UNIVERSIDADE FEDERAL FLUMINENSE FACULDADE DE ODONTOLOGIA
ESTABILIDADE DA UNIÃO ENTRE SUPERFÍCIES DE CERÂMICA Y-TZP VITRIFICADAS E UM CIMENTO RESINOSO AUTOADESIVO
Niterói 2017
FACULDADE DE ODONTOLOGIA
ESTABILIDADE DA UNIÃO ENTRE SUPERFÍCIES DE CERÂMICA Y-TZP VITRIFICADAS E UM CIMENTO RESINOSO AUTOADESIVO
EDUARDO VICTOR MAROUN
Dissertação apresentada à Faculdade de Odontologia da Universidade Federal Fluminense, como parte dos requisitos para obtenção do título de Mestre, pelo Programa de Pós-Graduação em Odontologia.
Área de Concentração: Dentística
Orientador: Prof. Dr. Eduardo Moreira da Silva
Niterói 2017
M356 Maroun, Eduardo Victor
Estabilidade da união entre superfícies de cerâmica Y-TZP vitrificadas e um cimento resinoso autoadesivo / Eduardo Victor Maroun; orientador: Prof. Dr. Eduardo Moreira da Silva – Niterói: [s.n.], 2017.
36 f.: Il.
xxInclui tabelas
xxDissertação (Mestrado em Dentística) – Universidade
Federal Fluminense, 2017.
xxBibliografia: f. 32-35
1.Cerâmicas Y-TZP 2.Vitrificação 3.Ciclagem
sssstermomecânica I.Silva, Eduardo Moreira da [orien.] II.Título CDD 617.675
BANCA EXAMINADORA
Prof. Dr. Eduardo Moreira da Silva
Instituição: Universidade Federal Fluminense - UFF
Decisão: _________________________Assinatura: ________________________
Profa. Dra. Renata Garcia Fonseca
Instituição: Universidade Estadual Paulista - UNESP
Decisão: _________________________Assinatura: ________________________
Prof. Dr. Paulo Francisco Cesar
Instituição: Universidade de São Paulo - USP
DEDICATÓRIA
Em memória de meu querido Pai, Jamil Eduardo Maroun, pelos ensinamentos da vida e pelas nossas conversas sobre odontologia. “Ora et Labora” – Regra de São Bento.
AGRADECIMENTOS
À minha querida Mãe, por toda ajuda e dedicação ao longo do ano, sem o qual nunca conseguiria finalizar esta etapa da minha vida.
Ao meu irmão Michel, pelo companheirismo e descontração que foram fundamentais no dia a dia em meio a uma turbulência de estudos e responsabilidades a serem cumpridas. Ao meu irmão Jamil, meu grande exemplo de vitória, inteligência e integridade.
Ao meu orientador Prof. Eduardo Moreira da Silva, primeiramente, pela compreensão e incentivos ao longo desses 2 anos que me permitiram conciliar o mestrado com a vida militar. Por me apresentar um novo mundo na Odontologia, escondido nas estruturas químicas dos materiais dentários e em suas propriedades, dentro do qual demonstrou um inesgotável conhecimento com o qual fez questão de nos lecionar de forma tão estimulante. Não esquecendo de mencionar o dia que me aconselhou a não viajar para apresentação no GBMD 2015, que ocorreu um dia antes da prova da Marinha, me evitando do risco de chegar atrasado ou até faltar, e no final, fez toda a diferença para minha aprovação.
Aos professores da Pós Graduação em Dentística da UFF, pelos ensinamentos e cobranças por trabalhos de qualidade que foram fundamentais para enriquecerem nosso aprendizado dentro da área de Dentística e Materiais Dentários.
Ao Prof. Alexandre Elias, por não só ter cedido a matéria prima para a pesquisa, mas pela atenção e dedicação em sanar as dúvidas ao longo da pesquisa, sempre disponível para contato. Da mesma forma, o Prof. Luciano que também muito me auxiliou na conclusão do trabalho.
Aos meus eternos professores Reinaldo, Irma, Fernanda Pitta e Cristiane, que serão sempre meus exemplos de ótimos profissionais e por me incentivarem a buscar a progressão acadêmica, além de reascenderem em mim a vontade de lecionar. Meus agradecimentos, também, à toda equipe da Dentística e demais militares da OCM.
Aos meus amigos de turma do Mestrado, que tornaram os dias de laboratório e seminários mais fáceis pelo coleguismo e descontração. Em especial, ao meu amigo Renato Paiva pela amizade e auxílio que foram de extrema importância na conclusão da pesquisa, ao José Maria que sempre safava a onça no laboratório, ao técnicos do LABA que foram muito eficientes no auxílio nos ensaios de microtração, e à minha companheira Caroliny Mello, que foi o meu estímulo para chegar cedo no laboratório às quartas-feiras e, hoje, muito me apoia nos desafios da vida.
RESUMO
Maroun EV. Estabilidade da união entre superfícies de cerâmica Y-TZP vitrificadas e um cimento resinoso autoadesivo. [Dissertação]. Niterói: Universidade Federal Fluminense, Faculdade de Odontologia; 2017.
O objetivo deste estudo foi avaliar a estabilidade da união entre cerâmica de ZrO2 tetragonal policristalina estabilizada com ítrio (Y-TZP) vitrificada e um cimento resinoso autoadesivo. Foram confeccionados 50 blocos de cerâmica, sendo 40 de uma cerâmica Y-TZP (Lava® Frame) e 10 de um vidro ceramizado - EM (IPS e.max® CAD). Os blocos sinterizados da cerâmica Y-TZP foram divididos em quatro grupos (n=10) em função do tratamento de superfície: AS (sinterizado), SB (jateamento com partículas de Al2O3 de 30 µm), LG (vitrificação com glaze de baixa fusão, VITA Akzent® Plus + condicionamento com ácido fluorídrico a 10% por 1 min) e HC (vitrificação com liner de baixa fusão, HeraCeram® Zirkonia, + condicionamento com ácido fluorídrico a 10% por 1 min). Os blocos fundidos do vidro ceramizado foram condicionados com ácido fluorídrico a 10% por 20 s. Após silanização por 1 min, blocos de compósito (Z250®) foram cimentados nas superfícies de cerâmica com um cimento resinoso autoadesivo (Rely X U200®). Metade dos blocos de cada grupo foram cortados em palitos e submetidos a teste de microtração após armazenagem em água destilada a 37°C / 24 h, e a outra metade após ciclagem mecânica (1.200.000 ciclos / 98 N / 2,5 Hz), corte dos palitos, e ciclagem térmica (5.000 ciclos térmicos / 5 C - 55 C / 30 s). Os dados foram analisados através de análise de variância de um fator, teste de Tukey HSD e teste t de Student (=0.05). Após 24 h, os grupos EM (37.3 MPa) e LG (30.6 MPa) apresentaram valores de resistência de união similares e estatisticamente superiores aos demais grupos, enquanto o menor valor foi apresentado pelo grupo AS (7.1 MPa), (p < 0,05). Após a termociclagem, o maior valor de resistência de união foi apresentado pelo grupo EM (34.8 MPa), seguido do grupo LG (24.1 MPa), (p < 0,05). Todos os blocos do grupo AS sofreram ruptura espontânea durante a termociclagem. Somente os grupos EM e LG mantiveram a estabilidade da resistência de união. Concluiu-se que a vitrificação da superfície da cerâmica Y-TZP pode ser um protocolo capaz de manter a estabilidade da adesão ao cimento auto-adesivo.
Palavras-chaves: Cerâmicas Y-TZP, vitrificação, resistência de união, ciclagem termomecânica
ABSTRACT
Maroun EV. Influence of the vitrification of a Y-TZP ceramic in the bond strength to a self-adhesive cement after termomechanicals cycles. Niterói: Universidade Federal Fluminense, Faculdade de Odontologia; 2017.
The purpose of this study was to evaluate the influence of thermomechanical cycling on bond strength of self-adhesive resin cement to vitrified TZP ceramic. Forty Y-TZP ceramic blocks (Lava Frame) were divided into four groups according to the surface treatments: AS - as sintered; SB - sandblasted with 30 μm Al2O3 particles; LG - vitrification with a low-fusing ceramic glaze (VITA AkzentPlus) and etching with 10% hydrofluoric acid; and HC - vitrification with a ceramic liner (HeraCeram Zirkonia) and etching with 10% hydrofluoric acid. Ten lithium disilicate ceramic blocks (IPS e.max CAD), etched with 10% hydrofluoric acid for 20 s were used as control. After silanization, blocks of resin composite were cemented on the Y-TZP ceramics surfaces using a self-adhesive resin cement. Half of the blocks from each group were cut into beams and submitted to microtensile bond strength (µTBS) test after 24 h of water immersion, and the other half after mechanical (1.200.000x, 98N, 2.5Hz) and thermo (5000x, 5-55 °C, 30 s dwell time) cycling (TMC). The µTBS data after 24 h and after TMC were separately analyzed using one-way ANOVA and Tukey´s HSD post hoc test. The effect of TMC in each group was evaluated by Student t-test. The analyses were performed at a significance of α=0.05. After 24 h, EM and LG presented similar and highest TBS (p < 0.05), whereas AS showed the lowest TBS. After TMC, EM presented the highest TBS, followed by LG (p < 0.05). All the blocks of AS underwent a spontaneous debonding during TMC. Only EM and LG maintained the stability of TBS after TMC. It can be conclude that the vitrification with low-fusing glaze could be seen as a suitable treatment to improve the stability of bonding to Y-TZP ceramics.
1 – INTRODUÇÃO
A introdução da zircônia à composição das cerâmicas odontológicas trouxe muitas possibilidades para a reabilitação oral, no qual foi possível substituir as infraestruturas metálicas em casos de pontes parciais fixas de dois a três pônticos em áreas anteriores e posteriores [1]. As propriedades mecânicas oferecidas de alta resistência à flexão e tenacidade à fratura permitiram a evolução no tratamento por meio da transformação da fase tetragonal para monoclínica quando a zircônia é submetida a tensões [2]. No entanto, a ausência de conteúdo vítreo na composição da cerâmica de zircônia determina que seja classificada como um biomaterial ácido resistente, impossibilitando o emprego do tratamento de superfície com ácido fluorídrico [3-5]. Como consequência, outras formas para conseguir uma maior adesão do cimento resinoso à zircônia foram estudas, como tratamento com monômeros adesivos fosfatados[6,7], jateamento com partículas de Al2O3 revestidas por sílica [8,9], tratamento com primers seletivos [10 - 13] e plasmas não térmicos [ 14-16]. Apesar destes protocolos terem sido capazes de aumentar a resistência de união imediata, apresentaram uma considerável redução quando submetidas a imersão em água destilada à longo prazo e ciclagem termomecânicas. Devido a possibilidade de interação química entre os grupos fosfatos presentes nos metacrilatos e grupos hidroxila da cerâmica Y-TZP, cimentos resinosos autoadesivos tem sido responsáveis por melhorar a adesão a superfícies cerâmicas de Y-TZP [7]. No entanto, estudos mostraram que esse mecanismo pode, também, sofrer uma degradação quando submetidas a métodos de envelhecimento [8,17].
Nos últimos anos, visando otimizar a resistência de união a cerâmicas Y-TZP foi desenvolvido um método que aborda um “ processo de’ vitrificação” da superfície cerâmica, e já demonstrou bons resultados [18-22], inclusive após envelhecimento por termociclagem ou imersão em água [23,24]. Este protocolo envolve a fusão de liners e glazes cerâmicos, criando uma camada rica em sílica, que torna susceptível ao condicionamento com ácido fluorídrico, e criação de retenções micromecânicas para penetração do cimento resinoso e, também, interação química com agente silano.
Apesar dos resultados positivos apresentados em estudos prévios, nota-se a ausência de pesquisas que envolvessem envelhecimentos mecânicos ou
termomecânicos. No ponto de vista clínico, o meio bucal é um sistema dinâmico, no qual as restaurações cerâmicas de Y-TZP estão sujeitas não só a mudanças de temperatura, mas também a cargas mastigatórias [25]. Logo, destaca-se a necessidade de investigação do efeito da ciclagem mecânica na resistência de união de cimentos resinosos a superfície cerâmica de Y-TZP previamente submetida a vitrificação. Esta é a principal contribuição adicionada aqui.
Com base nessas considerações, o objetivo do trabalho foi avaliar a influência da ciclagem termomecânica na resistência de união de cimento resinoso autoadesivo a cerâmica Y-TZP submetida a vitrificação. A hipótese testada foi que a ciclagem termomecânica não afetaria a resistência de união da cerâmica vitrificada.
2 - METODOLOGIA
2.1 Preparo dos Espécimes
Blocos de cerâmica (10 x 10 x 7 mm) foram produzidos em cortadeira metalográfica (ISOMET 1000, Büehler, Lake Bluff, IL, USA), sendo 40 de cerâmica de ZrO2 tetragonal policristalina estabilizada com ítrio (Y-TZP) (Lava® Frame, 3M ESPE, St. Paul, MN, EUA), e 10 de cerâmica de dissilicato de lítio (IPS e.max® CAD, Ivoclar Vivadent AG, Schaan, FL). Após sinterizados de acordo com as recomendações do fabricante (Lava™ Furnace 200, M ESPE, St. Paul, MN, EUA), os blocos de Lava Frame foram divididos em quatro grupos, de acordo com o tratamento de superfície (n=10): AS - superfícies sinterizadas - controle negativo; SB - jateamento com partículas de óxido de alumínio 30μm, a uma distância de 10 mm e perpendicular à superfície, durante 20 s, com pressão de 2,8 bar); LG - aplicação de glaze de baixa fusão (VITA Akzent® Plus Glaze, Dentsply, Tulsa, OK, EUA) em spray, sinterização em forno cerâmico a 780ºC por 1 min, condicionamento com ácido fluorídrico a 10% (Condicionador de Porcelanas,L070553H, Dentsply) por 1 min, lavagem com spray ar/água e limpeza em ultrassom por 5 min em água destilada; HC – aplicação de liner cerâmico (HeraCeram®
Zirkonia, Heraeus Kulzer, Hanaus, DE) com pincel, sinterização em forno cerâmico (Programat P310 Ivoclar Vivadent AG, Schaan, FL) por 10 min a 1050ºC, condicionamento com ácido fluorídrico a 10% (Condicionador de Porcelanas,L070553H, Dentsply) por 1 min, lavagem com spray ar/água e limpeza em ultrassom por 5 min em água destilada. Os blocos de IPS e.max® CAD foram condicionados com ácido fluorídrico a 10% por 20s, lavados com spray ar/água e limpos em ultrassom por 5 min em água destilada. Todas as superfícies foram silanisadas por 1 min (Silano, Dentsply, Petropolis, BR, lote 101338H).
Um molde de silicone de adição, destinado a confecção de blocos de compósito com as mesmas dimensões, foi obtido através da moldagem de um bloco cerâmico sinterizado. Os blocos de compósito (Z250®, 3M ESPE, St. Paul, MN, EUA) foram confeccionados utilizando a técnica incremental, de 2,0 em 2,0 mm, até atingir a altura de 4,0 mm. Cada incremento foi fotoativado (Radii-cal (SDI, Victoria, AUS) com 500mW/cm² por 30s. Após, os blocos foram armazenado em água destilada a
37°C por 24 h para dissipação das tensões de polimerização. O cimento resinoso autoadesivo RelyX U200® (3M ESPE, St. Paul, MN, EUA) foi manipulado em um bloco de espatulação por 15 s e aplicado na superfície da cerâmica para posterior assentamento do bloco de resina composta, sob o alinhamento de uma guia de silicone. Após a aplicação de uma carga de 5 N por 2 min e remoção dos excessos com pincel descartável, o cimento foi fotoativado por 40 s em cada face.
Grupo (n=10)
Tratamento de Superfície
EM Cerâmica IPS e.max CAD condicionada com ácido fluorídrico 10% por 20s, lavagem com spray ar e água, secagem, e banho em ultrassom com água destilada por 5 min
AS Cerâmica Y-TZP sem tratamento
SB Cerâmica Y-TZP jateada com partículas de óxido de alumínio 30μm por 20s a uma distância perpendicular a superfície de 10 mm a pressão de 2.8 bars, e banho em ultrassom com água destilada por 5 min.
HC Cerâmica Y-TZP vitrificada com um liner cerâmico (HeraCeram® Zirkonia, Heraeus Kulzer, Hanaus, DE), sinterização por 10 min a 1050°C, condicionamento com ácido fluorídrico 10% por 1 min, lavagem com spray ar e água, secagem, e banho em ultrassom com água destilada por 5 min (SiO2, Al2O3, K2O, CeO2).
LG Cerâmica Y-TZP vitrificada com glaze de baixa fusão ( VITA Akzent® Plus VITA Zahnfabrik, Bad Sackingen, Germany) seguindo as instruções do fabricante, condicionamento com ácido fluorídrico 10% por 1 min, lavagem com spray ar e água, secagem, e banho em ultrassom com água destilada por 5 min (SiO2, K2O, Na2O, Al2O3, isobutane, ethanol).
Após mantidos durante 24 h em estufa à temperatura de 37 1 C, para liberação das tensões de polimerização, metade dos blocos de cerâmica-compósito de cada grupo foram seccionados em dois planos ortogonais, em cortadeira metalográfica (Isomet1000, Buëhler, Lake Bluff, Illinois, EUA), utilizando um disco diamantado (Isomet Wafering Blade 15LC, Buëhler, Lake Bluff, Illinois, EUA) sob refrigeração, à velocidade de 800 rpm, obtendo-se palitos com área de seção transversal de aproximadamente 1.0 mm2 e comprimento de 10 mm. Silicone de condensação flúido foi inserido entre os cortes para reduzir as vibrações durante os cortes transversais. Os palitos foram armazenados durante 24 h em estufa a 37 1 C antes do teste de microtração.
2.2 Envelhecimento da interface adesiva
Metade dos blocos em cada grupo, selecionados aleatoriamente, foram submetidos ao envelhecimento por ciclagem termomecânica (TMC). Inicialmente os blocos foram submetidos a ciclagem mecânica com carga de 98 N, 1.200.000 ciclos a 2,5 Hz (ER-37000NG, ERIOS, São Paulo, BR). A carga foi aplicada em uma base plana adaptada no palpador da máquina de ciclagem, apoiada sobre a superfície do espécime, para que fosse possível a distribuição igualitária da carga durante os ciclos e a sua transmissão uniforme ao longo da interface adesiva. Após, os blocos foram seccionados como descrito anteriormente e os palitos submetidos a termociclagem (ODMTC05m, Odeme Biothecnology, SC, BR), com 5000 ciclos nas temperaturas de 5 ± 2°C e 55 ± 2°C, com tempo de 30 s em cada banho.
2.3 Ensaio de resistência de união por teste de microtração (µTBS)
Os espécimes referentes aos dois grupos (24 h e após TMC) tiveram a área de seção transversal mensurada com um paquímetro digital (MPI/E-101, Mytutoyo, Tokyo, Japão) e foram submetidos ao teste de microtração. Os palitos foram secos com papel absorvente, fixados com adesivo a base de cianoacrilato (SuperBonder, Lot # 15900545 , Henkel Ltda,, Itapevi, SP, Brazil) em dispositivo para teste de
microtração (ODMT03d, Odeme Dental Research, Luzerna, SC, Brasil) e tensionados por tração, em máquina de ensaios universais (Emic DL 2000, São José dos Pinhais, SP, Brasil), com célula de carga de 50 N e velocidade de deslocamento de 0,5 mm / min até a ocorrência de falha. Os valores de resistência de união (MPa) foram obtidos pela divisão da carga de ruptura (N) pela área de seção transversal dos palitos (mm2).
2.4 Análise do padrão de fratura da interface adesiva
Após o teste de microtração, todos os palitos foram avaliados em estereomicroscópio (SZ40, Olympus, Tokyo, Japão) para avaliação do padrão de falha, que foi classificada como adesiva (falha nas interfaces adesivas), coesiva (falhas ocorrendo no corpo da cerâmica, do compósito ou da película do cimento) ou mista (conjunção de falha adesiva e coesiva dentro de uma mesma área). Palitos apresentando diferentes padrões de falha e com valores de resistência de união próximos a média dos seus grupos foram analisados através de MEV. os palitos foram montados em porta amostra com redução de carga e observados em MEV (PhenomProX, PhenomWorld, Eindhoven, The Netherlands) operando em modo de elétrons retroespalhados, em ambiente de baixo vácuo. As imagens foram obtidas com ampliações de 270x.
2.5 Análise topográfica de superfície
Duas superfícies cerâmicas de cada grupo foram analisadas por microscópia eletrônica de varredura (MEV) e perfilometria 3D. Inicialmente, os espécimes foram observados no MEV (Phenom ProX, Phenom World, Eindhoven, Netherland), operando no modo de elétrons retroespalhados, aceleração de voltagem de 10kV e em ambiente de baixo vácuo. As imagens foram obtidas com aumento de 1000x. Em seguida, a análise foi realizada utilizando um perfilômetro 3D (Form Talysurf 60i, Taylor Hobson, Leicester, UK) em uma área de 1,0 mm², com resolução de 20 nm no eixo z, empregando 4000 pontos no eixo x e espaçamento de 2,0 μm no eixo y. A
reconstrução das imagens 3D foi realizada de acordo com o parâmetro Sa (μm), utilizando a seguinte fórmula:
1 0 1 0 ) ; ( 1 M k N l l k y x z MN Sa ,onde z é a altura dos pontos medidos nas coordenadas x e y.
2.6 Análise estatística
Os dados obtidos foram analisados utilizando o software Statgraphics Centurion XVI software (STATPOINT Technologies, Inc., Warrenton, VA, EUA). Como todos os blocos do grupo AS romperam espontaneamente durante a ciclagem mecânica (TBS = 0 MPa), estes não foram incluídos na análise estatística [23,26]. Os palitos que falharam prematuramente durante o teste de microtração foram incluídos na análise, com um valor correspondente a metade do valor mínimo da resistência de união de cada grupo experimental [27]. Após a distribuição normal dos erros e a homogeneidade das variâncias serem avaliadas pelos testes de Shapiro-Wilk e Levene, respectivamente, os dados de resistência de união após 24 h e após a ciclagem termomecânica foram separadamente analisados por análise de variância de um fator e teste de Tukey HSD. O efeito da ciclagem termomecânica, em cada grupo, foi analisada pelo teste t de Student. As análises foram realizadas ao nível de significância de 95% (α = 0,05). Os dados do tipo de fratura foram avaliados percentualmente e as imagens de MEV e de perfilometria 3D de forma qualitativa.
3. ARTIGO PRODUZIDO (será submetido ao periódico Journal of Dentistry)
Stability and effectiveness of the bond strength of self-adhesive resin cement to vitrified Y-TZP ceramic
Bonding to Y-TZP ceramic
Eduardo Victor Marouna, MSc Student
Walter Gomes de Miranda Júniorb, Associate Professor Alexandre Barbosa Eliasa, Adjunct Professor
Eduardo Moreira da Silvaa, Associate Professor
a
Analytical Laboratory of Restorative Biomaterials – LABiom-R, School of Dentistry, Federal Fluminense University, Niterói, Rio de Janeiro, Brazil
b
Department of Biomaterials and Oral Biology, School of Dentistry, University of São Paulo, São Paulo, Brazil
*Corresponding author: Dr. Eduardo Moreira da Silva– Universidade Federal Fluminense / Faculdade de Odontologia - Rua Mário Santos Braga, nº 30 - Campus Valonguinho, Centro, Niterói, RJ, Brazil - CEP 24040-110 - Phone: 55 21 2629-9832 - Fax: 55 21 2622-5739 - e-mail: [email protected]
ABSTRACT
Objectives: To evaluate the influence of thermomechanical cycling on bond strength
of self-adhesive resin cement to vitrified Y-TZP ceramic
Methods: Forty Y-TZP ceramic blocks (Lava Frame) were divided into four groups
according to the surface treatments: AS - as sintered; SB - sandblasted with 30 μm Al2O3 particles; LG - vitrification with a low-fusing ceramic glaze (VITA AkzentPlus) and etching with 10% hydrofluoric acid; and HC - vitrification with a ceramic liner (HeraCeram Zirkonia) and etching with 10% hydrofluoric acid. Ten lithium disilicate ceramic blocks (IPS e.max CAD), etched with 10% hydrofluoric acid for 20 s were used as control. After silanization, blocks of resin composite were cemented on the Y-TZP ceramics surfaces using a self-adhesive resin cement. Half of the blocks from each group were cut into beams and submitted to microtensile bond strength (µTBS) test after 24 h of water immersion, and the other half after mechanical (1.200.000x, 98N, 2.5Hz) and thermo (5000x, 5-55 °C, 30 s dwell time) cycling (TMC). The µTBS data after 24 h and after TMC were separately analyzed using one-way ANOVA and Tukey´s HSD post hoc test. The effect of TMC in each group was evaluated by Student t-test. The analyses were performed at a significance of α=0.05. Two ceramic surfaces submitted to each treatment were analysed by scanning electron microscopy (SEM) and by 3D-profilometry for surface topography analysis.
Results: After 24 h, EM and LG presented similar and highest TBS (p < 0.05), whereas AS showed the lowest TBS. After TMC, EM presented the highest TBS, followed by LG (p < 0.05). All the blocks of AS underwent a spontaneous debonding during TMC. Only EM and LG maintained the stability of TBS after TMC.
Conclusion: The bonding to vitrified Y-TZP ceramic was capable of resist to
thermomechanical cycling
Clinical significance: The vitrification with low-fusing glaze could be seen as a
suitable treatment to improve the stability of bonding to Y-TZP ceramics.
1. Introduction
Thanks to the possibility of replacement of the metallic frameworks in total crowns, implant abutments and larger fixed prosthesis in anterior and posterior areas
as well, the introduction of yttria-stabilized polycrystalline ZrO2 (Y-TZP) ceramics to the dental practice brought new possibilities to the esthetic oral rehabilitation treatments [1]. Allied to the aesthetic appearance, the principal advantage of Y-TZP ceramics is a stress-induced toughening mechanics that is started by stresses generated at the ceramic surface, causing a tetragonal to monoclinic phase transformation that occurs along with a volume increasing (3-5%) at the crack tips, which develops internal stresses that counterattack the crack propagation inside the ceramic bulk, thereby increasing the ceramic mechanical strength [2]. Irrespective of this welcome mechanism, however, the absence of vitreous phase, which torn Y-TZP ceramics resistant to hydrofluoric acid conditioning, still represent an Achilles hell to the clinical behavior of this class of restorative biomaterial[3-5].
In attempt to overcome this limitation, different strategies such as the treatment with phosphate adhesive monomers [6, 7], sandblasting with Al2O3 and modified Al2O3 particles [8, 9], treatment with selective primers [10, 11], Si-nanocoating [12, 13], and nonthermal plasmas [14-16] have been proposed to improve the interaction of resin-cements to Y-TZP ceramic surfaces. Although these protocols are really capable of increase the immediate Y-TZP ceramic-resin cement bond strength, this can undergo a drop when submitted to long-term water immersion and thermal and or mechanical cycling. Due to a possible chemical interaction at the interfacial grain level between the phosphate groups present in methacrylated phosphoric acid esters and the hydroxyl groups of the passive ZrO2 coating on the Y-TZP ceramic, self-adhesive resin cements have been advocated to better adhere to the Y-TZP ceramic surfaces [7]. Unfortunately, there are evidences that this mechanism can also suffer degradation when submitted to aging methods [8, 17]. These are clinical matters of concern.
In the last few years, a new approaching to optimize the bond strength to Y-TZP ceramic, involving the modification of ceramic surface with low-fusing glasses, which is a “vitrification process”, have been presented successful results [18-22], even after aging in water and thermocycling [23, 24]. This protocol involves the fusing of liners and ceramic glazes to the Y-TZP ceramic surface, creating a silica-rich layer that is etchable by the hydrofluoric acid, thereby favouring the micromechanical interlocking with the resin cement and the chemical interaction with the silane-coupling agent as well.
Irrespective of the positive results presented in these previous studies, however, it is noteworthy that none of them have submitted the specimens to mechanical loading. From the clinical point of view, the mouth is a dynamic system, in which the Y-TZP ceramic restorations will be subject not only to changes in temperature, but also to masticatory loading [25]. Thus, it seem of some relevance to investigate the effect of mechanical cycling on bond strength of resin cements to Y-TZP ceramic surface previously submitted to vitrification. This is the principal contribution added here. Therefore, the purpose of the current study was to evaluate the influence of thermomechanical cycling on bond strength of self-adhesive resin cement to Y-TZP ceramic submitted to two different protocols for vitrification. The tested hypothesis was that thermomechanical cycling would not affect the bond strength to vitrified Y-TZP ceramic.
2. Materials and methods
2.1. Bond strength evaluation
The experimental setup of this part of the study is depicted in Fig. 1.
2.1.1. Ceramic blocks preparation
Forty pre-sintered blocks of an Y-TZP ceramic (Lava Frame, 3M ESPE, Seefeld, Germany) and ten blocks of a lithium disilicate glass ceramic (IPS e.max CAD Ivoclar Vivadent AG, Schaan, FL), sectioned using a diamond disk, at 800 rpm, in a precision sectioning cutter (Isomet 1000 precision saw, Buehler, Lake Bluff, Il USA) were sintered and crystallized using the electrical induction furnaces recommended by the manufacturers: Lava™ Furnace 200 and Programat P310, respectively. After these processes, the final dimensions of all ceramic blocks were 10.0 mm x 10.0 mm x 7 mm. After being polished with 800 and 1200 grit SiC papers, the blocks were ultrasonically cleaned for 5 min in distilled water and randomly divided into five groups (n=10) according to the surface treatments (Table 1).
Table 1 – Ceramic surface treatments Group treatment
EM IPS e.max CAD ceramic etched with 10% hydrofluoric acid for 20 s, rinsed with air-water spray, dried, and ultrasonically cleaned in distilled water for 5 min
AS As-sintered Y-TZP ceramic with no treatment
SB Y-TZP ceramic sandblasted with 30-μm Al2O3 particles for 20 s at a perpendicular distance of 10 mm at 2.8 bar pressure, and ultrasonically cleaned in distilled water for 5 min
LG Y-TZP ceramic vitrified with a low-fusing ceramic glaze (*VITA AkzentPlus, VITA Zahnfabrik, Bad Sackingen, Germany) following the manufacturer's guideline, etched with 10% hydrofluoric acid for 1 min, rinsed with air-water spray, dried, and ultrasonically cleaned in distilled water for 5 min
*(SiO2, K2O, Na2O, Al2O3, isobutane, ethanol)
HC Y-TZP ceramic vitrified with a ceramic liner (**HeraCeram® Zirkonia, Heraeus Kulzer, Hanaus, DE) sintered for 10 min at 1050 ºC, etched with 10% hydrofluoric acid for 1 min, rinsed with air-water spray, dried, and ultrasonically cleaned in distilled water for 5 min
2.1.2. Resin composite blocks preparation
Fifty blocks of resin composite (Filtek Z250, 3M ESPE, St. Paul, MN, USA) were built up using a plastic mould with the same dimensions as the ceramic blocks (10.0 mm x 10.0 mm x 7.0 mm). The mould was filled with 2.0 mm thick increments of Z250, individually light polymerized for 30 s each with an irradiance of 500 mW/cm2 (Radii® call, SDI, Victoria, Australia). Afterwards, the resin composite blocks were polished, as previously described for the ceramic blocks, stored in distilled water at 37°C for 24 h (Q316B15, Quimis, Rio de Janeiro, Brasil), and dried for 50 min at 50°C (Q317M-22-EX, Quimis, Rio de Janeiro, Brasil).
2.1.3. Bonding Procedure
A self-adhesive resin cement (RelyX U200, 3M ESPE, St Paul, MN, USA) was used to luting the ceramic and resin composite blocks. Firstly, two coats of a silane coupling agent (Dentsply Caulk, Mildford, DE, USA) were applied onto all ceramic surfaces and air dried for 1 min. Afterwards, the resin cement was applied to the ceramic surface and the resin composite block was placed and held under a mass of 500 g for 2 min. After the excess being removed, the resin cement was light activated in the four sides of the Y-TZP ceramic-resin composite bonded interface for 40 s with an irradiance of 500 mW/cm2 (Radii® call, SDI, Victoria, Australia).
2.1.4. Microtensile bond strength (TBS) test
After storage in distilled water at 37 C for 24 h, half of the Y-TZP ceramic-resin composite blocks, randomly selected, were attached to a cutting machine (IsoMet 1000, Buehler, Lake Bluff, IL, USA) and longitudinally sectioned, across the bonded interfaces, in both x and y axes, with a water-cooled diamond disc (Isomet Wafering Blade 15LC #114254, Buehler, Lake Buff, IL, USA) at 800 rpm, producing beams with a cross-sectional area of approximately 1.0 mm2 and 10.0 mm in length. Fluid silicone impression material (Speedex, Vigodent-COLTÈNE, RJ, Brazil) was injected between the slices to absorb the vibration generated during the second cut. Afterwards, each beam was attached to a microtensile bond strength (µTBS) device (ODMT03d, Odeme Dental Research, Luzerna, SC, Brasil) with cyanoacrylate adhesive (SuperBonder, Lot # 15900545, Henkel Ltda,, Itapevi, SP, Brazil) and loaded in tension using a universal testing machine (Emic DL 2000, São José dos Pinhais, SP, Brazil), with a 50 N load cell, at a crosshead speed of 0.5 mm/min until
failure occurred. The µTBS (MPa) was obtained by dividing the load at failure (N) by the cross-sectional area of the beam (mm2).
Before the TBS test, the other half of the blocks were submitted to thermomechanical cycling as follow: First, the blocks were submitted to mechanical cycling in a chewing simulator (ER-37000NG, ERIOS, São Paulo, SP, Brazil), with a load of 98 N and frequency of 2.5 Hz for 1.2 x 106 cycles. Load was applied using a stainless steel plate adapted in the piston of chewing simulator in order to equally transmit the mechanical stresses to the bond interfaces. Afterwards, the blocks were also sectioned in beams that were thermocycled (5 - 55 °C with, dwell time of 30 s, transfer time of 2 s for 5 x 103 cycles).
2.1.5. Failure mode analysis
Each failed beam was evaluated with a stereomicroscope at 40x magnification (SZ40, Olympus, Tokyo, Japan) and the failure mode was classified as: adhesive (failures at the adhesive interfaces), cohesive (failures occurring mainly within resin composite), or mixed (mixture of adhesive and cohesive failure within the same fractured surface). Additionally, beams presenting different failure modes and with the value of TBS close to the mean of each group were randomly selected and viewed using scanning electron microscopy (SEM). The beams were mounted in a charge reduction sample holder and observed under SEM (PhenomProX, PhenomWorld, Eindhoven, The Netherlands) operating in the backscattered mode, in a low vacuum environment. The SEM images were taken at a magnification of x270.
2.2. Surface topography analysis
Two ceramic surfaces submitted to each treatment were analysed by scanning electron microscopy (SEM) and by 3D-profilometry. First, the ceramic specimens were observed under SEM (Phenom ProX, Phenom World, Eindhoven, Netherland) operating on backscattered mode under low vacuum. The images were taken employing 10 kV, at magnifications of x1,000. Afterwards, the topographic analysis was performed using a 3D-profilometer (Form Talysurf 60i, Taylor Hobson, Leicester, UK). For each specimen, an area of 1 mm2 was scanned with a 20-nm z-resolution, employing 4000 steps in the x-axis and a spacing of 2 μm in the y-axis. The reconstruction of 3-D images was made according to the parameter Sa (µm) using the following formula:
1 0 1 0 ) ; ( 1 M k N l l k y x z MN Sa ,where z is the height of measured points in x and y coordinates.
2.3. Statistical analysis
The obtained data were analyzed using Statgraphics Centurion XVI software (STATPOINT Technologies, Inc., Warrenton, VA, USA). As all blocks in the AS group spontaneously debonded during mechanical cycling (TBS = 0 MPa), its data were not included in the statistical analysis [23, 26]. The premature failed beams were included in the statistical analysis by assigning a value that corresponds to the half of the minimum TBS for their experimental group [27]. The normal distribution of errors and the homogeneity of variances were checked using Shapiro-Wilk´s and Levene´s test respectively. Based on these preliminary analyses, the µTBS data after 24 h and after TMC were separately analyzed using one-way ANOVA and Tukey´s HSD post hoc test. The effect of TMC in each group was evaluated by Student t-test. The analyses were performed at a significance of α=0.05.
3. Results
The means and standard deviation of TBS are depicted in Table 2. One-way ANOVA showed that after 24 h, E-max (EM) and glazed (LG) Y-TZP ceramic surfaces presented similar and higher TBS (p < 0.05), followed by sandblasted (SB) and ceramic liner (HC) covered Y-TZP ceramic surfaces, without statistical significant difference between them (p > 0.05). The lowest TBS after 24 h was presented by as-sintered (AS) Y-TZP ceramic surfaces (p < 0.05). After thermomechanical cycling, E-max presented the highest TBS (p < 0.05), followed by glazed Y-TZP ceramic surfaces, whereas sandblasted and ceramic liner covered Y-TZP ceramic surfaces presented statistically similar TBS (p > 0.05). All the specimens of as-sintered surfaces underwent a spontaneous debonding during mechanical cycling. Only E-max and glazed Y-TZP ceramic surfaces maintained the stability of TBS after thermomechanical cycling.
Tabel 2 - Mean (MPa) ± SD µTBS for all experimental groups
Groups 24 h Thermomechanical cycling
EM 37.3 ± 4.4A,a 34.8 ± 4.7A,a
AS 7.1 ± 2.7C,a 0D,b
SB 18.1 ± 2.0B,a 12.3 ± 2.7C,b
LG 30.6 ± 4.2A,a 24.1 ± 3.3B,a
HC 23.0 ± 2.6B,a 11.6 ± 1.4C,b
In each column, means followed by different uppercase letters are statistically different (Tukey´s HSD, p < 0.05).
In each row, means followed by different lowercase letters are statistically different (Student t-test).
Table 3 summarizes the number of specimens that failed prematurely, and the number of specimens that were submitted to microtensile bond strength test. All blocks in AS-TMC group spontaneously debonded during the mechanical cycling. The number of premature failed beams in the other groups were as follow: AS-24 > SB-24 > SB-TMC > HC-TMC > HC-24 > LG-24. The groups LG-TMC, EM-24 and EM-TMC did no present premature failed beams.
Table 3 – Total (T) of produced beams, number (n) and percentage (%) of premature failed beams (PFB), and total (N) of beams submitted to TBS test.
Groups T n (%) PFB N EM-24 80 0 (0) 80 EM-TMC 80 0 (0) 80 AS-24 80 64 (80) 16 AS-TMC 0 - 0 SB-24 80 39 (49) 41 SB-TMC 80 32 (40) 48 LG-24 80 13 (16) 67 LG-TMC 80 0 (0) 80 HC-24 80 14 (17) 66 HC-TMC 80 29 (36) 51
The percentage of failure modes are described in Fig. 2A. After 24 h, the groups AS and SB presented a predominance of adhesive failures, whereas group HC showed equilibrium between adhesive and mixed failures. On the other hand, the group EM presented half of mixed and cohesive failures. After TMC, SB and AS group still presented predominance of adhesive failures, whereas LG and EM groups showed a greater percentage of mixed failures. Representative SEM images of debonded specimens are presented in Fig. 2 (B, C, D, E). (B) adhesive failure in HC specimen showing the Y-TZP ceramic surface free of composite (c) and small remnants of resin cement (rc). (C) EM specimen showing a cohesive failure in the bulk of composite (c). (D) mixed failure in LG specimen. (E) mixed failure in SB specimen showing residual resin cement (rc) and composite (C) on Y-TZP ceramic surface.
Fig. 2. Failure mode distribution and representative SEM images of the failed beams.
Fig. 3 shows representative SEM images of IPS e.max CAD etched with 10% hydrofluoric acid for 20 s (a), and Y-TZP ceramic surfaces submitted to the
treatments: (b) as-sintered; (c) sandblasted with 30-μm Al2O3 particles for 20 s; (d) vitrified with low-fusing ceramic glaze and etched with 10% hydrofluoric acid for 1 min; and (e) vitrified with ceramic liner and etched with 10% hydrofluoric acid for 1 min. It can be noted that the surfaces of IPS e.max CAD and Y-TZP ceramic vitrified with low-fusing glaze presented similar aspect, with disperse porous characteristics of partially dissolved vitreous ceramics (blue pointers). Typical grooves are clear in sandblasted Y-TZP ceramic surface (black asterisks). A more irregular and porous surface, with several gaps dispersed over it (red asterisks), was presented by Y-TZP ceramic vitrified with ceramic liner.
Fig. 3. Representative SEM images of IPS e.max CAD etched with 10% hydrofluoric acid (a), and Y-TZP ceramic surfaces submitted to the treatments: (b) as-sintered; (c) sandblasted with 30-μm Al2O3 particles for 20 s; (d) vitrified with low-fusing ceramic glaze and etched with 10% hydrofluoric acid; and (e) vitrified with ceramic liner and etched with 10% hydrofluoric acid for 1 min.
Representative 3D images of groups EM and LG, before (A and B), and after (A’and B’) hydrofluoric acid etching are depicted in Fig 4. After acid etching, the EM surface presented deep craters, whereas the LG surface presented several peacks, characterizing a more homogeneous and deep action of the hydrofluoric acid.
Fig. 4. Representative 3D images of IPS e.max CAD and vitrified Y-TZP ceramic before (A and B) and after (A’and B’) hydrofluoric acid etching.
4. Discussion
Among other aspects, the establishment of stable bond between the resin cement and the ceramic is crucial to achieve clinical longevity of any kind of Y-TZP ceramic restoration. Thus, sound investigations in this field are welcome. The principal goal of the present study was to test the hypothesis that the bonding to vitrified Y-TZP ceramic (LG and HC groups) could be capable of resist to aging through thermomechanical challenge. The other tested groups were included for
specific reasons, that is. As-sintered Y-TZP ceramic was used as negative control because the literature clearly demonstrates that the bonding to this substrate is extremely poor [8, 23]. Contrarily, sandblasting was chosen as positive control because is one of the most reliable clinical protocol to luting Y-TZP ceramic restorations [4, 28]. IPS e.max CAD, a vitreous ceramic susceptible to hydrofluoric acid, was used to produce results intended to support the discussion about those obtained in vitrified Y-TZP ceramic.
The LG group maintained the bond strength stability after TMC. On the other hand, this did not occur in HC group. Therefore, the tested hypothesis of the present study was partially accepted. The mechanism involved in the Y-TZP ceramic vitrification can be described through the melting of the components (SiO2, Al2O3, K2O, Na2O, CeO2) present in both glaze and liner, which bond to each other creating a vitreous, Si-rich, layer that, according to Derand et al. [19], will interact with the Y-TZP ceramic surface through electrostatic and van der Waals forces. As a result, this Y-TZP vitrified ceramic surface is susceptible to hydrofluoric acid etching, thereby favouring the establishment of a -Si-O-Si- network with the silane and the microretention with the resin cement [18, 29, 30], a typical behaviour of vitreous ceramics.
After 24 h of water storage, AS group presented the worst TBS (Table 2), reinforcing the difficulty for establishes a good interaction between resin cements and the nonreactive Y-TZP ceramic surface, even using self-adhesive resin cements [8]. Contrarily, the three treatments tested here increased the immediate bond strength to Y-TZP ceramic (Table 2). In percentage terms, this increasing was 154.9% for SB, 223.9% for HC, and 330,9% for LG. Moreover, LG group was the only that presented TBS (30.6 MPa) statistically similar to that of EM group (37.3 MPa). This can be taken as the vitrification through low-fusing glaze covering being a good alternative to traditional sandblasting to improve the bond strength to Y-TZP ceramics.
In fact, previous studies have already been shown that low-fusing glaze vitrified ZrO2 ceramics provided strong and stable bond strength than traditional protocols (sandblasting and tribochemical coating). Cheung et al. [23] showed that Y-TZP ceramic vitrified with 2 layers of low-fusing glaze and etched with hydrofluoric acid presented bond strength stability after three weeks of water storage plus thermocycling (6,000x / 5 C-55 C), behaviour that was not presented by the groups
sandblasted with Al2O3 particles and tribochemically coated with Si-coated Al2O3 particles. In the study of Everson et al. [24], Y-TZP ceramic treated with five different low-fusing glazes and etched with hydrofluoric acid presented significant higher and stable bond strength (thermocycling for 1,800x / 5 and 55 C) than tribochemically coated surfaces. Thus, taking into account that in the current study the resin cement-Y-TZP ceramic interfaces were submitted not only to cutting protocol used to produce the TBS specimens, which is a stress-inducing process itself, but also to mechanical and thermal cycling, it is plausible to infer that the results obtained here are clinically relevant because represent a sound picture of the performance of the tested Y-TZP ceramic bonding protocols [31].
Even maintaining the bond stability, after TMC the LG group presented a significant lower TBS than EM group (Table 2). From Fig. 3a and d, it can be seen that both treatments present typical aspects of hydrofluoric acid etched surfaces [21, 24]. However, the 3D images (Fig. 4) clear show remarkable differences in the action of hydrofluoric acid in these groups, that is. While the surface of EM group presents several craters, these structures are less visible in LG surface, which presents picks protruding from it. Thus, it is possible that in EM group a more effective micromechanical interlocking with the self-adhesive resin cement took place due to the presence of these craters, thereby creating a better interaction between both, with a consequent higher TBS. Irrespective of this, and even being questionable to establish a minimal relationship between in vitro results and the clinical performance of adhesive protocols, by comparison with values of bond strength presented in previous studies [6, 8, 17, 26], it is reasonable to consider de number of 24.1 MPa presented by LG group after TMC as suitable to ensure good clinical performance of Y-TZP ceramic indirect restorations luted using this protocol.
Although the immediate TBS of HC group was statistically higher than that obtained in as-sintered Y-TZP ceramic surface and similar to that of traditional “gold standard" SB group, which means that this treatment might be suitable to prepare Y-TZP ceramics to bonding, this was lower than that of LG group (Table 2). As both VITA Akzent Plus and HeraCeram Zirkonia are vitreous materials with similar composition (Table 1), this finding was somewhat surprising. However, the features seen in Fig. 3 open some possibilities to explain this result, that is. From the comparison of Figs 3d and 3e, it can be noted that the surface vitrified with
HeraCeram Zirkonia (HC group) is inhomogeneous, possibly, due to the size of his particles and the application method used (brush), presenting several gaps, which are not viewed in the surface vitrified with of VITA AkzentPlus. Thus, it is reasonable to suppose that during etching, the hydrofluoric acid could have penetrated through these gaps and partially disrupted the interaction between the liner and the Y-TZP ceramic, thereby weakening the adhesive interface. The fact that this group did not maintain the TBS stability means that this effect was amplified after TMC. The higher percentage of premature failures after TMC observed for HC group, by comparison with LG group, reinforce this possibility.
The results observed for SB group are in good agreement with earlier studies [32, 33]. Its immediate TBS was 154.9% higher than that obtained in as-sintered surfaces, result that can be explained by the increase in the micromechanical interlocking by the self-adhesive resin cement into the grooves produced by air-abrasion (Fig. 3c), and by the chemical interaction between the PO4 groups present in self-adhesive resin cement and the hydroxyl groups produced by air abrasion itself [7]. On the other hand, the TBS of this group suffered a significant drop of 32% after TMC (Table 2). Although we did not find previous studies that have used similar experimental protocol, others that have used air-abrasion and resin cements containing phosphoric acid ester methacrylate monomers could be used to support this finding. Using MDP-containing Panavia, Bromicke et al. [4] and Quaas et al. [34] observed a reduction in tensile bond strength from 31.86 MPa to 4.93 MPa (84%) and from 23.6 MPa to 12.1 MPa (51%), respectively, after 150-days water storage and 37,500 thermocycles. Moreover, submitting the specimens to fatigue, Mirmohammadi et al. [35] found a reduction from 43.9 MPa to 22.0 MPa (50%) for flexural bond strength of Panavia to a ZrO2 ceramic. Concurrently with the present study, the analysis of all these results allow to infer that air-abrasion may not be the more efficient protocol to create reliable bond to Y-TZP ceramics in a clinical situation.
Beside the values of TBS itself, the analysis of the number of premature debonded specimens also provides important information regarding the behaviour of resin cement-ceramic interfaces. It is well known that during thermomechanical cycling, the water diffusion and thermal irradiation, and the stress generating into the adhesive interfaces may accelerate the hydrolytic degradation of the adhesive
polymer structures, thereby decreasing the bonding of resin cements to Y-TZP ceramics [23, 36, 37]. In the current study, all the resin composite/Y-TZP ceramic blocks from the AS group did not survive to the mechanical cycling. This find is noteworthy because means that the chemical interaction produced by the self-adhesive resin cement may be not strong enough to resist to the loading generated during chewing. Also, after 24 h of water storage, 80% of the beams from AS group prematurely failed during the TBs test (Table 3), while those that were tested presenting a predominance (93.75%) of adhesive failures (Figure 2A). These aspects reflect the lowest TBS found for this group, and reinforce once more the poor chemical interaction between the phosphate groups present in self-adhesive resin cements and the passive ZrO2 layer on Y-TZP ceramic surface [8].
The specimens from SB group also presented a great number of premature failures, 49% and 40%, after 24 h and TMC, respectively. Behaviour that fitted well with their intermediary values of TBS. Similar behaviour was observed for HC group. Contrarily, the LG group behaved similarly to EM group, with only 16% and 0% of premature failures after 24 h and TMC, respectively. Undoubtedly, this finding, associated with the maintenance of the bond strength stability observed in this group, allow to advocate the vitrification with low-fusing glaze as a suitable protocol to luting Y-TZP restorations. Of course, this assumption falls in the limits of the present investigation. Furthermore, previous studies have shown that the impact of Al2O3 particles during sandblasting may produces subcritical microcracks and t-m phase transformation in Y-TZP ceramics, which may affect their mechanical properties [38-40]. This is another factor to defend the vitrification of Y-TZP ceramics as a more suitable protocol to improve the bond strength to this class of ceramic material.
Although the present study add new aspects regarding the performance of vitrified Y-TZP ceramics, it still present some limitations such as the use of only one resin cement and Y-TZP ceramic. These aspects should be addressed in future investigations.
5. Conclusion
Within the limitations of the present investigation, the vitrification of the Y-TZP ceramic surface with low-fusing glaze, followed by hydrofluoric acid etching, allowed
the adhesive interface to resist to thermomechanical challenge. Also, the result of this protocol was better than that of the traditional sandblasting and similar to that observed in the IPS e.max CAD vitreous ceramic etched with hydrofluoric acid. Thus, it can be conclude that this protocol might be useful to improve the adhesion between Y-TZP ceramics and self-adhesive resin cements.
Acknowledgements
This study was carried out in partial fulfilment for a MSc degree in restorative Dentistry at School of Dentistry, Federal Fluminense University, NIterói, Rio de Janeiro, Brazil.
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4- CONCLUSÕES
Dentro das limitações desse trabalho, pode-se concluir que:
1) A vitrificação da superfície da cerâmica Y-TZP, seguida do condicionamento com ácido fluorídrico a 10%, aumentou os valores de resistência de união ao cimento resinoso autoadesivo quando comparado aos demais métodos.
2) A vitrificação com glaze de baixa fusão, seguida do condicionamento com ácido fluorídrico a 10%, manteve a estabilidade da adesão do cimento resinoso autoadesivo a cerâmica Y-TZP;
3) O protocolo de vitrificação com liner cerâmico, seguido do condicionamento com ácido fluorídrico a 10%, não foi capaz de manter a estabilidade da adesão do cimento resinoso autoadesivo a cerâmica Y-TZP;
4) O desempenho do protocolo de vitrificação com glaze de baixa fusão, seguido do condicionamento com ácido fluorídrico a 10%, apresentou desempenho similar ao grupo da cerâmica vítrea IPS e.max CAD;
Sumarizando os resultados, aceitou-se parcialmente a hipótese estabelecida para o presente estudo. Portanto, conclui-se que o protocolo de vitrificação com glaze de baixa fusão, seguido do condicionamento com ácido fluorídrico a 10%, pode ser um protocolo viável para manutenção da estabilidade da interface adesiva entre cimentos resinosos autoadesivos e cerâmicas de ZrO2 tetragonal policristalina estabilizada com ítrio (Y-TZP).
