Influence of cement degree of conversion and adhesive procedure on retention of root canal posts

Sistemas de união convencionais de dois passos e autocondicionantes de passo único podem ser incompatíveis com cimentos resinosos duais quando estes não são fotoativados. Os objetivos deste trabalho foram avaliar em três diferentes profundidades (terços cervical, médio e apical): (1) o grau de conversão do cimento resinoso RelyX ARC fotoativado através de dois pinos intra-radiculares com diferentes graus de translucidez, o pino de fibra de quartzo translúcido Light-Post (LP) e o pino de fibra de carbono envolto por fibra de quartzo Aestheti-Post (AP); (2) a resistência de união a push-out destes dois pinos e a influência do procedimento adesivo, utilizando um ativador químico ou a aplicação adicional de uma resina adesiva mais hidrófoba, sobre a retenção destes ao canal radicular. Para a mensuração do grau de conversão, foram confeccionadas matrizes de silicone de adição simulando canais radiculares. Os pinos, cinco de cada, foram ?cimentados? nestas matrizes e, após a fotoativação, estes foram removidos para a leitura do espectro do cimento resinoso através do espectrômetro FT-Raman. O cálculo do grau de conversão foi realizado através da análise da mudança na proporção entre as alturas dos picos das ligações duplas de carbono alifática e aromática. Os dados foram submetidos a ANOVA um fator com parcela sub-dividida e teste de Tukey (?=0,05). Apenas no terço médio o cimento resinoso apresentou maior grau de conversão quando fotoativado através do pino LP em relação ao AP. Para LP, o grau de conversão do cimento nos terços cervical e médio não diferiu estatisticamente, sendo inferior no terço apical. Já para AP, não houve diferença estatisticamente significante entre os terços apical e médio, que apresentaram graus de conversão inferiores ao terço cervical. Para a segunda proposição, foram utilizadas sesseenta raízes de incisivos bovinos para avaliar a retenção dos pinos, sendo alocadas dez para cada procedimento adesivo: PB (Prime&Bond 2.1), PB + SC (Self-cure activator), PB + SBM (adesivo do sistema Scotchbond Multi-purpose), BB (Brush&Bond), BB + CAT (catalisador químico) e BB + SBM. Para cada procedimento adesivo, foram utilizados os pinos LP e AP (n=5). Após tratamento endodôntico e cimentação dos pinos com cimento resinoso RelyX ARC, as raízes foram seccionadas no sentido mesio-distal de forma a obter duas secções terço, uma para o ensaio de push-out e outra para análise das interfaces de união em MEV. O teste push-out foi realizado em máquina de ensaio EMIC a uma velocidade de 0,5 mm/min. O padrão de fratura das amostras foi avaliado em estereomicrocópio e classificado em: tipo 1- interface cimento/pino, tipo 2 - mista e tipo 3 - interface cimento/dentina. A análise estatística dos dados foi feita através de ANOVA dois fatores com parcela sub-dividida e teste de Tukey (?=0,05). Não houve diferença estatisticamente significante entre as médias dos dois pinos. O terço apical apresentou os menores valores de retenção e não houve diferença estatisticamente significante entre os terços médio e cervical. Para os dois sistemas adesivos, PB e BB, a utilização da resina adesiva hidrófoba SBM aumentou a retenção dos pinos. Já a utilização dos catalisadores SC e CAT não alterou os valores de resistência de união por push-out. Entretanto, não houve diferença estatística entre a utilização dos catalisadores e a aplicação da resina adesiva SBM. _________________________________________________________________________________________ ABSTRACT: Two-step etch-and-rinse and one-step self-etching bonding systems may be incompatible with dual-cured resin cements when these are not photo activated. The aims of this study were to assess the following, at three different depths (cervical, middle and apical thirds): (1) the degree of conversion of the resin cement RelyX ARC, photo activated through two intra-radicular posts with different degrees of translucence, the translucent quartz fiber-post Light-Post (LP) and and the quartz-coated-carbon-fiber post Aestheti-Post (AP); (2) the push-out bond strength of these posts and the influence of the adhesive procedurea, using a chemical co-initiator or an additional coat of a more hydrophobic bonding resin, on their retention in the root canal. In order to measure the degree of conversion, polyvinylsiloxane matrices were confected to simulate root canals. The posts, five of each one, were cemented in these matrixes and, after photo activation, these were removed for reading the resin cement spectrum with the FT-Raman spectrometer. The degree of conversion calculation was made by analyzing the changes in the ratio between the heights of the peaks of aliphatic and aromatic carbon double bonds. Data were submitted to the split-plot ANOVA one-way and Tukey test. The resin cement presented the highest degree of conversion only in the middle third, when photo activated through the LP post in comparison with AP. For LP, cement degree of conversion in the cervical and middle thirds did not differ statistically, being inferior in the apical third. Whereas for AP, there was no difference statistically significant between the apical and middle thirds, which presented degrees of conversion inferior to that of the cervical third. For the second proposition, sixty bovine incisor roots were used to assess post retention, ten roots were used for each adhesive procedure: PB (Prime&Bond 2.1), PB + SC (Self-cure activator), PB + SBM (Scotchbond Multi-purpose system adhesive), BB (Brush&Bond), BB + CAT (chemical catalyzer ) and BB + SBM. For each adhesive procedure, the LP and AP posts were used (n=5). After endodontic treatment and cementing the posts one with RelyX ARC resin cement, the roots were mesio-distally sectioned to obtain two sections per third, one for the push-out test and one for SEM analysis of the bonded interfaces. The push-out test was performed in an EMIC test machine at a crosshead speed of 0.5 mm/min. The failure mode of the specimens was analyzed under a stereomicroscope and classified as follows: Type 1- cement/post interface, Type 2 - mixed and Type 3 - cement/dentin interface. Data were statistically analyzed by split-plot ANOVA two-way and Tukey test (?=0.05). There was no difference statistically significant between the mean values of the two posts. The apical third presented the lowest retention values, and there was no difference statistically significant between the middle and cervical thirds. For the two adhesive systems, PB and BB, the use of hydrophobic adhesive resin SBM increased post retention. Whereas the use of SC and CAT catalyst did not alter the push-out bond strength values. Nevertheless, there was no statistical difference between the use of the catalysts and the application of SBM adhesive resin

Effec of activation mode of dual-cured resin cements on polymerization kinetics, mechanical properties, bond strength and stress generation

Durante os procedimentos de cimentação de restaurações indiretas e pinos intra-radiculares usando cimentos resinosos, a polimerização apropriada do cimento é essencial para o sucesso clínico da restauração. Entretanto, o potencial de polimerização dos componentes de ativação química e por luz de cimentos resinosos duais demonstra ser muito variável. Em adição, o rápido aumento da viscosidade causado pela fotoativação pode inibir a polimerização ativada quimicamente e reduzir o grau de conversão (GC) final. Assim, os objetivos deste estudo foram avaliar o efeito da fotoativação (ausência, imediata ou tardia) de três cimentos resinosos duais (Enforce, RelyX ARC e Panavia F) sobre: 1 - cinética de taxa de polimerização (Tp); 2 - resistência à tração diametral (RTD) e rigidez relativa (RR); 3 - tensão de contração de polimerização (TC); 4 - resistência máxima à tração (RMT) e 5 - resistência de união ao cisalhamento (RU). Para este último, o tempo do teste (10 minutos ou 24 horas) também foi avaliado. A fotoativação aumentou o GC para todos os cimentos resinosos. A ativação tardia melhorou o GC para o Enforce, reduziu para o RelyX ARC e para o Panavia F. Entretanto, este modo de ativação reduziu a Tp para todos os cimentos. O Panavia F apresentou a mais lenta reação de polimerização e os menores GC quando usado na ausência de fotoativação. O uso do ED Primer com este cimento aumentou o GC para todos os modos de ativação. A ausência de fotoativação reduziu a RTD apenas para o Panavia F. Para a fotoativação tardia, o RelyX ARC mostrou maior RTD que os outros cimentos. Para RR, não houve diferença entre os modos de ativação, mas o RelyX ARC mostrou maiores valores que o Panavia F para fotoativação imediata. A ausência de fotoativação gerou as menores TC e a fotoativação imediata levou aos maiores valores. Para os cimentos, o RelyX ARC mostrou maior TC que o Panavia F. Não houve efeito do modos de ativação na RMT. Os menores valores de RMT foram encontrados para o Panavia F. O RelyX ARC apresentou os maiores valores de RU e o Panavia F os menores. A fotoativação dos cimentos aumentou a RU, independentemente do momento em que foi realizada. Os corpos-de-prova testados após 24 horas apresentaram maiores valores que aqueles avaliados após 10 minutos. _________________________________________________________________________________________ ABSTRACT: During the cementation procedures of indirect restorations and intraradicular posts using resin cements, proper polymerization of the luting material is essential for the clinical success of restorations. However, the polymerization potential of chemically cured and light-cured components of commercially available dual-cured cements was found to vary greatly. In addition, the rapid increase in viscosity caused by light-activation may inhibit the chemically induced polymerization and reduce the ultimate degree of conversion (DC). Therefore, the aims of this study were to evaluate the effect of the light-activation (absence, immediate or delayed) of three dual-cured resin cement (Enforce, RelyX ARC and Panavia F) on: 1 - kinetics and rate of polymerization (Rp); 2 - diametral tensile strength (DTS) and relative rigidity (RR); 3 - polymerization shrinkage stress (SS); 4 - ultimate tensile strength (UTS) and 5 - shear bond strength (BS). For latter, the testing times (10 minutes or 24 hours) were also evaluated. Light-activation improved the DC for all resin cements. Delayed light-activation improved the DC for Enforce, reduced it for RelyX ARC and Panavia F. However, this activation mode reduced the maximum Rp for all cements. Panavia F presented slower polymerization reaction and the lowest DC when used in the absence of lightactivation. The use of ED Primer with this cement increases the DC for all activation modes. The absence of light-activation reduced the DTS only in Panavia F. For delayed light-activation, RelyX ARC showed higher DTS than the other cements. For RR, there was no difference between the activation modes, but RelyX ARC presented higher values than Panavia F for immediate light-activation. The absence of light-activation generated the lowest SS and the immediate lightactivation led to the highest values. For the cements, RelyX ARC showed higher SS than Panavia F. The activation mode had no effect on UTS. The lowest UTS values were found for Panavia F. RelyX ARC presented the highest BS values and Panavia F the lowest. Light-activation of the cements improved the BS, independently of the time that this was done. The specimens tested at 24 hours presented higher values than those evaluated at 10 minutes

Marginal adaptation of class V composite restorations submitted to thermal and mechanical cycling

Objective This study evaluated the effect of the margin location and an adhesive system on the marginal adaptation of composite restorations. Material and Methods Class V cavities were prepared in bovine teeth with the gingival margin on the dentin and the incisal margin on the enamel. The cavities were restored with a micro-hybrid composite resin using an etch-and-rinse [Single Bond 2 (SB)] or a self-etching adhesive [Clearfil SE Bond (CL)]. After finishing and polishing the restorations, epoxy replicas were prepared. The marginal adaptation was analyzed using scanning electronic microscopy (SEM, 500 x magnification). The higher gap width in each margin was recorded (T0). After the first evaluation, the samples were submitted to thermal cycling (2,000 cycles of 5°C±2°C followed by 55°C±2°C – T1) and mechanical cycling (100,000 cycles of 50 kN and 2 Hz – T2). Replicas of samples were rebuilt after each cycling and analyzed under SEM. The data were submitted to Mann-Whitney, Wilcoxon and Friedman testing (α=0.05). Results The SB presented higher gaps in the dentin than the enamel, while there was no difference between the substrate for the CL. In the dentin, the CL showed better marginal sealing than the SB. The opposite occurred in the enamel. There were no significant differences between the baseline, thermal and mechanical cycling for any experimental condition. Conclusions The outcomes of the present study showed that the adhesive system and margin location have an important effect on the marginal adaptation of composite restorations

Fiber Post Etching with Hydrogen Peroxide: Effect of Concentration and Application Time

AbstractIntroductionEtching is necessary to expose the fibers and enable both mechanical and chemical bonding of the resin core to the fiber post. This study evaluated the effect of concentration and application time of hydrogen peroxide on the surface topography and bond strength of glass fiber posts to resin cores.MethodsFiber posts were etched with 24% or 50% hydrogen peroxide for 1, 5, or 10 min (n = 10). Posts without any treatment were used as a control. After etching, the posts were silanated and adhesive resin was applied. The posts were positioned into a mold to allow a self-cured resin core to be inserted. The post/resin assembly was serially sectioned into five beams that were subjected to a tensile bond strength test. Data were subjected to two-way ANOVA and Tukey test (α = 0.05). The surface topography was analyzed using scanning electronic microscopy.ResultsNon-etched post presents a relatively smooth surface without fiber exposure. Application of hydrogen peroxide increased the surface roughness and exposed the fibers. All experimental conditions yielded similar bond strength values that were higher than those obtained in the control group.ConclusionBoth 24% and 50% hydrogen peroxide exposure increased the bond strength of resin to the posts, irrespective of the application time