Interfacial fracture of dentin adhesively bonded to quartz-fiber reinforced composite

The paper presents the results of an experimental study of interfacial failure in a multilayered structure consisting of a dentin/resin cement/quartz-fiber reinforced composite (FRC). Slices of dentin close to the pulp chamber were sandwiched by two half-circle discs made of a quartz-fiber reinforced composite, bonded with bonding agent (All-bond 2, BISCO, Schaumburg) and resin cement (Duo-link. BISCO, Schaumburg) to make Brazil-nut sandwich specimens for interfacial toughness testing. Interfacial fracture toughness (strain energy release rate, G) was measured as a function of mode mixity by changing loading angles from 0 degrees to 15 degrees. The interfacial fracture surfaces were then examined using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX) to determine the failure modes when loading angles changed. A computational model was also developed to calculate the driving forces, stress intensity factors and mode mixities. Interfacial toughness increased from approximate to 1.5 to 3.2 J/m(2) when the loading angle increases from approximate to 0, 0 to 15 degrees. The hybridized dentin/cement interface appeared to be tougher than the resin cement/quartz-fiber reinforced epoxy. The Brazil-nut sandwich specimen was a suitable method to investigate the mechanical integrity of dentin/cement/FRC interfaces. (C) 2011 Elsevier B.V. All rights reserved.

Bond strengths, degree of conversion of the cement and molecular structure of the adhesive-dentine joint in fibre post restorations

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

ANALYTIC STUDY ON HIGH-VOLTAGE CROWBAR SYSTEM

Crowbar switches are largely used in plasma devices, such as field-reversed configuration (FRC) machines and tokamaks, to avoid energy return from the discharge coil to the capacitor bank. A method of identification of all resistances, inductances and currents involved in capacitor bank discharges using a crowbar is proposed based on the derivation of the general analytical form of the coil current. This analysis can also be used for optimization of the discharge, reducing the ripple amplitude inherent in the crowbar-switched current. Fitting results of the TC-1 UNICAMP FRC device are also presented in this work.

Effect of mechanical cycling on the push-out bond strength of fiber posts adhesively bonded to human root dentin

This study evaluated the effect of mechanical cycling on the bond strength of fiber posts bonded to root dentin. The hypotheses examined were that bond strength is not changed after fatigue testing and bond strength does not present vast variations according to the type of fiber post. Sixty crownless, single-rooted human teeth were endodontically treated, with the space prepared at 12 mm. Thirty specimens received a quartz fiber post (Q-FRC (DT Light-Post), and the remaining 30 specimens received a glass fiber post (G-FRC) (FRC Postec Plus). All the posts were resin luted (All Bond+Duolink), and each specimen was embedded in a cylinder with epoxy resin. The specimens were divided into six groups: G1-Q-FRC+no cycling, G2- Q-FRC+20,000 cycles (load: 50N, angle of 45 degrees; frequency: 8Hz); G3- Q-FRC+2,000,000 cycles; G4- G-FRC+no cycling; G5- G-FRC+20,000 cycles; G6- GFRC+2,000,000 cycles. The specimens were cut perpendicular to their long axis, forming 2-mm thick disc-samples, which were submitted to the push-out test. ANOVA (alpha=.05) revealed that: (a) QFRC (7.1 +/- 2.2MPa) and G-FRC (6.9 +/- 2.1MPa) were statistically similar (p=0.665); (b) the no cycling groups (7.0 +/- 2.4MPa), 20,000 cycles groups (7.0 +/- 2.1MPa) and 2,000,000 cycles groups (7.0 +/- 2.0MPa) were statistically similar (p=0.996). It concluded that mechanical cycling did not affect the bond strength of two fiber posts bonded to dentin.

Effect of post length on the fatigue resistance of bovine teeth restored with bonded fiber posts: A pilot study

This study evaluated the influence of the cementation length of glass fiber-reinforced composite (FRC) on the fatigue resistance of bovine teeth restored with an adhesively cemented FRC. Thirty roots of single-rooted bovine teeth were allocated to 3 groups (n = 10), according to the ratio of crown length/root length (post cementation length): group 1 = 2/3, group 2 = 1/2, and group 3 = 1/1. The roots were prepared, the fiber posts (FRC Postec Plus) were cemented, and the specimens were submitted to 2 million mechanical cycles. After fatigue testing, a score was given based on the number of fatigue cycles until fracture, and data were submitted to statistical analysis. All specimens were resistant to fatigue. Taking into account the methodology and results of this study, the evaluated fiber posts can be cemented based on the ratio of crown/root at 1/1. Further clinical studies must be conducted to verify this ratio.

A lung computed tomographic assessment of positive end-expiratory pressure-induced lung overdistension

The aim of this study was to assess positive end-expiratory pressure (PEEP)-induced lung overdistension and alveolar recruitment in six patients with acute lung injury (ALI) using a computed tomographic (CT) scan method. Lung overdistension was first determined in six healthy volunteers in whom CT sections were obtained at FRC and at TLC with a positive airway pressure of 30 cm H2O. In patients, lung volumes were quantified by the analysis of the frequency distribution of CT numbers on the entire lung at zero end-expiratory pressure (ZEEP) and PEEP. In healthy volunteers at FRC, the distribution of the density histograms was monophasic with a peak at -791 ± 12 Hounsfield units (HU). The lowest CT number observed was -912 HU. At TLC, lung volume increased by 79 ± 35% and the peak CT number decreased to -886 ± 26 HU. More than 70% of the increase in lung volume was located below -900 HU, suggesting that this value can be considered as the threshold separating normal aeration from overdistension. In patients with ALI, at ZEEP the distribution of density histograms was either monophasic (n = 3) or biphasic (n = 3). The mean CT number was -319 ± 34 HU. At PEEP 13 ± 3 cm H2O, lung volume increased by 47 ± 19% whereas mean CT number decreased to -538 ± 171 HU. PEEP induced a mean alveolar recruitment of 320 ± 160 ml and a mean lung overdistension of 238 ± 320 ml. In conclusion, overdistended lung parenchyma of healthy volunteers is characterized by a CT number below -900 HU. This threshold can be used in patients with ALI for differentiating PEEP-induced alveolar recruitment from lung overdistension.

The effect of adhesive systems on the pullout strength of a fiberglass-reinforced composite post system in bovine teeth

Purpose: To evaluate the pullout strength of a glass fiber-reinforced composite post (glass FRC) cemented with three different adhesive systems and one resin cement. The null hypothesis was that pullout strengths yielded by the adhesive systems are similar. Materials and Methods: Thirty bovine teeth were selected. The size of the specimens was standardized at 16 mm by sectioning off the coronal portion and part of the root. The specimens were divided into three groups, according to the adhesive system, which were applied following the manufacturers' instructions: G1, ScotchBond Multi-Purpose Plus; G2, Single Bond; G3, Tyrian SPE/One-Step Plus. The glass FRCs (Reforpost) were etched with 37% H3PO4 for 1 min and silanized (Porcelain Primer). Thereafter, they were cemented with the dual resin cement En-Force. The specimens were stored for 24 h, attached to an adapted device, and submitted to the pullout test in a universal testing machine (1 mm/min). The data were submitted to the one-way ANOVA and Tukey's test (α = 0.05). Results: G1 (30.2 ± 5.8 Kgf) displayed the highest pullout strength (p < 0.001) when compared to G2 (18.6 ± 5.8 Kgf) and G3 (14.3 ± 5.8 Kgf), which were statistically similar. Analysis of the specimens revealed that all failures occurred between the adhesive system and the root dentin (pullout of the post cement), regardless of group. Conclusion: The multiple-bottle, total-etch adhesive system provided higher pullout strength of the glass FRC when compared to the single-bottle, total-etch, and single-step self-etching adhesive systems. The null hypothesis was rejected (p < 0.001).

Effect of silica coating on flexural strength of fiber posts

Purpose: Fiber-reinforced composite (FRC) posts can be air-abraded to obtain good attachment to the resin cement. This study tested the effect of silica coating on the flexural strength of carbon, opaque, and translucent quartz FRC posts. Materials and Methods: Six experimental groups of FRC posts (n = 10 per group) were tested, either as received from the manufacturer or after chairside silica coating (30-μm CoJet-Sand). Results: There was no significant difference in the flexural strength of nonconditioned (504 to 525 MPa) and silica-coated (514 to 565 MPa) specimens (P > .05) (analysis of variance). The type of post did have a significant effect on flexural strength (P < .05). Conclusion: Chairside silica coating did not affect the flexural strength of both carbon and quartz FRC posts.

Microtensile bond strength between a quartz fiber post and a resin cement: Effect of post surface conditioning

Purpose: To test the bond strength between a quartz-fiber-reinforced composite post (FRC) and a resin cement. The null hypothesis was that the bond strength can be increased by using a chairside tribochemical silica-coating system. Materials and Methods: Thirty quartz-FRCs (Light-Post) were divided into 3 groups according to the post surface treatment: G1) Conditioning with 32% phosphoric acid (1 min), applying a silane coupling agent; G2) etching with 10% hydrofluoric acid (1 min), silane application; G3) chairside tribochemical silica coating method (CoJet System): air abrasion with 30-μ SiO x-modified Al2O3 particles, silane application. Thereafter, the posts were cemented into a cylinder (5 mm diameter, 15 mm height) with a resin cement (Duo-Link). After cementation, the specimens were stored in distilled water (37°C/24 h) and sectioned along the x and y axes with a diamond wheel under cooling (Lab-cut 1010) to create nontrimmed bar specimens. Each specimen was attached with cyanoacrylate to an apparatus adapted for the microtensile test. Microtensile testing was conducted on a universal testing machine (1 mm/min). The data obtained were submitted to the one-way ANOVA and Tukey test (α = 0.05). Results: A significant influence of the conditioning methods was observed (p < 0.0001). The bond strength of G3 (15.14 ± 3.3) was significantly higher than the bond strengths of G1 (6.9 ± 2.3) and G2 (12.60 ± 2.8) (p = 0.000106 and p = 0.002631, respectively). Notwithstanding the groups, all the tested specimens showed adhesive failure between the resin cement and FRC. Conclusion: The chairside tribochemical system yielded the highest bond strength between resin cement and quartz-fiber post. The null hypothesis was accepted (p < 0.0001).

Does the thickness of the resin cement affect the bond strength of a fiber post to the root dentin?

This study aimed to evaluate the influence of cement thickness on the bond strength of a fiber-reinforced composite (FRC) post system to the root dentin. Eighteen single-rooted human teeth were decoronated (length: 16 mm), the canals were prepared, and the specimens were randomly allocated to 2 groups (n = 9): group 1 (low cement thickness), in which size 3 FRC posts were cemented using adhesive plus resin cement; and group 2 (high cement thickness), in which size 1 FRC posts were cemented as in group 1. Specimens were sectioned, producing 5 samples (thickness: 1.5 mm). For cement thickness evaluation, photographs of the samples were taken using an optical microscope, and the images were analyzed. Each sample was tested in push-out, and data were statistically analyzed. Bond strengths of groups 1 and 2 did not show significant differences (P = .558), but the cement thicknesses for these groups were significantly different (P < .0001). The increase in cement thickness did not significantly affect the bond strength (r2 = 0.1389, P = .936). Increased cement thickness surrounding the FRC post did not impair the bond strength.

Influence of brush type as a carrier of adhesive solutions and paper points as an adhesive-excess remover on the resin bond to root dentin

Purpose: To evaluate the influence of the brush type as a earner of priming adhesive solutions and the use of paper points as a remover of the excess of these solutions on the push-out bond strength of resin cement to bovine root dentin. The null hypotheses were that brush type and the use of paper points do not affect the bond strength. Materials and Methods: The canals of 80 single-root bovine roots (16 mm in length) were prepared at 12 mm using the preparation drill (FRC Postec Plus, Ivoclar). Half of each root was embedded in acrylic resin and the specimens were divided into 8 groups, considering the factors brush type (4 levels) and paper point (2 levels) (n = 10): Gr 1: small microbrush (Cavi-Tip, SDI); Gr 2: Microbrush (Dentsply); Gr 3: Endobrush (Bisco); Gr 4: conventional brush (Bisco); Gr 5: Cavi-Tip (SDI) + paper points; Gr 6: Microbrush (Dentsply) + paper points; Gr 7: Endobrush (Bisco) + paper points; Gr 8: conventional brush (Bisco) + paper points. The root dentin was treated with a multistep total-etch adhesive system (All Bond 2). The adhesive system was applied using each microbrush, with and without using paper points. One fiber post was molded with addition silicon and 80 posts were made of resin cement (Duolink), The resin posts were luted (Duolink resin cement), and the specimens were stored for 24 h in water at 37°C. Each specimen was cut into 4 disk-shaped samples (1.8 mm in thickness), which were submitted to the push-out test. Results: The brush type (p < 0.0001) (small microbrush > microbrush = endobrush = conventional brush) and the use of paper points (p = 0.0001) (with > without) influenced the bond strength significantly (two-way ANOVA). The null hypotheses were rejected. Conclusion: The smallest brush (Cavi-Tip) and the use of paper points significantly improved the resin bond to bovine root dentin.

Fatigue resistance of bovine teeth restored with resin-bonded fiber posts: Effect of post surface conditioning

This study evaluated the effect of post surface conditioning on the fatigue resistance of bovine teeth restored with resin-bonded fiber-reinforced composite (FRC). Root canals of 20 single-rooted bovine teeth (16 mm long) were prepared to 12 mm using a preparation drill of a double-tapered fiber post system. Using acrylic resin, each specimen was embedded (up to 3.0 mm from the cervical part of the specimen) in a PVC cylinder and allocated into one of two groups (n = 10) based on the post surface conditioning method: acid etching plus silanization or tribochemical silica coating (30 μm SiOx + silanization). The root canal dentin was etched (H2PO3 for 30 seconds), rinsed, and dried. A multi-step adhesive system was applied to the root dentin and the fiber posts were cemented with resin cement. The specimens were submitted to one million fatigue cycles. After fatigue testing, a score was given based on the number of fatigue cycles until fracture. All of the specimens were resistant to fatigue. No fracture of the root or the post and no loss of retention of the post were observed. The methodology and the results of this study indicate that tribochemical silica coating and acid etching performed equally well when dynamic mechanical loading was used.

Resin bonding to root canal dentin: Effect of the application of an experimental hydrophobic resin coating after an all-in-one adhesive

Aim: Based on the hypothesis the application of a low-viscosity hydrophobic resin coating improves the bond of all-in-one adhesive, the purpose of the study was to evaluate the bond strength of four adhesive systems to bovine root dentin using the push-out test method. Methods and Materials: The root canals of 32 bovine roots (16 mm) were prepared to a length of 12 mm using a FRC Postec Plus preparation drill. The specimens were allocated into four groups according to the adhesive system used: (Group 1) All-in-one Xeno III; (Group 2) All-in-one Xeno III+ScotchBond Multi-Purpose Plus Adhesive; (Group 3) Simplified Etch & Rinse One Step Plus; and (Group 4) Multi-Bottle Etch & Rinse All-Bond 2. A fiber-reinforced composite retention post was reproduced using an additional silicon impression and fabricated with DuoLink resin cement. The root specimens were treated with the selected adhesive systems, and the resin posts were luted in the canals with DuoLink resin cement. Each root specimen was cross sectioned into four samples (±1.8 mm in thickness), and the post sections were pushed-out to determine the bond strength to dentin. Results: Group 2 (2.9±1.2) was statistically higher than Group 1 (1.1±0.5) and Group 3 (1.1±0.5). Groups 1 and 3 showed no statistically significant difference while Group 4 (2.0±0.7) presented similar values (p>0.05) to Groups 1, 2, and 3 [(one-way analysis of variance (ANOVA)] and Tukey test, α=0.05). Conclusion: The hypothesis was accepted since the application of the additional layer of a low-viscosity bonding resin improved the bond of the all-in-one adhesive. Further studies must be conducted to evaluate the long-term bond.

Cementation of fiber post: influence of the cement insertion techniques on the bond strength of the fiber post-root dentin and the quality of the cement layer.

The aim of this study was to assess the influence of resin cement insertion methods on the bond strength of a fiber post to root dentin and quality of the cement layer. Forty bovine single-roots (length =16 mm) were randomly allocated into four groups, according to the cement insertion methods (N.=10): Gr1- Lentulo drill #40, Gr2- Centrix syringe, Gr3- Explorer #5, Gr4- fiber post. The root canals were prepared at 12 mm, using preparation bur # 3 of a cylinder quartz-FRC post (Aesthet post-plus, Bisco). The fiber posts were cemented using a multi-step etch-and-rinse adhesive system (All Bond 2®, Bisco) and a dual-cured resin cement (Duolink, Bisco). Each root was cut into seven samples: four samples of 1.8 mm thickness for push-out testing, and three with 0.5 mm for cement layer quality analyzing. One-way ANOVA was used for the push-out test values and the One-Way Kruskal-Wallis (P<0.05) and Dunn (10%) tests for the cement layer analyzes. ANOVA showed that the cement layer quality was affected by the cement insertion methods (P=0.0044): Gr1 (3.8 ± 1.3a), Gr2 (3.2 ± 1.3a), Gr3 (5.2 ± 1.5a,b) and Gr4 (5.2 ± 1.5b) (Dunn test), whereas the bond strength (MPa) was not affected by cement insertion methods: G1 (4.2 ± 1.3), G2 (3.2 ± 1.8), G3 (4.5 ± 0.9), G4 (3.1 ± 1.3). The fiber posts should be cemented with the assistance of the lentulo drill or centrix syringe to promote the best cement layer results.

Associação entre fatores de risco cardiovascular e capacidade funcional de idosos longevos

Study design: cross-sectional study. Objective: To assess the association between the presence of cardiovascular risk factor (CRP) and functional capacity of the oldest old. Methods: The sample 9onsisted of 91 elderly aged 80 and 90 years (83.0 ± 2.5 years) with 60 women (82.2 ± 2.1 years) and 31 men (83.2 ± 2,6 years) residing in the city of Presidente Prudente - SP. The FRC were analyzed: arterial hypertension (AH) and excess body fat (total and trunk). The presence of hypertension was verified by means of self-reported questionnaire based on the Standard Health Questionnaire (SHQ). Assessment of body was made by absorpiometria dual energy X-ray absorptiometry (DXA) and functional capacity was assessed by the functional tests (static balance, normal walking speed and force of the lower limbs). For statistical analysis we carried out the chi-square test, the software used was SPSS (13.0) and the significance level was set at 5%. Results. In males, with hypertension and the presence of excess %BF had lower performance in the lower limbs (83.3% lower and 16.7% higher), p = 0.011 compared to those with only a VCF. The elderly women with hypertension and the presence of excess GTron% also had lower performance on the same test (80.6% lower and 19.4% higher), p = 0.018 and the test of walking speed (80.6% lower and 19.4% higher), p = 0.034. Conclusion: Arterial hypertension and excess body fat (total and trunk) aggregated are FRC, which are associated with reduced functional capacity of the oldest old.