Biomedical subjects

Masayuki Kaga

Publications and source records attributed to Masayuki Kaga.

13 recordsLinked to original sources

PubMed2006

Diffusion-induced water movement within resin-dentin bonds during bonding.

It is thought that water-filled channels and nanovoids in resin-dentin bonds represent potential sites for degradation of bonds or hydrolysis of collagen or both. How water gains access to bonded interfaces is not clear. This study evaluated the diffusion-induced water uptake through resin-dentin interfaces during bonding. Two light-cured total-etch adhesive systems (Excite and One-Step Plus) and a chemical-cured adhesive (Amalgambond Plus) were used in this study. Dentin disks were placed in a split-chamber device, and the fluid movement across dentin was measured, with and without a physiological pressure, during bonding procedures and 24 h after bonding. For light-cured adhesives in the experimental groups, a 6 min interval of dark storage was conducted prior to light-curing, to evaluate the diffusion of water through the uncured resin monomers, and to test the effect of prolonged infiltration time of adhesives on water permeability of bonds. Prolonged adhesive infiltration reduced the water permeability of resin-dentin bonds for light-cured adhesives. Water gradients produced by bonding systems contribute to water movement across the dentin-adhesive interfaces during bonding procedures. Differences in chemical formulations for adhesive systems may lead to differences in the extent of diffusion-induced water movement and the amount of water within the resin-dentin bonds.

Dentin↗

PubMed2005

The effects of common errors on sealing ability of total-etch adhesives.

OBJECTIVES: This study evaluated the effect of errors commonly made in using total-etch adhesives, on the resulting bond strength, fluid movement and nanoleakage of resin dentin bonds. METHODS: Two total-etch adhesives were used for bonding to dentin according to the manufacturers' recommendations, with meticulous solvent evaporation (control), or with the introduction of common bonding errors-wet bonding without solvent evaporation (no evaporation), and dry bonding. RESULTS: The 24-hour bond strength of the control was significantly higher than the other groups (p <0.05). For all groups, the higher initial permeability declined significantly after 24 h. The fluid movement across bonded dentin was similar in the control and dry bonding for both adhesives, whereas significantly higher permeability (p<0.05) was recorded for the no evaporation groups even after 24 h. Extensive silver impregnation within hybrid layers was seen by TEM in the no evaporation and dry bonding specimens after 24 h. Dry bonding caused collapse of the collagen matrix and interfered with resin infiltration. In contrast, inadequate solvent evaporation and/or residual water during dentin bonding results in dilution or incomplete polymerization of the resin, leading to severe nanoleakage formation. SIGNIFICANCE: Increased permeability associated with incomplete solvent evaporation in total-etch adhesives may lead to poor bond strength.

Acid Etching, Dental↗

PubMed2005

Permeability of adhesive resin films.

The purpose of this study was to quantify the permeability of adhesive resin films to water by measuring convective flow across thin films. Cured resin films were prepared with the use of five commercially available adhesive resins and an experimental resin. Two types of resin films were prepared from solvated comonomer blends within each product; resin films made before or after evaporation of solvent (10 s of drying with air-syringe). The permeability of the resin films was measured 30 min or 24 h after polymerization by placing the films in a split-chamber device. Fluid filtration rate through the resin films was measured with the use of 20 cm of water pressure. Osmotically induced water movement was measured by applying hypertonic aqueous solutions of CaCl2 or HEMA to the resin films. The results showed that evaporation of solvent before polymerization reduced the permeability of adhesive resin films, compared to permeabilities obtained without solvent evaporation. The cured adhesive resin films were all permeable to water, but to varying degrees.

Adhesives↗

PubMed2004

Deproteinizing effects on resin-tooth bond structures.

This study investigated the effects of NaOCl on resin-tooth bonds to simulate the situations of long-term durability and caries invasion. Resin-tooth bonded specimens were produced with the use of two resin adhesives (Excite and One-Bond). Resin-tooth bonded beams (adhesive area; 0.9 mm2) were serially sectioned and the specimens were immersed in 10% NaOCl medium for 0 (control), 2, 4, and 6 h after being stored in water for 24 h. After immersion, microtensile bond tests were performed. SEM fractography was conducted to calculate each failure mode by image analysis. In addition, the adhesive interface was examined with the use of TEM. In the control specimens, enamel bond strengths had no difference between Excite (45.6 +/- 15.0) and One-Bond (56.9 +/- 12.9). On the other hand, dentin bond strengths had significant difference between Excite (80.6 +/- 21.2) and One-Bond (50.7 +/- 11.2). The bond strengths decreased with increased storage time for both systems with enamel and dentin bonds. The deteriorated mineralized dentin of beams resulted in bond-strength reduction for resin-enamel bonds. For dentin bonding, the adhesive interface was gradually dissolved from the outer to the center portion of the beam. The depletion of collagen fibrils within the demineralized dentin or hybrid layer deformation was found under SEM and TEM examinations. These morphological changes are responsible for bond strength reduction of resin-dentin bonds.

Dental Materials↗

PubMed2004

In vitro testing of all-in-one adhesives as fissure sealants.

PURPOSE: To evaluate the clinical efficacy of all-in-one adhesives as fissure sealants. METHODS: Resin-enamel bonded specimens were fabricated between polished and ground enamel surfaces using two all-in-one adhesives (One-Up Bond F and Xeno CF Bond) and two resin sealants (Teethmate F-1 and Helioseal F). Specimen beams were prepared and microtensile bond tests were performed at a crosshead speed of 1 mm/minute. The bond strengths obtained were subjected to one-way ANOVA and Scheffe's F test (P < 0.05: n=12 for each group). To evaluate the etching effect of phosphoric acid and the all-in-one adhesives, the treated enamel surfaces (37% phosphoric acid, 40% phosphoric acid, or all-in-one adhesives) were examined by FE-SEM. RESULTS: The bond strengths of the two all-in-one adhesives tested to the polished enamel surface were significantly lower (P < 0.05) than to ground enamel. However, no significant differences (P > 0.05) were found between the polished and ground enamel surfaces for resin sealants using phosphoric acid. Under SEM examination, 37% or 40% phosphoric acid etched the enamel surface more than all-in-one adhesives.

Acid Etching, Dental↗

PubMed2003

Degradation patterns of different adhesives and bonding procedures.

Various types of resin adhesives and procedures are available in the clinical field, so comprehensive understanding of degradation is required for each material and bonding procedure. The objective of this study was to investigate the bond durability for different adhesives and bonding procedures. Resin-dentin bonded beams were prepared with the use of two adhesives (One-Up Bond F/self-etching primer system and One Bond/total-etch adhesive) and two experimental groups for the bonding procedure (wet and dry bonding of the total-etch adhesive). Those samples were soaked in water for 24 h(control), 6 and 12 months. After the water immersion, the bond strengths were measured by the microtensile bond test, and subsequently fractography was performed with the use of SEM. Statistically significant reduction of the bond strength (p < 0.05) was apparent after 12 months of water exposure in the range 22-48% of the control. The bonding resin was eluted from the hybrid layer of the self-etching and the total-etch adhesives for the wet bonding. Micromorphological alterations were found due to the hydrolysis of collagen fibrils with the total-etch adhesive for the dry bonding mode. These pathologic alterations were in accord with the bond strength.

Adhesives↗

PubMed2003

SEM and TEM analysis of water degradation of human dentinal collagen.

Recently several long-term studies have reported evidence of the hydrolytic degradation of collagen fibrils based on fractured surface observations after bond testing. Those studies suggested that one cause of the decline in the bond strength was the degradation of the collagen fibrils within the bonds. However, one concern has been raised that the dentinal collagen fibrils may be stable in water that does not contain oral bacteria or enzymes. Therefore, the present study aimed to clarify the micromorphological change in naked collagen fibrils after 500 days of water storage. To prepare exposed collagen fibrils, sectioned and polished human dentin surfaces were acid conditioned for 15 s with the use of two commercially available acid conditioners: All-Etch (10% phosphoric acid) and Uni-Etch (32% phosphoric acid) (Bisco, Inc.). Those specimens were stored in distilled water at 37 degrees C for 1 day (control) for 500 days. After the storage periods, the samples were examined with the use of SEM and TEM. Under SEM and TEM examination, micromorphological alterations (disarrangement of collagen web, widening the interfibrillar space, and the thinning diameter of collagen fibrils) were found in the specimens after 500 days in water.

Acid Etching, Dental↗

PubMed2003

Sublethal, 2-week exposures of dental material components alter TNF-alpha secretion of THP-1 monocytes.

OBJECTIVES: The aim of this study was to investigate the hypothesis that dental material components alter cytokine secretion from monocytes if applied for several weeks at sublethal doses. The current study significantly extended exposure times of monocytes to the components over times published in previous studies. These exposure times approached the estimated average life span of monocytes in the bloodstream. METHODS: Human THP-1 monocytes were exposed to 2-hydroxyethylmethacrylate (HEMA, 0-1.2mmol/l), triethyleneglycoldimethacrylate (TEGDMA, 0-0.75mmol/l), Hg(2+) (0-2 micromol/l), or Ni(2+) (0-20 micromol/l) for 2 weeks. The cells were then collected and additionally incubated for 24h, with or without bacterial lipopolysaccharide (LPS), a common component of dental plaque. TNF-alpha secretion from THP-1 was determined using by enzyme-linked immunosorbent assay. RESULTS: None of the dental material components induced TNF-alpha from THP-1 by themselves, but LPS alone strongly induced TNF-alpha secretion as expected. HEMA and TEGDMA significantly suppressed (40-70%) TNF-alpha secretion from cells stimulated with LPS. Hg(2+) at 2.0 micromol/l doubled TNF-alpha secretion from THP-1s stimulated with LPS over LPS alone. Ni(2+) did not significantly affect TNF-alpha secretion, with or without LPS exposure. Significance. The results in this study suggest that sublethal, 2-week exposures of some dental material components may alter TNF-alpha secretion from THP-1 monocytes when the cells are challenged. These alterations may influence the biological response of tissues to materials in an inflammatory intraoral environment.

Analysis of Variance↗

PubMed2003

In vitro degradation of resin-dentin bonds analyzed by microtensile bond test, scanning and transmission electron microscopy.

Our knowledge of the mechanisms responsible for the degradation of resin-dentin bonds are poorly understood. This study investigated the degradation of resin-dentin bonds after 1 year immersion in water. Resin-dentin beams (adhesive area: 0.9mm(2)) were made by bonding using a resin adhesive, to extracted human teeth. The experimental beams were stored in water for 1 year. Beams that had been stored in water for 24h were used as controls. After water storage, the beams were subjected to microtensile bond testing. The dentin side of the fractured surface was observed using FE-SEM. Subsequently, these fractured beams were embedded in epoxy resin and examined by TEM. The bond strength of the control specimens (40.3+/-15.1MPa) decreased significantly (p<0.01) after 1 year of water exposure (13.3+/-5.6MPa). Loss of resin was observed within fractured hybrid layers in the 1 year specimens but not in the controls. Transmission electron microscopic examination revealed the presence of micromorphological alterations in the collagen fibrils after 1 year of water storage. These micromorphological changes (resin elution and alteration of the collagen fibrils) seem to be responsible for the bond degradation leading to bond strength reduction.

Biocompatible Materials↗

PubMed2003

Resin-enamel bonds made with self-etching primers on ground enamel.

Self-etching primer adhesives have recently been introduced to simplify bonding. However, the fundamental bonding mechanism of self-etching primers to enamel is not yet fully understood. This study aimed to investigate resin-enamel bonds of self-etching primer adhesives on ground enamel. Two self-etching primer adhesives (Clearfil Liner Bond 2 V and Clearfil SE Bond) were used in this study. A total-etch adhesive (One-Step) was used as a control. Resin-enamel beams were subjected to the microtensile bond test. Subsequently, the failure modes of all specimens were quantified using image analysis. Undemineralized and demineralized ultrathin sections of the resin-enamel bonded specimens were examined using transmission electron microscopy. The bond strengths of Clearfil SE Bond (39.8 +/- 11.9 MPa) and One-Step (46.2 +/- 12.7 MPa) were significantly greater than that of Clearfil Liner Bond 2V (30.4 +/- 6.2 MPa). Scanning electron microscopy of the fractured surfaces revealed the failure direction and weakest portion within each bond. Transmission electron microscopy showed a thin hybridized complex of resin in enamel produced by the self-etching primers without the usual micrometer-sized resin tags seen in resin-enamel bonds produced using the total-etch adhesive. The morphological features of the resin-enamel bonds produced by two self-etching primers tested were different from that created with the total-etch adhesive.

Adhesives↗

PubMed2002

Micromorphological changes in resin-dentin bonds after 1 year of water storage.

The purpose of this study was to evaluate the degradation of resin-dentin bonds after 1 year of water storage. Resin-dentin-bonded specimens were prepared with the use of an adhesive resin system (One-Step: Bisco). Half of the experimental specimens were sectioned perpendicular to the adhesive interface to produce a beam (adhesive area: 0.9 mm(2)) before being stored in distilled water at 37 degrees C for 1 year. The remaining half of the bonded specimens were sectioned into beams of similar dimensions after 1 year of water storage. Additional bonded specimens that had been stored in water for 24 h before sectioning into beams were used as controls. The beams in the two experimental groups and the control group were subjected to microtensile bond testing. Fractography was performed on all fractured beams with the use of FE-SEM. There were significant (p <.05) differences in bond strength among the control specimens (55.9 +/- 12.9 MPa), specimens that had been sectioned into beams after water storage (68.9 +/- 18.6 MPa), and specimens that had been sectioned into beams before water storage (28.1 +/- 9.3 MPa). Fractography revealed that the resin material was gradually extracted from the periphery to the center portion of the beam. This probably accounted for the decrease in bond strength after 1 year of water storage.

Bicuspid↗

PubMed2002

Secretion of macrophage migration inhibitory factor differs from interleukin-6 in hydrogen peroxide- and LPS-stimulated human fibroblasts.

To investigate the mechanism for secretion of macrophage migration inhibitory factor (MIF) in cultured human fibroblasts, we compared it with the secretion of interleukin-6 (IL-6) after stimulation with lipopolysaccharides (LPS) and H2O2. MIF content of the medium of 2.0 x 10(6) cells/20 ml after 20 h culture of nonstimulated fibroblasts was 0.30 +/- 0.06 ng/ml, whereas LPS-stimulation (10 microg/ml) only led to a 1.5-fold increase as compared with the nonstimulated cells. In contrast, a significant increase of IL-6 was induced by LPS-stimulation (6048 +/- 488 pg/ml in LPS-stimulated cells vs. 58 +/- 36 pg/ml in control cells). On the other hand, higher concentrations of H2O2 (0.6-1.2 mM) caused an increase of MIF secretion into the culture medium irrespective of LPS-stimulation; with 1.2 mM H2O2-stimulation for 20 h, it was increased to 40-fold as compared with the nonstimulated cells. However, lower concentrations (0.1-0.4 mM) did not cause this. Interestingly, H2O2-stimulation not only failed to increase IL-6 production from fibroblasts, but also repressed induction of IL-6 by LPS-stimulation in a dose-dependent manner. Genistein, a tyrosine kinase inhibitor, and H-7, a protein kinase C inhibitor, also inhibited IL-6 secretion but not MIF secretion in both LPS- and H2O2-stimulated fibroblasts. From analysis of trypan blue exclusion, formazan formation, morphological changes, and intracellular MIF content by Western blotting, we found that MIF secretion by H2O2 seemed to be mainly due to cell death and subsequent leakage of intracellular MIF. Taken together, these results suggest that MIF secretion differs from IL-6 via LPS-mediated signaling pathways.

Fibroblasts↗

PubMedDate not supplied

Effects of multiple adhesive coatings on dentin bonding.

Simple changes to bonding techniques can improve resin-dentin bond strengths. This study evaluated the effect of multiple consecutive coatings of adhesive resin on dentin by measuring both microtensile bond strength and nano-leakage following exposure to ammoniacal silver nitrate. Resin-dentin bonded specimens were prepared using two total-etch adhesives (OptiBond Solo Plus/Kerr or Single Bond/3M ESPE). During bonding, resin application and air evaporation were done 1, 2, 3, 4, 6 or 8 times on acid-etched, moist dentin surfaces. Mean microtensile bond strengths were evaluated by two-way ANOVA and Fisher's PLSD test (p<0.05; n=16 for each group). Additionally, nanoleakage of silver nitrate was evaluated by transmission electron microscopy (TEM). The results indicated that bond strengths increased with each coating up to four coats. Nanoleakage decreased with each coat, becoming very small after four or more coats. This adhesive application method can be easily applied to clinical practice, thereby improving the quality of resin-dentin bonds.

Bicuspid↗