Step-stress vs. staircase fatigue tests to evaluate the effect of intaglio adjustment on the fatigue behavior of simplified lithium disilicate glass-ceramic restorations.

The aim of the study was to compare the outcomes for the fatigue mechanical behavior of bonded simplified lithium disilicate restorations, with and without an internal adjustment by grinding with diamond bur in running two fatigue tests: Staircase and Step-stress testing approaches. Ceramic discs (IPS e.max CAD) were prepared (Ø = 10 mm; thickness = 1.0 mm), submitted to an in-lab simulation of CAD/CAM milling (#60 SiC paper) and allocated into 2 groups according to the internal adjustment by grinding of the cementation surface: no adjustment (CTRL); or grinding with a coarse diamond bur (GR). Adhesive cementation (Multilink N) was performed onto epoxy resin discs (Ø = 10 mm; thickness = 2 mm) after ceramic/epoxy surface treatments. The cemented assemblies of each group were randomly assigned into 2 subgroups considering two fatigue tests (n = 15): Staircase - SC (250,000 cycles; 20 Hz), or Step-stress - SS (10,000 cycles per step; 20 Hz). Roughness, topographic and fractographic analyses were additionally performed. Statistical analyses were carried out using the Dixon and Mood method for Staircase data, and Kaplan-Meier and Mantel-Cox (log-rank) tests for Step-stress data. Ceramic restorations having its intaglio surface ground (GR group: SC test = 306.67 N; SS test = 646.67 N) presented lower fatigue failure load (FFL) values than the CTRL group (SC test = 879.28 N; SS test = 1090.00 N), regardless of the fatigue testing approach. The percentage of mean FFL decrease comparing the CTRL to GR group was higher for SC (65.1%) than the SS (40.7%) approach. However, a different total number of cycles was applied for each method. Both fatigue tests were able to detect the negative effect of internal adjustments of lithium disilicate glass-ceramic simplified restorations on their mechanical behavior. Therefore, both methods can be applied for similar evaluations (fatigue testing for ceramic restorations).

Endodontic sealers and post-endodontic waiting time affect the bond strength of the fiber posts / Cimentos endodônticos e tempo de espera após endodontia afeta a resistência de união de pinos de fibra

Introduction: The resistance adhesive of a fiber post can be affected by several factors, such as the endodontic sealer and post-endodontic waiting time. Objective: The aim of this study was to evaluate the effect of different endodontic sealers and two different post-endodontic waiting times on the bond strength of fiber posts. Material and method: Seventy-two bovine teeth were endodontically treated and filled using three endodontic sealers: eugenol-based, epoxy resin-based, or mineral trioxide aggregate-based. The specimens were stored at 37°C for 24 hours or for 30 months. After the respective storage times, the root canals were prepared for luting fiber posts using RelyX U200. Push-out tests and analysis of failures were performed. The push-out data were analyzed by two-way analysis of variance to compare the effects of the endodontic sealer and with the t-test to compare the effects of post-endodontic waiting time. Result: The AH Plus sealer yielded the highest bond strength values at 30 months post-endodontics (11.26 Mpa) (p < 0.05), however no had difference with Endofill sealer at the same time. Endofill and MTA Fillapex sealers did not differ significantly in their effects, irrespective of the post-endodontic waiting time. Conclusion: In conclusion, the endodontic sealer used and post-endodontic waiting time affect the adhesive resistance of fiber posts. The adhesion increases significantly when the fiber post is cemented 30 months after the root canal filling, while the adhesion is reduced when cementing immediately after root canal treatment, in particular for eugenol-based endodontic sealers.

Introdução: A resistência de união de um pino de fibra pode ser afetada por vários fatores, como o cimento endodôntico e o tempo de espera pós-endodontia. Objetivo: Avaliar o efeito de diferentes cimentos endodônticos e dois tempos de espera pós-endodontia na resistência de união de pinos de fibra. Material e método: Setenta e dois dentes bovinos foram tratados endodonticamente e obturados usando três cimentos endodônticos: à base de eugenol, à base de resina epóxia ou à base de mineral trióxido agregado. Os espécimes foram armazenados a 37 ° C por 24 horas ou por 30 meses. Após, os canais radiculares foram preparados para cimentação dos pinos de fibra usando o RelyX U200. Foram realizados testes de push-out e análise de falhas. Os dados foram analisados por análise de variância bidirecional e com o teste t. Resultado: O cimento AH Plus obteve os maiores valores de resistência de união aos 30 meses pós-endodontia (11,26 Mpa) (p <0,05), no entanto, não houve diferença com o cimento Endofill no mesmo tempo. Os cimentos Endofill e MTA Fillapex não diferiram significativamente em seus efeitos, independentemente do tempo de espera pós-endodontia. Conclusão: O cimento endodôntico utilizado e o tempo de espera pós-endodontia afetam a resistência adesiva dos pinos de fibra. A adesão aumenta significativamente quando o pino de fibra é cimentado 30 meses após a obturação do canal radicular, enquanto a adesão é reduzida ao cimentar imediatamente após o tratamento do canal radicular, principalmente para cimentos endodônticos à base de eugenol.

Can Endodontic Irrigating Solutions Influence the Bond Strength of Adhesives to Coronal Dental Substrates? A Systematic Review and Meta-Analysis of In Vitro Studies.

PURPOSE: To systematically review the literature to analyze the influence of endodontic irrigating solutions on the bond strength of adhesives to coronal enamel or dentin. MATERIALS AND METHODS: The PubMed/MEDLINE, Web of Science and Scopus electronic databases were used to select laboratory studies related to the research question, without publication year or language limits. From 2461 potentially eligible studies, 2451 were selected for full-text analysis, and 97 were included in the systematic review. Two authors independently selected the studies, extracted the data, and assessed the risk of bias. Pooling bond strength data were calculated using RevMan5.1 with random effects model (α = 0.05), comparing control (no endodontic irrigating solution) and experimental groups (one or more endodontic solutions). RESULTS: No significant difference was found between the control and experimental groups (p = 0.12) in the overall meta-analysis and in the meta-analysis excluding chlorhexidine (p = 0.06). High heterogeneity was found in the meta-analyses. Most included studies in the systematic review were scored as having a high risk of bias. CONCLUSION: The different endodontic irrigating solutions evaluated showed no negative influence on the bond strength of dental adhesives to coronal dental substrates.

Endodontic Sealers Affect the Bond Strength of Fiber Posts and the Degree of Conversion of Two Resin Cements.

PURPOSE: To evaluate the effect of two endodontic sealers on the push-out bond strength between fiber posts and root canal wall after different storage times and verify the influence of the endodontic sealers on the degree of conversion of composite cements. MATERIALS AND METHODS: A total of 180 bovine teeth were endodontically treated using two endodontic sealers, eugenol-based (Endofill, Dentsply Maillefer) or epoxy resin-based (AH Plus, Dentsply Maillefer). Subsequently, the specimens were stored in 100% relative humidity at 37°C for 24 h, 6 or 12 months. After the respective storage times, the root canals were prepared for fiber post cementation using two composite cements, RelyX U200 (3M) or Multilink Automix (Ivoclar Vivadent). The push-out test and the failure analysis were performed. Degree of conversion was analyzed using a Raman microscope, for which samples were prepared using composite cement only or composite cement plus endodontic sealer. Finally, the push-out data were subjected to statistical analysis and the degree of conversion in percent was calculated. RESULTS: AH Plus sealer obtained the highest push-out bond strengths at 24 h and 6 months. There was no difference between the push-out bond strengths of AH Plus and Endofill sealer at 1 year (p < 0.05). Moreover, the degree of conversion was affected by the Endofill sealer. CONCLUSION: The use of a eugenol-based sealer is not recommended because it affects the push-out bond strength of fiber posts. AH Plus sealer and a post-endodontic waiting time of 24 h is recommended.

The effect of immediate and delayed polishing on the color stability of a composite resin.

Polishing techniques are known to enhance the longevity and appearance of composite resin restorations. However, the influence of the timing of polishing on the final results of a restoration is not well documented. The aim of this study was to determine the effect of immediate and delayed polishing on the color stability of a composite resin. Sixty composite resin specimens were fabricated and randomly divided into 2 groups according to immersion solutions: group 1, deionized water (control); and group 2, coffee (as staining solution). The groups were further divided according to polishing time periods (immediate, 1 day, 7 days, 14 days, and 21 days). The polishing was performed by 1 calibrated operator using a sequence of aluminum oxide discs with different granulations. Color measurements were assessed at baseline and after a 48-hour immersion in the assigned medium by a reflection spectrophotometer, according to CIE L*a*b* parameters. The data were submitted to an analysis of variance (ANOVA) and the post hoc Tukey test at a significance level of 0.05. The ANOVA showed that the immersion solutions had a statistically significant difference (α = 0.05) on color stability. The composite resin color stability was not influenced by the timing of polishing, and all subgroups showed clinically unacceptable discoloration after exposure to coffee. Thus, with regard to color stability, the timing of final polishing may be established according to the preferences of the clinician.