Hideaki Shintani

Comparative Study on Adhesive Performance of Functional Monomers

Mild self-etch adhesives demineralize dentin only partially, leaving hydroxyapatite around collagen within a submicron hybrid layer. We hypothesized that this residual hydroxyapatite may serve as a receptor for chemical interaction with the functional monomer and, subsequently, contribute to adhesive performance in addition to micro-mechanical hybridization. We therefore chemically characterized the adhesive interaction of 3 functional monomers with synthetic hydroxyapatite, using x-ray photoelectron spectroscopy and atomic absorption spectrophotometry. We further characterized their interaction with dentin ultra-morphologically, using transmission electron microscopy. The monomer 10-methacryloxydecyl dihydrogen phosphate (10-MDP) readily adhered to hydroxyapatite. This bond appeared very stable, as confirmed by the low dissolution rate of its calcium salt in water. The bonding potential of 4-methacryloxyethyl trimellitic acid (4-MET) was substantially lower. The monomer 2-methacryloxyethyl phenyl hydrogen phosphate (phenyl-P) and its bond to hydroxyapatite did not appear to be hydrolytically stable. Besides self-etching dentin, specific functional monomers have additional chemical bonding efficacy that is expected to contribute to their adhesive potential to tooth tissue.

In vitro color change of composite-based resins

The adsorption of staining materials to resin restoratives was considered to be influenced by the physico-chemical properties of the resin-based monomers. To study the effects of the surface characteristics of resins on staining, we prepared five visible-light-cured experimental resins without fillers. Staining of these resins was colorimetrically measured. The staining solutions used were the Oil Orange and the Food Red 3 solutions. With the Oil Orange solution, the materials with higher hydrophobicity showed higher staining. With the Food Red 3 solution, the materials with higher water sorption showed higher staining.

Effects of various finishing methods on staining and accumulation of Streptococcus mutans HS-6 on composite resins

Abstract Microfilled and conventional composite resins, polished by different methods were tested for their staining and for bacterial accumulation in vitro. All 4 composite resins showed their characteristic staining tendencies for either Tobacco or Oil orange depending on their physicochemical properties and surface roughness. The effect of these factors seemed to depend on the substance adsorbed and the nature of the resins. Thus, in Tobacco solution immersion test, white point-polished surface showed the highest value of staining, which was followed by smooth surface and finished surface in this order, except one (Clearfil), in which the order was reversed. In the Oil orange solution immersion test, staining tendencies showed little correlation with surface roughness, but the hydrophobicity of the resin seemed to be an important factor. Polished surface accumulated more bacteria than smooth surface in the in vitro test of bacterial accumulation. However, no appreciable difference was observed among these 4 resins having an equal roughness.

Streptococcal Adherence on Various Restorative Materials

The adherence of Streptococcus sanguis ATCC 10556, S. sanguisATCC 10557, S. mutans Ingbritt, and S. mutans OMZ 176 to the surfaces of composite resins, amalgam alloys, and a Au-Ag-Pd alloy was measured. Adhesion was correlated with values for hydrophobicity and ζ-potential of the bacteria and the restorative materials. The hydrophobicity of the restoratives showed a positive correlation between the numbers of adherent S. sanguis cells, suggesting that hydrophobic interactions are important for the adherence of this bacterial species. In contrast, the numbers of adherent S. mutans cells showed a positive correlation with the ζ-potential of the restoratives, suggesting that electrostatic interactions are important in adherence of this bacterium.

Bonding efficacy of polyalkenoic acids to hydroxyapatite, enamel and dentin

Previously, we introduced a methodology to determine the chemical bonding potential of polyalkenoic acids to mineralized tissues through quantification of the degree of ionic bond formation between the carboxyl groups of a polyalkenoic acid with calcium of hydroxyapatite. In a continuation of that study, we now investigated in how far the chemical bonding potential to synthetic hydroxyapatite is influenced by the molecular structure of the polyalkenoic acid and if this also may affect the self-adhesiveness to enamel and dentin. X-ray photoelectron spectroscopy and inductively coupled plasma atomic emission spectrometry were used to quantitatively analyze the chemical bonding efficacy of a polyalkenoic acid consisting of acrylic acid units (PAA) to synthetic hydroxyapatite (HAp) in comparison to the chemical bonding potential of the previously investigated synthesized polyalkenoic acid (s-PA) co-polymer consisting of 90w/w% acrylic and 10w/w% maleic acid units. In addition, the analysis was carried out for enamel and dentin samples. PAA revealed a significantly lower bonding effectiveness with only half of its carboxyl groups bonded to HAp versus about two-third of the carboxyl groups of s-PA. The difference in bonding potential was confirmed by the considerably lower adhesiveness of PAA to enamel and dentin as compared to that of s-PA The present findings indicate that the molecular structure of the polyalkenoic acid significantly influences the chemical bonding efficacy to Hap-based substrates.

Regional distribution of parkinsonism-preventing endogenous tetrahydroisoquinoline derivatives and an endogenous parkinsonism-preventing substance-synthesizing enzyme in monkey brain.

1,2,3,4-Tetrahydroisoquinoline (TIQ) and 1-benzyl-1,2,3,4-tetrahydroisoquinoline (1BnTIQ), which exist in the brain of several mammalian species, are parkinsonism-inducing substances, and 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), which is enzymatically synthesized in rat brain, is a parkinsonism-preventing substance. In this study, we examined the regional distribution of contents of TIQ, 1MeTIQ, and 1BnTIQ, and activity of 1MeTIQ-synthesizing enzyme in monkey brain. The TIQ and 1BnTIQ contents in cerebrum and substantia nigra, and the 1MeTIQ contents in striatum and substantia nigra were higher than those in other brain regions, and 1MeTIQ-synthetic activity was high in cerebrum and thalamus. We speculate that 1MeTIQ-synthesizing enzyme may play an important role in idiopathic Parkinsons disease.

Analysis of camphorquinone in visible light-cured composite resins

Abstract Gas-liquid chromatography on a 10% polyethylene glycol column was found to be suitable for quantitative analysis of 2,3-diketo-1,7,7-trimethylnorcamphane which is used as an initiator for polymerization of visible light-cured resins. Five visible light-cured resin samples commercially available were analyzed by this method and it was found that all the samples tested contained more or less similar amounts of quinone, indicating that quinone is widely used as initiator in visible light-cured resins. Quinone was found not only in resin pastes but also in bonding agents, the concentration of quinone in these samples varied from brand to brand, and conventional resins which contained more filler showed a higher concentration of quinone than the microfilled resins tested.

Improved Filler-Matrix Coupling in Resin Composites:

Ineffective silane coupling between filler and matrix within dental composites is prone to accelerated in vivo degradation. In this study, we examined to what degree a procedure involving chemical decontamination of filler prior to silanization could improve the filler-matrix bonding, and thus the physico-mechanical properties, of composites. X-ray photoelectron spectroscopy revealed that filler-matrix coupling largely depended upon siloxane bridge (Si-O-Si) formation between the silica surface and the silane molecule, rather than on intermolecular bonding between adjacent silane molecules. Pre-silanization decontamination based upon boiling silica in 0.05-5% sodium peroxodisulfate, followed by ultrasonic rinsing in acetone, most effectively decontaminated filler. Consequently, it significantly improved the bonding of silane molecules to silanol groups at the silica surface. Experimental composites produced following pre-silanization decontamination of filler revealed a diametral tensile strength that was resistant to degradation by thermocycling.

Cutting effectiveness and wear of carbide burs on eight machinable ceramics and bovine dentin.

As a first approach in evaluating the feasibility of industrial machinable ceramics in dentistry, we performed weight-load-cutting tests on eight machinable ceramics and bovine dentin, using #1557 carbide burs driven by an air-turbine handpiece. While the transverse load applied to the bur was cyclically varied between 20 and 80 g, we measured the cutting speed (i.e., the steady-state handpiece speed during cutting) and the cutting volume. The greater the applied load, the more the cutting speed decreased and the cutting volume increased. The degree of this trend, however, differed among the workpieces. When dentin and mica-based glass ceramics were being cut, the cutting speed was moderately reduced, the cutting effectiveness of the bur remained high, and the wear of the bur was small. When other ceramics--such as AIN-based, Si3N4-based, and CaO.SiO2-based ceramics--were being cut, however, the cutting speed was less diminished, and the cutting efficiency of the bur was smaller and decreased rapidly, along with extensive wear of the bur. We speculate that mica-based glass ceramics could be used as the substitute for dentin in the pre-clinical cutting exercise, and that another potential use of machinable ceramics examined might be in the production of future machined dental prostheses.

Clinical evaluation of two posterior composite resins retained with bonding agents

Two hundred thirteen carious cavities were restored with two brands of chemically adhesive posterior composite resins by totally etching both the enamel and dentin walls after removing only the caries detector-stainable tissue and with no mechanical retention form in the cavity preparation. Most cavities were extensive, involving more than two surfaces in 74%. The dentin floor was not covered with cement although a spot lining was placed when the cavity was deep. All restorations were examined, usually after 4 years, by photographs and scanning electron microscope observation of replicas, and by criteria established by the U.S. Public Health Service. The materials and the technique proved to be clinically useful.