Satoshi Inoue

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.

Four-year Water Degradation of Total-etch Adhesives Bonded to Dentin

Resin-dentin bonds degrade over time. The objective of this study was to evaluate the influence of variables like hybridization effectiveness and diffusion/elution of interface components on degradation. Hypotheses tested were: (1) There is no difference in degradation over time between two- and three-step total-etch adhesives; and (2) a composite-enamel bond protects the adjacent composite-dentin bond against degradation. The micro-tensile bond strength (μTBS) to dentin of 2 three-step total-etch adhesives was compared with that of 2 two-step total-etch adhesives after 4 years of storage in water. Quantitative and qualitative failure analyses were conducted correlating Fe-SEM and TEM. Indirect exposure to water did not significantly reduce the μTBS of any adhesive, while direct exposure resulted in a significantly reduced μTBS of both two-step adhesives. It is concluded that resin bonded to enamel protected the resin-dentin bond against degradation, while direct exposure to water for 4 years affected bonds produced by two-step total-etch adhesives.

Monomer-Solvent Phase Separation in One-step Self-etch Adhesives:

One-step adhesives bond less effectively to enamel/dentin than do their multi-step versions. To investigate whether this might be due to phase separation between adhesive ingredients, we characterized the interaction of 5 experimental and 3 commercial self-etch adhesives with dentin using transmission electron microscopy. All adhesives were examined for homogeneity by light microscopy. Bonding effectiveness to dentin was determined with the use of a micro-tensile bond-strength protocol. The lower bond strength of the one-step adhesives was associated with light-microscopic observation of multiple droplets that disappeared slowly. Interfacial analysis confirmed the entrapment of droplets within the adhesive layer. The prompt disappearance of droplets upon application of a small amount of HEMA (2-hydroxyethyl methacrylate) or a HEMA-containing bonding agent, as well as the absence of droplets at the interface of all HEMA-containing adhesives, strongly suggests that the adhesive monomers separate from water upon evaporation of ethanol/acetone. Upon polymerization, the droplets become entrapped within the adhesive, potentially jeopardizing bond durability. This can be avoided by strong air-drying of the adhesive, thereby removing interfacial water and thus improving bonding effectiveness.

Hydrolytic Stability of Self-etch Adhesives Bonded to Dentin

Functional monomers chemically interact with hydroxyapatite that remains within submicron hybrid layers produced by mild self-etch adhesives. The functional monomer 10-MDP interacts most intensively with hydroxyapatite, and its calcium salt appeared most hydrolytically stable, as compared with 4-MET and phenyl-P. We investigated the hypothesis that additional chemical interaction of self-etch adhesives improves bond stability. The micro-tensile bond strength (μTBS) of the 10-MDP-based adhesive did not decrease significantly after 100,000 cycles, but did after 50,000 and 30,000 cycles, respectively, for the 4-MET-based and the phenyl-P-based adhesives. Likewise, the interfacial ultrastructure was unchanged after 100,000 thermocycles for the 10-MDP-based adhesive, while that of both the 4-MET- and phenyl-P-based adhesives contained voids and less-defined collagen. The findings of this study support the concept that long-term durability of adhesive-dentin bonds depends on the chemical bonding potential of the functional monomer.

Effect of remaining dentin thickness and the use of conditioner on micro-tensile bond strength of a glass-ionomer adhesive

OBJECTIVESnThe purpose of this study is to investigate the effect of remaining dentin thickness and the use of a 20% polyalkenoic acid conditioner on the micro-tensile bond strength of a glass-ionomer adhesive to dentin.nnnMETHODSnResin composite was bonded to flat dentin surfaces from 14 extracted human teeth using Fuji BOND LC (GC) with or without a polyalkenoic acid conditioner, then sectioned to thin slabs, trimmed into an hourglass shape with the area of the interface being approximately 1mm(2), and subjected to micro-tensile testing at a cross-head speed of 1mm/min. Micro-tensile bond strengths were determined at three depth levels with a remaining dentin thickness of more than 3mm, between 2 and 3mm, and less than 2mm. Failure modes of the broken interfaces were determined using field-emission scanning electron microscopy.nnnRESULTSnThe micro-tensile bond strength to dentin significantly improved when the remaining dentin thickness increased and the conditioner was used. When the conditioner was used (irrespective of remaining dentin thickness), failures mainly occurred adhesively at the interface between the adhesive and resin composite. When no conditioner was used, no adhesive failures between the adhesive and resin composite occurred, but failures occurred mainly adhesively between dentin and the adhesive, or mixed adhesive-cohesively.nnnSIGNIFICANCEnThe bonding effectiveness of the glass-ionomer adhesive tested was affected by the area of intertubular dentin available for micro-mechanical retention through hybrid-layer formation. Removal of the smear layer improved the bond strength of the adhesive to dentin.

Effect of air-drying and solvent evaporation on the strength of HEMA-rich versus HEMA-free one-step adhesives

OBJECTIVESnThe objectives of this study were (1) to clarify the relationship between the duration of air-drying of one-step self-etch adhesives (1-SEAs) and the evaporation degree (ED) of solvents, and (2) to evaluate the effect of ED on the ultimate micro-tensile strength (microTS) of the adhesives.nnnMETHODSnThe ED of one HEMA-rich 1-SEA, Clearfil S3 Bond (Kuraray), and two HEMA-free 1-SEAs, iBond (Heraeus-Kulzer) and G-Bond (GC), was determined without air-drying and after, respectively, 5- and 10-s air-drying using a gravimetric method. Next, the microTS of the adhesives at ED equivalent to 0-, 5- and 10-s air-drying was measured.nnnRESULTSnThe ED increased with extension of air-drying time. Among the adhesives tested, iBond showed the largest ED, followed by G-Bond and Clearfil S3 Bond in this order. A longer air-drying time for 10-s resulted in a statistically significantly higher microTS for the HEMA-rich Clearfil S3 Bond. The microTS of the latter was higher than that of the other two HEMA-free adhesives for each air-drying time.nnnSIGNIFICANCEnAir-drying of 1-SEAs had a significant effect on the degree of solvent evaporation (ED) and also on the mechanical properties (microTS) of the 1-SEAs upon setting. It is therefore beneficial to remove solvents of the 1-SEAs as much as possible by thorough, strong air-drying in order to achieve a strong adhesive layer at the interface.

Gel Phase Formation at Resin-modified Glass-ionomer/Tooth Interfaces

Ionic bonding between polyalkenoic acid and hydroxyapatite may explain the excellent bonding retention of glass-ionomers in clinical trials. We have here investigated the extent to which the self-adhesiveness of resin-modified glass-ionomers (RMGIs) can be attributed to this chemical bonding capacity. Therefore, the interaction of 3 RMGIs with tooth substrates was comprehensively characterized, with electron and atomic force microscopy correlated with x-ray photoelectron spectroscopy (XPS). Interfacial ultrastructural analysis for 2 RMGIs disclosed a shallow hybridization of hydroxyapatite-coated collagen, on which a submicron gel phase was deposited through reaction of the polyalkenoic acid with calcium extracted from the dentin surface. One RMGI, however, bonded to dentin without hybrid layer or gel phase formation. XPS indicated that polycarboxylic acids included in the RMGIs electrostatically interacted with hydroxyapatite. We conclude that the self-adhesiveness of RMGIs should be attributed to ionic bonding to hydroxyapatite around collagen, and to micro-mechanical interlocking for those RMGIs that additionally hybridize dentin.

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.

Dynamic elastic modulus of ‘packable’ composites

OBJECTIVEnA new type of so-called packable, condensable or mouldable composite has been developed and aims at replacing amalgam for posterior restorations. The purpose of the present investigation was to study the dynamic elastic modulus of 12 packable composites, and to follow the evolution of this property following prolonged water absorption.nnnMETHODSnOf each material ten rectangular samples (1.5x5x35 mm) were prepared. The elastic modulus (GPa) of each sample was determined with a non-destructive dynamic method using a Grindo-Sonic after 24 h of dry storage at room temperature, and after 24h, 1, 3 and 6 months of wet storage at 37 degrees C. All data were analyzed using two-way ANOVA, Bonferroni/Dunns test for multiple comparisons and paired t-test with a significance level of p<0.05. In addition, inorganic filler volume percentages were derived from the phenomenological model introduced by Braem et al. [11].nnnRESULTSnThe studied materials varied widely in terms of elastic modulus, ranging between composites classified as Compact-Filled Densified (elastic modulus of 23.4+/-2.4 GPa) and as Microfine (elastic modulus of 8.5+/-2.1 GPa).nnnSIGNIFICANCEnThe great diversity observed in the elastic modulus of this type of composites necessitates clear specifications with regard to first the definition of marketing terms such as packable and so on, and second the justified use in posterior teeth.

Extraction of Trap States at the Oxide-Silicon Interface and Grain Boundary for Polycrystalline Silicon Thin-Film Transistors

A technique to extract trap states at the oxide-silicon interface and grain boundary has been developed for polycrystalline silicon thin-film transistors with large grains. From the capacitance–voltage characteristic, the oxide-silicon interface traps can be extracted. Potential and carrier density are also extracted. From the potential, carrier density, and current–voltage characteristic, the grain boundary traps can be extracted by considering the potential barrier at the grain boundary. Since these trap states are sequentially extracted, any shape of energy distribution of the trap states can be extracted. The correctness of this extraction technique is confirmed by comparison with two-dimensional device simulation.