Biomedical subjects

M Iwaku

Publications and source records attributed to M Iwaku.

At least 19 recordsLinked to original sources

PubMed1995

Immunoelectron-microscopic study of the localization of fibronectin in the odontoblast layer of human teeth.

Indirect immunofluorescence-based studies have shown similarities in the distribution patterns of fibronectin-positive fibrous structures and so-called von Korff fibres. The aim of the present study was to analyse the reactivity of fibronectin in the odontoblast layer of fully developed human teeth by means of immunoelectron microscopy. Between the odontoblasts, discrete and undulatory fibrillar fascicles with peroxidase labelling were observed. They seemed to be in contact with odontoblasts in some areas, while in others they appeared to be intervening between two neighbouring odontoblasts. Higher magnifications of the fibrillar material demonstrated axial periodic staining of about 70 nm. Peroxidase reaction of fibronectin was also recognized along the cell membrane of odontoblasts facing predentine. The fibronectin in fibrillar fascicles observed between odontoblasts would be held in place by the direct molecular interaction with collagen fibrils and contribute to the pulpward migration of these cells and maintenance of their specific morphology. At the distal end of odontoblasts, a tight seal would be maintained by means of odontoblast-fibronectin adhesion.

Actin Cytoskeleton↗

PubMed1995

Effects of antibacterial capping agents on dental pulps of monkeys mechanically exposed to oral microflora.

The effects of antibacterial drugs on bacterially contaminated dental pulps were investigated in monkeys. Class V buccal cavities with pulpal exposures were prepared and then left open to the oral environment for 24 h. The exposed pulps were capped with alpha-tricalcium phosphate (alpha-TCP) containing a mixture of antibacterial drugs. Either alpha-TCP or Ca(OH)2 was used as a control. Pulpal responses were histologically evaluated after 4 wk. Those teeth capped with alpha-TCP alone showed total pulp necrosis and bacterial growth within the pulp chamber. By contrast, the pulps capped with alpha-TCP containing mixed antibacterial drugs remained almost normal without any necrotic layer, but showed persistent absorbing response to capping materials and no signs of hard tissue barrier formation. In teeth capped with Ca(OH)2, a hard tissue barrier was formed below the exposure site, with a wide loss of pulp tissue. No inflammation was seen under the barrier. These results indicate that mixed antibacterial drugs added to alpha-TCP effectively disinfected pulpal lesions, without destroying any of the sound pulp tissue. However, hard tissue barrier formation was delayed by this mixture as compared with Ca(OH)2.

Animals↗

PubMed1994

The metabolism of phenylalanine and leucine by a cell suspension of Eubacterium brachy and the effects of metronidazole on metabolism.

Degradation of phenylalanine and leucine by resting cells of Eubacterium brachy ATCC 33089 were studied under strict anaerobic conditions. The effects of metronidazole and air on the metabolism were also studied. The organism principally produced phenylpropionate and isocaproate from phenylalanine and leucine, respectively. Other products were cinnamate and phenylacetate from phenylalanine, and alpha-ketoisocaproate and isovalerate from leucine. The organism also produced hydroxylated end-products, i.e. phenyllactate from phenylalanine and hydroxyisocaproate from leucine. When metronidazole was added to the reaction mixture, the production of phenylpropionate, cinnamate, phenylacetate, isocaproate, alpha-ketoisocaproate and isovalerate was inhibited, while that of hydroxylated products was not, suggesting that the organism has metronidazole-sensitive and -tolerant pathways of metabolism. A similar inhibitory effect was also found when the reaction was done aerobically, suggesting that the inhibitory mode of metronidazole is similar to that of oxygen.

Aerobiosis↗

PubMed1994

A confocal laser scanning microscopic study of the immunofluorescent localization of fibronectin in the odontoblast layer of human teeth.

The distribution of fibronectin in dental pulp was studied in developing and developed human teeth by indirect immunofluorescence using a confocal laser scanning microscope. In the apical region of developing teeth, intense fluorescence was found along the basement membrane facing the mesenchyme of Hertwig's epithelial sheath and first-formed (mantle) predentine. With further elongation of odontoblasts, fibronectin was observed between the cells, appearing as corkscrew fibres passing from the pulp into predentine parallel to the long axis of the odontoblasts. In the coronal region of developing and developed teeth a similar distribution of fibronectin was observed in the odontoblast layer. At the border zone between odontoblasts and predentine the reaction was intense, but was weak in the predentine itself. In the calcified dentinal matrix it had disappeared completely, except for the area along the dentinal tubules. The results demonstrate that fibronectin is present in the odontoblast layer during all stages of dentinogenesis. Fibronectin-positive fibrous structures between odontoblasts probably correspond to von Korff fibres, and are closely related to odontoblast differentiation and dentinogenesis.

Adult↗

PubMed1994

Bacteria invading periapical cementum.

The aim of this study was to determine whether microorganisms invade periapical cementum of human teeth from the adjacent periapical lesions. We therefore attempted to isolate microorganisms from periapical cementum through the adoption of standard anaerobic procedures for obligate anaerobes. Samples of cementum were taken from 10 amputated tooth roots at the time of apicoectomy. From two of these samples, bacteria were recovered after anaerobic incubation, but no bacteria were recovered after aerobic incubation of the same samples. Of a total of eight isolates from the cementum, seven were obligate anaerobes and one was aerotolerant. The obligate anaerobes isolated were assigned to the genera Prevotella, Peptostreptococcus, Eubacterium, and Fusobacterium. The aerotolerant anaerobe was Campylobacter. From this, we conclude that bacteria can successfully invade cementum via periapical periodontal tissue, and that such bacteria may play a significant role in chronic periapical pathosis.

Actinomyces↗

PubMed1994

Histological observations of hard tissue barrier formation in amputated dental pulp capped with alpha-tricalcium phosphate containing calcium hydroxide.

This study was performed to evaluate the pulpal response to alpha-tricalcium phosphate (alpha TCP) containing calcium hydroxide (Ca(OH)2). The dental pulps of monkeys were amputated and dressed with four agents: alpha TCP, alpha TCP containing 1% Ca(OH)2, alpha TCP containing 5% Ca(OH)2, and Ca(OH)2 being used as a control. The pulpal responses were histologically evaluated after 4 and 8 weeks. The pulp tissue treated with alpha TCP proliferated above the level of the original wound surface, and a thin layer of hard tissue barrier was formed directly against the capping agent. The barrier demonstrated atubular matrix lined with flattened or cuboidal cells, but occasionally appeared irregular in form. Ca(OH)2 dressing resulted in destruction of pulp tissue, with a thick hard tissue barrier being formed below the level of the exposure site. The barrier consisted coronally of osteodentin and pulpally of tubular dentin lined with odontoblast-like cells. By contrast, 1% Ca(OH)2 added to alpha TCP produced a slight proliferation of pulp tissue. An atubular matrix barrier, pulpally lined with cuboidal cells, formed above the exposure site. It was later followed by the formation of tubular matrix lined with columnar cells. Teeth treated with 5% Ca(OH)2 showed a thin necrotic layer and a thick barrier formation. The barrier was composed of tubular dentin-like tissue lined with odontoblast-like cells. It would appear that alpha TCP containing a small amount of Ca(OH)2 may be clinically useful as a capping agent, as it induced consistent hard tissue formation, without excessive destruction of underlying pulp tissue.

Animals↗

PubMed1994

In vivo wear pattern of experimental composite resins containing different filler components.

Using a scanning electron microscope (SEM) and an electron probe surface roughness analyzer (ERA), we conducted the in vivo study of the effect of various filler components on the wear of composite resins. Experimental light-cured composite resins were prepared employing three different filler components; -(1) Silica type, (2) Strontium type, and (3) Barium type. The filler content for all three types was 80 wt%, with the mean particlesize being 2.6 microns in diameter. The resin monomers consisted of 40 wt% Bis-GMA, 40 wt% TEGDMA and 20 wt% UTMA. These materials were placed in 2 mm diameter cylindrical cavities located in the OCA (occlusal contact area) or the CFA (contact free area) of cast crowns temporarily set in a volunteer patient's mouth. The crowns were removed at monthly intervals for longitudinal SEM observation. After two months, worn surfaces were also analyzed by ERA. The result showed that the wear patterns of the composites were characterized by the filler components, especially in the OCA.

Adult↗

PubMed1993

Pulpal response to a new light-activated fluoride releasing liner.

The purpose of this study was to investigate the degree of pulp irritation of a newly developed light-activated fluoride-releasing adhesive resin liner using canine teeth compared to the amount caused by a negative control, zinc oxide eugenol cement (ZOE), and a positive control, silicate cement (silicate). In the cases of unexposed pulp, this experimental liner showed none, slight or moderate pulpal changes at 3 d postoperatively. At 30 and 90 d, no pulpal response to the experimental liner was detected in almost all cases. These findings were similar to the ZOE and better than the silicate. There was less evidence of pulpal irritation produced by the experimental liner. This material seems to be safe to the pulp under the conditions of this study.

Analysis of Variance↗

PubMed1993

In vivo wear pattern of experimental composite resins based on different resin monomers.

This study investigated the effects of various monomer systems on composite resin wear in vivo. Experimental light-cured composite resins were prepared employing four different monomer systems: (1) Bis-GMA type, (2) D-2. 6E type, (3) UDMA type, (4) UTMA type. The resin monomers consisted of 70wt% main monomer and 30wt% TEGDMA. These composites contained 80wt% fine quartz. The resins were placed in 2 mm diameter cylindrical cavities located in the occlusal contact area or the contact free area in cast crowns, temporarily set in a mouth. The crowns were removed at monthly intervals, for longitudinal SEM observation. Two months after setting, wear was analyzed, using an electron probe surface roughness analyzer. Microabrasion of the resin matrix and loss of filler particles were observed for all types of monomer systems. The effect of matrix resin systems on occlusal wear was smaller than that of filler systems.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1993

In vivo wear pattern of experimental light-cured hybrid composite resins.

This study evaluated the effect of various types of microfiller on the in vivo wear resistance of composite resins. Experimental light-cured composites with two different microfiller systems were prepared: (1) 56 wt % fine quartz filler, 21 wt% organic filler and 3 wt% colloidal silica filler (Hybrid type 1), and (2) 64 wt% fine quartz filler and 21 wt% colloidal silica filler (Hybrid type 2). The resin monomer consisted of 50 wt % Bis-GMA and 50 wt% TEGDMA. These materials were placed in 2 mm diameter cylindrical cavities located in the OCA (occlusal contact area) or the CFA (contact free area) in cast gold-silver-palladium alloy full coverage crowns, which were temporarily set in a volunteer patient's mouth. The crowns were removed at monthly intervals for SEM observation. Hybrid type 1, which contained organic fillers, showed bulk fractures in the OCA, by the second month of the experiment. However, reinforcement of the resin matrix by dispersion of microfiller provided Hybrid type 2 with superior wear resistance for up to two months.

Adult↗

PubMed1992

A new light-activated adhesive composite: shear bond strength and microleakage.

A new light-activated adhesive composite has been formulated. Its shear bond strength and marginal microleakage were compared with glass ionomer cements: Fuji Ionomer Type II, Ketac-Fil and Ketac-Bond. The new material showed significantly (p < 0.05) higher bond strength to non-etched enamel (7.9 MPa) and dentin (7.3 MPa) than commercially available materials. It also performed significantly better (p < 0.05) in the microleakage test. Ease of use and the excellent marginal sealing ability of the new material are expected to allow considerable innovation in restorations of root caries, cervical erosion and other conditions where the marginal seal of the gingival cavosurface is difficult.

Aluminum Silicates↗

PubMed1992

A new light-activated adhesive cavity liner: an in vitro bond strength and microleakage study.

A new formulation of a light-activated calcium hydroxide-based cavity liner was developed for this study. Its shear bond strength and marginal microleakage in a Class V cavity preparation were compared to those of commercially available light-activated liners and conventional glass ionomer liners: GC Lining Cement (GC), Ketac-Bond (ESPE), Time Line (Caulk), Vitrabond (3M), XR lonomer (Kerr), and Zionomer (DenMat). The new formulation had significantly higher shear bond strength to dentin than the commercially available materials. Its microleakage along gingival (cemento-dentin) walls was statistically equivalent to one of the other materials and significantly better than all the others.

Analysis of Variance↗

PubMed1992

Alveolar bone remodeling in the early stage of experimental apical periodontitis in the rat mandible.

Apical periodontitis was surgically induced in the mandibular first molar of rats and chronological changes in the periapical bone tissue were observed by histochemistry and electron microscopy. On the second postoperative day (Day 2), tartrateresistant acid phosphatase (TRACPase)-positive cells emerged on the bone surface facing the inferior alveolar nerve, whereas alkaline phosphatase (ALPase)-positive cells proliferated on the bone marrow surface of the mandibular canal wall. On Day 3, the active resorption of the mandibular canal wall appeared on the surface facing the inferior alveolar nerve. The bone of the upper wall of the canal was completely resorbed. On Day 4, however, numerous ALPase-positive cells emerged over the bone surface facing the inferior alveolar nerve intermingled with TRACPase-positive cells. On Day 5, repair of the upper wall of the mandibular canal by new bone progressed. Bone formation was also observed on the bone surface facing the inferior alveolar nerve. On Day 6, the upper wall of the mandibular canal was remodeled by the new bone, whereas TRACPase-positive cells had already migrated over the bone surface in the vicinity of ALPase-positive cells. From Days 2 to 5, active trabecular bone formation continued in the bone marrow cavity close to the mandibular canal, while TRACPase-positive cells were found only on Day 6. These demonstrate that inflammatory stimuli activate bone formation coupled with bone resorption, as well as direct trabecular bone formation without a bone resorption phase. A rapid bone turnover in the early stage of apical periodontitis is also suggested. We conclude that bone defects in apical periodontitis are not the result of sole bone resorption but rather, active bone remodeling.

Acid Phosphatase↗

PubMed1992

The effects of various clinical factors on marginal enamel micro-cracks produced around composite restoration.

In this study, enamel micro-cracks produced around composite restorations were observed on surfaces and vertical sections, using a stereomicroscope and a scanning electron microscope (SEM). The effects of various clinical factors, i.e. the curing system, the marginal form and the polishing period after filling, on the incidence of marginal enamel micro-cracks were examined. Enamel micro-cracks were observed on all of the class 1 and 5 composite restorations when the cavity had no marginal bevel and the restorations were polished immediately after filling. Enamel micro-cracks distributed approximately parallel to the cavity margin and located 0.01-0.3 mm from the restored cavity margin. The occurrence of enamel micro-cracks was higher in light-cured composite resin restorations than in chemical-cured ones, for non-beveled cavities when polished 10 min or 24 hours after filling. The occurrence of micro-cracks was reduced by marginal beveling and delayed polishing.

Composite Resins↗

PubMed1990

An ultrastructural study of the process of hard tissue formation in amputated dental pulp dressed with alpha-tricalcium phosphate.

This study was undertaken to determine the reaction of amputated dental pulp to the capping agent, alpha-tricalcium phosphate (alpha TCP), and to reveal the exact nature of the processes involved in both the healing of, and new hard tissue formation in the pulp when dressed with alpha TCP. The dental pulps of the anterior teeth of Macaca fuscata were dressed with alpha TCP ceramic 4-10 microns in diameter. The teeth were fixed by perfusion, then observed with light and electron microscopes. At 10 and 14 days postoperatively, the phagocytosis of the alpha TCP layer by the many macrophages and multinucleated giant cells, both of which had emerged beneath it, was seen. The synthesis of collagenous matrix underlying the alpha TCP layer began at 14 or 21 days, the cells involved exhibiting morphologic characteristics similar to those seen in osteoblasts. By the 90th day, only a bone-like hard tissue remained. No inflammation was observed in the residual dental pulp at any time during the experimental period. At 14 days, needle-like crystals were seen to have formed on the surface of alpha TCP particles, and by the 21st day, these crystals had extended to the newly synthesized matrix, with the result that calcification of the matrix was initiated, a calcified layer being superficially produced in the matrix. In the region of the matrix adjacent to the superficial calcified layer, a number of matrix vesicles were also found to function as another mechanism of matrix mineralization. Thus, it was concluded that the bone-like hard tissue was induced in the pulp capped with alpha TCP, and its potential for clinical application to exposed dental pulp was confirmed.

Animals↗

PubMed1989

Bactericidal efficacy of metronidazole against bacteria of human carious dentin in vivo.

The bactericidal efficacy of metronidazole (MN) against bacteria of carious dentin was estimated by measuring bacterial recovery with or without application of MN to dentinal lesions in vivo. More than 10(3) colony-forming units of bacteria per milligram of sample were recovered from the samples of carious dentin. However, none were recovered from the samples of dentinal lesions which had been covered by alpha-tricalcium phosphate (TCP) cement containing MN in situ for 1 day, 1 month, 1 year and/or 2 years in vivo. Placebo experiments in which carious dentin was covered by TCP cement without MN showed that TCP itself was not bactericidal. Bactericidal efficacy of MN in situ is clearly demonstrated, indicating that MN is a valuable material in caries treatment to disinfect carious dentin.

Adolescent↗

PubMed1989

Culture conditions for efficient recovery of bacteria from infected dental root canals.

For better bacterial recovery from endodontic lesions, several bacterial culture conditions were studied. Samples taken from endodontic lesions of 26 freshly extracted teeth, and the bacterial growth was determined in 11 kinds of growth media under aerobic (in air with or without addition of 5% CO2) or anaerobic conditions (in an anaerobic glove box). Among the media tested, bacteria of endodontic lesions were most efficiently recovered in brain heart infusion medium containing 4% sheep blood (BHI-Blood) under anaerobic conditions. For routine dental practice, serum can be substituted for blood which makes the media opaque, resulting in clear media, and thus bacterial growth can be judged more easily.

Bacteriological Techniques↗

PubMed1988

Bactericidal efficacy of metronidazole against bacteria of human carious dentin in vitro.

The bactericidal efficacy of metronidazole against bacteria in carious dentin was clarified by measuring (1) the difference between bacterial recovery from suspensions of carious dentin on metronidazole-containing BHI-Blood agar plates (10 micrograms/ml) and control plates and (2) the difference between bacterial recovery from carious lesions of freshly extracted teeth, covered by alpha-tricalcium phosphate (TCP) cement containing metronidazole (5%) for 1-3 days and that covered by TCP only. More than 10(3) bacteria per milligram sample were recovered from carious dentin. More than 99% of the bacteria were, however, not recovered when samples were inoculated on metronidazole-containing BHI-Blood agar plates or when the lesions were covered by TCP cement containing metronidazole, indicating that metronidazole effectively disinfected the carious dentin.

Bacteria↗