Biomedical subjects

Y Akagawa

Publications and source records attributed to Y Akagawa.

At least 19 recordsLinked to original sources

PubMed2001

Gramicidin-perforated patch analysis on HCO3- secretion through a forskolin-activated anion channel in rat parotid intralobular duct cells.

Forskolin-induced anion currents and depolarization were investigated to clarify the mechanism of HCO3- secretion in the intralobular duct cells of rat parotid glands. Anion currents of the cells were measured at the equilibrium potential of K+, using a gramicidin-perforated patch technique that negligibly affects intracellular anion concentration. The forskolin-induced anion current was sustained and significantly (54%) suppressed by glibenclamide (200 microM), a blocker of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel. The anion current was markedly suppressed by addition of 1 mM methazolamide, a carbonic anhydrase inhibitor, and removal of external HCO3-. Forskolin depolarized the cells in the current-clamp mode. Addition of methazolamide and removal of external HCO3- significantly decreased the depolarizing level. These results suggest that activation of anion channels (mainly the CFTR Cl- channel located in luminal membranes) and production of cytosolic HCO3- induce the inward anion current and resulting depolarization. Inhibition of the Na(+)-K(+)-2Cl- cotransporter and the Cl(-)-HCO3- exchanger had no significant effect on the current or depolarization, indicating that the uptake of Cl- via the Na(+)-K(+)-2Cl- cotransporter or the Cl(-)-HCO3- exchanger is not involved in the responses. Taken together, we conclude that forskolin activates the outward movement (probably secretion) of HCO3- produced intracellularly, but not of Cl- due to lack of active Cl- transport in parotid duct cells, and that the gramicidin-perforated patch method is very useful to analyze anion transport.

Amiloride↗

PubMed2001

An in vitro wear study of posterior denture tooth materials on human enamel.

This in vitro study evaluated the wear effects of five posterior denture tooth materials on human enamel. The tooth specimen was cusp shaped and enamel specimen was formed as a 10 C 10 C 5 mm plate. All material-enamel combinations were tested using a machine designed to produce sliding contact 20 C 104 times at 60 cycles min-1 and a 4-mm sliding distance per stroke in the bucco-lingual direction under a load of 1 kg. Wear analysis was measured as the total height loss of each combination. In addition, the surface roughness (Ra) of each worn specimen was also evaluated. The least total height loss occurred with poly (methyl methacrylate) (PMMA) enamel pair, and the greatest did with porcelain (Po)-enamel pair. The lowest compound Ra value was measured in high-strength resin (HR)-enamel pair, and the highest in Po-enamel pair. These findings suggest that the best combination is PMMA-enamel, and the poorest combination is Po-enamel.

Acrylates↗

PubMed2001

Finite element analysis on preferable I-bar clasp shape.

An I-bar clasp is one of the most popular direct retainers for distal-extension removable partial dentures. However, no adequate information is available on preferable shape as determined by biomechanics. This study aimed (1) to investigate, by finite element analysis (FEA), the dimensions and stress of I-bar clasps having the same stiffness, and (2) to estimate a mechanically preferable clasp design. Three-dimensional FEA models of I-bar clasps were created with vertical and horizontal straight sections connected by a curved section characterized by six parameters: thickness of the clasp tip, width of the clasp tip, radius of the curvature, horizontal distance between the base and the vertical axis, vertical dimension between the tip and the horizontal axis, and taper (change of width per unit length along the axis). Stress was calculated with a concentrated load of 5 N applied 2 mm from the tip of the clasp in the buccal direction. A thinner and wider clasp having an taper of 0.020-0.023 and radius of curvature of 2.75-3.00 showed less stress. The results suggest that such a shape might be the preferable I-bar clasp shape as biomechanical viewpoint.

Algorithms↗

PubMed2000

Morphogenetic behavior of periodontium on inorganic implant materials: an experimental study of canines.

Periodontal ligament derived cells have the potential to regenerate all the components of the periodontium on the surface of inorganic implants, as well as on dentin. This suggests the hypothesis that the nature of the material affects the migration, proliferation, and differentiation of the progenitor cells for periodontium formation. To clarify this hypothesis, we evaluated the material-specific morphogenetic potential of periodontium-derived cells using an animal model for inducing cell migration from the functioning periodontium onto bioactive (hydroxyapatite, HA) and bioinert (titanium alloy, TA) material. Histologically, total periodontium including calcified cementum-like tissue only formed on HA and not on TA. Morphometrically, however, the length of fibrous connective tissue formed on HA was the same as on TA. This suggests that the bioactivity of the material does not affect the migration of periodontium-derived cells but strongly influences cell differentiation.

Animals↗

PubMed2000

Diverse mechanisms of osteoblast spreading on hydroxyapatite and titanium.

Hydroxyapatite (HA) is an osteoconductive implant material. We previously demonstrated that RGD peptides regulate the spreading of HOS cells on HA but not on titanium, speculating that the osteoconductivity of HA might be attributed to this RGD domain-dependent spreading of osteoblasts. To confirm this hypothesis, the molecules which regulate the spreading of HOS cells on HA and on titanium were investigated. The 50% effective dose (ED50) of RGD peptide for the spreading on HA was five fold lower comparing to titanium. Anti-alphaV integrin antibody, vitronectin, and fibronectin inhibited the spreading on HA but not on titanium. In Western blot analysis, vitronectin and fibronectin were found in components adsorbed to HA but not to titanium. Taken together, the spreading of HOS cells on HA but not on titanium requires the interaction of alphaV integrin and its ligands. The ED50 of the RGD peptides on titanium but not on HA was remarkably reduced by neuraminidase treatment, that by itself could not inhibit the spreading on both materials. This phenomenon suggests that RGD domain and sialic acid cooperatively but not independently mediate the spreading of HOS cells on titanium. Collectively, the molecules regulating the spreading on HA are apparently different from those on titanium. The spreading of osteoblasts mediated by RGD domain of vitronectin and fibronectin might contribute to the osteoconductive ability of HA.

Biocompatible Materials↗

PubMed2000

Controlled local application of basic fibroblast growth factor (FGF-2) accelerates the healing of GBR. An experimental study in beagle dogs.

This animal study was performed to ascertain whether the regeneration of membrane-protected bone defects can be accelerated by the controlled application of basic fibroblast growth factor (FGF-2) using a new drug delivery system. Standardized alveolar bone defects were made surgically in 9 beagle dogs, and FGF-2 was administered using specially made collagen minipellets. A minipellet containing either 0.15 microgram FGF-2 (FGF) or 0 microgram FGF-2 (placebo) was placed in the defect or no minipellet was used (control), and bone regeneration was evaluated radiologically, histologically, and histometrically 8 weeks after the operation. Radiographs showed a surprisingly large radiopaque region in FGF sites compared with placebo or control sites. Histologically, mature bone filled the majority of the inner space of the membrane-protected defect in FGF sites. New bone formation was also seen in the control and the placebo sites, however, it filled less than half the area of the defect. Histometrically, the area of regenerated bone in FGF sites was significantly higher than in the other sites (P < 0.01). These results demonstrate that the controlled application of FGF-2 accelerates bone regeneration in membrane-protected bone defects in the canine model.

Alveolar Process↗

PubMed2000

A biomechanical effect of wide implant placement and offset placement of three implants in the posterior partially edentulous region.

To prevent loosening or fracture of screws retaining the prosthesis to the implants in the posterior partially edentulous region, the use of staggered buccal and lingual offset placement or wide implants is suggested. However, it is not known how this usage compensates for the torque produced by lateral occlusal forces. This study evaluated the effectiveness of offset placement of three implants and a wide implant placement at the most posterior site. Three-dimensional geometric analysis was used to calculate the tensile force applied to gold screws in clinical situations with buccal or lingual loading perpendicular to cuspal inclination (10 or 20 degrees ). Four variations of the placement of three implants (3.75 mm) are: (1) straight; (2) buccal offset of the second implant; (3) lingual offset of the second implant; (4) a wide implant (5 mm) placement at most posterior site. The offset placement did not always decrease tensile force at the gold screw, but wide implant placement and decrease in cuspal inclination did.

Bicuspid↗

PubMed2000

A method for quantifying overall satisfaction of complete denture patients.

Reproducible and quantitative evaluation of patient satisfaction with their complete dentures is of great importance for preoperative diagnosis, treatment planning and assessment of complete denture treatment outcome. This study attempted (1) to clarify the degree of contribution of various factors to overall satisfaction, and (2) to develop a method for quantitative assessment of overall satisfaction with complete dentures. Twelve satisfaction factors and a three-grade scale were used to assess 302 complete denture patients. The contribution of each grade of the 12 factors to the overall satisfaction level was determined by multiple regression analysis. Seven factors were highly correlated to the overall satisfaction. Based on the level of contribution by these seven significant factors, a scoring method for satisfaction was established. Category scores for these factors were calculated and the sum of the category scores was converted to an integer between 0 and 100. The resulting quantification score was closely correlated with overall satisfaction. A protocol for scoring overall satisfaction was developed based on the scientifically analysed contribution of each satisfaction factor.

Aged↗

PubMed2000

Biomechanical effects of double or wide implants for single molar replacement in the posterior mandibular region.

Double implants have been thought to have biomechanical advantages for single molar replacement. To evaluate the effectiveness of double implants versus a wide implant, the vertical forces and torque on each implant were calculated by three-dimensional geometric analysis. Buccal load (100N) perpendicular to cuspal inclination (20 degrees) was applied at the occlusal surface of the superstructure. The three kinds of load points (A, B, C) were 1.5, 3.5, and 5.5 mm from the mesial contact point, respectively. Three implants were compared: mesial and distal double implants (phi 3.3 mm), and a wide implant (phi 5 mm). The wide implant showed torque around the long axis (1.8-15.0 N x cm) whereas double implants had no torque. On the other hand, the vertical forces on the mesial double implant were both smaller (60%: loaded at point C) and larger (140%: loaded at point A) than the wide implant. Given the smaller surface area of the mesial double implant, this large force may generate much higher stress in the peri-implant bone. These results suggest that the biomechanical advantage of double implants for single molar replacement is questionable when the occlusal force is loaded at the occlusal surface near the contact point.

Biomechanical Phenomena↗

PubMed2000

Dimensional measurement and finite element analysis of I-bar clasps in clinical use.

An I-bar clasp is a popular retainer for distal-extension removable partial dentures. However, there have been almost no evidence-based criteria on the mechanically preferable shape. The present study aimed to investigate the variations of dimension in I-bar clasps used in patients, and to clarify the effect of the variations on stiffness and stress of I-bar clasps by finite element analysis. Dimensions (thickness, width, taper, radius of curvature, length, relation to oral structures) of 23 I-bar clasps were measured. A three-dimensional finite element model was made for each measured I-bar clasp with vertical and horizontal straight sections connected with a curved section. A concentrated load of 5 N was applied at the lowest point of the tip that contacted the abutment in the buccal direction. Maximal equivalent stress and stiffness of each clasp were evaluated. The measured dimension, stiffness, and maximum stress showed wide variations. Mean stiffness was far from the proper one, and mean stress was near the proportional limit of Co-Cr alloy. Considering the stiffness and stresses in this study, only six clasps out of 23 were appropriate. These results suggest that evidence-based criteria of preferable shape of I-bar clasps should be determined.

Dental Clasps↗

PubMed2000

Isolation and serum-free culture of epithelial cells derived from epithelial rests of Malassez in human periodontal ligament.

To study biological character and function of epithelial rests of Malassez (ERM) in human periodontal ligament, we have developed a serum-free culture system of epithelial cells (ME) derived from ERM. The mitogenic effects of fibroblast growth factor (FGF)-1, FGF-2, and FGF-7/keratinocyte growth factor (KGF) on ME, human periodontal ligament-derived fibroblasts (PLF), human oral epithelial cells (OE), and human submandibular gland-derived epithelial cells (SGE) were investigated under a serum-free culture condition. FGF-1 and FGF-7/KGF stimulated the growth of both ME and SGE but FGF-2 had no effect. On the other hand, FGF-1, FGF-2, and FGF-7/KGF increased the OE proliferation. These results suggested that the divergent requirement of FGF ligands among these cells would be attributed to the different expression pattern of FGF receptor (FGFR) messenger ribonucleic acid (mRNA) isotypes. Therefore, we examined the expression of FGFR isotypes in these cells. Reverse transcription-polymerase chain reaction (RT-PCR) analysis of ME-and SGE-derived mRNAs revealed the presence of mRNA encoding FGFR2-IIIb, a high affinity receptor for FGF-1 and FGF-7/KGF. However, no mRNAs for other FGFR isotypes were detected in both ME and SGE. On the contrary, OE expressed FGFR1-IIIc, FGFR3-IIIb, and FGFR4 mRNAs as well as FGFR2-IIb. These results indicate that FGF binding sites on ME dominantly bind to FGF-1 and FGF-7/KGF, which transduce their signals via FGFR2-IIIb. Immunohistochemical analysis, PCR-Southern, ribonuclease protection assay (RPA), and Western blotting revealed that PLF expressed FGF-7/KGF mRNA and its peptide. These observations suggest that FGF-7/KGF might mediate epithelial-mesenchymal interactions between ME and PLF to maintain normal structure and function of periodontal ligament.

Blotting, Southern↗

PubMed1999

Dynamic viscoelastic properties of antimicrobial tissue conditioners containing silver-zeolite.

OBJECTIVES: The purpose of this study was to determine the effects of including the antimicrobial silver-zeolite (SZ) on the dynamic viscoelastic properties of various tissue conditioners. METHODS: The dynamic viscoelastic properties of five commercially available tissue conditioners: Visco-gel (VG), GC Soft-Liner (SL), FITT (FT), SR-Ivoseal (IV) and Shofu Tissue Conditioner (TC) containing SZ were evaluated after 1 and 28 days of water- and artificial saliva immersions with the use of complex modulus and loss tangent parameters. Values for these two parameters for each tissue conditioner were statistically analyzed by one- and two-way ANOVA and Bonferroni's test. RESULTS: Complex modulus and loss tangent values of TC were not significantly different among specimens containing 0, 2, 5 and 10 wt.%-SZ, respectively. In FT and TC containing 2 wt.%-SZ, these values were not significantly different between 1 and 28 days in both water- and saliva immersions. CONCLUSION: The results suggest that incorporating SZ does not affect TC's inherent dynamic viscoelastic properties, while the other tissue conditioners investigated may be found to have changed viscoelastic properties as a consequence of the inclusion of SZ.

Acrylic Resins↗

PubMed1999

Finite element analysis of the effect of vertical curvature on half-oval cast clasps.

High stresses in half-oval cast clasps are the main causes of deformation or fracture. A vertical curvature in clasps is said to be effective in reducing stress. However, such claims lack scientific basis. The purpose of the present study was to evaluate stress and stiffness in a three-dimensional (3D) finite element analysis (FEA) model of clasps with different vertical curvatures, cross-sectional forms and tapers, and to clarify the effect of vertical curvature on the half-oval cast clasp. Circumferential clasp arms for the mandibular second premolar were analysed by 3D FEA. The clasp arms were approximated by curved cantilever beams with a half-oval cross-section around a cylinder. The radius of curvature was set at 4 mm and the angle subtended by the clasp arm was 120 degrees. The clasp tip was set at a point 2 mm lower than the base. In the 'No-taper' half-oval clasp arm, stress increased and stiffness decreased with the increase in vertical curvature. In the shape of a preformed wax pattern (thickness/width = 0.80, tip/base = 0.70), stress and stiffness decreased slightly. In an 'Original' form (thickness/width = 0.33, tip/base = 0.80), vertical curvature had a very slight effect on stress and stiffness, and stress was the lowest. These findings suggest the superiority of the 'Original' form, with less stress and no effect of vertical curvature.

Dental Casting Technique↗

PubMed1999

Developmental and pharmacological features of mouse emotional piloerection.

We demonstrated emotional piloerection in mice given conditioned fear stress by means of a pass-through apparatus. The emotional piloerection was first assessed in mice of different ages. The results showed that the piloerection changed with age. Pharmacological studies showed that the piloerection was inhibited by an alpha 1-adrenoceptor antagonist prazosin, but, surprisingly, was not inhibited by anxiolytic diazepam. These findings strongly suggest that the neuronal system of piloerection is different from that of freezing behavior, and that the neuronal system of piloerection develops with age.

Adrenergic alpha-Antagonists↗

PubMed1999

The fragment of complement 3a lacking the primary 9 amino acids induces promoting activity on mouse voluntary running.

We have newly found that interleukin-2 (IL-2) increases mouse voluntary running 24 hours, but not 30 minutes, after the injection. We suspected that IL-2 induced a substance increasing the voluntary running for 24 hours after injection. Serum obtained from mice 24 hours after the IL-2 treatment was fractioned with the use of an ion-exchanger and an ultra-filtration method, and the amino acid sequence analysis indicated that the substance purified from the effective fraction was a fragment of mouse complement 3a (C3a) lacking the primary 9 amino acids. The 20 amino acid peptide synthesized according to the fragment showed the activity increasing the voluntary running, but the 20 amino acid peptide synthesized according to the C3a itself did not. The effect of the synthesized peptide was demuted by haloperidol but not by a specific dopamine 2 antagonist (-)sulpiride. The present findings clearly indicate that IL-2 produces the C3a fragment lacking the primary 9 amino acids which directly promotes the voluntary running, and that the effect of the fragment is mediated by an activity of haloperidol on the neurons, except for the dopamine 2 antagonism.

Amino Acid Sequence↗

PubMed1999

Effects of repeated selective serotonin reuptake inhibitor paroxetine treatments on mouse forced swimming.

Studies were performed in the mouse forced swimming model, a well known experimental depression model, in order to detect the mechanism of the antidepressive effects induced by repeated serotonin reuptake inhibitor (SSRI) dosing. Five-day repeat dosing of a typical SSRI, paroxetine, increased climbing, a distinctive antidepressive behavior, 1 h after but not 1 h before treatment. The coinjection of paroxetine and serum in mice treated with four repeated doses of paroxetine distinctively increased the behavior, but the coinjection of paroxetine and serum in mice without paroxetine did not. These results indicate that repeated dosing of paroxetine produces a serum substance related to the antidepressive effects induced by serotonin neuron activities. Furthermore, the behavior induced by 5-day repeated dosing of paroxetine was decreased by 100 and 10 micrograms/kg of ketanserin (5-HT2 antagonist) and 100 micrograms/kg of LY-278584 (5-HT3 antagonist). The present findings strongly suggest that repeated dosing of paroxetine produces a serum substance stimulating the antidepressive neuronal pathway sensitively mediated by 5-HT2 and 5-HT3 receptor activity.

Animals↗

PubMed1998

Comparison between freestanding and tooth-connected partially stabilized zirconia implants after two years' function in monkeys: a clinical and histologic study.

STATEMENT OF PROBLEM: Partially stabilized zirconia implants placed by a 1-stage procedure have been previously shown to obtain initial osseointegration under clinically unloaded condition. However, it is unknown whether freestanding and tooth-connected partially stabilized zirconia implants can maintain a long-term direct bone-implant interface. PURPOSE: This study examined the possibility of the long-term stability of osseointegration around partially stabilized zirconia implants with a 1-stage procedure with different loading designs. MATERIAL AND METHODS: Thirty-two partially stabilized zirconia implants were placed into the mandibles of 8 monkeys. Three months after implant placement, 3 types of superstructure were provided in each animal to obtain different concepts of support as (1) single freestanding implant support, (2) connected freestanding implant support, and (3) a combination of implant and tooth support. At 12 and 24 months after loading, clinical, histologic, and histomorphometric evaluations of peri-implant tissues were performed on 28 implants. RESULTS: No clear difference in clinical features was observed among the different types of support. Direct bone apposition to the implant was generally seen in all groups. Histometrically, bone contact ratio ranged between 66% and 81%, and bone area ratio varied between 49% and 78% at 24 months after loading. These values showed almost no difference among single freestanding, connected freestanding, and implant-tooth supports of partially stabilized zirconia implants. CONCLUSION: In a primate model, partially stabilized zirconia implants placed with a 1-stage procedure achieve long-term stability of osseointegration with the use of single freestanding, connected freestanding, and implant-tooth supports.

Analysis of Variance↗

PubMed1998

A method for quantifying complete denture quality.

STATEMENT OF PROBLEM: Reproducible and quantitative clinical evaluation of complete denture prostheses is of great importance for preoperative diagnosis, treatment planning, and assessment of quality of denture treatment. PURPOSE: This study attempted (1) to clarify the degree of contribution each clinical factor made to the general assessment of experienced prosthodontists to complete denture prostheses, and (2) to develop a method for quantitative assessment of complete denture quality. METHODS: Sixteen clinical factors with a three-grade scale were used to evaluate complete denture prostheses in 320 patients. The general assessment of the dentures was conducted with a 10-point scale. The contribution of each grade of the 16 factors to the general assessment level was determined by a multiple regression analysis. RESULTS: Seven factors were highly correlated to the general assessment. On the basis of these significant contributions, a complete denture scoring method was established followed by the calculation of the category scores of these factors and conversion of the total sum of each category score to an integer number between 0 and 100. The resultant quantification score was closely correlated with the general assessment of the denture. CONCLUSION: An evaluation protocol used for scoring of complete dentures was developed based on the scientifically analyzed knowledge of experienced prosthodontists.

Aged↗