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H Kamemizu

Publications and source records attributed to H Kamemizu.

13 recordsLinked to original sources
PubMed1998

Effect of primers on bonding agent polymerization.

The aim of the present study was to evaluate the effect of primers on the polymerization of bonding agent. We measured the degree of conversion (radical production) and mechanical properties (surface hardness and direct tensile strength) of various adhesives/primers mixed at different ratios and the effect of varying the visible-light curing time. With and without primer treatment, the tensile bond strength of adhesive resin to micacious glass ceramic and human enamel was measured. After the tensile bond test, using the Image Capture System, the failure patterns of adhesive resin bonded to micacious glass-ceramic were analysed. The results show that the mixtures containing the higher amounts of primer yielded a lower degree of conversion and inferior mechanical properties when compared with the mixtures containing a lower proportion of primer, except in the experimental bonding system. The adhesive/primer mixtures inhibited free radical polymerization. The value for the Knoop hardness number and the direct tensile strength of the adhesive/primer mixtures were significantly decreased compared with those of the adhesive bonding agent alone with no primer added. The tensile bond strength of adhesive resin bonded to micacious glass-ceramic or human enamel without primer treatment was significantly greater than that of adhesive resin with primer treatment in certain cases. Most of the fractures of ceramic surfaces were cohesive (within resins) and/or interface (at the ceramic surface) failure.

Adhesiveness↗
PubMed1995

Pyrolysis-gas chromatography of carbonate apatites used for sintering.

Gas chromatography was employed to quasi-continuously determine the amount of carbon dioxide that evolved from carbonate apatite specimens during sintering. Assuming that the carbonate in the specimens decomposed to carbon dioxide on a mole-for-mole basis, the determination of the carbon dioxide evolved allowed for the determination of the amount of carbonate that remained in the specimens during different stages of sintering. Previously, this measurement could be carried out only after sintering was completed. Comparison of data obtained from specimens compacted isostatically at 600 MPa for sintering with powder specimens indicated that the amount of carbonate remaining in the sintered apatite mass strongly depended on heating rates, heating temperatures, and holding-time intervals.

Apatites↗
PubMed1993

Influence of carbonate on sintering of apatites.

Sintering of carbonate apatite, prepared at 100 degrees C and pH 9.0 for 3 days, was studied by thermal analysis, x-ray diffraction, and infrared spectroscopy. The sintering temperature, at which the linear thermal shrinkage of isostatically compacted specimens increased sharply, decreased in proportion to the amount of carbonate initially present in the apatite. For example, specimens with over 8 wt% carbonate could be sintered at a temperature (650 degrees C) which was nearly 400 degrees C lower than that needed for sintering a specimen with no carbonate. Amounts of carbonate lost at the end of sintering, estimated chemically and by infra-red spectroscopy, were approximately equal to sample weight losses estimated thermogravimetrically.

Carbonates↗
PubMed1991

Thermal decomposition of Lingula shell apatite.

Lingula shell is composed of apatite with a preferred orientation. The shell apatites of Lingula unguis(Lu) and Lingula shantoungensis(Ls) were characterized and compared with apatite of human tooth enamel. Insight into the Lingula apatite was studied by following the change of lattice parameter, transformation to beta-tricalcium phosphate (beta-TCP), and the loss and change of CO3, OH, and H2O after heating up to 1,000 degrees C in air and N2 for 24 hours. The OH stretching band was not observed in unheated apatites and in apatites heated in dried N2. Lu and Ls apatite produced 26 and 17 wt% of beta-TCP at 700 degrees C, respectively. Fifty to 60% of H2O was lost at 200 degrees C, being accompanied by a drastic contraction of the a- and c-axis and a drastic decrease in the crystallinity. These results indicate that (1) Lu and Ls shell apatite is CO3 containing F + Cl-apatite, and (2) the structural H2O of the Lingula apatite is loosely bounded such that they are lost at lower temperature than tooth enamel.

Animals↗
PubMed1990

[Weibull statistical analysis of bending strength data measured either in air or in distilled water for sintered hydroxyapatite ceramics coated on the metal substrate].

To assess the effects of H2O on the fracture stress of sintered hydroxyapatite (HAP) ceramics prepared by procedures similar to those used for HAP coated on the metal substrate, four-point bending tests were carried out at 0.5 mm/min either in air (20 C, R.H. 73%) or in distilled water (37 degrees C). Then, strength data obtained were analyzed using two-parameter weibull statistics. In each condition, the bending strength data gave a good fit to single-mode weibull distribution. Weibull analysis of the data gave weibull parameter m = 7.8, sigma 0 = 26.2 MPa in air and m = 8.1, sigma 0 = 18.5 MPa in distilled water, which were calculated assuming a surface flaw model. The mean value of bending strength was 27.3 MPa in air and 18.2 MPa in distilled water. These results indicated that a corrosive environment such as H2O affects fracture stress when measured at a constant stress rate. This effect is considered to be caused by slow crack growth of cracks, occurring at a loading level lower than those at which specimens will fail. Using the weibull distribution function estimated in this study, the effects of both dimension of specimen and stress distribution in the specimen on the mean fracture stress have been predicted.

Air↗
PubMed1990

[Estimation of fatigue parameter and life-time prediction using SPT diagram for hydroxyapatite coating layer in 37 degrees C distilled water].

Lifetime and survival probability of brittle materials under given conditions of stress distribution, environment and component size can be predicted using an SPT (Strenght-Probability-Time) diagram. The SPT diagram for sintered hydroxyapatite (HAP) coated on the metal substrate via the fused glass was drawn and the safe working stress in 37 degrees C distilled water was estimated. The dynamic fatigue test carried out in 37 degrees C distilled water gave the fatigue parameter n = 19 for sintered HAP. This parameter is constant except that it depends on material and environment, and the greater the value of n, the greater the resistance to fatigue failure. For sintered HAP, therefore, the resistance to fatigue failure under this wet condition is low. To draw the SPT diagram, anchor points were taken from the fracture stress and time-to-failure data measured at 1 mm/min. The SPT diagram obtained suggested that a lifetime of 20 years with survival probability of 99.9% required the safe working stress of less than 3.2 MPa. The effects of accuracy of fatigue parameter on the uncertainty in SPT diagram were estimated.

Corrosion↗
PubMed1989

[Self-setting apatite cement. 6. Possibility as bone substitute].

Self-setting apatite cement was investigated to evaluate its use as a possible bone substitute in the rat femur. The implant sites were recovered at intervals up 12 weeks postoperatively and investigated by the use of x-ray diffraction, contact microradiography, light and electron microscopy. By x-ray diffraction analysis, the cement placed for at least one day in the medullary canal of rats was found to be completely converted to a set phase of hydroxyapatite resembling the main inorganic phase of bone. In any specimens prepared at 1, 4, 12 weeks after implantation, no appreciable foreign body response was observed in the tissue around the set cement. At four weeks after implantation the set cement was in tight contact with the newly formed bone which appeared to involve osteocytes in lacunae and osteoblastic cells on its surface. At twelve weeks after implantation, the newly formed bone tended to grow into the interior of the set cement. With scanning electron microscopy, the newly formed bone was found to be directly deposited on the set cement. The newly formed bone consisted of fine needle-like crystals. These results strongly suggest that this cement is well tolerated by bone tissue and osteogenesis when used as a bone substitute. The advantage of the present material as a promising bone substitute is that it can be filled in surgical or traumatic bone defect as a slurry or paste.

Animals↗
PubMed1989

[Self-setting apatite cement. 8. Dissolution and remineralization behavior of 45Ca-apatite cement].

Self-setting apatite cement hardens into a mass of single phase apatite when mixed with diluted phosphoric acid. Structurally this mass consists of two types of apatite, i.e. the seed apatite used as a setting accelerator and the matrix apatite formed afterward in the reaction of dicalcium phosphate dihydrate (DCPD) and tetracalcium phosphate (Te-CP). To investigate the dissolution behavior of self-setting apatite cement in detail, two types of 45Ca labeled apatite cement were prepared. In one, the seed apatite was labeled with 45Ca (45Ca-HAp cement) and in the other the matrix apatite was labeled with 45Ca through use of 45Ca-DCPD (45Ca-DCPD cement). Solubility, estimated from the concentration of 45Ca released in 1 mM of organic acid (e.q. acetic, lactic, or citric acid) with initial pH adjusted to 4.0 at 37 degrees C, was approximately zero for 45Ca-HAp cement, whereas the solubility of 45Ca-DCPD cement was approximately the same as unlabeled cements used so far. This finding suggests that dissolution of the matrix apatite governs dissolution of the set cement, though comparison of X-ray diffraction patterns and electron micrographs of the seed apatite and apatite in the set cement showed no essential difference in crystallinity and crystal shape. The fact that the matrix apatite was formed by enveloping the seed apatite may account for the preferential dissolution of matrix apatite. In synthetic saliva labeled with 45Ca having a degree of supersaturation with respect to apatite comparable to rest saliva, 45Ca concentration in solution decreased once the cement pellet was introduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Apatites↗
PubMed1989

[Self-setting apatite cement. VII. Barium-apatite as radio-opaque medium].

Addition of barium hydroxyapatite (BaAp) successfully bestowed clinically acceptable radioopacity to the self-setting apatite cement consisting of an equimolar mixture of tetracalcium phosphate and dicalcium phosphate dihydrate. To accelerate the setting reaction which was retarded by Ba2+ released from BaAp at a lower pH during first stage of spatulation with 20 mM phosphoric acid, calcium hydroxyapatite (CaAp) was added to the cement mixture. At about 20 wt% of BaAp and 20 wt% CaAp, the setting reaction proceeded at a neutral or weak alkaline pH, which is one of the most promising aspects of the self-setting cement and assures that this type of cement may be the least irritating of the dental cements presently available. The cement spatulated at L/P = 0.4 set within 10 minutes and its radiopacity was comparable to or more than that of tooth enamel. The wet compressive strength of the set cement stored for one day in synthetic saliva at 37 degrees C was approximately 100 kgf/cm2. Although this value is almost one fourth that of 40 wt% CaAp cement, this cement appears to be strong enough to apply as root canal filling material.

Barium↗