Interfacial strengths of various alloy surface treatments for resin-bonded fixed partial dentures

A practical method for bonding or rebonding the resin-bonded retainer is eagerly being sought by general practitioners. This research introduces a new test apparatus for evaluating bond strength of base metal alloys after various alloy surface treatments. Five commercial base metal alloys and a resin luting cement for resin-bonded fixed partial dentures were examined. Sandblasting, oxidation, or etching treatment were determined to be effective in increasing the adhesive strength for the tested alloys. No statistical differences between various surface treatments were found for bonding of Unitbond metal. Inexpensive sandblasting, along with ultrasonic washing, provided superior bonding strengths for Biobond II and Litecast B materials. Electrochemical treatment was suitable for Wiron 77 and Lab metals.

The relationship between composition and properties of posterior resin composites

The effects of filler concentration and resinous components on the properties of highly filled composites were determined for prediction of the durability of the restorative resins. Resinous components of seven proprietary light-cured posterior resin composites were extracted by chloroform solvent and examined by the Fourier Transform Infrared (FTIR) method. Filler concentration was determined by the thermogravimetric method. Diametral tensile strength, Knoop hardness, and Barcol hardness tests for the composite, as well as extracted resinous matrix, were performed by standard experimental procedures. Toothbrush abrasion test of the resin composites was evaluated by a toothbrushing machine giving the equivalent of five years' toothbrushing and examined with a roughness meter. The degree of conversion of resin composites ranged from 43.5 to 73.8%. The volume fraction of filler varied from 58.2% to 74.2%. The ranges of diametral tensile strength and Knoop and Barcol hardness numbers obtained were 39.8 MPa to 60.0 MPa, 41.8 to 81.9, and 76.3 to 89.2, respectively. Significant correlations (p less than 0.01) were obtained between filler fraction and diametral tensile strength (r = 0.89, S.E. = 3.66) and between filler fraction and Knoop hardness number (r = 0.89, S.E. = 8.39). The increase in strength with increased filler concentration might be related to filler/matrix bonding.

New 4-hydroxypyridine and 4-hydroxyquinoline derivatives as inhibitors of NADH-ubiquinone reductase in the respiratory chain

Many derivatives of 2,3-dimethoxy-4-hydroxypyridine, which were designed from examination of the structure-activity relationship of piericidins, were tested for inhibition of NADH-UQ reductase. The lipophilic side chain of those compounds was indicated to be a key part for activity and its optimal length was conjectured. By the use of two different phases of assay material, intact mitochondria and submitochondria, the size of a membrane effect was shown to depend on the structure of the side chain. 4-Hydroxyquinoline derivatives were also tested for an analogous role in relation to the electron transport function of menaquinone, and they were proven to be inhibitors of NADH-UQ reductase as good as the pyridine derivatives.

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.

Creep in a palladium-enriched high-copper amalgam

Palladium additions to a dispersed phase high-copper amalgam have been shown recently to suppress markedly the eta' (Cu6Sn5) concentration and decrease creep. A detailed study of the dental and 24 h creep for Pd containing high-copper amalgams and six commercial controls as a function of applied temperature and stress was performed. One part of Ag-Cu or Ag-Cu-Pd dispersants with substitutions of up to 20wt/o Pd for either Ag or Cu was blended with two parts of traditional amalgam alloy. Various temperatures from 25 to 60 degrees C and stresses from 36 to 72 MPa were applied to the samples during the test. For commercial controls and experimental amalgams with no Pd, creep is a strong function of temperature and stress. The experimental amalgam containing up to 10wt/o Pd, Pd substituted for Ag, demonstrated essentially constant creep over the temperature and stress range applied.

Purification, characterization, and action-pattern studies on the endo-(1 linked to 3)-beta-D-glucanase from Rhizopus arrhizus QM 1032

The extracellular (1 linked to 3)-beta-D-glucanase [(1 linked to 3)-beta-D-glucan glucanohydrolase, EC 3.2.1.6] produced by Rhizopus arrhizus QU 1032 was purified 305-fold in 70% overall yield. This preparation was found to be homogeneous by ultracentrifugation (sedimentation velocity and equilibrium studies), electrophoresis on acrylamide gel with normal, sodium dodecyl sulfate, and urea-acetic acid gels, and upon isoelectric focusing. The amino acid composition of the enzyme has been determined and it possesses a carbohydrate moiety compose of mannose and galactose (in the ratio approximately 5:1) that is linked to the protein through a 2-acetamido-2-deoxyglucose residue. The molecular weight, as determined by equilibrium sedimentation, is 28,800 and this number was confirmed by electrophoresis on gels of sodium dodecyl sulfate. The enzyme does not possess subunit structure. It hydrolyzes its substrates with retention of configuration and possesses transglycosylating ability. The rates of hydrolysis of a wide variety of substrates were determined, and its action pattern on a series of oligosaccharides containing mixed (1 linked to 3)-, (1 linked to 4)-, and (1 linked to 6)-beta-D-glucopyranosyl residues was investigated. The enzyme favors stretches of beta-D-(1 linked to 3) linkages, but it can hydrolyze beta-D-(1 linked to 4) linkages that are flanked on the non-reducing side with stretches of beta-D-(1 linked to 3) links. The enzyme will not act on (1 linked to 6)-beta-D-glucosyl linkages located in stretches of beta-D-(1 linked to 3) and will not act on (1 linked to 3) beta-D-glycosidic linkages involving sugars other than D-glucose.