Adsorbed behavior of spin-labeled silane coupling agent on colloidal silica studied by electron spin resonance

[Aging effect of one bottle-type ceramic primer on bonding efficacy of resin cement]

PURPOSE

To understand the degradation mechanisms of commercially available one bottle-type ceramic primer, we prepared one bottle-type experimental ceramic primer consisting of gamma-methacryloxy-propyl-trimethoxysilane, gamma-MPTS, and 90% ethanol solution. The effects of aging of the experimental primer on the hydrolysis and condensation behavior of gamma -MPTS and on the bonding efficacy of gamma-MPTS at the interface between cement and ceramic were studied.

METHODS

We used two lamina bond porcelain primers (LB), that had been aged for 20 months and newly purchased. Experimental primer was aged at 20 degrees C. After aging, we measured 29Si NMR spectrum of the gamma-MPTS and the shear bond strength of the cement to silane-treated ceramic by varying aging periods.

RESULTS

When the LB was aged for 20 months, the mean bond strength decreased from 26 to 11 MPa. To understand the degradation mechanism in the bond strength, the effects of aging of experimental primer on molecular species of gamma-MPTS were examined. With prolonging its aging period, the methoxy group of the silicone functional portion in the gamma-MPTS hydrolyzed and the hydrolyzed gamma-MPTS species condensed together. The molecular weight of condensed gamma-MPTS species increased. On the other hand, when the dimer species of gamma-MPTS were produced, a maximum mean bond strength of 28 MPa was observed. Thereafter, the bond strength dropped down and leveled off at 16 MPa.

CONCLUSION

When the LB was aged for 20 months, the bond strength dramatically decreased. This decrease in the mean bond strength was probably attributed to ester exchange reaction of the methoxyl group in the gamma-MPTS by the ethanol used as diluent solvent.

Characterization of adsorbed silane on fillers used in dental composite restoratives and its effect on composite properties

The purpose was to study the effect of silane treatment of fillers on viscosity, flexural strength, and hydrolytic degradation of experimental dental composite resins fabricated with these fillers. The fillers consisted of a mixture of barium glass and amorphous silica. The resin was mainly based on ethoxylated bisphenol A dimethacrylate and polycarbonate dimethacrylate. The adsorption of silane on the filler surface was characterized by FTIR. There was significant correlation between the adsorbed silane on filler surface and the silane concentration in silane/methanol solution used for filler treatment. The silane concentration varied from 0.75 to 14% by weight. An increase in silane concentration led to a decrease in viscosities of the corresponding composite resins. The flexural strengths of composites with silanated fillers were greater than that of composites with unsilanated fillers: however, no significant difference was found between the flexural strengths of various silanated groups. The resistance to hydrolytic degradation of different composites increased when the fillers were treated with silane and was the highest at 1.1% silane.

Experimental and computational approach for evaluating the mechanical characteristics of dental composite resins with various filler sizes

This study aimed to investigate the influence of particle size of fillers on flexural properties of dental composite resins by laboratory testing with computational analysis validation. Four kinds of silica fillers with mean particle sizes of 3.3, 4.3, 7.9, and 15.5 microm were used. Filler content was kept constant at 70 mass% (or 53.8 vol.%). The three-point bending test was performed with a constant loading speed of 1.0mm/min, and a span length of 20mm using an Instron machine, in order to measure flexural strength and modulus of composite resins with various particle sizes. Test specimens were 2-mm wide, 2-mm thick, and 25-mm long rectangular bars. Furthermore, a numerical simulation using three-dimensional finite element (FE) analysis was performed to investigate stress distribution in composite resins under loading. As a result, flexural strength decreased with increasing particle size of the filler of the composite resins (p<0.05). On the other hand, there was no significant difference in Young's modulus among composite resins with various filler sizes (p>0.05). Moreover, FE analysis indicated that stress concentration increased with increasing particle size in agreement with experimental results of flexural strength. In conclusion, within the limitations of this investigation, we confirmed that flexural strength of composite resins decreased with increasing filler particle size. In addition, FE analysis was effective for evaluating stress distributions of dental composite resins with various filler sizes.

Effect of filler content on bending properties of dental composites: Numerical simulation with the use of the finite-element method

The purpose of this work is to investigate the influence of filler content on the bending properties of dental composites by use of the finite-element method (FEM). The proposed numerical model was constructed from isotropic shell elements representing silica filler, and isotropic beam elements representing the remaining matrix resin. The proposed model was applied to failure analysis under three-point bending conditions. The validity of applying the numerical model to the failure progression analysis of composites was checked through comparison with experimental results. The results show that, in both the analytical and experimental results, the bending properties, such as maximum bending stress and bending modulus, increase with filler content. Also, the proposed method of failure progression analysis could better simulate the failure process of composites under three-point bending conditions. In addition, close agreement between the analytical and experimental results was confirmed. The above results indicate that the proposed numerical model is effective for evaluating the bending properties of dental filler composites of any content range.

Filler-coupling agent-matrix interactions in silica/polymethylmethacrylate composites

The interactions of the silane coupling agent methacryloxypropyltrimethoxysilane (MPS) with both fumed silica and a polymethylmethacrylate (PMMA) resin matrix were investigated using thermogravimetric analysis and Fourier transform infrared spectroscopy. OX 50 fumed silica was silanated with MPS at concentrations of 1% and 5% in aqueous ethanol (95%), acetone, and anhydrous toluene. Methyl methacrylate was polymerized with the silanated fumed silica (5% wt/wt) to form composites. The amount of MPS adsorption on the fumed silica and the amount of PMMA attached to the silanated fumed silica were determined by thermogravimetric analysis. MPS could be removed from the fumed silica after washing with methanol, but not after it underwent a drying process at 25 degrees C under vacuum. After vacuum drying at 25 degrees C, two types of adsorbed silane were found, i.e., firmly adsorbed and loosely adsorbed silane. The loosely adsorbed silane could desorb from silica and be incorporated into the polymer matrix through copolymerization with monomeric methyl methacrylate, resulting in crosslinking of the matrix. When the silanated silica was dried at 110 degrees C for 2 h, the loosely adsorbed silane was removed and the amount of firmly adsorbed silane increased. There was a positive correlation between the amount of firmly adsorbed MPS and the amount of PMMA attachment. The highest efficiency for PMMA attachment was found when MPS was adsorbed as a monolayer, because the loosely adsorbed silane did not contribute to the bonding of PMMA, and this suggested that not all of the double bonds of the MPS were accessible for reaction with the methacrylate monomer. Drying at 110 degrees C may also decrease the number of unsaturated double bonds of MPS.

Reactions of a Trifunctional Silane Coupling Agent in the Presence of Colloidal Silica Sols in Polar Media

Reactions of 3-glycidoxypropyltrimethoxysilane (GPS) in a water-rich environment with silica colloids were studied. (29)Si NMR spectroscopy was used to monitor quantitatively the variation in GPS hydrolysis, condensation, and adsorption with pH and water concentration. The results show the competition between adsorption on the silica surface and condensation polymerization of GPS in the bulk liquid and are used to identify conditions favorable to surface modification. The presence of colloidal silica was shown to increase the apparent GPS dimerization rate, suggesting either surface catalysis or an increased local reactant concentration in the electrical double layer around the silica colloids. Copyright 1999 Academic Press.

Novel polyfunctional silanes for improved hydrolytic stability at the polymer-silica interface

Polyfunctional silanes were designed to promote the formation of a stable multisilane layer on the silica surface. The hydrolytic stability of polyfunctional silanes at the interface between silica and polymeric resin was investigated using conventional tensile testing. The specimens were immersed in boiling water and a decrease was observed in the tensile bonding strength of polymeric resin against the silane-treated silica surface as the immersion time increased. The failure mechanism changes from cohesive failure of the matrix resin to failure of the interface. The time necessary to start the interfacial failure is dependent on the silane concentration in the treating solution and the number of silicone functional groups within the silane molecules. The silane with two silicone functional groups is more stable at the interface between silica and polymeric resin than those which have mono- or trisilicone functional groups.