Hydroxyapatite was studied by computer graphics.The data of structural coordinates of hydroxyapatite crystal was put into a protein graphics program in A units.The connection of each element, with what comes front and rear, was displayed by the shade-line erasing method, and the solid-image was expressed by the degree of lightness from the light source.The tint of color was drawn by Raster graphics method.A fine picture can be obtained with the program.Rotating the graphics freely in an angle around X, Y or Z axis, gives a view from any direction .Crystal graphics model of fluoridated hydroxyapatite, in which F^- ions substituted in part into OH^-position, was also drawn.

View full abstract

Ti-6Al-4V alloy has both excellent biocompatibility and superior mechanical properties.This Ti-6Al-4V can be deformed greatly and easily at the superplastic temperature of 800℃ to 900℃.The superplastic forming of Ti-6Al-4V was made to apply to fabrication of denture base.Almost the same procedure as for dental casting mold was employed in producing the superplastic forming die by the improved phosphate bonded investment.In the pressure vessel of heat resistant alloy, Ti-6Al-4V plate was formed superplastically on the die by argon gas pressure at 850℃.The fit of superplactic forming Ti-6Al-4V denture base was better than that of casting Co-Cr alloy denture bases.The Ti-6Al-4V alloy might react a little with the die. Because micro Vikers hardness of the cross-section did not go up too much near the surfaces.Even just after being formed, the surfaces were much smoother than that of Co-Cr alloy casting.The tensile strength and yield strength of superplastic forming Ti-6Al-4V were higher than those of Co-Cr castings.The elongation was about 10%.These results show that superplastic forming of Ti-6Al-4V would be suitable for a denture base.

View full abstract

The three dimensional shape measurement system of teeth was improved.The system was assembled by using a high precision laser displacement meter and computer controlled scanning machine (CAMM-3). At the fissure of the occlusal plane, the abnormal data caused by multiple scattering of the reflected beam were observed, but they were dissolved by painting the stone model teeth gray and measured by using a laser displacement meter of MD-40 type with a short measurement length. Another error observed when the reflected beam was shielded by the model tooth itself, was corrected by connecting some data which were measured by rotating the teeth model on the gonio stage. A software program was composed to connect the data. The accuracy of measurement of this system was examined on the slope of 7| abutment tooth. When the model teeth were measured without tilting, the difference between the true value and the measured value was -240μm (-2.8%). However, by tilting the model teeth ± 20° on the gonio stage and connecting a couple of data obtained with two tilting angles by means of the software program, the difference was considerably decreased into +10μm and the accuracy was +0.1%. By tilting the model teeth, the measurements on their slope became more precise because the density of measuring points increased, and besides, the measurements on the portion with undercut also became possible. For the practical application, the measuring procedure upon rotation and tilting must be simplified, and the measurement time will be reduced.

View full abstract

To establish the most efficient polishing technique for composite resins, four kinds of silicone cup hards were experimentally designed, and the surface texture of two semihybrid composite resins polished with these experimental polishing tools were examined using a surface roughness recorder and by SEM. The individual silicone cup hard consisted of a hard rubber and silicone carbide abrasive particles being sized into #180(P₀), #360 (P₂), #600 (P), and #2500 (P₄), respectively.Combination polishing with both P₃ and P₄, as well as from P₀ through P₄ in this order, efficiently created the smoothest surfaces for the semihybrid composite resine, which are generally considered to be hard to polish in the routine clinic.

View full abstract

The effects of the curing mode on mechanical properties of composite resins were examined.Four resins as inlay, and three chemically-cured and five visible light-cured restorative resins were employed.The resin specimens were prepared by three kinds of curing modes;regular setting(according to the manufacturer's instruction), subsequently added light and heat curing after regular setting, and subsequently added heat and pressure curing after regular setting. Knoop hardness, flexure strength, compressive strength, and diametral tensile strength were determined.All restorative composites were remarkably increased in knoop hardness number due to the subsequently added curing methods.Both subsequently added curing methods provided higher flexure strength to all restorative resins, and particularly in the chemically-cured resins the flexure strength provided by the subsequently added light and heat curing was higher than those by the subsequently added heat and pressure curing. Compressive strength and diametral tensile strength were slightly increased by the subsequently added curing methods wtih the restorative resins. No correlation was found between the filler distribution and the mechanical properties provided by the subsequently added curing methods. The subsequently added heat curing seems to be preferable for creating higher mechanical properties of resins. The IC-2 resin, experimentally designed for resin inlay, seems to be the most promising resin for inlay restoration, based on the mechanical properties, and further detailed laboratory and clinical researches are required.

View full abstract

Molecular composite PMMA resin (Oct-PPTA-PMMA) can be reinforced with poly-N-octyl-p-phenylene terephthalamide (Oct-PPTA) as rigid core molecule.Compounding 3 wt% of Oct-PPTA to PMMA increased compresssive, diametral and bending strength by 10 to 15%.The molecular interaction between Oct-PPTA as the core molecule and PMMA as a polar matrix and polystyrene (PS) as a non-polar matrix was examined with respect to dynamic viscoelasticity. Compounding 3 wt% of Oct-PPTA (Oct-PPTA-PS) to PS decreased compressive, diametral and bending strength by 15 to 30 %. The dynamic storage modulus (G') value of Oct-PPTA-PS is lower than G' of PS in the region form rubbery state to viscous flow state.These results revel a significant effect of the polar groups on the molecular interaction between the core molecule and matrices in the molecular composites compounding Oct-PPTA as core molecule.

View full abstract

To investigate the effect of silica fillers on the mechanical properties of visible light-cured composite resins, Bis-GMA-based composites with four types of silica fillers were prepared.The mechanical properties of the composites with splinter-shaped silica fillers increased with increasing the filler fraction.Although the spherical silica filler could be filled more with resin monomer than the splinter-shaped silica filler, the mechanical properties of spherical silicafilled composite were relatively lower than those of the composite with splinter-shaped silica fillers.The micro particle silica-filled composite showed no obvious increase in the mechanical properties in either the dry or wet conditions. SEM observations of the fractured resin surface revealed that fracture occurred through the resin matrix as well as the resin/filler interface and the mechanical properties of each composite resin were correlated with the nature of crack propagation.

View full abstract

To improve the fracture resistance of the composite resin system under highly stressed conditions, a variable amount of microfiller was incorporated into the light-cured composite resins containing splinter-shaped silica filler.With the increasing the microfiller content (10〜30 wt%) in the resin matrix, the elastic modulus, compressive proportional limit and compressive fracture strength of the composite resin were increased.The plastic deformation of the composite resins under compressive stress were decreased with increasing microfiller content. These findings suggested that the combination of a larger silica filler and microfiller would increase the compressive fracture resistance of the composite resin systems.

View full abstract

To study the dimensional changes due to the release of casting stress in metal-ceramic alloys, a wheel-like pattern in which casting stress is liable to occur and rod-and barrel-like wax patterns in which the likelihood of such stress is low, were investigated with a phosphatebonded investment compound. Furthermore, simultaneous casting was done using Au-Pd-Ag system alloys, 21 types of mother alloys and alloys with tin or indium or both, and accurate determinations of the thermal expansion rate with increased or decreased temperature were carried out.The results obtained were as follows. The mean thermal expansion rates of the mother alloys and the alloys with tin and indium upon increase and decrease of temperature were lowest for the large wheel-like pattern, followed by the small wheel-like pattern, rod-like pattern and barrel-like pattern, in that order. The mean thermal expansion rates of the mother alloys and the alloys with tin or indium or both were decreased when the palladium content was increased, but tended to increase when the silver content was higher.Gold had no influence on the thermal expansion rate. When the temperature decreased, the complex addition of tin and indium provided alloys showing only a slight deformation.

View full abstract

The relationship between mechanical properties and thermal behavior of super-elastic Ni-Ti alloy orthodontic wires was investigated in order to use them effectively in clinics.Three types of super-elastic Ni-Ti alloy orthodontic wires, SENTALLOY^®-BLUE (SB), YELLOW (SY) and RED (SR), were used.Two parameters were introduced from the load-deflection curves in three point bending test to evaluate their mechanical properties.One was the super-elastic index (SEI) for super-elasticity, and the other was the E-load for the load in the super-elastic region¹⁾. Their thermal behavior in the course of the transformation analyzed with DSC, and compared with the mechanical properties.The specimens heat-treated at 500℃ for 30 min were also examined. The differences in mechanical properties of the super-elastic Ni-Ti alloy orthodontic wires used in this study were thought to be more affected by the height of the thermic peak and the form of the DSC curves than the transformation temperature.The higher the thermic peak, the higher tended to be the SEI and the lower E-load.To the contrary, the lower thermic peak, the higher was the E-load and the lower was the SEI, and the continuous force could not be achieved.The remaining work-hardened structure was thought to influence these differences.

View full abstract

Three types of super-elastic Ni-Ti alloy orthodontic wires, SENTALLOY^®-BLUE (SB), YELLOW (SY) and RED (SR), on the change of properties were studied especially the reversible change of the load level, using three point bending test and DSC. The heat treatment at 440℃ caused the largest reduction in mechanical properties of SB and SY, and the 400℃ treatment did that of SR.The load level of SR was less changeable than those of SB and SY by the difference of heat treatment temperature.Mechanical properties of SY were almost reversible by the alternate heat treatment at 440℃ and 510℃.Then the 440℃-heat treatment increased the transformation temperature, and the 510℃-heat treatment decreased them.The variation of the mechnical properties completely corresponded to the change in transformation temperature.The variation appears to result from some internal structure changes.Changes in mechanical properties are observed by heat treatment at 360, 400 and 480℃, but the reversibilities were not so clear.The change of the properties of super-elastic wires are influenced by the kind of wire and the heat treatment condition.The reversible change in the mechanical properties seems to have many advantages over super-elastic Ni-Ti alloy orthodontic wires.

View full abstract

For the development of a new delivery system for bone morphogenetic protein (BMP), BMP was bound to β-tricalcium phosphate (β-TCP). Powder β-TCP was synthesized from calcium hydrogenphosphate and calcium carbonate by the dry process method to make the best use of the advantages of the BMP, which show good bone inductive activity on the surface and enhancement of new tissue by reducing the area that the implant material occupies, The β-TCP + BMP complex and β-TCP for the controls only were implanted in the muscle pouches of mice. Three weeks later new bone formation was observed on the exterior surface of β-TCP + BMP complex but not of β-TCP controls. The bone inductive activity of the β-TCP + BMP complex is better than the BMP alone.The histological relation between the original tissue and the newly induced bone formation was normal and that of new bone and β-TCP was also good. Consequently, the β-TCP + BMP complex has good histocompatibility when implanted.

View full abstract

An attempt was made to determine the castability of Nickel-Chromium alloys which contained an additional element.80Ni-20Cr binary alloy was prepared in the argon atmosphere and saved as control alloy.Then three sets of different components alloys, each set contains different composition (5, 10, 15%) of Co, Mo, or Cu to the control alloy, were prepared and used as test materials.The fluidity was evaluated by casting them into the cyrindrical coil shaped mould cavity and examining their ability to flow into the mould cavity before solidification took place.The fluidity of Nickel-Chromium alloy was not changed by addition of Co or Mo up to 5%.However, the fluidity was significantly decreased by addition of Cu, or Mo when its concentration was increased over 5%. Thus, from the viewpoint of castability a large amount of Mo or Cu should not added to the Nickel-Chromium alloy.

View full abstract

To evaluate their chemical durability, samples of posterior composite resins were stored in NaOH (0.1mol, 1mol), HCl (0.1mol, 1mol), acetone (99%), and distilled water at 37℃ for a week and subjected to the direct tensile test, measurement of surface roughness and SEM observation. NaOH caused the degradation of composite resins, decrease of tensile strength and increase of surface roughness.The SEM photograph of fractured surface of tensile specimens revealed the degradation zone under the surface.It was considered that NaOH caused the hydrolysis of silan coupling of composite resins .HCl also caused the degradation of composite resins, but some resins showed the durability in this condition.More examination is needed to clarify the mechanism of degradation.Acetone caused the degradation of matrix resin and some composite resins.It was considered to dissolve the low degree of polymerized matrix resin of composite resins.Immersion in chemicals of composite resins was thought to be useful to evaluate the chemical durability and to accelerate the degradation in water.

View full abstract

Gypsum crystal growth on human dentin surface was investigated using a crystal growth agent composed of 4〜20% ammonium sulfate and 5〜60% acrylic acid aqueous admixtures.In the treatment with 4% ammonium sulfate which contains the concentration of acrylic acid from 5% to 60%, fine half-spherical aggregates of 25μm in diameter of needle-like crystals ware obtained from 35% acrylic acid and large ones from 30% acrylic acid. Using the crystal growth agent of 4% ammonium sulfate-35% acrylic acid aqueous admixture, the human dentin surface pretreated with sulfates of different cations was evaluated from crystal growth.All sulfates without 4% ZnSO₄ formed half-spherical aggregates of needle-like crystals. Diameter of their half-spherical aggregates increased as follows; 4% Na₂SO₄< nonetreatment < saturated CaSO₄・2H₂O < 4% K₂SO₄ < 4% MgSO₄ < 4% ZnSO₄. The half-spherical aggregates from sulfates of Na⁺ and K⁺ (alkali metal) grew finer than those from sulfates of Ca²⁺ and M²⁺ (alkali-earth metal) and Zn²⁺ (zinc) and their area on dentin surface increased more with sulfates of alkali metal than with those of alkali-earth.

View full abstract

A mixture of α-tricalcium phosphate [α-Ca₃(PO₄)₂; α-TCP] with a citric acid solution produces a hardened α-TCP-citric acid complex.The influence of tannic acid as an additive in the solution on the physical and chemical properties of the obtained complex was examined as a basic study for new calcium phosphate materials incorporating α-TCP.α-TCP was mixed with mixing liquids containing citric and tannic acids at various ratios [tatal acid = 45% (w/w)] at a powder/liquid = 2.2/1.0 (g/g). Compressive strength, setting time, and solubility & disintegration of the resulting complexes were measured by the methods specified by ADAS No.61. After immersing the plates of the complexes in distilled water for 1 and 7 days, the surface structure of the plates was examined by using X-ray diffraction, scanning electron microscopy and IR spectroscopy. The substances solubilized and disintegrated in the water for 1 day were also examined by measuring quantitative Ca and P concentration. When the ratio of tannic acid to total acids (T/A) was higher than 30% (w/w), both setting time and solubility & disintegration increased remarkably. In the case of the complex at T/A = 30%, both setting time and solubility & disintegration showed the minimum value (6.25 min and 1.70 %). For compressive strength, the maximum value (139 MPa) was obtained at T/A = 10%. Although the strength decreased markedly with increasing T/A beyond 10%, that of the complex at T/A = 30% was still a high level (103 MPa). The products on the surfaces before and after immersing the plates in distilled water were also discussed.

View full abstract

Differences in environmental strength of high-copper amalgams and photo-cured composite resins for posterior after storage in deionized water at 37℃ for 1 year were evaluated by examining compressive strength and acoustic emission (AE) characteristics. The results were as follows: Microfailure in amalgams and composite resins was detected from the onset of stress and their microfailures toward catastrophic failure occurred at 70 to 90% of their ultimate strength.One-year compressive strength for amalgam decreased to 80 to 98% of its 24-hour compressive strength and that for composite resin to 65 to 75%.

View full abstract

Calcium phosphate remineralizing slurry (CPRS), consisting of an equimolar mixture of tetracalcium phosphate (TTCP) and dicalcium phosphate dihydrate (DCPD), has previously been shown to form hydroxyapatite (HAp) spontaneously at physiological pH. Since considerable amounts of HAp may be formed in situ by CPRS, it may be effective for desensitizing hypersensitive dentin by obturating exposed dentinal tubule openings.In the present study, the effects of topically applied CPRS to etched dentin surfaces were investigated.The samples were randomly divided into 3 groups: (1) the control specimens were soaked in a saliva-like (SL) solution (2) the specimens received either 10-minute or 1-hour treatment with CPRS and (3) the specimens ware treated with viscous CPRS, containing carboxymethyl cellulose (CMC) gel.for 8 hours. The SEM observations revealed that the control specimens were covered with a thin layer of Plate-like crystals indicative of octacalcium phosphate (OCP). No significant penetration of the crystals into the dentinal tubules was detected. In CPRS group, the 10-minute treatment produced a 10 to 15μm thick dense layer of precipitation consisting of needle-, rod-, and plate-like crystals.The 1-hour treatment produced a similar precipitation except that th crystals were mostly needle-like.A cross section view of the samples indicated remarkable penetration of the crystals into the tubules, thus providing significant obturation of tubule openings.Samples in the CMC-gel group were covered with an even more impervious layer of precipitation consisting of crystals of a variety of morphologies. The methylene blue penetration test results confirmed that the precipitation formed on the dentin surface significantly obturated the tubule openings and reduced the dye penetration into the dentin.Since the crystals formed by CPRS and CMC-gel are HAp, they are relatively stable in the oral environment.The HAp similar to the dentin minerai appeared to adhere firmly to the dentinal surfaces thus forming an effective barrier to dye penetration.Both the CPRS and CMC-gel treatments, which can be easily applied in practice, are potentially useful for treating dentin hypersensitivity. (This study was supported by the NIDR Research Grant DE 05354)

View full abstract

The Vickers hardness number (VHN) of pure metals (tin, aluminum, copper and gold) and dental gold alloy was measured using an automatically indenting and reading Vickers hardeness tester (AKASHI・AUTOVICK) under a load of 1, 000 gf with different loading times of 5 to 55 seconds. The samples of pure metals were cold rolled and softened by heating above recrystallization temperatures. The samples of ADAS No.5 gold casing alloys were cold rolled, and then subjected to a softening heat treatment by water quenching (Types I, II, III and IV) or a hardening heat treatment by 450 → 250 ℃/30 min oven cooling (Types III and IV). The results showed that there were no statistically significant differences between the measured values of VHE of a sample with different loading times as for the metals studied except pure tin which had a VHN of 5〜6. The measured values of VHN by AUTOVICK were affected by the brightness of a light source for measurement, and they increased by 1.1 approximately as the voltage of the light source increased by 0.1 V. This was considered to be due to the protuberance caused by plastic flow of metals or slip lines on the surface around the indentation.

View full abstract