Biomedical subjects

Osamu Miyakawa

Publications and source records attributed to Osamu Miyakawa.

17 recordsLinked to original sources

PubMed2006

Surface texture and composition of titanium brushed with toothpaste slurries of different pHs.

OBJECTIVES: This in vitro study characterized the surface texture and composition of titanium brushed with toothpaste slurries of different pHs, and thereby elucidated mechanochemical interactions between the metal and abrasive material in dentifrice. METHODS: Two fluoride-free toothpastes, which contained crystalline CaHPO(4).2H(2)O and amorphous SiO(2) particles as abrasive, were mixed with acidic buffers to provide slurries of pH 6.8 and 4.8. Specimens were cast from CP Ti, mirror-polished, and then toothbrushed at 120strokes/min for 350,400 strokes under a load of 2.45N. Specimen surfaces were characterized by means of SPM and EPMA. The obtained data were compared with the already reported results of water-diluted alkaline slurries. SPM data of each paste were analyzed using one-way ANOVA, followed by post hoc Tukey test. RESULTS: Irrespective of toothpaste, neutral slurries, as with alkaline slurries, yielded a chemically altered surface with rough texture, whereas acidic slurries formed a chemically clean surface with relatively smooth texture. Mechanochemical polishing effect might be mainly responsible for the cleanness and smoothness. SIGNIFICANCE: Acidic slurry-induced smooth surface may minimize plaque formation. However, the augmentation of released titanium ions may be adverse to the human body. For evaluation of toothpaste abrasion effects on titanium, paste slurry pH should be taken into account.

Acids↗

PubMed2006

Abutment rotational displacement of external hexagon implant system under lateral cyclic loading.

PURPOSE: This in vitro study investigated the effect of lateral cyclic loading with different load positions and periods on abutment rotational displacement (RD) of external hexagon implant system. MATERIALS AND METHODS: Four groups of five implant assemblies each were used. Each assembly consisted of Brånemark System Mk IV implant (Nobel Biocare AB, Göteborg, Sweden), CeraOne abutment (Nobel Biocare AB), and a cement-retained casting. A cyclic load of 50 N was applied centrally and perpendicular to the long axis of the implant for groups A and B for 0.25 and 0.50 x 10(6) cycles, respectively, while for groups C and D, the same load was applied at 4-mm distance eccentrically for 0.25 and 0.50 x 10(6) cycles, respectively. The displacement was evaluated by hand drawing a longitudinal line across the implant-abutment interface. Before and after loading, the lateral distance between two reference points on the abutment and implant was measured under high resolution (x200) and the difference formed the RD value. The data were analyzed with one-way analysis of variance and compared with Tukey test (alpha=0.05). RESULTS: Group D had the highest mean of RD value (55.00 +/- 1.871 microm), while group A had the lowest (2.800 +/- 0.837 microm). Groups A and B had a high statistically significant difference in RD values, as compared to groups C or D (p < .001). Moreover, group C had statistically significant difference from group D (p=.011). Conversely, no statistical significance was obtained when group A was compared with group B. CONCLUSION: Within the limits of this in vitro study, the RD of the external hexagon joint components occurred significantly under eccentric lateral loading when compared to centric loading. The displacement increased significantly with longer period of eccentric lateral loading.

Dental Abutments↗

PubMed2006

Abrading increases oxygen and hardness of titanium surface.

CP Ti was mirror-polished and then abraded with waterproof SiC papers of two different grit sizes: 16 and 3 microm. As-polished and abraded surfaces were characterized by means of EPMA, XPS, XRD, and hardness test. Oxygen in the mirror-polished surface was uniformly distributed at the lowest level. Comparatively, abrading with SiC papers increased the surface oxygen amount and hardness. Owing to its excellent abrasivity, the coarse grit efficiently scratched the surface and hindered the regenerated oxide film from growing thick, but allowed only the metal-oxide interfacial gradient zone to extend. But, the fine grit merely rubbed the surface and allowed both the oxide film and interfacial zone to extend. Further, the surface appeared to be lightly yellow-colored, suggesting that the oxide film was thicker, probably within 10 nm, than the nominal one. When compared with the bulk, the interfacial zone was rich in oxygen and therefore subjected to high coherency strain, which was introduced to relieve the great lattice mismatch between the outer and inner layers of titanium substrate. Effects of solute oxygen hardening and strain hardening were speculated to be responsible for the surface hardening of both SiC-abraded surfaces. In conclusion, abrading with a coarse grit led to accumulation of a high, non-uniform strain in the titanium substrate, thereby hardening the surface further.

Analysis of Variance↗

PubMed2005

Effect of toothbrushing on titanium surface: an approach to understanding surface properties of brushed titanium.

OBJECTIVES: This in vitro study aimed to characterize the surface morphology and composition of tooth-brushed titanium casting and thereby to elucidate interactions between the metal and abrasive material in dentifrice. METHODS: Specimens were cast from CP Ti ingots and then mirror-finished. Two fluoride-free toothpastes containing crystalline CaHPO4.2H2O and amorphous SiO2 particles as abrasive were slurried with distilled water (15 g/30 mL). While toothbrushes were reciprocated at 120 strokes/min for 350,400 strokes, the specimens were brushed with the respective slurries under a load of 2.45 N. The brushed and non-brushed surfaces were characterized by means of SPM, EPMA, and XPS. SPM data were analyzed using one-way ANOVA, followed by post hoc Tukey test (p<0.01). RESULTS: Irrespective of toothpastes, toothbrushing had a significant influence on surface roughness. The CaHPO4.2H2O-containing paste produced much rougher surface than the SiO2-containing paste. Both the surfaces were chemically altered due to reactions with the respective abrasive materials. Abrading chips had dimensions of micron to submicron order. A number of chips were attached to abrasive particles. SIGNIFICANCE: The alterations of surface morphology and composition may affect biological responses of titanium in the oral environment. Dentifrice with lower abrasivity might be advisable for daily oral hygiene practice of patients with dental titanium devices.

Calcium Phosphates↗

PubMed2005

Development of a frequency-detuned interferometer as a prototype experiment for next-generation gravitational-wave detectors.

We report on our prototype experiment that uses a 4-m detuned resonant sideband extraction interferometer with suspended mirrors, which has almost the same configuration as the next-generation, gravitational-wave detectors. We have developed a new control scheme and have succeeded in the operation of such an interferometer with suspended mirrors for the first time ever as far as we know. We believe that this is the first such instrument that can see the radiation pressure signal enhancement, which can improve the sensitivity of next-generation gravitational-wave detectors.

Journal Article↗

PubMed2005

Surface composition and texture of titanium polished with colloidal silica suspension and chromic oxide slurry.

CP titanium was polished with a colloidal silica suspension and chromic oxide slurry under low and high pressures. The polished surfaces were characterized by means of EPMA and XPS. Irrespective of polishing pressure, colloidal silica suspension successfully created a mirror-like surface that was clean at EPMA level. However, XPS detected a small amount of silicon on the outermost surface. On the other hand, chromic oxide slurry under high pressure yielded a very uneven surface with numerous scratches. The EPMA and XPS results suggested the presence of chromium-containing species in the polished surface, which might include hydroxides as well as oxides. In addition, the level of oxygen concentration was noticeably raised, which probably resulted from the increase of surface oxide film thickness or the extension of oxide-to-metal transition zone.

Chromium Compounds↗

PubMed2004

Internal porosity of cast titanium removable partial dentures: influence of sprue direction and diameter on porosity in simplified circumferential clasps.

OBJECTIVE: The behavior of molten titanium in molds of complicated shape is still insufficiently understood; consequently, definite spruing criteria are not yet available for titanium RPD frameworks. This study investigated the influence of sprue design on porosity in pressure-cast titanium circumferential clasps. METHODS: The patterns of 90 circumferential clasps were sprued with three directions (0, 30 and 60 degrees , as measured between the sprue and the symmetry plane of the clasp assembly) and three sprue diameters (1.5, 2.0 and 2.5mm). CPTi was cast in a one-chamber pressure casting machine. Pore number and size were assessed on radiographs of the castings. Statistical analysis was done by two-way analysis of variance (ANOVA), followed by Fisher's PLSD post hoc test. RESULTS: The porosity in lingual arms increased significantly with increase of sprue diameter and sprue angle, while the porosity in minor connectors had an inversely proportional distribution. Very low porosity, uninfluenced by sprue design, was found in buccal arms. In conclusion, internal porosity in titanium circumferential clasp arms can be minimized through sprue design: the 0 degrees sprue direction produced the least porosity, while for the 30 and 60 degrees directions, 1.5mm diameter sprues produced lower porosity than 2.0 and 2.5mm diameter sprues. SIGNIFICANCE: In this study, the lowest porosity in titanium circumferential clasp arms was obtained with sprues attached perpendicularly to the minor connectors, regardless of sprue diameter. Conventional sprue directions produced significantly higher porosity in clasp lingual arms, the amount of porosity increasing with sprue diameter.

Analysis of Variance↗

PubMed2004

Effect of lateral cyclic loading on abutment screw loosening of an external hexagon implant system.

STATEMENT OF PROBLEM: Efforts to reduce the recurrence of abutment screw loosening with single tooth implant-supported restorations have been reported. However, the current knowledge about the role of the implant external hexagon is incomplete. PURPOSE: This in vitro study investigated the effect of lateral cyclic loading with different load positions on abutment screw loosening of an external hexagon implant system. MATERIAL AND METHODS: Fifteen Brånemark implant assemblies were divided equally into 3 groups, A, B, and C. Each assembly consisted of a Mark IV implant (4 x 10 mm) mounted in a brass block, a CeraOne abutment (3 mm), and an experimental cement-retained superstructure. For group A, a cyclic load of 50 N was applied centrally and perpendicular to the long axis of the implant, whereas for group B, the same load was applied eccentrically (at a distance of 4 mm) in a loosening direction. A target of 1.0 x 10(6) cycles (40 months of simulated function) was defined. Group C (control) was left unloaded for the same loading time period as groups A and B. Reverse torque was recorded before and after loading and the difference was calculated. The data were analyzed with 1-way analysis of variance and compared with the Tukey test (alpha=.05). RESULTS: Group A exhibited a significant difference in the reverse torque difference values ([-5.6 to -3.4] +/- 0.86 N.cm) compared with groups B ([-1.9 to 0.5] +/- 0.99 N.cm) and C ([-0.7 to 0.0] +/- 0.26 N.cm) (P<.001). Groups B and C were not significantly different from each other. CONCLUSION: Within the limitations of this study, reverse torque values of the screw joint were preserved under eccentric lateral loading, as compared with centric loading (P<.001).

Analysis of Variance↗

PubMed2004

Biomechanical aspects of marginal bone resorption around osseointegrated implants: considerations based on a three-dimensional finite element analysis.

OBJECTIVES: Although bone loss around implants is reported as a complication when it progresses uncontrolled, resorption does not always lead to implant loss, but may be the result of biomechanical adaptation to stress. To verify this hypothesis, a three-dimensional finite element analysis was performed and the influence of marginal bone resorption amount and shape on stress in the bone and implant was investigated. MATERIAL AND METHODS: A total of nine bone models with an implant were created: a non-resorption (Base) model and eight variations, in which three different resorption depths were combined with pure vertical or conical (vertical-horizontal) resorption. Axial and buccolingual forces were applied independently to the occlusal node at the center of the superstructure. RESULTS: Regardless of load direction, bone stresses were higher in the pure vertical resorption (A) models than in the Base model, and increased with resorption depth. However, cortical bone stress was much lower in the conical resorption models than in both the Base and A models of the same resorption depth. An opposite tendency was observed in the cancellous bone under buccolingual load. Under buccolingual load, highest stress in the implant increased linearly with the resorption depth for all the models and its location approached the void existing below the abutment screw. CONCLUSIONS: The results of this analysis suggest that a certain amount of conical resorption may be the result of biomechanical adaptation of bone to stress. However, as bone resorption progresses, the increasing stresses in the cancellous bone and implant under lateral load may result in implant failure.

Adaptation, Physiological↗

PubMed2004

Morphological and chemical characterizations of the interface of a hydroxyapatite-coated implant.

The present study aimed at morphological and chemical characterization of the coating-substrate interface of a commercially available dental implant coated with plasma-sprayed hydroxyapatite (HA). For this purpose, elements in the chemically and mechanically exposed substrate surfaces were analyzed by EPMA and XPS. A thin titanium oxide film containing Ca and P was found at the interface. When the implant was subjected to mechanical stress, a mixed mode of cohesive and interfacial fractures occurred. The cohesive fracture was due to separation of the oxide film from the substrate, while the interfacial fracture was due to exfoliation of the coating from the oxide film bonded to the substrate. Analysis showed diffusion of Ca into the metal substrate, hence indicating the presence of chemical bond at the interface. However, mechanical interlocking seemed to play the major role in the interfacial bond.

Calcium↗

PubMed2004

Surface properties of electrochemically buffed titanium casting.

Electrochemical buffing, a combined process of electrochemical and mechanical polishing, was applied to titanium casting. Mixture of alpha-Al2O3 suspension (average grain diameter of 5 microm) and 5% KNO3 solution was used as abrasive slurry. Specimen and experimental wheel buff were respectively connected to the positive and negative poles of a DC source, whose potential ratings ranged from 0 V (MEP) to 10 V (ECB10). Surface roughness, hardness, color, and cleanness were investigated. ECB10 surface produced a gold color and attained a mirror finish, as its roughness value was only one-quarter that of MEP. High amount of aluminum was present in MEP surface. Its bond state entirely differed from that of alpha-Al2O3, hence indicating surface alteration due to chemical reactions with the abrasive material. At higher potentials, reaction products might be dissolved anodically, so that the surface was chemically clean to some extent. The surface also became rich in OH-.

Aluminum Oxide↗

PubMed2003

Fatigue resistance of cast occlusal rests using Co-Cr and Ag-Pd-Cu-Au alloys.

STATEMENT OF PROBLEM: Fatigue failure in a removable partial denture framework includes fracture of the occlusal rest at the rest-minor connector angle. PURPOSE: This in vitro study evaluated the fatigue resistance of 0.8-mm-thick occlusal rests cast with Co-Cr and Ag-Pd-Cu-Au alloys. MATERIAL AND METHODS: The specimen consisted of occlusal rest (0.8 x 2.0 x 10 mm), vertical minor connector (0.9 x 2.0 x 5.0 mm), and denture base connector (1.5 x 5.0 x 25 mm). Twenty-five specimens each were cast with Co-Cr and Ag-Pd-Cu-Au alloys. From each group, 5 specimens were subjected to a load-deflection test conducted to determine the amount of deflection to be used in fatigue test. The fatigue test was performed such that the occlusal rest component was deflected by displacing the denture base component in a tissueward direction. Predetermined denture base displacement values of 0.25 and 0.49 mm for Co-Cr and Ag-Pd-Cu-Au specimens, respectively, were repeated at a rate of 500 cycles/min by use of a displacement-controlled fatigue testing machine, until occlusal rest failure occurred or a preset limit of 2 million cycles was achieved. The survival rates of the occlusal rests were calculated assuming a chewing cycle of 2 x 10(5) per year. Scanning electron microscopy (SEM) photographs were made to examine the fracture surfaces and to identify casting defects. The relationship between fatigue cycles and number of casting defects was determined by Spearman rank correlation analysis (P<.01). RESULTS: All 20 Co-Cr specimens outran the preset limit, whereas 18 Ag-Pd-Cu-Au specimens fractured. After 3 years of simulated clinical use, only 50% of the Ag-Pd-Cu-Au occlusal rests survived. Statistical analysis showed that the fatigue cycles and number of casting defects were inversely related (P<.01). Fatigue crack initiation occurred at the inner-curvature surface of the rest-minor connector angle. The typical Ag-Pd-Cu Au fatigue fracture surface consisted of smooth propagation and dimpled and smooth final fracture areas. CONCLUSIONS: This study suggests that cast Co-Cr rests are more rigid and fatigue resistant than Ag-Pd-Cu-Au rests. The fatigue resistance of 0.8-mm-thick occlusal rests may be adequate if cast with Co-Cr alloy. An increased number of casting defects may hasten the fatigue failure of occlusal rests.

Chromium Alloys↗

PubMed2002

Internal porosity of cast titanium removable partial dentures: Influence of sprue direction on porosity in circumferential clasps of a clinical framework design.

STATEMENT OF PROBLEM: Although internal porosity is a potential risk factor for clasp fracture, little is known about its frequency in the clasps of titanium removable partial dentures. PURPOSE: This study investigated the influence of the direction of auxiliary sprues on porosity in the circumferential clasps of a pressure-cast titanium removable partial denture. MATERIAL AND METHODS: Wax patterns of a removable partial denture framework were made on 10 identical refractory casts of a Kennedy class II, modification 1, mandibular partially edentulous arch. For the auxiliary sprues directed to the circumferential clasps, 2 designs were used: straight and curved. Casting was performed in a 1-chamber pressure casting machine. Pore number and size were assessed on radiographs of the castings. The data were analyzed with the 2-tailed Student t test (P <.05). Randomly selected specimens were sectioned for morphologic observation of the internal surface of the pores. RESULTS: The number of pores >or=0.5 mm diameter and the total number of pores were significantly lower in the molar lingual arms of the curved sprue group than in the corresponding clasp arms of the straight sprue group (P =.03 and P =.009, respectively). No significant differences between the 2 groups were found for pores of any size in other locations. The pores had smooth internal surfaces. CONCLUSION: Within the limitations of this study, the curved sprue design produced significantly less porosity in the circumferential clasp arms of a cast titanium removable partial denture than the conventional straight design. The results suggest that internal porosity in titanium castings can be controlled through sprue design.

Dental Casting Technique↗

PubMed2002

Fatigue resistance of two implant/abutment joint designs.

STATEMENT OF PROBLEM: Because of reported mechanical failures, alternative implant system components with suggested optimized strength have been manufactured. However, the endurance of these products has not been well investigated. PURPOSE: This study was designed to assess the effect of joint design on the fatigue strength and failure mode of 2 single-tooth implant systems: Brånemark and ITI, in which a hex mediated-butt joint and 8-degree internal conical implant/abutment interface are used, respectively. MATERIALS AND METHODS: Seven 10-mm implants from each implant system were embedded to a depth of 7 mm in cylindrical acrylic resin blocks. CeraOne and Solid abutments with cement-retained castings were assembled to the Brånemark and ITI implants, respectively. The assembled units were mounted in a lever-type-testing machine that was equipped with an automatic counting device and shutoff sensors, enabling the recording of the number of cycles till failure. A cyclic load of 100 N was applied perpendicular to the long axis of the assemblies at a rate of 75 cycles/min. To investigate specimen resistance to fatigue during 6 years of simulated function, a target of 1,800,000 cycles was defined. Specimen preparation and testing was performed by the same operator. The association of the joint design with the occurrence of failure was verified by Fisher's exact probability test (P<.05). RESULTS: For the Brånemark group, the gold alloy abutment screw in all specimens fractured between 1,178,023 and 1,733,526 cycles with a standard deviation of 224,477 cycles. For the ITI group, all specimens had no failure until 1,800,000 cycles. Statistical analysis showed a highly significant difference between the 2 groups (P=.000582). CONCLUSIONS: Within the limitations of this in vitro study, the effect of joint design on the fatigue strength and failure mode of the ITI single tooth implant system was significantly better (P>.001) than the Brånemark single-tooth implant system tested.

Cementation↗

PubMedDate not supplied

Influence of implant design and bone quality on stress/strain distribution in bone around implants: a 3-dimensional finite element analysis.

PURPOSE: A 3-dimensional finite element analysis was performed to evaluate the influence of implant type and length, as well as that of bone quality, on the stress/strain in bone and implant. MATERIALS AND METHODS: Two types (screw and cylinder) and 4 lengths (9.2, 10.8, 12.4, and 14.0 mm) of titanium implants were buried in 4 types of bone modeled by varying the elastic modulus for cancellous bone. Axial and buccolingual forces were applied to the occlusal node at the center of the abutment. RESULTS: Regardless of load direction, maximum equivalent stress/strain in bone increased with a decrease in cancellous bone density. Under axial load, especially in the low-density bone models, maximum equivalent strain in cancellous bone was lower with the screw-type implant than with the cylinder-type implant. It was also lower with the longer implants than with the shorter implants. Under buccolingual load, equivalent stress/strain was influenced mainly by bone density. DISCUSSION: This study confirms the importance of bone quality and its presurgical diagnosis for implant long-term prognosis. Implant length and type can also influence bone strain, especially in low-density bone. CONCLUSIONS: The results of this study suggest that cancellous bone of higher rather than lower density might ensure a better biomechanical environment for implants. Moreover, longer screw-type implants could be a better choice in a jaw with cancellous bone of low density.

Biomechanical Phenomena↗

PubMedDate not supplied

Influence of superstructure materials on strain around an implant under 2 loading conditions: a technical investigation.

PURPOSE: This investigation was concerned with the effect of 3 superstructure materials on the strain around an implant under static and nonimpact dynamic loading. MATERIALS AND METHODS: Five highly filled composite resin-veneered crown analogs, 5 autopolymerized acrylic resin-veneered crown analogs, and 5 gold-alloy full cast crown analogs were prepared. The resin veneers were applied to gold-alloy frameworks. These crown analogs were prepared to fit an ITI implant-abutment assembly, which was screwed into a block of acrylic resin to simulate implantation in bone. The crown analogs were successively placed on the abutment, and a lateral load of 100 N was applied to the superstructure by a lever-type testing machine. Strains were recorded under static and dynamic loading by a 2mm-long strain gauge bonded to the surface of the bone simulant tangential to the implant. The dynamic load simulated masticatory cycles (75 strokes/min). RESULTS: Although the strain values differed significantly between the static and dynamic loading (P < .05), there was no significant difference among the superstructure materials under either loading condition (P > .05). DISCUSSION: These findings are in agreement with in vivo measurements, thus suggesting that cyclic rather than impact loading should be used in the investigation of occlusal material behavior under functional loading. CONCLUSION: Under static and nonimpact dynamic loading, the 3 superstructure materials tested (highly filled composite resin, acrylic resin, and gold alloy) had the same influence on the strain transmitted to a bone simulant that surrounded a single implant.

Acrylic Resins↗

PubMedDate not supplied

Peri-implant stress analysis in simulation models with or without trabecular bone structure.

Most 3-dimensional (3D) finite element analyses (FEAs) simplify the cancellous bone to a block and completely ignore its trabecular structure. Thus, a 3D FEA was performed to compare the peri-implant stress distribution of a model in which the trabecular structure was accurately simulated (precise model) with that of a model with a homogenous cancellous bone component (simplified model). In contrast to the simplified model, the distribution patterns and higher stresses in the precise model may explain the overall bone resorption at the implant-bone interface in load-related implant failures. Further studies using data from the jawbone and a more detailed implant simulation are planned.

Animals↗