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Biomedical subjects

Y Akagawa

Publications and source records attributed to Y Akagawa.

At least 55 records · Page 3Linked to original sources
PubMed1997

Effect of friction coefficient on Akers clasp retention.

STATEMENT OF PROBLEM: Retentive force control of clasp retainers is one of the most essential factors for the successful function of removable partial dentures. However, it is not yet known how the friction coefficients differ among restored abutments and clasp materials, and how the friction coefficients affect the retention of clasps. PURPOSE: The purposes of this study were to clarify the friction coefficients among restored abutments and clasp materials and to estimate the effect of friction coefficients on the retention of clasps. MATERIAL AND METHODS: The coefficients of static friction between three clasp materials (type IV gold, high Pd, and cobalt-chromium [Co-Cr] alloys) of two surface treatments (polished and sandblasted) and four abutment materials (human enamel, porcelain, type IV gold, and high Pd alloys) were evaluated under three conditions (dry, wet with water, and wet with saliva), and theoretically, the effect of the friction coefficients on clasp retention was estimated. RESULTS: The friction coefficients under various conditions ranged from 0.08 (polished Co-Cr clasp on type IV abutment in dry condition) to 0.37 (sandblasted Co-Cr clasp on high Pd abutment in dry condition). The theoretical estimation clarified that the retentive force of the clasp was linear to the friction coefficient. CONCLUSION: The retentive force increased linearly with increasing friction coefficient between abutment material and clasp material according to the newly developed formula. This study suggested that clasp designs should be changed depending on abutment materials.

Analysis of Variance↗
PubMed1997

Clinical application of short hydroxylapatite-coated dental implants to the posterior mandible: a five-year survival study.

STATEMENT OF PROBLEM: The surgical and restorative procedures at the posterior region of the maxilla and the mandible present a complex task in the treatment of partially edentulous patients. PURPOSE: The purpose of this study was to investigate the applicability of short hydroxylapatite-coated dental implants to the posterior mandible of partially edentulous patients. MATERIAL AND METHODS: Eight and 11 mm implants were evaluated as to their cumulative survival rate, clinical status (plaque index, gingival index, probing depth), and marginal bone loss over a 5-year period. RESULTS AND CONCLUSIONS: The verified overall cumulative survival rate was 94% for implants and 91% for prostheses. These results suggest predictable success for the application of short implants to the posterior mandible.

Alloys↗
PubMed1997

Prolonged antimicrobial effect of tissue conditioners containing silver-zeolite.

OBJECTIVES: The purpose of this study was to elucidate the in vitro antimicrobial effect of tissue conditioners containing silver-zeolite on Candida albicans and nosocomial respiratory infection-causing bacteria, Staphylococcus aureus and Pseudomonas aeruginosa. METHODS: Five commercially available tissue conditioners were selected: Visco-gel (VG), GC Soft-Liner (SL), Fitt (FT), SR-Ivoseal (IV) and Shofu Tissue Conditioner (TC). Samples, 10 x 10 x 2.5 mm in size, contained silver-zeolite (SZ sample) and no SZ (N sample). The antimicrobial effects of these two samples were evaluated as a percentage of viable cells (CFU) in a microbial suspension (100 microliter) in phosphate-buffered saline with or without immersion in artificial saliva for four weeks. The borderline of the antimicrobial effect was determined at 0.1% viable cells. RESULTS: With the SZ samples, all tested microbes were killed under both conditions of no immersion and immersion in saliva. In non-immersed N samples, however, no cells of C. albicans (except with VG) and S. aureus survived, whereas the percentage of viable cells of P. aeruginosa was similar to that found in the control. However, with immersion in saliva, viable cells of C. albicans in some N samples (VG, SL and TC) increased compared with non-immersion samples by more than 0.1%. CONCLUSION: Tissue conditioners containing SZ have been shown to have antimicrobial effects for four weeks on C. albicans and nosocomial respiratory infection-causing bacteria in saliva in vitro.

Acrylic Resins↗
PubMed1997

Trabecular bone pattern of the mandible. Comparison of panoramic radiography with computed tomography.

OBJECTIVES: To analyse the possible correlation between the trabecular bone pattern of the edentulous mandible visualized by panoramic radiography and the bone mineral density (BMD) measured by computed tomography (CT). METHODS: Panoramic radiography and CT were performed on 28 patients with edentulous mandibles. The trabecular bone pattern of 47 regions on the panoramic radiographs was classified into one of five grades. BMD was measured within circular regions of interest on the axial CT images in the corresponding trabecular area. The gradings were correlated with the CT values using one-way analysis of variance. RESULTS: There was a significant correlation between the grade of the trabecular bone pattern and the BMD (P < 0.0001). CONCLUSION: The proposed classification for the trabecular bone pattern on panoramic radiographs might be a useful aid for the evaluation of the edentulous mandible prior to implant placement.

Adult↗
PubMed1997

Observer agreement in the assessment of mandibular trabecular bone pattern from panoramic radiographs.

OBJECTIVES: To study the observer agreement in the assessment of trabecular pattern of the mandible from panoramic radiographs. METHODS: Seven observers were asked to classify the trabecular pattern of 100 edentulous regions of the mandible in 80 randomly selected panoramic radiographs into one of five grades with the aid of a written description and reference images. Intra- and interobserver agreement was calculated as overall agreement and Kappa index. RESULTS: The intra-observer agreement varied between 65% and 79%. The Kappa index for intra-observer agreement was moderate for three observers and substantial for four. For all seven observers, it varied according to the grade of trabecular bone pattern, but the majority deviated from each other by only one grade. CONCLUSION: The relatively high rates of observer agreement indicate that panoramic radiography can be used for the clinical assessment of the trabecular pattern of the mandible.

Adult↗
PubMed1997

High incidence of Staphylococcus aureus from dentures and tongues of maxillary resection patients.

The incidence and virulence of Staphylococcus aureus from upper dentures and tongues of maxillary resection and edentulous patients were examined. The incidence rates of S. aureus on dentures and tongues from the 8 maxillary resection patients were significantly higher than those from the 20 maxillary edentulous patients. Some S. aureus strains in both patient groups were resistant to antibiotics, and 1 methicillin-resistant S. aureus strain was isolated in each group. Exfoliative toxin was not produced, whereas diverse types of enterotoxin were detected in 4 of the 8 maxillary resection patients and in 3 of 13 maxillary edentulous patients. These findings show that S. aureus inhabits dentures and tongues of maxillary resection patients more often than those of maxillary edentulous patients and that some strains have potential virulence, suggesting that maxillary resection patients are potentially more exposed to a threat from S. aureus and would be the carriers.

Aged↗
PubMed1997

Stimulation of platelet-activating factor synthesis by neurotransmitters in salivary glands.

Platelet-activating factor (PAF), a phospholipid mediator exhibiting potent biological activities, has been shown to stimulate amylase release from the pancreas and salivary glands. The capacity of salivary glands for PAF biosynthesis in response to stimulation has also been demonstrated. To elucidate the role of PAF in salivary glands, we studied the regulation of platelet-activating factor synthesis by the autonomic nervous system in canine salivary glands. Acetylcholine and ionomycin stimulated PAF production in dispersed cells from parotid, submandibular, and sublingual glands of dogs. Norepinephrine and phenylephrine, but not isoproterenol, also stimulated PAF production in submandibular gland cells. Norepinephrine-induced PAF production was blocked by phentolamine but not by propranolol. Acetylcholine and norepinephrine increased both the PAF production and liberation of [14C]arachidonic acid from cells pre-labeled with [14C]arachidonic acid in the presence of Ca2+ in the medium. These stimulants increased [14C]arachidonic acid liberation without the accompanying production of PAF in Ca(2+)-deprived medium. No activators or inhibitors of protein kinase C produced or affected acetylcholine-induced PAF production. Lyso-PAF:acetyl-CoA acetyltransferase was activated in the cells treated with acetylcholine, norepinephrine, isoproterenol, and 8Br-cyclic AMP. Deprivation of Ca2+ in the medium markedly reduced acetylcholine-induced activation of the transferase, but little affected norepinephrine-, isoproterenol-, and 8Br-cyclic AMP-induced activation. Dithiothreitol-insensitive cholinephosphotransferase activity was also increased by acetylcholine, norepinephrine, isoproterenol, and 8Br-cyclic AMP, and the deprivation of Ca2+ in the medium further increased the activation of the enzyme activity by these agents. These results suggest that PAF synthesis in canine salivary glands is under the control of muscarinic cholinergic and alpha-adrenergic systems via Ca(2+)-dependent remodeling pathways, and that the independent activation of either phospholipase A2 or acetyltransferase is insufficient for PAF production in submandibular gland cells, i.e., the concurrent activation of these enzymes is required.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1996

The three-dimensional bone interface of an osseointegrated implant. I: A morphometric evaluation in initial healing.

Direct bone-implant interface as an indicator of endosseous implant success appears to have been overinterpreted because 100% bone apposition is not necessarily obtained at the surface of the endosseous dental implant. The purpose of this study was to obtain quantitative information about the three-dimensional bone structure around three hydroxyapatite-coated titanium alloy dental implants. Implants were placed in the mandible in three monkeys, and the surface bone contact ratio in the buccal, lingual, mesial, and distal directions was computed. Computer graphics were generated by the integration of data for serial ground surfaces obtained at 75 microm intervals of the tissue block involved with the implant. The bone contact ratio of the whole surface of each of the three implants was 80.8%, 68.1%, and 68.8%, and the bone contact ratio for each direction and portion varied with the conditions of implant placement. The bone volume ratios around the implant at the 0 to 300 microm zone were also calculated, and total ratios ranged from 58% to 81%. These results may provide useful quantitative information about the bone structure around the hydroxyapatite-coated implants and contribute to the development of realistic finite element analysis models based on the biologic bone structure around the implants.

Animals↗
PubMed1996

The three-dimensional bone interface of an osseointegrated implant. II: A morphometric evaluation after three months of loading.

To clarify the three-dimensional bone structure around two plasma-sprayed hydroxyapatite-coated titanium implants loaded for 3 months in a monkey, computer graphic evaluation was performed after computer-assisted integration of 70 serial buccolingual sections at 75 microm intervals. Quantitative analysis of the bone contact ratio (BCR) was also conducted with programmed software. The graphics revealed the macroscopic bone structure. The BCR values varied in portions from the top to the bottom of the implant and in the buccolingual or mesiodistal directions. Because these two implants had more cortical bone at the top portion in the lingual direction, the BCR was greatest in the lingual direction. The BCR values at the bottom portion of the two implants were greater than those at the top portions along the horizontal plane, which suggested the effect of loading. The lowest BCR value was observed at the top portion of one implant at a site where moderate periimplant gingivitis was observed. The total surface BCR value for the implants was 69.3% and 64.5%. These results provide additional detailed information on the bone structure around the hydroxyapatite-coated implant after short-term loading.

Animals↗
PubMed1996

Isolation and characterization of teichoic acid-lake substance as an adhesin of Staphylococcus aureus to HeLa cells.

A cell wall component that bound to HeLa cells (HeLa cell-binding CWC) was isolated from a clinical isolate of Staphylococcus aureus. The HeLa cell-binding CWC was resistant to heat (100 C, 1 hr) and proteases, did not stain with Coomassie Brilliant Blue R-250 on SDS-PAGE but stained as a broad band with antiserum against the strain on Western blots. These data suggest that the HeLa cell-binding CWC is not a protein, and may be teichoic acid. Purified teichoic acid bound to HeLa cells, whereas fractions without teichoic acid did not. In Western blots, HeLa cell-binding CWC appeared as a broad band of less than 35 kDa, similar to that of purified teichoic acid. These data suggest that the HeLa cell-binding CWC obtained in this study is teichoic acid. Teichoic acid inhibited S. aureus adherence to HeLa cells and bound to the cells time and dose dependently, in a saturable and reversible manner, and therefore appears to be an adhesin of S. aureus to HeLa cells.

Adhesins, Bacterial↗
PubMed1995

Hardness and fracture toughness of four commercial visible light-cured composite resin veneering materials.

Four commercial visible light (VL)-cured composite resin veneering materials with a dentine shade were examined for their Knoop hardness and fracture toughness. Composite specimens were classified into three groups. The first group was cured by VL only, the second group was cured by VL and post-cured by VL and the third group was cured by VL and post-cured by heat. It became evident that one composite containing four-functional urethane monomer had both hardness and fracture toughness greater than those of the other three composites containing two-functional urethane monomer. The filler content (vol%) in the composite tended to be linearly proportional to both hardness and fracture toughness. Post-curing by VL and heat were proven to effectively increase both hardness and fracture toughness of once light-cured composites. These results suggest that the clinical performance (e.g. wear resistance and colour stability) of VL-cured composite resin veneering materials might be improved with the aid of post-curing.

Composite Resins↗
PubMed1995

Periodontal tissue regeneration on the surface of synthetic hydroxyapatite implanted into root surface.

Several studies have demonstrated that periodontal ligament (PDL)-derived cells can form a new connective tissue attachment (NCTA) not only on denuded dentin but also on nondental inorganic materials. Although the cellular response to these materials may be different than that to denuded dentin, the process of NCTA formation on the surface of non-dental inorganic materials is still undetermined. In the present study, we compared the process of NCTA formation on the surface of an inorganic material with that on a denuded root surface by implanting a block of synthetic hydroxyapatite (HA) into a root cavity prepared on the first molar of a rat. We then observed tissue regeneration under conditions where the PDL-derived cells could populate the HA surface using an occlusive membrane. After fibrinous exudation at 3 days postoperatively, granulation tissue from the PDL filled the space between the HA block and the membrane at 1 week. Four weeks after the operation, although the granulation tissue increased in density at the interface to the HA block, no obvious deposition of cementum-like tissue was seen on the HA block. Six weeks after the operation, the deposition of cementum was observed on the surface of the HA block. The deposition of cementum became more extensive and insertion of collagen fibers into the cementum layer became more obvious 8 weeks postoperatively. Twelve weeks after the operation, the cementum covered almost the entire surface of the HA block. On the surface of the denuded dentin in control teeth, cementum deposition was seen at 4 weeks after the operation and increased in thickness from 6 weeks on.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

The effects of early occlusal loading on one-stage titanium alloy implants in beagle dogs: a pilot study.

The initial stages of bone healing with titanium alloy implants were compared clinically and histologically in three groups of beagle dogs: unloaded one-stage (group 1), loaded one-stage (group 2), and unloaded two-stage (group 3). No implant mobility was reported in any of the three groups. For the most part direct bone contact was achieved, but there was a significant difference in the histologic results of the interface among the animals in all three groups. Significant crestal bone loss was evident in group 2, which showed poor bone apposition to the bottom of the threads in the upper portion of the implant. New bone growth to these same areas of the threads was seen in the animals in groups 1 and 3, with the ratio of direct bone contact significantly higher for those in group 3. These differences could be attributed to the effect of early occlusal loading on the implant during initial bone healing.

Alveolar Bone Loss↗
PubMed1993

Changes of subgingival microflora around single-crystal sapphire endosseous implants after experimental ligature-induced plaque accumulation in monkeys.

A study was performed to evaluate the change of subgingival microflora with plaque accumulation around the single-crystal sapphire implant. Four implants were inserted into mandibular and maxillary edentulous regions, and the super-structure was inserted 1 month after implant insertion in each of nine monkeys. Plaque control was maintained for 3 months after insertion to establish the baseline. Plaque was allowed to accumulate on one side by placement of ligatures around the implants and natural teeth with no plaque control. On the other side plaque control was continued for 9 months. Both the implants and natural teeth on the ligature side showed significant increases in proportions of motile rods and spirochetes. No significant difference of microflora was detected between the implants and natural teeth. These findings indicate that plaque control is necessary to maintain the normal microflora around the implant.

Aluminum Oxide↗
PubMed1993

Interface histology of unloaded and early loaded partially stabilized zirconia endosseous implant in initial bone healing.

Clinical and histologic evaluations of partially stabilized zirconia endosseous implants under unloaded and early loaded conditions in four beagle dogs were performed to examine the possibility of osseointegration of a newly developed one-stage zirconia implant during initial bone healing. No clear difference in clinical features was observed. Direct bone apposition to the implant was generally seen in both implants. However, loss of crestal bone height was quite evident around the loaded implants. These findings suggest that the initial unloaded condition is preferable to achieve osseointegration of one-stage zirconia implants.

Alveolar Bone Loss↗
PubMed1993

New periodontal ligament formation on a synthetic hydroxyapatite surface.

The aim of this study was to investigate whether a new connective tissue attachment can occur on a surface of hydroxyapatite (HA) when periodontal ligament (PDL)-derived cells with the ability to form new connective tissue attachment are allowed to populate the surface of HA. Six maxillary canines from 3 cats were used for this experiment. Under anesthesia, fenestration of the buccal alveolar bone was performed over the canine root and a cavity was prepared on the root surface. A synthetic HA block was inlaid and cemented into the root cavity. A Teflon membrane was then placed to cover the access opening of the alveolar bone to guide PDL-derived cell proliferation into the surface of the HA block. Finally, the gingival tissue flap was replaced and sutured. Six months after the operation, histologic evaluation was done by serial sections. In 4 of the 6 canines, PDL-derived cells successfully populated the HA surfaces and a layer of cementum-like tissue was formed on the HA blocks. A PDL-like connective tissue layer was seen between the cementum-like layer covering the exposed HA surface and the newly formed alveolar bone sealing the bone fenestration. Collagen fibers in the PDL-like tissue inserted their ends into the newly formed bone and the cementum-like tissue. The present findings demonstrated that PDL-derived cells can form a new connective tissue attachment on HA.

Animals↗