by adsorption, allowing substantivity (24). The RelyX U200 cement contains a high concentration of acidic hydrophilic monomers which result in more permeability to water (33). The properties of CHX associated with the hydrophilicity of resin cement may have allowed greater water sorption within the hybrid layer, which resulted in the plasticizing of the resin cement (33). This plasticizing effect can compromise the mechanical properties of the cement (33, 34) and may have been the cause of decrease in the bond strength after 1 year in water storage, as seen in G9.
When this study was performed, it was hypothesized that NaOCl would have negative effects on the adhesion of the self-adhesive resin cement and Na2S2O3 would neutralize the oxidizing effects through redox reaction, thus increasing the bond strength. However, no effect on the bond strength of RelyX U200 was found in NaOCl groups, whether associated or not with EDTA, after 24 hours or after 1 year. Thus, the second null hypothesis was confirmed.
Sodium thiosulfate has been used in many in vivo studies in Endodontics to neutralize NaOCl during microbiological analysis due to its biocompatibility (16, 35). It was also used in an in vitro study (16), showing to be successful in increasing the bond strength to NaOCl-treated dentin when used at a concentration of 5% for 10 minutes. Although this effect in increasing significantly the resin cement-dentin bonding was not demonstrated in this study, it is in accordance with a previous study (16) in which 5% Na2S2O3 was applied for 10 minutes in the immediate test, resulting in higher bond strength compared to the group with Na S O for 1 minute and negative control, but with no statistical difference between them. In
fact, the higher mean values can also be evidenced by the higher percentage of mixed failures when Na2S2O3 was used for 10 minutes.
In conclusion, it has been shown that the several irrigation protocols used in endodontic therapy did not affect the immediate and mediate bond strengths of the self-adhesive resin cement and that Na2S2O3 was not required to neutralize the oxidizing effect of NaOCl on the bonding of resin cement to root dentin.
Acknowledgements
This study was supported by CNPQ/Brazil according to grant protocol number 2014/ 141129.
References
1. Morgano SM. Restoration of pulpless teeth: application of traditional principles in present and future contexts. J Prosthet Dent 1996;75:375-80.
2. Ebert J, Leyer A, Günther O, et al. Bond strength of adhesive cements to root canal dentin tested with a novel pull-out approach. J Endod 2011;37:1558-61.
3. Schmitter M, Rammelsberg P, Gabbert O, Ohlmann B. Influence of clinical baseline findings on the survival of 2 post systems: a randomized clinical trial. Int J Prosthodont 2007; 20:173-8.
4. Cheung W. A review of the management of endodontically treated teeth. Post, core and the final restoration. J Am Dent Assoc 2005;136:611-9.
2011;1:77-83.
6. Grandini S, Goracci C, Monticelli F, Borracchini A, Ferrari M. SEM evaluation of the cement layer thickness after luting two different posts. J Adhes Dent 2005;7:235-40.
7. Simões TC, Luque-Martinez Í, Moraes RR, Sá A, Loguercio AD, Moura SK. Longevity of Bonding of Self-adhesive Resin Cement to Dentin. Oper Dent 2016;41:E64-72.
8. Stevens CD. Immediate shear bond strength of resin cements to sodium hypochlorite-treated dentin. J Endod 2014;40:1459-62.
9. Santos JN, Carrilho MR, De Goes MF, et al. Effect of chemical irrigants on the bond strength of a self-etching adhesive to pulp chamber dentin. J Endod. 2006;32:1088–90.
10. Jungbluth H, Marending M, De-Deus G, Sener B, Zehnder M. Stabilizing sodium hypochlorite at high pH: effects on soft tissue and dentin. J Endod 2011;37:693-6.
11. Zehnder M. Root canal irrigants. J Endod 2006;32:389–98.
12. Yesilsoy C, Whitaker E, Cleveland D, Phillips E, Trope M. Antimicrobial and toxic effects of established and potential root canal irrigants. J Endod 1995;21:513–5.
13. White RR, Hays GL, Janer LR. Residual antimicrobial activity after canal irrigation with chlorhexidine. J Endod 1997;23:229–31.
14. Neelakantan P, Subbarao C, Subbarao CV, De-Deus G, Zehnder M. The impact of root dentine conditioning on sealing ability and push out Bond strength of epoxy resin root canal sealer. Int Endod J 2011;44:491–8.
15. Galvan RR, West LA, Liewehr FR, Pashley DH. Coronal microleakage of five materials used to create an intracoronal seal in endodontically treated teeth. J Endod 2002;28:59–61.
16. Pimentel Corrêa AC, Cecchin D, de Almeida JF, Gomes BP, Zaia AA, Ferraz CC. Sodium Thiosulfate for Recovery of Bond Strength to Dentin Treated with Sodium Hypochlorite. J Endod 2016;42:284–8.
17. Rueggeberg FA, Margeson DH. The effect of oxygen inhibition on an unfilled/filled composite system. J Dent Res 1990;69:1652–8.
18. Vongphan N, Senawongse P, Somsiri W, Harnirattisai C. Effects of sodium ascorbate on microtensile bond strength of total-etching adhesive system to NaOCl treated dentine. J Dent 2005;33:689–95.
19. Weston CH, Ito S, Wadgaonkar B, Pashley DH. Effects of time and concentration of sodium ascorbate on reversal of NaOCl-induced reduction in bond strengths. J Endod 2007;33:879– 81.
20. Ari H, Erdemir A. Effect of endodontic irrigant solutions on mineral content of root canal dentin using ICP-AES technique. J Endod 2005;31:187–9.
21. Sim TPC, Knowles JC, Ng Y-L, Shelton J, Gulabivala K. Effect of sodium hypochlorite on mechanical properties of dentine and tooth surface strain. Int Endod J 2001;34:120–32.
22. Marending M, Paqué F, Fischer J, Zehnder M. Impact of irrigant sequence on mechanical properties of human root dentin. J Endod 2007;33:1325–8.
23. Zhang K, Kim YK, Cadenaro M, et al. Effects of different exposure times and concentrations of sodium hypochlorite/ethylenediaminetetraacetic acid on the structural integrity of mineralized dentin. J Endod 2010; 36: 105–9.
24. Gomes BPFA, Vianna ME, Zaia AA, Almeida JFA, Souza-Filho FJ, Ferraz CCR. Chlorhexidine in endodontics. Braz Dent J 2013;24:89–102.
25. Mai S, Kim YK, Arola DD, et al. Differential aggressiveness of ethylenediamine tetraacetic acid in causing canal wall erosion in the presence of sodium hypochlorite. J Dent 2010;38:201-6.
26. Nikaido T, Takano Y, Sasafuchi Y, Burrow MF, Tagami J. Bond strengths to endodontically-treated teeth Am J Dent1999;12:177–80.
27. Moreira DM, de Andrade Feitosa JP, Line SR, Zaia AA. Effects of reducing agents on birefringence dentin collagen after use of different endodontic auxiliary chemical substances. J Endod 2011;37:1406-11.
28. Hawkins CL, Davies MJ. Hypochlorite-induced oxidation of proteins in plasma: for- mation of chloramines and nitrogen-centered radicals and their role in protein fragmentation. Biochem J 1999;340:539–48.
29. Bitter K, Paris S, Pfuertner C, Neumann K, Kielbassa AM. Morphological and bond strength evaluation of different resin cements to root dentin. Eur J Oral Sci 2009;117:326-33.
30. Kokkas AB, Boutsioukis ACh, Vassiliadis LP, Stavrianos CK. The influence of the smear layer on dentinal tubule penetration depth by three different root canal sealers: an in vitro study. J Endod 2004;30:100-2.
31. Vilanova WV, Carvalho-Junior JR, Alfredo E, Sousa-Neto MD, Silva-Sousa YT. Effect of intracanal irrigants on the bond strength of epoxy resin-based and methacrylate resin-based sealers to root canal walls. Int Endod J 2012;45:42-8.
32. Lambrianidis T, Kosti E, Boutsioukis C, Mazinis M. Removal efficacy of various calcium hydroxide/chlorhexidine medicaments from the root canal. Int Endod J 2006;39:55-61.
33. Shafiei F, Memarpour M. Effect of chlorhexidine application on long-term shear bond strength of resin cements to dentin. J Prosthodont Res 2010;54:153–8.
34. Sauro S, Pashley DH, Montanari M, et al. Effect of simulated pulpal pressure on dentin permeability and adhesion of self –etch adhesives. Dent Mater 2007;23:705–13.
35. Gomes BP, Martinho FC, Vianna ME. Comparison of 2.5% sodium hypochlorite and 2% chlorhexidine gel on oral bacterial lipopolysaccharide reduction from primarily infected root canals. J Endod 2009;35:1350–3.
2.2 Artigo: Effect of Endodontic Irrigants, Antioxidant Agents, and Artificial Aging on Bond Strength of a Self-Adhesive Resin Cement to Root Dentin
Abstract
Introduction: This study investigated the effects of root dentin pretreatment with endodontic irrigants and antioxidant agents on the bond strength of a self-adhesive resin cement after thermomechanical cycling (TMC). Methods: Fifty single-rooted premolars were
endodontically treated. After post space preparation, the root canals were divided into five
groups (n = 10) according to the final rinse protocol: G1 – distilled water (DW); G2 – 5.25% sodium hypochlorite (NaOCl); G3 and G4 – similar to G2 followed by 10% sodium thiosulfate (Na2S2O3) or 10% sodium ascorbate (SA) for 1 minute, respectively; and G5 – 2% chlorhexidine gel (CHX). Fiberglass posts were then luted with RelyX U200 (3M ESPE, St Paul, MN, USA). After cementation, half of the specimens (n = 5) were tested after 24 hours and the other half submitted to TMC. All roots were sectioned, producing three 1-mm-thick slices for each third. The push-out test was performed. The data in MPa were analyzed by ANOVA and Tukey-Kramer tests (α = 0.05). Results: There was no difference between irrigation protocols (P > 0.05) and negative control before and after TMC, although pretreatment with DW (G1) and NaOCl (G2) increased (P < 0.05) the bond strength to the coronal third after TMC. The middle third of the root dentin showed significantly higher
values (P < 0.05) for adhesion than did the coronal third of G1, G3, and G4 in the immediate
test, and of G4 in TMC. Conclusions: Endodontic irrigants did not compromise the bond
strength of self-adhesive resin cement after aging. Antioxidant agents did not increase the adhesion of NaOCl-treated root dentin after TMC.
Key Words: Root canal dentin, pretreatment, antioxidant agent, thermomechanical cycling, push-out bond strength
Introduction
The association of fiberglass post with resin cement has improved bond integrity and stability of endodontic post cementation due to the better performance of mechanical properties and biological advantages of these materials, guaranteeing the long-term success of endodontically treated teeth (1, 2). Nevertheless, luting of posts inside the root canal is still unpredictable and also a challenge because of extremely high C-factor in the root canal (3), limited moisture control, and lack of visibility (4, 5, 6). Furthermore, the presence of debris and remnants of sealer and gutta-percha may hamper the bonding to the root canal dentin (5, 7).
Sodium hypochlorite (NaOCl) has a long history as successful irrigant in endodontics because of its dissolving capacity and its broad antimicrobial spectrum (9). However, it may affect dentin bonding negatively because it causes alterations on its surface (10, 11, 12). Chlorhexidine gel (CHX) has been recommended as an auxiliary chemical substance for root canal treatment owing to its antimicrobial activity, substantivity, and relative absence of cytotoxicity (10, 13, 14). CHX has been shown not to compromise the bond strength of self-adhesive resin cement (1, 4, 5) because it does not affect the organic and inorganic matrix of dentin (15) and inhibits dentinal collagenolytic matrix metalloproteinases (1, 10, 13).
On the other hand, the self-adhesive resin cement manufacturer just recommends the use of 2.5 to 5.25% NaOCl as the only chemical substance that can be applied immediately after post space preparation. Consequently, it would be interesting to confirm the application of NaOCl and to evaluate the effects of CHX on the bond strength of fiber posts luting with self-adhesive resin cement, mainly after aging.
In the literature, several studies have documented the decrease of bond strength to dentin after its exposure to NaOCl; however, after the use of antioxidant agents to neutralize the effects of NaOCl, the strength values have increased (11, 16, 17, 18). A previous study (11) proposed the use of sodium thiosulfate (Na2S2O3), a chemical agent with antioxidant properties, as an alternative to overcome the limitations of sodium ascorbate (SA), the most widely studied antioxidant, which has short shelf life and high costs. The new alternative was effective in increasing the bond strength to NaOCl-treated pulp chamber dentin.
Therefore, the aim of the present study was to analyze the effects of different pretreatment protocols using 5.25% NaOCl, 2% CHX gel, and antioxidant agents (10% sodium thiosulfate and 10% sodium ascorbate) on the bond strength of fiber posts luted with a self-adhesive resin cement in the immediate test or after thermomechanical cycling (TMC). The null hypothesis was that the bond strength of a self-adhesive resin cement would not be affected by pretreatment, root location or aging.
Materials and Methods Sample preparation
Fifty single-rooted premolars with straight roots, mature root apices were used in this study after the approval of the Ethical Committee of the Piracicaba Dental School, SP, Brazil. The crowns were removed at the cementoenamel junction by using a double-sided diamond disc (KG Sorensen, Barueri, SP, Brazil) under running water, and root canal preparations were performed at a working length when the instrument reached the apical foramen.
First, a size 10 K-file (Dentsply Maillefer, Ballaigues, VD, Switzerland) was used to verify the patency of the canals and to determine root canal length. The root canal and apical region were enlarged with a single file (R25 #25.08) using the RECIPROC® technique (VDW, Munich, BY, Germany) according to the manufacturer’s recommendations. Irrigation was performed using 1 mL of 5.25% NaOCl solution (Drogal, Piracicaba, SP, Brazil) after instrumentation of each root third. Thereafter, 5 mL of distilled water was used to remove the NaOCl. The teeth were dried with paper points (Endopoints, Paraíba do Sul, RJ, Brazil), obturated with AH Plus sealer® (Dentsply, Petrópolis, RJ, Brazil) and gutta-percha (Odous, Belo Horizonte, MG, Brazil), and stored in water.
After 24 hours of incubation at 37o C, the gutta-percha was removed and a #5 Largo bur (Dentsply Maillefer) was used to standardize the preparation of the fiber post space. The depth of the post space preparation was 8 mm, leaving at least 4 mm of gutta-percha inside the canal to guarantee an apical seal. The post space was checked for cleanliness using an operating microscope (Alliance, São Paulo, SP, Brazil). The specimens were randomly divided into five groups (n = 10) and irrigation was performed following the
protocol for each group: G1 (control) – 5 mL of distilled water (DW) for 1 minute; G2 – 5mL of 5.25% NaOCl for 1 minute; G3 and G4 – similar to G2 followed by 5 mL of 10% sodium thiosulfate (Drogal) or 5 mL of a freshly prepared solution of 10% sodium ascorbate (Sigma Aldrich, St. Louis, MO, USA), respectively for 1 minute; and G5 – 1 mL of 2% CHX gel for 1 minute. All root canals were then irrigated with 5 mL of distilled water to remove the remaining solutions and dried with paper points (Endopoints).
The posts, 1.5-mm diameter fiberglass-reinforced epoxy system (Reforpost® # 3, Angelus, PR, Brazil), were cleaned with ethanol, dried, and silanized with Silano® (Angelus) for 1 minute. Subsequently, the fiber posts were placed in each group using a self-adhesive resin cement (RelyX U200®, 3M ESPE, St Paul, MN, USA), according to the manufacturer’s instructions. The resin cement was mixed and a thin layer was applied to the post and into the root canal with Centrix Needle tubes® (DFL, Rio de Janeiro, RJ, Brazil). The posts were placed inside the root canal and kept there under finger pressure. The excess cement was removed and the system was light-cured at 1,200 mW/cm2 (Optilight LD MAX LED, Gnatus, Ribeirão Preto, SP, Brazil) for 40 seconds on occlusal surface.
Half of the specimens in each group (n = 5) were submitted to push-out test 24 hours after fiber post luting. The other half was subjected to thermomechanical cyclic loads after crown preparation.
Crown preparation and thermomechanical cyclic loading
The coronal portion was built using Filtek Z250 B1 (3M ESPE) composite resin around the post. For standardization of crown size, the same prefabricated acetate matrix was used to position the last layers. All specimens were finished with a diamond bur (No. 3216; KG Sorensen) mounted on a high-speed handpiece with water spray. Rectangular stops with a central concavity were made on the occlusal surface of the patterns to locate and stabilize the metal tip during load testing.
The teeth were embedded in polystyrene resin up to 3 mm below the cervical portion using a circular PVC matrix with 25 mm in diameter × 20 mm in height (Tigre, São
Paulo, SP, Brazil). A polyether molding material (Impregum Soft, 3M ESPE) was used to simulate the artificial periodontal ligament. The set (tooth, matrix, and resin) remained immobile for 72 hours to ensure resin setting. All specimens were exposed to 250,000 loading cycles at 30 N. The force was applied to the occlusal surface of the crowns at a frequency of 2.6 Hz. Thermal cycling was performed simultaneously by 30-second water filling and 15-second drainage steps, with temperatures ranging between 5 and 55 °C (ER 37000 Plus; Erios, São Paulo, SP, Brazil). The mechanical loading pattern was equivalent to 1-year stress of clinical function (19). The 30 N force mimicked previously measured occlusal forces that occur during mastication and swallowing with restored dentitions (20).
Push-out Assessment
Each root was horizontally sectioned with a slow-speed, water-cooled diamond saw (Buehler Isomet 2000, Lake Bluff, IL, USA) to produce slices of approximately 1 mm in thickness for each root region (coronal and middle). Seven slices were obtained from each root canal. The first coronal slice was discarded. Thus, the first three slices were considered the coronal third and the next three slices the middle third.
The push-out test was performed by applying a 1mm/min load at the apex toward the crown until the fiber post was dislodged from the root slice. To express the bond strength in megapascals (MPa), the load at failure recorded in Newton (N) was divided by the area (mm2) of the post-dentin interface. The formula π (R+r)[(h2 +(R–r)2 ]0.5 was used to calculate the bonding area, where “R” represents the coronal root canal radius, “r” is the apical root canal radius, and “h” is the slice thickness. These values were measured using the Leica Image Manager IM 50 software associated with a stereomicroscopic magnifying glass at a 25x magnification (Leica MZ7.5, Meyer instruments, Houston, TX, USA), and the thickness of the slices was measured using a digital caliper (Vonder, Curitiba, PR, Brazil).
After the push-out test, the failure modes of all specimens were evaluated under a stereomicroscope (Leica MZ7.5) at a 40x magnification, and two slices with representative failure from each group was prepared and analyzed by scanning electron microscopy (SEM). The specimens were sputter-coated with gold in a Denton Vacuum Desk II Sputtering device (Denton Vacuum, Cherry Hill, NJ) and observed by SEM (JSM-5600LV, JEOL Ltd.,
Akishima, Tk, Japan). The failure modes were classified as follows: (1) cohesive in post; (2) adhesive failures between post and cement; (3) adhesive failures between cement and dentin, and (4) mixed failures.
The means and standard deviations of bond strength were calculated. Three-way ANOVA was performed using the irrigation protocol, root third, and TMC. Multiple comparison post-hoc analysis was made using the Tukey-Kramer test, with the significance level set at α = 0.05. The statistical analysis was performed using the SAS software (SAS Institute, Cary, NC, 2010, USA).
Results
The means and standard deviations are presented in Table 1. The ANOVA revealed significant interaction among the three factors in this study (P = 0.0131). The statistical analysis indicated that the root third and TMC significantly influenced bond strength (P < 0.05); however, there was no statistical difference in adhesion in the final rinse protocols (P = 0.5867) compared to the negative control. In the immediate test, the middle third of G4 exhibited a higher bond strength (P < 0.05) than that of G2 (NaOCl). By comparing the middle thirds, those of G1, G3, and G4 in the immediate test and of G4 in the
TMC test showed significantly higher values (P < 0.05) for bond strength than their coronal
thirds. After TMC, the coronal thirds of G1 and G2 presented higher bond strength (P < 0.05)
compared with their coronal thirds in the immediate test. Antioxidant agents did not influence the adhesion of NaOCl-treated root dentin after TMC.
Table 2 shows the failure modes of each group. The mixed failures were predominant in all groups after TMC and in most groups of the immediate test, except for groups 2 and 3, in which the adhesive failure at the resin cement-dentin interface was more pronounced.
Table 1. Mean (Standard Deviation) of Bond Strength (Mpa) to Dentin According to Pretreatment, Root Third and Aging
Uppercase letters indicate comparisons among columns and lowercase letters show comparison in the rows for immediate test and for the test after TMC. Different uppercase letters in the columns and different lowercase letters in the rows indicate a statistically significant difference (P < 0.05). * shows statistical significant difference in the rows after TMC (P < 0.05).
Figure 1. Failure Mode Distribution (%) in the Experimental Groups (n=30)
Groups-Pretreatment Immediate Thermomecanical Cycling (TMC)
Coronal Middle Coronal Middle
1-DW 6.58(2,37)A,a* 15.17(1.94)A,B,b 15.54(0.86)A,a* 13.60(2.95) A,a 2-NaOCl 4.35(1,32)A,a* 9.79(1.59)A,a 17.40(3.99) A,a* 15.27(4.37) A,a 3- NaOCl + Na2S2O3 6.34(1.13)A,a 12.51(1.99)A,B,b 14.09(6.15) A,a 14.73(4.20) A,a 4-NaOCl + SA 8.54(2.94)A,a 18.10(1.72)B,b 9.67(3.12) A,a 16.60(4.49) A,b 5-CHX 7.65(3.27)A,a 13.08(3.19)A,B,a 9.98(3.7) A,a 15.73(3.81) A,a
0 20 40 60 80 100 120
24 h A&er TMC 24 h A&er TMC 24 h A&er TMC 24 h A&er TMC 24 h A&er TMC
1 2 3 4 5 P er ce n ta ge s Groups
Discussion
In the present study, the adhesion of fiber posts to root dentin luted with a self-adhesive resin cement differed significantly in the root thirds and after TMC. However, the application of the various irrigation protocols before post cementation did not alter the bond strength of RelyX U200. Therefore, the null hypothesis was partially rejected.
Irrigation of the post space preparation using CHX did not affect the bond strengths of any of the experimental conditions investigated in this study compared with the control group. This is in accordance with previous studies that showed CHX did not negatively affect immediate and long-term bond strength of self-adhesive resin cement in post cementation, irrespective of root third (4, 5, 21). Thus, the results of the present study indicate that the use of CHX for final rinse is as effective as NaOCl and also confirm that the application of the latter improves adhesion after aging, as reported by the RelyX U200 manufacturer.
The susceptibility of adhesive materials to NaOCl was documented previously (10, 11, 12, 15, 16, 17, 18), demonstrating that the oxidizing effect, proteolytic activity, and alterations in the mineral content of dentin (15) caused by NaOCl may compromise the bond strength of resin materials. In this study, the negative effect of NaOCl on self-adhesive resin cement was negligible because the bond strength of NaOCl-treated dentin (G2) and of dentin treated solely with distilled water (G1) had no statistical difference in the immediate test and after aging, regardless of root location.
Several studies have shown improvements of dentin bond strength after NaOCl exposure by application of antioxidant agents (11, 16, 17, 18). In this study, no final irrigation protocol followed by the use of SA or Na2S2O3 differed from the control. However, in the middle third in the immediate test, the use of sodium ascorbate after NaOCl produced a significantly higher bond strength than NaOCl alone, corroborating the findings of previous investigations (11, 16, 17). Sodium ascorbate was assessed in various in vitro research studies and proved to increase the bond strength of NaOCl-treated dentin (17, 23).
The bond strength of resin cement used was influenced by location inside root canal. In this study, the middle third of the root dentin presented significantly higher mean
values for adhesion than the coronal part of negative control, Na2S2O3 andSA groups in the
immediate test and of the SA group after TMC test. This finding is at odds with previous
