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At least 19 recordsLinked to original sources
PubMed1989

Hardness tests in highly filled composite resins.

The hardness of seven proprietary, light-cured, posterior composite resins was evaluated by three different hardness testers: the Knoop hardness tester, the Barcol indenter and the Rockwell 15T hardness meter. Specimens were measured after light-curing and 24-hour immersion in 37 degrees C water. Barcol hardness numbers ranged from 79.2 to 85.0. The Rockwell 15T hardness data had a range from 73.3 to 80.3 and the Knoop hardness numbers varied from 39.9 to 79.0. Relatively small variations were determined between results of Barcol hardness numbers and Rockwell 15T hardness data. Great variation was revealed in the results from Knoop hardness numbers. According to the dimensions of the indentations, the results of Barcol and Rockwell hardness represent the bulky part of tested composites rather than superficial hardness. Knoop hardness testing is found to be relatively feasible and a suitable measurement for the determination of superficial hardness of highly filled composite resins.

Composite Resins↗
PubMed1977

Hardness testing of some fissure-sealing materials.

The mechanical properties of fissure-sealing materials are of significant importance for their durability, i.e. their wear resistance. One of the methods of evaluating a material's resistance to attrition is to apply a hardness test. In the present investigation, the surface hardness of some fissure-sealing materials was tested. Sealants made from diluted composite materials and with inclusion of inorganic filler particles appeared to have a considerable higher surface hardness than the other sealing materials tested.

Composite Resins↗
PubMed1978

Creep and hardness testing of some denture base polymers.

A method of measuring creep, recovery, hardness, and the effect of cyclic loading on denture base polymers using a modified Wallace hardness tester is described. This apparatus is particularly sensitive and is capable of detecting very small variations in these properties of the materials. A representative group of denture base polymers that include heat-cured, pour-type, and other modified materials was tested. The results obtained are in good agreement with those shown by other workers.

Denture Bases↗
PubMed1991

[Dental enamel hardness tests in diabetics].

The authors studied by in vivo methods (Fosse et al. 1986) the microhardness of dental enamel in diabetic patients compared to healthy persons. No differences of enamel microhardness values between diabetics and healthy persons, neither by longer diabetes duration nor by worse diabetes attitude have been found.

Adolescent↗
PubMed1975

[Water uptake and solubility of 3 filling plastic materials in relation to hardness tests and time].

10 samples each of 0.25 mm, 0.5 mm, and 1 mm thickness of a conventional PMMA, a PMMA composite, and a Bowen composite were tested according to FDI specification no. 3 for 60 days. Sample thickness influences the rate of water uptake, and especially solubility. The sample size of 50 plus or minus 1 mm diameter and 0.5 plus or minus 0.1 mm thickness is suitable for obtaining reproducible, comparable, and clinically characteristic results. Water saturation is normally obtained after 3 to 5 days. Because of the varying sample thickness during production and due to different density of the materials, water uptake should only be expressed in per cent by volume. Solubility should not be disregarded when determining water uptake. It may simulate saturation or equilibrium. Solubility amounts to up to 2 per cent by weight after 60 days. Clinical findings regarding loss in substance may be explainable by this.

Acrylic Resins↗
PubMed1990

[Development of visible-light cured FRP denture].

Acrylic denture may be fractured easily because it has a relatively poor resistance to stresses of impact, and the thick acrylic denture base also uncomforted to denture wearers. In this study, for improvement of the mechanical properties, the FRP is applied to the denture base, and try to make a thin denture base. Using the visible light-curing system, the laboratory fabrication time is saved dramatically. To develop the visible light-cured FRP denture base, with various combination of matrix resins and reinforcements, the physical properties of FRP plates were investigated first. From the results of the bending test, hardness test, and manipulation considering, the sateen weave's glasscloth was choose as the reinforcement of the prepreg. The matrix resin of Bis-GMA/UDMA/3G at 48/48/4 wt% was determined. The 3 plies glasscloth included FRP plate is 0.8 mm thickness has the maximum bending strength about 50 kgf/mm2, which is about 5 times larger than that of acrylic resin. Succeeding the study of above, the FRP denture base was fabricated by using the 0.8 mm thickness 3 plies included prepreg. This repreg is manufactured in sheet form beforehand, which is ease to manipulate at laboratory. By using the visible light curing system, it is only taken 10 min. to make a FRP denture base. The following procedures of fabricating a FRP denture is the same as metalplate denture. The visible-light cured FRP denture has some advantages such as accuracy of fit, ease of fabrication and manipulation, and only 0.8 mm thickness but has superior strength.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1989

[Development of denture base resin. 2. Manufacturing of visible-light cured prepreg and physical properties of FRP].

To develop the visible light-cured FRP denture base, we investigated the physical properties and the warp of FRP plate by using various combinations of matrix resin and reinforcement. From the results of the bending test, hardness test and manipulation processing, the matrix resin of Bis-GMA/UDMA/3 G at 48/48/4 wt% was determined. The sateen weave's glasscloth as the reinforcement of the prepreg was used. The maximum plies included FRP of 0.5 mm, 0.8 and 1.0 mm thickness have the same maximum bending strengths of 45 kgf/mm2, which is about 5 times larger than that of conventional acrylic resin. The warp of these FRP plates were not found.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1991

Effect of the polishing technique at low or high speed on the micro-hardness of dental amalgam.

Dental cavities were prepared and restored with amalgam, using three different silver alloys. The surface of the restorations was finished 24 hours after condensation, with a rotatory instrument using a low- or high-speed handpiece. The specimens were then submitted to metallographic polishing and one of the margins of the amalgam restoration were then submitted to Vickers' micro-hardness test. Another micro-hardness test was accomplished 168 hours after condensation and the two sets of micro-hardness values were compared. No significant statistical differences were detected between the micro-hardness values obtained with low or high speed in the polishing technique.

Dental Amalgam↗
PubMed1990

[Determination of copper alloy hardness, in original form and after casting as a function of casting techniques].

It was evaluated the Vickers hardness of five high-copper casting alloys, in their original package form and after casting, according to the casting method used. That way, ten ingots, supplied by the manufacturers of each alloy, were included in self-curing acrylic resin, polished, numerated and submitted to Vickers hardness test at load of 200 g during 30 seconds. Afterwards the numerated ingots were removed from the acrylic resin and five of those were cast in an electrical casting machine and the other five in a centrifugal casting machine with an air/gas torch. The specimens obtained were included in self-curing acrylic resin, polished and submitted to Vickers hardness test. As a result it was verified that there is a variation of hardness among the alloys tested, and the use of the electrical casting machine produced lower hardness values than those produced when used the centrifugal casting machine with an air/gas torch. Also, there is a decrease of hardness of the cast alloys when they are tested in their original form and after casting.

Copper↗
PubMed1977

[Recrystallization process in the 20 carat dental gold alloy (author's transl)].

An annealing process of the 20 carat dental gold alloy was studied by hardness testing, electrical resistivity measurement and optical microscopic observation. The material was cold rolled to 67.4% and 90.7% in reduction and subsequently annealed in the temperature range from 300 degrees to 500 degrees C. Microscopic observation, electrical resistivity and hardness testing revealed that the annealing process were three distinguishable stages, recovery, recrystallization and grain boundary migration. Activation energies, the order of the reaction involved, and frequency factors for various annealing processes were established.

Crystallization↗
PubMed1977

A study on the evaluation of local shati starch as a substitute of polysaccharides used in the preparation of capsules and tablets of antibiotics.

Local shati starch was extracted, purified and used as an excipient for the preparation of capsules and tablets of oxytetracycline and chloramphenicol. The weight variation test, disintegration time and hardness test of these dosage forms were done and compared with the conventional maize starch containing tables and capsules of the antibiotics. The results in respect of their potency test were found to conform to official pharmacopoeias (B.P. and U.S.P). Stability study for over one year of both varieties of tablets and capsules revealed that they retained their potencies equally well.

Anti-Bacterial Agents↗