Development of calcium phosphate cement for rapid crystallization to apatite. (1/4659)

The purpose of this study was to develop an alpha-tricalcium phosphate (alpha-TCP) cement which transforms to hydroxyapatite (HAP) in a relatively short period. We used calcium and phosphate solutions as the liquid phase for the alpha-TCP cement. The alpha-TCP powder was first mixed with CaCl2 solution, and then mixed with NaH2PO4 or Na2HPO3 solution for a total powder/liquid ratio of 1.8. The setting time became shorter with the increase in the concentration of calcium and phosphate solutions, reaching 5 min, whereas the setting time was longer than 30 min when distilled water was used as the liquid phase. X-ray diffraction analysis revealed that the cement was mostly transformed to HAP within 24 h when kept in an incubator. We concluded that alpha-TCP should be mixed with calcium and phosphate solutions since this results in a moderate setting time and fast transformation to HAP even if the method of mixing becomes a little complex.  (+info)

Steric effects of N-acyl group in O-methacryloyl-N-acyl tyrosines on the adhesiveness of unetched human dentin. (2/4659)

We have prepared various O-methacryloyl-N-acyl tyrosines (MAATY) to reveal the relationship between molecular structure near carboxylic acid and adhesive strength of MAATY-HEMA type adhesive resin to unetched dentin. In this study, we attempted to change the steric hindrance effect without changing the HLB value, i.e., introducing an iso-acyl group instead of n-acyl group into MAATY. O-methacryloyl-N-ethylbutyryl tyrosine (MIHTY) showed significantly lower adhesive strength when compared with O-methacryloyl-N-hexanoyl tyrosine even though both MAATY have the same HLB value. The possible explanation of the significantly different adhesive strength was that the 2-ethylbutyryl group in MIHTY was bulky, resulting in inhibition of the hydrogen bonding of the carboxylic group. The HLB value is independent of the steric effect of molecular structure, and thus the steric factor should be taken into consideration for the explanation of different adhesive strengths within the adhesive monomers having the same HLB value but different molecular structures.  (+info)

Fatigue and tensile strength of dental gallium alloys after artificial saliva immersion. (3/4659)

Fatigue strength using the stair-case method and tensile strength of dental gallium alloys after artificial saliva immersion were measured for evaluating the effects of corrosive environment storage on the mechanical properties of the gallium alloys. The fatigue and the tensile strengths of both gallium alloys stored in artificial saliva were significantly decreased after 12-month storage, while those stored in air increased with storage period. The fracture surfaces of the specimens in artificial saliva showed not only metallic luster but also dark areas. In the dark area, the matrix might have dissolved during immersion. These results suggested that the concern over corrosion resistance of gallium alloys still remained.  (+info)

Adhesion of adhesive resin to dental precious metal alloys. Part I. New precious metal alloys with base metals for resin bonding. (4/4659)

New dental precious metal alloys for resin bonding without alloy surface modification were developed by adding base metals (In, Zn, or Sn). Before this, binary alloys of Au, Ag, Cu, or Pd containing In, Zn, or Sn were studied for water durability and bonding strength with 4-META resin. The adhesion ability of the binary alloys was improved by adding In equivalent to 15% of Au content, Zn equivalent to 20% of Ag content, and In, Zn, or Sn equivalent to 5% of Cu content. There was no addition effect of the base metals on Pd, however 15% of In addition improved adhesion with Pd-based alloys containing equi-atomic % of Cu and Pd. The alloy surfaces were analyzed by XPS and showed that oxides such as In2O3, ZnO, or SnO play an important role in improving the adhesive ability of the alloys.  (+info)

Marginal adaptation of commercial compomers in dentin cavity. (5/4659)

The dentin cavity adaptation and setting characteristics of four commercial compomers were evaluated by measuring the wall-to-wall contraction gap width in the cylindrical dentin cavity and measuring the compressive strength for a maximum of 14 days after setting. The dentin cavity wall was pretreated by the dentin adhesives according to each manufacturer's instructions or the experimental contraction gap-free dentin bonding system. Complete marginal integrity was obtained in only one compomer and two resin composites which were combined with the experimental dentin bonding system. The compressive strength of two resin composites and two compomers ten minutes after setting was comparable to that after 14 days which indicated that the compomers exhibited setting characteristics as rapidly as the resin composite. It was concluded that a high efficacy dentin bonding system is required for commercial compomers to prevent gap formation during irradiation caused by the rapid setting shrinkage.  (+info)

Influence of archwire and bracket dimensions on sliding mechanics: derivations and determinations of the critical contact angles for binding. (6/4659)

There is every indication that classical friction controls sliding mechanics below some critical contact angle, theta c. Once that angle is exceeded, however, binding and notching phenomena increasingly restrict sliding mechanics. Using geometric archwire and bracket parameters, the theta c is calculated as the boundary between classical frictional behaviour and binding-related phenomena. What these equations predict is independent of practitioner or technique. From these derivations two dimensionless numbers are also identified as the bracket and the engagement index. The first shows how the width of a bracket compares to its Slot; the second indicates how completely the wire fills the Slot. When nominal wire and bracket dimensions are calculated for both standard Slots, the maximum theta c theoretically equals 3.7 degrees. Thus, knowledge of the archwire or bracket alone is insufficient; knowledge of the archwire-bracket combination is necessary for theta c to be calculated. Once calculated, sliding mechanics should be initiated only after the contact angle, theta, approaches the characteristic value of theta c for the particular archwire-bracket combination of choice--that is, when theta approximately theta c.  (+info)

An ex vivo investigation into the bond strength of orthodontic brackets and adhesive systems. (7/4659)

The aim of this study was to compare the shear bond strength of Adhesive Precoated Brackets (APC) with that of two types of uncoated bracket bases, Straight-Wire and Dyna-Lock. Two types of orthodontic adhesives were used, Transbond XT and Right-On. Three different curing times were evaluated with the APC brackets in order to find the best. Adhesive remnants on the enamel surface following debond were evaluated using the Adhesive Remnant Index (Artun and Bergland, 1984). Bond strengths ranged from 11.00 to 22.08 MPa. For both types of brackets Transbond produced a significant increase in bond strength compared to Right-On. The Dyna-Lock/Right-On combination produced the poorest results. APC brackets cured for 40 s had similar bond strengths to uncoated brackets fixed by means of Transbond. Overall, 79 per cent of specimens had less than half the tooth surface covered with adhesive following debond. Significantly more adhesive remained on tooth surfaces following debond of the Straight-Wire/Right-On group than any other bracket/adhesive combination. Bond strengths were higher with light-cured Transbond than with chemically-cured Right-On. When Transbond is used in association with APC brackets a 40-second cure time is recommended.  (+info)

Effect of permeability on indices of haemodialysis membrane biocompatibility. (8/4659)

BACKGROUND: Increases in plasma anaphylatoxins frequently are used as an index of haemodialysis membrane biocompatibility; however, their plasma levels may be influenced by the loss of anaphylatoxins into the dialysate compartment. METHODS: We compared the generation and compartmental distribution of anaphylatoxins, C3a and C5a, in a high flux and a low flux polysulfone membrane dialyser when whole human blood was recirculated through an in vitro haemodialysis circuit. RESULTS: Plasma C3a levels in high flux polysulfone (2.31 +/- 0.81 microg/ml) and low flux polysulfone (3.02 +/- 0.98 microg/ml) dialysers were comparable after 120 min (P = NS). In contrast, dialysate C3a in high flux polysulfone (0.65 +/- 0.31 microg/ml) accounted for 37.5 +/- 7.0% of the total detected (plasma + dialysate) C3a mass in the dialysers, while dialysate C3a in low flux polysulfone dialysers (0.01 +/- 0.01 microg/ml) accounted for only 0.3 +/- 0.3% of the total mass (P < 0.05; high flux vs low flux). Anaphylatoxin C5a was undetectable in the dialysate compartment of either dialyser examined. CONCLUSIONS: Our results indicate that anaphylatoxins readily traverse certain high flux dialysis membranes; consequently, plasma C3a levels may not accurately reflect the C3-activating potential of these membranes.  (+info)