Influence of the Resin Cement Thickness on the Push-Out Bond Strength of Glass Fiber Posts

Abstract The objective of the present study was to evaluate the influence of resin cement thickness on the bond strength of prefabricated and customized glass fiber posts after storage in distilled water. Thirty human uniradicular roots were treated endodontically. The roots were divided into 3 groups: THIN (thin cement layer) - post space preparation with #0.5 drill and cementation of #0.5 post; THICK (thick cement layer) - post space preparation with #1 drill and cementation of #0.5 post; and CUSTOM (customized cement layer) - post space preparation with #1 drill and cementation of a customized post (#0.5 glass fiber posts customized with resin composite). All posts were luted with self-adhesive resin cement. The push-out test was carried out after storage for 24 h and 90 days in distilled water at 37 °C. The data were analyzed with three-way ANOVA and Tukey's test (a=0.05). Bond strengths were significantly higher for CUSTOM (9.37 MPa), than for THIN (7.85 MPa) and THICK (7.07 MPa), which were statistically similar. Considering the thirds, the bond strength varied in the sequence: apical (7.13 MPa) < middle (8.22 MPa) = coronal (8.94 MPa). Bond strength for 24 h storage was significantly higher (8.80 MPa) than for 90-day storage (7.40 MPa). It may be concluded that the thickness of resin cement influenced the bond strength of glass fiber posts. The customized posts presented higher bond strength. Storage in water for 90 days affected negatively the values of bond strength, especially for thick cement layers in the apical third.

Resumo O objetivo deste estudo foi avaliar a influência da espessura da linha de cimento na resistência de união de pinos de fibra de vidro após armazenamento em água destilada. Trinta dentes humanos hígidos unirradiculares tiveram os canais tratados endodonticamente. As raízes foram distribuídas em três grupos: THIN (linha de cimento fina): conduto preparado com broca 0,5 e cimentação de pino 0,5; THICK (linha de cimento espessa): conduto preparado com broca 1 e cimentação de pino 0,5; e CUSTOM (linha de cimento personalizada): conduto preparado com broca 1 e cimentação de pino personalizada (pino 0,5 personalizado com resina composta). Os pinos foram cimentados com cimento auto-adesivo. Após armazenamento das raízes em água destilada a 37 °C por 24 h e 90 dias, o teste de cisalhamento por extrusão push-out foi realizado. Os resultados foram analisados estatisticamente por ANOVA a três fatores e teste de Tukey (a=0,05). A resistência de união foi significativamente maior para CUSTOM (9,37 MPa), do que para THIN (7,85 MPa) e THICK (7,07 MPa), que foram semelhantes entre si. Considerando-se os terços radiculares, a resistência de união variou na sequência: apical (7,13 MPa) < médio (8,22 MPa) = coronal (8,94 MPa). A resistência de união após 24 h de armazenamento em água foi significativamente maior (8,80 MPa) do que para 90 dias (7,40 MPa). Pode-se concluir que houve influência da espessura da linha de cimento na resistência de união de pinos de fibra de vidro, sendo que o uso de pinos personalizados apresentou maiores valores de resistência de união. O armazenamento em água por 90 dias afetou negativamente os valores de resistência de união, especialmente no terço apical, no grupo com linha de cimento mais espessa.

Evaluation of the resin cement thicknesses and push-out bond strengths of circular and oval fiber posts in oval-shapes canals

PURPOSE: The aim of this study was to evaluate whether the push-out bond strength varies between oval and circular fiber posts, and to examine the effect on the resin cement thicknesses around the posts. MATERIALS AND METHODS: Eighteen mandibular premolar roots were separated into two groups for oval and circular fiber posts systems. Post spaces were prepared and fiber posts were luted to the post spaces. Roots were cut horizontally to produce 1-mm-thick specimens. Resin cement thicknesses were determined with a metallographic optical microscope and push-out tests were done. RESULTS: No significant differences were observed in terms of push-out bond strength between the oval and circular fiber posts (P>.05) The resin cement thicknesses of the oval posts were greater than those of the circular posts group in the coronal, middle and apical specimens (P<.05). CONCLUSION: In the light of these results, it can be stated that resin cement thickness does not affect the push-out bond strength.

Influence of cement thickness on resin-zirconia microtensile bond strength

PURPOSE: The aim of this study was to evaluate the influence of resin cement thickness on the microtensile bond strength between zirconium-oxide ceramic and resin cement. MATERIALS AND METHODS: Thirty-two freshly extracted molars were transversely sectioned at the deep dentin level and bonded to air-abraded zirconium oxide ceramic disks. The specimens were divided into 8 groups based on the experimental conditions (cement type: Rely X UniCem or Panavia F 2.0, cement thickness: 40 or 160 microm, storage: thermocycled or not). They were cut into microbeams and stored in 37degrees C distilled water for 24 h. Microbeams of non-thermocycled specimens were submitted to a microtensile test, whereas those of thermocycled groups were thermally cycled for 18,000 times immediately before the microtensile test. Three-way ANOVA and Sheffe's post hoc tests were used for statistical analysis (alpha=95%). RESULTS: All failures occurred at the resin-zirconia interface. Thermocycled groups showed lower microtensile bond strength than non-thermocycled groups (P.05). The number of adhesive failures increased after thermocycling in all experimental conditions. No cohesive failure was observed in any experimental group. CONCLUSION: When resin cements of adhesive monomers are applied over air-abraded zirconia restorations, the degree of fit does not influence the resin-zirconia microtensile bond strength.

Numerical Analysis of the Influence of Cement Thickness on Stress Distribution in All-ceramic Crowns / 航天医学与医学工程

Objective To provide theoretical basis for clinical treatment of all-ceramic crown prosthodontics,the influence of cement thickness on the stress distribution in all-ceramic crowns under load was studied numerically.Methods The finite element analysis(FEA) model of a standard mandibular first molar was established using spiral CT and CAD software,and then it was applied to analyze the stress distribution of all-ceramic crowns under vertical loading using FEA software.Results Stress concentration was found in mesial and distal cement;the stress distribution at the cement upper and lower interface was found to be similar,and the stress magnitude discrepancy between the two interfaces was small;the stress of the model with 0.15 mm cement in the cervix was lower about 30% than the one of the 0.05 mm model.Conclusions The cement thickness plays an important role in the stress distribution of all-ceramic restoration system.The model with 0.15 mm cement shows a better resistance to destruction among the three models investigated.