Line analysis of interface layer on dentin by means of electron-probe microanalysis

Three types of brominated methacrylates, SBPPM, BPylM, and BNEM, were synthesized. The distribution of Br, Ca, and Fe at the interface between dentin treated with the 10-3 solution and resin containing these monomers was analyzed using an electron-probe microanalyzer (EPMA) in order to predict the composition and thickness of the interface layer on dentin for the corresponding unbrominated methacrylates. There was no significant difference between the brominated and unbrominated methacrylates in either the bond strength to the treated dentin or in the thickness of the interface layer on dentin observed with a scanning electron microscope (SEM). The thickness determined with EPMA was equivalent to that observed with SEM. The concentration of each brominated methacrylate in the interface layer was higher than the original concentration in the resin monomers, and BNEM showed higher concentration than the others. The presence of Fe in the layer was confirmed by EPMA.

[Mechanical properties and curing depth of urethane tetramethacrylate-based composite resins]

Mechanical properties and curing depth of light-cured composite resins based on five types of urethane tetramethacrylate (UTeMA; IP-4 M, XY-4 M, MC-4 M, HM-4 M and TM-4 M) were investigated, and compared them with those of UDMA-based composite resins. Composites based on UTeMA monomers containing an aromatic or cyclohexane ring in their chemical structure (IP-4 M, XY-4 M and MC-4 M) showed a relatively rigid properties than those based on aliphatic UTeMA (HM-4 M and TM-4 M). The composite resins based on XY-4 M monomer showed a curing depth and transmission coefficient superior to the other composite resins. UTeMA-based composites showed a significantly higher rigid properties than UDMA-based composites, while their rigidity did not improve the flexural strength.

Influence of water on bonding of various methacrylates to dentin treated with 10% citric acid-3% ferric chloride solution

The bond strength of resins (MMA-TBB resin system), containing 2-hydroxyethyl methacrylate (2-HEMA), 3-methacryloyloxypropionic acid (3MPA), 2-phenylethyl methacrylate (Py1EM) and 2-(1-naphthyl) ethyl methacrylate (NEM), to dentin treated with a solution of 10% citric acid and 3% ferric chloride was measured after being immersed in water at 37 degree C for a long period of time to investigate the influence of water on bonding, and the relationship between the monomer structure and the decrease in bond strength in water. The bond strength of the resins did not change with the time spent immersed in water up to 6 months, but decreased with any further increase in time. The decrease in bond strength of all the resins tested was caused by either the degeneration and swelling of collagen or a difference in the degradation of the resin inside and outside the acid-proof dentin layer. There was no significant relationship between the decrease in bond strength in water and the monomer structure.

[Electron-probe microanalysis examination of acid-proof dentin layer]

To predict the presence and thickness of the acid-proof dentin layer by the method of combining the halogenated methacrylate and electron-probe microanalyzer (EPMA), 2-methacryloyloxyethyl hydrogen chloromaleate (CIMEM) used as a base monomer for a bonding agent and 2-bromoethyl methacrylate (2 BEM), 2-(4-bromophenyl)ethyl methacrylate (BPy1EM), 2-(4-bromo-1-naphthyl)ethyl methacrylate (BNEM) and 2,4,6-tribromophenoxy methacrylate (TriBr-PM) used as tracers were synthesized. The bond strength to dentin treated with 37% phosphoric acid solution for 30 sec. was not statistically different for the bonding agents with and without tracers. The SEM micrographs revealed that the layers, which may be acid-proof dentin layers, were 3-4 microns thick at the resin-dentin interface for all bonding agents. According to EPMA analysis, cps of C1Ka and BrLa increase at the same points and the acid-proof dentin layer thickness was about 4 microns.

Correlation between air-drying duration and bond strength of composite resins to teeth

Cavity preparations involve both enamel and dentinal walls, but moisture contamination of these surfaces adversely influences the effectiveness of bonding interface. This in vitro study investigated the relationship between air-drying time and the bond strength to bovine enamel and dentin for two types of composite resins and their bonding agents. Comprehensive shear bond tests were performed with a universal testing machine, and mean bond strengths were computed by an analysis of variance and by Scheffé's multiple comparison test. No statistical differences were noted between the bond strength to the unetched and etched enamel and air-drying duration for bondings. The bond strengths to the etched dentin was comparable despite the time of air drying, but the bond strengths to unetched dentin were dependent upon the length of air drying.

[Studies on gallium alloys for dental restorations. 2. Electron probe microanalysis for hardened gallium alloys]

Hardened gallium alloys were analyzed by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The cores, matrix and white irregular shape phases were visible with SEM. The round or irregular shape cores contained Ag, Pd, Cu and Zn but did not contain Ga and In. The dark irregular shape matrix, which surrounded the core, consisted of Ga-Ag, Ga-Pd, Ga-Cu and Ga-Sn phases. However, the amount of Ga-Sn phase was very low. The white phase in the matrix was Ag-In phase.

[Mechanical properties and cure depth of UDMA-based composite resins]

Mechanical properties and cure depth of visible light-cured composite resins based on six types of UDMA (IP-HEMA, IP-HPMA, XY-HPMA, MC-HPMA, UEDMA and UPDMA) monomers were investigated. Under wet conditions, the mechanical properties of the composite resins based on aliphatic UDMA (UEDMA and UPDMA) monomers were inferior to those based on the other UDMA monomers containing aromatic or cyclohexane rings in their chemical structures. The cure depth for these UDMA-based composite resins increased with increasing irradiation time. The composite resin based on the XY-HPMA monomer showed a cure depth and transmission coefficient superior to the other composite resins.

A scanning electron microscopic investigation of bonding of methacryloyloxyalkyl hydrogen maleate to etched dentin

Three types of methacryloyloxyalkyl hydrogen maleates--2-(methacryloyloxy)ethyl hydrogen maleate (2MEM), 1-(methacryloyloxy-methyl)ethyl hydrogen maleate (MMEM), and 1-(methacryloyloxymethyl)propyl hydrogen maleate (MMPM)--were prepared for use as bonding agents. The relationships between the thickness of an acid-proof dentin layer and the bond strength and chemical structure of the synthesized monomers were investigated. The bond strengths of 2MEM/composite system to dentin treated with either 37% phosphoric acid solution or 10% citric acid-3% ferric chloride solution (10-3 solution) were superior to those of the others. The acid-proof dentin layer for all bonding agents containing the synthesized monomers at the resin-dentin interface was clearly visible in a scanning electron microscope, regardless of the types of dentin etching agents used. After treatment of the dentin with the phosphoric acid solution, the layers of 2MEM, MMEM, and MMPM were 5-6 micron, 3-4 micron, and 2-3 micron thick, respectively. When the dentin was treated with the 10-3 solution, the layer for each bonding agent was approximately 1 micron thick.

[Relationship among the composition and the physical and chemical properties of photo-cured composites for crown and bridge]

In this study, the relationship among the chemical composition and the physical and chemical properties of four photo-cured composites and one heat curing composite for crown and bridge were investigated. Five composites were composed of the base monomer, UDMA, TriEGDMA, 1, 3-BDMA, 1, 4-BDMA, 1, 10-DDMA, 1, 12-DDDMA or those mixture, and the composite-filler consist of the resin (TMPTMA, UDMA, 1, 10-DDMA or 1, 12-DDDMA) and micro-silica particles. Four photo-curing composites had a high elastic modulus and Vickers hardness and a low thermal expansion coefficient and water sorption compared with the heat-cured composite (Is). The effects of filler contents in the composites examined were positively on the elastic modulus and the hardness, and were inversely on the bending strength and the thermal expansion coefficient of the cured products. While the organic phase in the composite fillers had effect on the abrasive resistance of the composites. But no significant correlation between the abrasive resistance and the filler contents and the physical properties of the materials tested was noted.

Effect of monomer structure on the mechanical properties of light-cured composite resins

The effects of monomer structure on the mechanical properties of visible light-cured composite resins based on the seven types of aromatic dimethacrylates were investigated. The results of this study suggested that the mechanical properties of the composite resins were dependent upon the chemical structure of the dimethacrylate monomers employed. The composites based on dimethacrylates with hydroxy groups showed a relatively significant decrease in flexural strength, elastic modulus, and compressive proportional limit under wet conditions. The segmental mobility of dimethacrylate monomers considerably influenced the nature of cured composites. Bis-GMA-F-based composite showed superior mechanical properties to a conventional Bis-GMA-based material. The SEM observation of fractured surfaces revealed that failure mainly occurred through the resin matrix of the composite resins.

[Effect of filler system on the mechanical properties of light-cured composite resins. I. Effect of various types of silica fillers on the mechanical properties of the composite resins]

To investigate the effect of silica fillers on the mechanical properties of visible light-cured composite resins, Bis-GMA-based composites with four types of silica fillers were prepared. The mechanical properties of the composites with splinter-shaped silica fillers increased with increasing the filler fraction. Although the spherical silica filler could be filled more with resin monomer than the splinter-shaped silica filler, the mechanical properties of spherical silica-filled composite were relatively lower than those of the composite with splinter-shaped silica fillers. The micro particle silica-filled composite showed no obvious increase in the mechanical properties in either the dry or wet conditions. SEM observations of the fractured resin surface revealed that fracture occurred through the resin matrix as well as the resin/filler interface and the mechanical properties of each composite resin were correlated with the nature of crack propagation.

[Effect of filler system on the mechanical properties of light-cured composite resins. II. Mechanical properties of visible light-cured composite resins with binary filler system]

To improve the fracture resistance of the composite resin system under highly stressed conditions, a variable amount of microfiller was incorporated into the light-cured composite resins containing splinter-shaped silica filler. With the increasing the microfiller content (10-30 wt%) in the resin matrix, the elastic modulus, compressive proportional limit and compressive fracture strength of the composite resin were increased. The plastic deformation of the composite resins under compressive stress were decreased with increasing microfiller content. These findings suggested that the combination of a larger silica filler and microfiller would increase the compressive fracture resistance of the composite resin systems.

Polymerization of multifunctional methacrylates and acrylates

The cross-linking reaction of 15 dimethacrylates, one trimethacrylate and five diacrylates was studied by means of differential scanning calorimetry (DSC) and high performance liquid chromatography (HPLC) to investigate the relationship between the polymerization characteristics and the chemical structure of these monomers. The amount of pendant double bonds (Dp) and the efficiency of cross-linking (Ec) were calculated from both the extent of polymerization (Ep) and the amount of residual monomer (Rm) obtained by DSC and HPLC analyses, respectively. The Ep and Ec values of various monomers increased with an increase in the number of chain members between the functional groups, while Rm and Dp values decreased. The dimethacrylates consisting of aliphatic chains polymerized more readily than those containing aromatic units. High Ep was obtained in the aliphatic dimethacrylates and diacrylates with more than eight chain members and the aromatic dimethacrylates with more than 20 chain members among the monomers examined. These results depend presumably on the flexibility of the functional groups in the polymer network. With most dimethacrylates and diacrylates, high Ep was also observed in thermal scanning polymerization compared to isothermal polymerization at 90 degrees C. The diacrylates showed a high rate of polymerization compared to the corresponding dimethacrylates.