Structural study of aged saturated silica gels obtained from tetramethoxysilane sonohydrolysis with different water/tetramethoxysilane molar ratio

The structural characteristics of saturated silica sonogels were studied by means of small-angle x-ray scattering (SAXS) and thermogravimetric analysis (TG), after a long time of aging in saturated conditions. The sonogels were obtained by a sol-gel routine from ultrasound stimulated tetramethoxysilane (TMOS) hydrolysis carried out with the initial water/TMOS molar ratio (r) ranging from 2 to 10. The saturated sonogel structure can be described as composed by mass fractal-like aggregates (clusters) of primary silica particles, all imbibed in a liquid phase. The values of the mass fractal dimension (D) of the clusters was found all around 2.5, while the characteristic size of the clusters (ξ) was found generally increasing with r, going from approximately 2.3 nm (r = 2) to 4.5 nm (r = 10). The volume fraction of the clusters was estimated from the SAXS data. The results were compared to the values of weight loss fraction at the inflection point that has been found in the derivative of the TG curve, which should accounts for the instant in which the meniscus of the liquid phase penetrates into the clusters under a rapid evaporation process as in a TG test.

Adsorption of silanes bearing nitrogenated Lewis bases on SiO 2/Si (100) model surfaces

The present paper describes the one-pot procedure for the formation of self-assembled thin films of two silanes on the model oxidized silicon wafer, SiO2/Si. SiO2/Si is a model system for other surfaces, such as glass, quartz, aerosol, and silica gel. MALDI-TOF MS with and without a matrix, XPS, and AFM have confirmed the formation of self-assembled thin films of both 3-imidazolylpropyltrimethoxysilane (3-IPTS) and 4-(N- propyltriethoxysilane-imino)pyridine (4-PTSIP) on the SiO2/Si surface after 30 min. Longer adsorption times lead to the deposition of nonreacted 3-IPTS precursors and the formation of agglomerates on the 3-IPTS monolayer. The formation of 4-PTSIP self-assembled layers on SiO2/Si is also demonstrated. The present results for the flat SiO2/Si surface can lead to a better understanding of the formation of a stationary phase for affinity chromatography as well as transition-metal-supported catalysts on silica and their relationship with surface roughness and ordering. The 3-IPTS and 4-PTSIP modified SiO2/Si wafers can also be envisaged as possible built-on-silicon thin-layer chromatography (TLC) extraction devices for metal determination or N-heterocycle analytes, such as histidine and histamine, with on-spot MALDI-TOF MS detection. © 2005 Elsevier Inc. All rights reserved.

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).

Microtensile bond strength of a resin cement to glass infiltrated zirconia-reinforced ceramic: The effect of surface conditioning

This study evaluated the effect of three surface conditioning methods on the microtensile bond strength of resin cement to a glass-infiltrated zirconia-reinforced alumina-based core ceramic. Thirty blocks (5×5×4 mm) of In-Ceram Zirconia ceramics (In-Ceram Zirconia-INC-ZR, VITA) were fabricated according to the manufacturer's instructions and duplicated in resin composite. The specimens were polished and assigned to one of the following three treatment conditions (n=10): (1) Airborne particle abrasion with 110 μm Al2O3 particles + silanization, (2) Silica coating with 110 μm SiOx particles (Rocatec Pre and Plus, 3M ESPE) + silanization, (3) Silica coating with 30 μm SiOx particles (CoJet, 3M ESPE) + silanization. The ceramic-composite blocks were cemented with the resin cement (Panavia F) and stored at 37 °C in distilled water for 7 days prior to bond tests. The blocks were cut under coolant water to produce bar specimens with a bonding area of approximately 0.6 mm2. The bond strength tests were performed in a universal testing machine (cross-head speed: 1 mm/min). The mean bond strengths of the specimens of each block were statistically analyzed using ANOVA and Tukey's test (α≤0.05). Silica coating with silanization either using 110 μm SiOx or 30 μm SiOx particles increased the bond strength of the resin cement (24.6±2.7 MPa and 26.7±2.4 MPa, respectively) to the zirconia-based ceramic significantly compared to that of airborne particle abrasion with 110-μm Al2O3 (20.5±3.8 MPa) (ANOVA, P<0.05). Conditioning the INC-ZR ceramic surfaces with silica coating and silanization using either chairside or laboratory devices provided higher bond strengths of the resin cement than with airborne particle abrasion using 110 μm Al2O3. © 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

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).

Fatigue resistance of the bond of a glass-infiltrated alumina ceramic to human dentin

Purpose: To evaluate the fatigue resistance of the bond between dentin and glass-infiltrated alumina ceramic, using different luting protocols. Materials and Methods: The null hypothesis is that the fatigue resistance varies with the luting strategy. Forty blocks of In-Ceram Alumina were prepared, and one surface of each block was abraded with 110-μm aluminum oxide particles. Then, the blocks were luted to flat dentin surfaces of 40 human third molars, using 4 different luting strategies (luting system [LS]/ceramic surface conditioning [CSC]) (n=10): (G1) [LS] RelyX-Unicem/[CSC] airborne abrasion with 110-μm Al2O3 particles; (G2) [LS] One-Step + Duo-Link (bis-GMA-based resin)/[CSC] etching with 4% hydrofluoric acid + silane agent; (G3) [LS] ED-Primer + Panavia F (MDP-based resin)/[CSC] Al2O 3; (G4) [LS] Scotchbond1+RelyX-ARC (bis-GMA-based resin)/[CSC] chairside tribochemical silica coating (air abrasion with 30-μm SiO x particles + silane). After 24 h of water storage at 37°C, the specimens were subjected to 106 fatigue cycles in shear with a sinusoidal load (0 to 21 N, 8 Hz frequency, 37°C water). A fatigue survivor score was given, considering the number of the fatigue cycles until fracture. The failure modes of failed specimens were observed in a SEM. Results: G3 (score = 5.9, 1 failure) and G4 (score = 6, no failures) were statistically similar (p = 0.33) and had significantly higher fatigue resistance than G1 (score = 3.9, 5 failures) and G2 (score = 3.7, 6 failures) (p < 0.03). SEM analysis of fractured specimens of G1 and G2 showed that almost all the failures were between ceramic and cement. Conclusion: The MDP-based resin cement + sandblasting with Al2O3 particles (G3) and bis-GMA-based resin cement + tribochemical silica coating (G4), both using the respective dentin bonding systems, were the best luting protocols for the alumina ceramic. The null hypothesis was confirmed.

Bond strength of a resin cement to high-alumina and zirconia-reinforced ceramics: The effect of surface conditioning

Purpose: The aim of this study was to evaluate the effect of two surface conditioning methods on the microtensile bond strength of a resin cement to three high-strength core ceramics: high alumina-based (In-Ceram Alumina, Procera AllCeram) and zirconia-reinforced alumina-based (In-Ceram Zirconia) ceramics. Materials and Methods: Ten blocks (5 ×6 × 8 mm) of In-Ceram Alumina (AL), In-Ceram Zirconia (ZR), and Procera (PR) ceramics were fabricated according to each manufacturer's instructions and duplicated in composite. The specimens were assigned to one of the two following treatment conditions: (1) airborne particle abrasion with 110-μm Al2O3 particles + silanization, (2) silica coating with 30 μm SiOx particles (CoJet, 3M ESPE) + silanization. Each ceramic block was duplicated in composite resin (W3D-Master, Wilcos, Petrópolis, RJ, Brazil) using a mold made out of silicon impression material. Composite resin layers were incrementally condensed into the mold to fill up the mold and each layer was light polymerized for 40 s. The composite blocks were bonded to the surface-conditioned ceramic blocks using a resin cement system (Panavia F, Kuraray, Okayama, Japan). One composite resin block was fabricated for each ceramic block. The ceramic-composite was stored at 37°C in distilled water for 7 days prior to bond tests. The blocks were cut under water cooling to produce bar specimens (n = 30) with a bonding area of approximately 0.6 mm2. The bond strength tests were performed in a universal testing machine (crosshead speed: 1 mm/min). Bond strength values were statistically analyzed using two-way ANOVA and Tukey's test (≤ 0.05). Results: Silica coating with silanization increased the bond strength significantly for all three high-strength ceramics (18.5 to 31.2 MPa) compared to that of airborne particle abrasion with 110-μm Al2O3 (12.7-17.3 MPa) (ANOVA, p < 0.05). PR exhibited the lowest bond strengths after both Al2O3 and silica coating (12.7 and 18.5 MPa, respectively). Conclusion: Conditioning the high-strength ceramic surfaces with silica coating and silanization provided higher bond strengths of the resin cement than with airborne particle abrasion with 110-μm Al2O3 and silanization.

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.

Bond strength of acrylic teeth to denture base resin after various surface conditioning methods before and after thermocycling

This study aimed to evaluate the durability of adhesion between acrylic teeth and denture base acrylic resin. The base surfaces of 24 acrylic teeth were flatted and submitted to 4 surface treatment methods: SM1 (control): No SM; SM2: application of a methyl methacrylate-based bonding agent (Vitacol); SM3: air abrasion with 30-μm silicone oxide plus silane; SM4: SM3 plus SM2. A heat-polymerized acrylic resin was applied to the teeth. Thereafter, bar specimens were produced for the microtensile test at dry and thermocyled conditions (60 days water storage followed by 12,000 cycles). The results showed that bond strength was significantly affected by the SM (P < .0001) (SM4 = SM2 > SM3 > SM1) and storage regimens (P < .0001) (dry > thermocycled). The methyl methacrylate-based adhesive showed the highest bond strength.

Resin microtensile bond strength to feldspathic ceramic: Hydrofluoric acid etching vs tribochemical silica coating

This study aimed to compare the microtensile bond strength of resin cement to alumina-reinforced feldspathic ceramic submitted to acid etching or chairside tribochemical silica coating. Ten blocks of Vitadur-α were randomly divided into 2 groups according to conditioning method: (1) etching with 9.6% hydrofluoric acid or (2) chairside tribochemical silica coating. Each ceramic block was luted to the corresponding resin composite block with the resin cement (Panavia F). Next, bar specimens were produced for microtensile testing. No significant difference was observed between the 2 experimental groups (Student t test, P> .05). Both surface treatments showed similar microtensile bond strength values.

Bond strength durability of direct and indirect composite systems following surface conditioning for repair

Purpose: This study evaluated the effect of surface conditioning methods and thermocycling on the bond strength between a resin composite and an indirect composite system in order to test the repair bond strength. Materials and Methods: Eighteen blocks (5 x 5 x 4 mm) of indirect resin composite (Sinfony) were fabricated according to the manufacturer's instructions. The specimens were randomly assigned to one of the following two treatment conditions (9 blocks per treatment): (1) 10% hydrofluoric acid (HF) for 90 s (Dentsply) + silanization, (2) silica coating with 30-Ìm SiOx particles (CoJet) + silanization. After surface conditioning, the bonding agent was applied (Adper Single Bond) and light polymerized. The composite resin (W3D Master) was condensed and polymerized incrementally to form a block. Following storage in distilled water at 37°C for 24 h, the indirect composite/resin blocks were sectioned in two axes (x and y) with a diamond disk under coolant irrigation to obtain nontrimmed specimens (sticks) with approximately 0.6 mm2 of bonding area. Twelve specimens were obtained per block (N = 216, n = 108 sticks). The specimens from each repaired block were again randomly divided into 2 groups and tested either after storage in water for 24 h or thermocycling (6000 cycles, 5°C to 55°C). The microtensile bond strength test was performed in a universal testing machine (crosshead speed: 1 mm/min). The mean bond strengths of the specimens of each block were statistically analyzed using two-way ANOVA (α = 0.05). Results: Both surface conditioning (p = 0.0001) and storage conditions (p = 0.0001) had a significant effect on the results. After 24 h water storage, silica coating and silanization (method 2) showed significantly higher bond strength results (46.4 ± 13.8 MPa) than that of hydrofluoric acid etching and silanization (method 1) (35.8 ± 9.7 MPa) (p < 0.001). After thermocycling, no significant difference was found between the mean bond strengths obtained with method 1 (34.1 ± 8.9 MPa) and method 2 (31.9 ± 7.9 MPa) (p > 0.05). Conclusion: Although after 24 h of testing, silica coating and silanization performed significantly better in resin-resin repair bond strength, both HF acid gel and silica coating followed by silanization revealed comparable bond strength results after thermocycling for 6000 times.

Microtensile bond strength of a repair composite to leucite-reinforced feldspathic ceramic

The purpose of this study was to evaluate the microtensile bond strength of a repair composite resin to a leucite-reinforced feldspathic ceramic (Omega 900, VITA) submitted to two surface conditionings methods: 1) etching with hydrofluoric acid + silane application or 2) tribochemical silica coating. The null hypothesis is that both surface treatments can generate similar bond strengths. Ten ceramic blocks (6x6x6 mm) were fabricated and randomly assigned to 2 groups (n=5), according to the conditioning method: G1- 10% hydrofluoric acid application for 2 min plus rinsing and drying, followed by silane application for 30 s; G2- airborne particle abrasion with 30 μm silica oxide particles (CoJet-Sand) for 20 s using a chairside air-abrasion device (CoJet System), followed by silane application for 5 min. Single Bond adhesive system was applied to the surfaces and light cured (40 s). Z-250 composite resin was placed incrementally on the treated ceramic surface to build a 6x6x6 mm block. Bar specimens with an adhesive area of approximately 1 ± 0.1 mm2 were obtained from the composite-ceramic blocks (6 per block and 30 per group) for microtensile testing. No statistically significant difference was observed between G1 (10.19 ± 3.1 MPa) and G2 (10.17 ± 3.1 MPa) (p=0.982) (Student's t test; á = 0.05). The null hypothesis was, therefore, accepted. In conclusion, both surface conditioning methods provided similar microtensile bond strengths between the repair composite resin and the ceramic. Further studies using long-term aging procedures should be conducted.

Surface conditioning of a composite used for inlay/onlay restorations: Effect on μTBS to resin cement

Purpose: To assess the effect of the composite surface conditioning on the microtensile bond strength of a resin cement to a composite used for inlay/onlay restorations. Materials and Methods: Forty-two blocks (6 × 6 × 4 mm) of a microfilled composite (Vita VMLC) were produced and divided into 3 groups (N = 14) by composite surface conditioning methods: Gr1 - etching with 37% phosphoric acid, washing, drying, silanization; Gr2 - air abrasion with 50-l̀m Al2O3 particles, silanization; Gr3 - chairside tribochemical silica coating (CoJet System), silanization. Single-Bond (one-step adhesive) was applied on the conditioned surfaces and the two resin blocks treated with the same method were cemented using RelyX ARC (dual-curing resin cement). The specimens were stored for 7 days in water at 37°C and then sectioned to produce nontrimmed beam samples, which were submitted to microtensile bond strength testing (μTBS). For statistical analysis (one-way ANOVA and Tukey's test, · = 0.05), the means of the beam samples from each luted specimen were calculated (n = 7). Results: μTBS values (MPa) of Gr2 (62.0 ± 3.9a) and Gr3 (60.5 ± 7.9a) were statistically similar to each other and higher than Gr1 (38.2 ± 8.9b). The analysis of the fractured surfaces revealed that all failures occurred at the adhesive zone. Conclusion: Conditioning methods with 50-l̀m Al2O3 or tribochemical silica coating allowed bonding between resin and composite that was statistically similar and stronger than conditioning with acid etching.

Influence of acid-etching and ceramic primers on the repair of a glass ceramic

The objective of this study was to evaluate the influence of different primers on the microtensile bond strength (μT BS) between a feldspathic ceramic and two composites. Forty blocks (6.0 × 6.0 × 5.0 mm 3) were prepared from Vita Mark II . After polishing, they were randomly divided into 10 groups according to the surface treatment: Group 1, hydrofluoric acid 10% (HF) + silane; Group 2, CoJet + silane; Group 3, HF + Metal/Zirconia Primer; Group 4, HF + Clearfil Primer; Group 5, HF + Alloy Primer; Group 6, HF + V-Primer; Group 7, Metal/Zirconia Primer; Group 8, Clearfil Primer; Group 9, Alloy Primer; Group 10, V-Primer. After each surface treatment, an adhesive was applied and one of two composite resins was incrementally built up. The sticks obtained from each block (bonded area: 1.0 mm2 ± 0.2 mm) were stored in distilled water at 37°C for 30 days and submitted to thermocycling (7,000 cycles; 5°C/55°C ± 1°C). The μT BS test was carried out using a universal testing machine (1.0 mm/min). Data were analyzed using ANOVA and a Tukey test (α = 0.05). The surface treatments significantly affected the results (P < 0.05); no difference was observed between the composites (P > 0.05). The bond strength means (MPa) were as follows: Group 1a = 29.6; Group 1b = 33.7; Group 2a = 28.9; Group 2b = 27.1; Group 3a = 13.8; Group 3b = 14.9; Group 4a = 18.6; Group 4b = 19.4; Group 5a = 15.3; Group 5b = 16.5; Group 6a = 11; Group 6b = 18; Groups 7a to 10b = 0. While the use of primers alone was not sufficient for adequate bond strengths to feldspathic ceramic, HF etching followed by any silane delivered higher bond strength.

Osteryoung square wave voltammetric determination of lactose in food samples by a derivative procedure

A method for determination of lactose in food samples by Osteryoung square wave voltammetry (OSWV) was developed. It was based on the nucleophilic addition reaction between lactose and aqua ammonia. The carbonyl group of lactose can be changed into imido group, and this increases the electrochemical activity in reduction and the sensitivity. The optimal condition for the nucleophilic addition reaction was investigated and it was found that in NH4Cl–NH3 buffer of pH 10.1, the linear range between the peak current and the concentration of lactose was 0.6–8.4 mg L−1, and the detection limits was 0.44 mg L−1. The proposed method was applied to the determination of lactose in food samples and satisfactory results were obtained.