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Results for “Compressive Strength”

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PubMed1990

[Effect of addition of calcia on the properties of zirconia investments].

The zirconia investments with calcia were studied of the compressive strength, setting expansion, thermal expansion, total expansion, thermogravitometry, differential thermal analysis on fabrication method, concentration, particle size of zirconia, calcia and mixing liquid. Addition of calcia caused the change from contraction to expansion in setting expansion. The optimum concentration of calcia was determined to be 10 mol% as judged from total expansion, strength and operability.

Calcium↗

PubMed1990

[An experimental study of the effect of food on osteoporosis especially on the mandible].

Three-week-old male rats of the Wistar strain given standard formed food (MF formed food) were grouped as controls. Those given calcium-deficient food for three weeks and then standard formed food after experimental osteoporosis induced in the rats were grouped as the experimental group. Experimental periods were for 4 and 6 weeks and the effect of the food on osteoporosis was investigated. The results were as follows: 1. Bone density of the alveolar bone showed significantly lower values for the experimental group than for the controls. 2. In comparison of relative Ca ratios (Ca/[Ca]c) and of P ratios (P/[P]c) on an X-ray microanalyzer, the controls showed higher values each week than the experimental group. 3. Compressive strength of the mandible in the experimental group decreased compared with the controls.

Animals↗

PubMed1990

[The surface degradation of various light-cured composite resins by thermal cycling].

The durability of four commercially available light-cured composite resins was investigated by thermal cycling, GR containing inorganic fillers treated with the graft polymerization of acryl ester, LF inorganic fillers treated with a silane coupling agent, PC silanized inorganic fillers and organic composite fillers, and the MFR-type SI containing the organic composite fillers. These materials were given 10,000, 30,000 and 50,000 thermal cycles (4 degrees C-60 degrees C) and the deterioration of materials by thermal cycling was evaluated by the measurement of the mechanical properties and the SEM observations of the surface of the thermocycled materials. Compressive strength and bending elastic moduli for all materials did not change greatly by thermal cycling. However, bending strength, toothbrush abrasion resistance and surface hardness decreased with increasing number of thermal cycles between 0 and 30,000, and changed little after 30,000 cycles. The percentage of bending strength after 50,000 thermal cycles to that of the non-thermocycled sample was 75% for GR, 60% for LF, 50% for PC and 65% for SI, respectively. Deterioration of materials was observed as cracks on the surface, which generated at the interface of the filler and matrix. The cracks generated relatively earlier during thermal cycling for SI and PC which contained the organic composite filler, later for LF which contained the silanized inorganic fillers, and the number of cracks on LF were fewer than SI and PC. On the other hand, for GR, no cracks were observed even after 50,000 thermal cycles. From these results, it can be presumed that the pre-treatment of filler by the graft polymerization is more effective to improve the durability of composite resin.

Composite Resins↗

PubMed1990

[Application of gypsum-bonded investment containing niobium carbide on casting of alloy for metal-ceramic restoration].

Experimental gypsum-bonded investments containing 0.5-5.0 wt% NbC were prepared by mechanical mixing of each powder. Setting and thermal expansion measurement, compressive strength and casting accuracy for Ni-Cr alloy for metal-ceramic restoration were investigated. Analysis of NbC during heating was carried out by X-ray diffraction, TG-DTA and SEM. NbC was oxidized to Nb2O5 with a volume change between 300-600 degrees C, as in the following equation: 2NbC + 4 1/2O2----Nb2O5 + 2CO2 The theoretical volume of 1/2Nb2O5 calculated from the lattice constants according to JCPDS file was approximately 4 times larger than that of NbC. The experimental investments of 70 wt% cristobalite and 30 wt% gypsum containing 2.0, 3.0 and 5.0 wt% NbC showed large thermal expansion of 7.0, 10.0 and 13.0% respectively. The investment containing 2.0 wt% NbC showed nearly the same casting accuracy for Ni-Cr alloys for metal-ceramic restoration as the commercial phosphate-bonded investment.

Calcium Sulfate↗

PubMed1990

[Development of dental quick casting with zircon-phosphoric acid investments].

The application of zircon (ZrSiO4) that has high refractoriness, high thermal conductivity and a low coefficient of thermal expansion, to quick casting investment was studied. Various zircon powders and phosphoric acid solutions were tested with respect to the higher thermal shock resistance. The formulation and properties of zircon-phosphoric acid investment materials such as water/powder ratio, fluidity of slurry, setting time, setting expansion, thermal expansion, thermal analysis, green and fired compressive strength were measured. Formulation of zircon slurry for coating was zircon flower #600 30%, zircon flower #350 10%, and zircon sand CP 60%, and that for sanding was zircon flower #200. The mixing liquid was 15% phosphoric acid and liquid/powder ratio was 0.1. The slurry using phosphoric acid had good fluidity and good workability. The 24-hour green strength was 1 MPa, fired strength was 10 MPa, 24-hour setting expansion was -0.04% and the thermal expansion at 1000 degrees C was 0.31%. Immediately after coating with zircon slurry, the coating layer was dried, sintered and dewaxed by thermal shock. The thermal shock consisted of the following four-step manipulations. The first is hot air drying (50 degrees C, 5 minutes), the second is heat shock (900 degrees C, 3 seconds), the third is redrying (220 degrees C, 3 minutes) and the fourth is dewaxing (550 degrees C, 3 minutes). Small casting of pure titanium and K-metal could be done successfully by the quick casting method using the zircon-phosphoric acid investments. It was found that the total expansion of the secondary investments influenced the casting adapatability.

Dental Casting Investment↗

PubMed1990

[Basic studies on radiopaque monomer. (3) Synthesis of monomers having Di-, tri-bromophenoxy groups, their properties, radiopacity and physical properties of their bulk polymers].

Radiopaque monomers were synthesized to examine their properties and the physical properties of their bulk polymers, to obtain basic data for new radiopaque filling composite resin. Octachlorocyclotetraphosphazene (P4N4Cl8) was used as material to be synthesized, and 2,4,6-tribromophenol, (Br3C6H2OH) and 2,4-dibromophenol (Br2C6H3OH) were selected as organic compounds having radiopacity. As a polymerizing functional group, 2-hydroxyethylmethacrylate (HEMA) was used. Radipaque monomers were synthesized as follows: 1 Cl of P4N4Cl8 was replaced by 1 mol of 2,4,6-tribromophenol, or 2 Cls by 2 mols of 2,4-dibromophenol, and the remaining 7 or Cls were replaced by HEMA, polymerizing functional group, to obtain 2 kinds of radiopaque monomers; 4 PN-(Br3Ph)1-(EMA)7 and 4 PN-(Br2Ph)2-(EMA)6. The specific gravity of these monomers was 1.4629 and 1.4978, refractive index 1.5315 and 1.5423 and viscosity, 70 and 80 poise respectively. Radiopacity was measured by an X-ray apparatus. Al equivalent, of specimen, 10 phi x 3 mm, 4 PN-(Br3Ph)1-(EMA)7 was 5.8 mm and 4 PN-(Br2Ph)2-(EMA)6 7.0 mm. 4 PN-(Br3Ph)1-(EMA)7 and 4 PN-(Br2Ph)2-(EMA)6, both wet specimens, had compressive strength of 83.7 and 81.3 MPa, in transverse strength of 45.5 and 53.0 MPa and knop hardness of 25.8 and 22.6 respectively. After 7 days, 4 PN-(Br3Ph)1-(EMA)7 had water sorption of 1.46 wt%, and 4 PN-(Br2Ph)2-(EMA)6, 0.84 wt%, and solubility of 0.15 and 0.14 wt%, respectively.

Absorption↗

PubMed1979

[Preparation of hard crown and bridge resin without PMMA powder (author's transl)].

Elimination of PMMA powder to prepare better hard crown and bridge resin had been pointed out by the authors even though polyfunctional methacrylates were used. Application of hydrophobic coloidal silica instead of PMMA pearl with triethyleneglycol dimethacrylate and Bis-GMA was studied. Polyermization was carried out in the hot air stream at 120 degrees approximately 130 degrees C or in a pressure vessel at 4.5 kg/cm2 gauge, 100 degrees C. Mechanical properties, brinell hardness, compressive strength, an amount of water sorption, comparative average abrasion loss depth with those of PMMA, were measured. They were improved very much by this new system.

Acrylates↗

PubMed1990

Chairside repair of ceramo-metallic restorations.

The ceramo-metallic crown has enjoyed increasing universal popularity as the full-coverage restoration of choice where long-term esthetics is desirable. The porcelain veneer is colour stable and relatively wear resistant. It has excellent compressive strength but poor tensile and shear strength, which unfortunately can result in fracture. Consequently, there is a need for chairside repair, since remake is often contraindicated. Commercially available repair systems are inconsistent and unpredictable and provide, at best, only temporary results despite recent improvements in materials and technique. Two new adhesive composite resins appear promising, although long-term clinical studies are not available. This article deals first with prevention and a review of the literature. Secondly, clinically proven methods of providing mechanical retention for resin and composite resin repairs of fractured porcelain are presented. The combination of mechanical retention and recently developed adhesive composite resins should provide the dentist with a reliable chairside repair system that could last for many years.

Composite Resins↗

PubMed1990

Vertebral body trabecular density at the thoracolumbar junction using quantitative computed tomography. A post-mortem study.

Quantitative computed tomography was used to assess vertebral trabecular density in 26 post-mortem spines from individuals aged between 14 and 80 years. All vertebrae from T10 to L1 were scanned transversely near the mid-vertebral level with calculations of trabecular density in HUs averaged and referenced to a mineral equivalent phantom. An age-related decline in trabecular density was recorded (r = 0.55, p less than 0.0001). Density measures from the anterior aspect of the vertebral body were significantly greater than from postero-lateral regions. From T10 to L1, there was a significant decrease in trabecular density, whereas density measures multiplied by vertebral body cross-sectional area were constant. Predictions of vertebral compressive strength using quantitative computed tomography may become more accurate by increasing the sampling area per scan and including vertebral body cross-sectional area as part of the radiologic assessment.

Adolescent↗

PubMed1990

[Morphological aspects of the mineral phase of the bone].

By means of light, scanning and transmission electron microscopy structure of the mineral phase of human compact bone have been studied. Mechanical properties of deorganified bone samples have been determined. High compressive strength may be in connection with interactions of plate-like mineral particles at the level of hydrate shell of the bone mineral crystallites.

Adult↗

PubMed1989

[Water sorption, solubility, MeOH sorption and THF sorption of visible light cured resin--on resin using cyclophosphazene monomers and commercial monomers].

Studies were done to decrease both the water sorption and solubility of visible light cured resin. As monomer, three kinds of cyclophosphazene monomers and three kinds of commercial monomers were prepared to the visible light cured unfilled resins. When these set products were immersed in water, MeOH and THF, water sorption and solubility in water, MeOH sorption and solubility in MeOH, THF sorption, and mechanical properties were examined. Water sorption was increased by degrees for all the monomers. In the cases of 4 PN-(EMA)8, 4 PN-(TF)1-(EMA)7, 4 PN-(TF)2-(EMA)6, Tri-EDMA, BMPEPP and Bis-GMA + Tri-EDMA, the value of solubility in water after 30 days, was 0.16, 0.20, 0.51, 0.65, 0.17 and 0.81% respectively. MeOH sorption showed a tendency to increase, except for Bis-GMA + Tri-EDMA and 4 PN-(TF)2-(EMA)6. Solubility in MeOH after 30 days, for cyclophosphazene monomers and commercial monomers, was 0.09-0.36% and 1.36-5.40%. THF sorption after 30 days, for cyclophosphazene monomers, was small in comparison with that of commercial monomers. Compressive strength was 230-275 MPa in all cases. But, transverse strength, for all the cyclophosphazene monomers, was 45 MPa or below. In the cases of commercial monomers, the value of transverse strength was 55-90 MPa.

Acrylic Resins↗

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↗

PubMed1989

[Studies on physico-chemical properties of self-setting apatite cement].

A new dental cement was developed by use of tetracalcium phosphate monoxide (Te-CP) and dicalcium phosphate dihydrate (DCPD). When an equimolar mixture of the two calcium phosphates was mixed with diluted phosphoric acid, it hardened into a phase of hydroxyapatite (HAp) resembling the main inorganic phase of hard tissues. The present study was undertaken to investigate physico-chemical properties of this newly developed apatite cement and to evaluate its potential as dental cement to clinical application. The setting time was reduced in the presence of synthetic HAp, indicating added HAp to be an accelerator in the setting reaction. The pH of paste rapidly increased to a neutral range from initial solution acidity of about 2.0 and the subsequent setting reaction proceeded in a neutral and weak alkaline pH range. The hardened solid 4 hours after saturation was identified as single phase of apatite by X-ray diffraction. The HAp crystallinity of the set cement varied with the crystallinity of HAp added as setting accelerator. The wet compressive strength of the cement stored for one day in synthetic saliva at 37 degrees C increased to 400 kg/cm2 as added HAp crystallinity decreased. Moreover no disintegration took place when the cement was stored at 37 degrees C in synthetic saliva, which was undersaturated with respect to DCPD but well supersaturated for HAp. In clinical application to animals, no significant cleavage was observed between the hard tissues and the cement by SEM even three months after the cement paste was filled in the tooth cavity of monkeys. In the specimen prepared one week after implantation in the medullary canal of rats, no inflammatory cell appeared. The specimen prepared one month after implantation showed that the set cement was tightly contacted with newly formed bone. These findings strongly suggest that the newly developed self-setting apatite cement is useful as a pulp capping agents, root canal fillings and bone substitute.

Animals↗

PubMed1989

[Dental application of superplastic forming for titanium complete denture bases].

In order to investigate the application of superplastic in forming dental prosthesis, the sheets of titanium and its alloy were deformed to the complete denture bases by using a trial hot press and ceramic die. The results are summarized as follows: 1) By the hot press. It was possible to deform the sheet at a deformation speed ranging from 1 x 10(-3) to 3 x 10(-2) mm/sec at a temperature up to 900 degrees C under a vacuum down to 10(-3) Torr. 2) The trial ceramic die was prepared by sintering the green of the CaO-TiO2-ZrO2-MgCl2 system at 1150 degrees C for 6 hours in the atmosphere. The compressive strength, the thermal expansion, and the surface roughness of the test piece of the die were 11 kg/cm2, 0.8%, Ra = 1.4 microns and Rz = 6.8 microns, respectively. 3) Both the sheet of pure chemical titanium and commercial superplastic titanium alloy Ti-6Al-4V were deformed under the conditions of about 0.1 mm/min, 850 degrees C, and 10(-3) Torr. The deformed surface of the complete denture bases appeared to be nearly the same metallic color of each raw sheet and the pattern was the same as the detail of the die. The oxygen enriched layer of the article determined by EPMA was far thinner than that of a dental cast.

Dental Alloys↗

PubMed1989

[An experimental study on the osteoconductive properties of porous calcium phosphate glass ceramics].

Porous blocks of calcium phosphate glass ceramics (CaO 52 mol %, P2O5 47 mol %, Al2O3 1 mol %, mean pore size 200 microns, mean porosity 85%) were implanted in the distal femoral metaphysis of rats and were observed for up to one year. The materials were evaluated histologically and morphometrically using contact microradiography and Masson-Goldner staining. Comparative experiments were conducted employing similar methods as described above, with calcium phosphate glass ceramics, sintered hydroxyapatite and alumina ceramics, each having 70% porosity. The compressive strength of each implanted material was measured at a certain intervals up to 6 months after implantation. Bone formation was seen from the periphery to the center of the block. Mass of the regenerated bone and infiltrating depth of the new bone increased with the passage of time. New bone formation with the glass ceramics was observed to be almost equivalent to that obtained with hydroxyapatite, and was significantly higher than that with the alumina ceramics.

Animals↗

PubMed1989

[Visible-light cured resin. Selection of reducing agent amine, its appropriate amount and effect on physical properties].

Studies were done to improve the physical properties, especially degree of conversion of visible-light cured resin (VLCR), and accordingly to lower its water sorption and solubility in water. Trial products of VLCR were prepared using various kinds of amine, reducing agent, and the photoinitiator to be mixed with cyclophosphazene monomer, 4 PN-(TF)1-(EMA)7. As amines ethyl-p-dimethylaminobenzoate (DMAB), methacryloxyethyl-p- dimethylaminobenzoate (DMAB-EMA) and methacryloxyglycidyl-p-dimethylaminobenzoate (DMAB-GMA) were used. Of their set products immersed in water and MeOH, their water sorption, solubility in water, MeOH sorption and solubility in MeOH were examined. The resin with DMAB-EMA used was preferable, showing comparatively small solubility. Next, VLCR, with various amounts of DMAB-EMA mixed, 0.5-5.0 in mol ratio to photosensitizer (CQ + DB), and of their set products water sorption, solubility in water, MeOH sorption, solubility in MeOH, THF sorption and their mechanical properties after immersion in water were examined. Immersion of the resin products in water and MeOH for 30 days, lowered the solubility in water and MeOH to a minimum at the mixing ratio of 3.0 in mol ratio. Solubility in MeOH (HPLC) became minimum at 2.0 in mol ratio, and at less than 2.0, the photosensitizer and monomer were dissolved, while at more than 2.0, the photosensitizer and DMAB-EMA were dissolved. THF sorption decreased in accordance with the increase in the mixed amount of DMAB-EMA, became almost constant at more than 3.0 in mol ratio. The compressive strength of set product after immersion in water for 7 days increased in accordance with the increase of the mixed amount of DMAB-EMA, while the transverse strength also increased up to 2.0 in mol ratio. The optimum reducing agent to be mixed with VLCR was DMAB-EMA, and the mixing ratio should be 2.0-3.0 in mol ratio to photosensitizer.

Acrylic Resins↗

PubMedDate not supplied

[2 amalgam formulation mechanisms with high copper alloys].

Two high copper-containing amalgam alloys, one of them gas atomized and the other water atomized were used to study the reaction mechanism with mercury. Normal and subtrituration time were used. The observations of structures and evaluation of compressive strengths allowed the understanding of two different mechanisms of reaction.

Copper↗

PubMed1989

[Fluoridated amalgams. Bibliographic review].

A review on fluoride containing amalgam is reported in this paper. The inhibitory effects of fluoride on dental caries are well known for many years. Thus, the incorporation of fluoride to an amalgam restoration prevents the occurrence of marginal caries. Other physical properties of fluoride amalgams such as compressive strength, dimensional changes, creep and corrosion are also reviewed in this paper.

Dental Amalgam↗