The effect of primers on bond strength of polyacid-modified resin composites (compomers).
(41/1852)
This study evaluated the effect of primer on shear bond strength and marginal gaps of six new compomers immediately after light-activation. A resin-modified glass ionomer cement, a conventional glass-ionomer cement and a microfilled composite were used for comparison. The marginal gap widths of each of the four compomers and a microfilled composite used with the primer were significantly smaller compared with those used without the primer. The bond strength values of five compomers used with the primer were significantly higher than those used without the primer. The bond strength of conventional glass-ionomer was not affected by the primer (or the conditioner). (+info)
Effect of functional monomer in commercial dentin bonding agents use of an experimental dentin bonding system.
(42/1852)
The objective of the present study was to understand the role of the functional monomers in dentin bonding agents of an experimental dentin bonding system by measuring the wall-to-wall contraction gap and tensile bond strength measurement. The efficacy of three commercial dentin bonding agents after using EDTA for conditioning and GM for priming was evaluated by measuring the contraction gap of the resin composite in a cylindrical dentin cavity, and by measuring the tensile bond strength of the composite to a flat dentin surface. The effect of the functional monomers was demonstrated by the contraction gap measurement alone. The value of the contraction gap was significantly different between the commercial dentin bonding agents and these agents without functional monomers (p < 0.05). It was concluded that the functional monomers were essential to obtaining the marginal integrity of the resin composite in the dentin cavities. (+info)
Gold alloys for resin bonding including small amount base metals--structural changes of alloy surface by the high-temperature oxidation.
(43/1852)
To achieve durable bonding with adhesive resin, the surface roughness and the kinds of oxides, respectively to increase mechanical retention to enhance the chemical affinity of adhesive monomer with the gold alloy, were regulated by high-temperature oxidation together with the addition of small amounts of base metals. Alloys containing 2 mass% of Ni, In, or Cr with Cu were oxidized at 800 degrees C for 20 min in air, pickled in thioglycolic acid, and subsequently oxidized at 500 degrees C for 10 min in air. The morphology of the internal oxidation zone changed markedly according to the added base metals. Although the internal oxide particle composed of only Cu2O was removed by pickling, NiO, In2O3, and chromium oxides could not removed and remained on the alloy surface. The surface roughness was increased by addition of Ni, In, or Cr. Applying the present method can control the roughness and chemical states on a gold alloy surface to increase its adhesive ability with adhesive resins. (+info)
Relationship between Af temperature and load changes in Ni-Ti orthodontic wire under different thermomechanical conditions.
(44/1852)
Simple three point bending tests were performed on Ni-Ti wires with three different Af points (1 degree C, 13 degrees C and 34 degrees C) to clarify the relationship between Af temperature and load changes under constant deformation. Each wire was deformed at 37 degrees C and then thermal changes were imposed by temperatures of 2 degrees C or 60 degrees C. The load changes with thermal changes from 37 degrees C to 2 degrees C or 60 degrees C showed the same tendency on the wires with different Af points: In the loading stage, the load became lower than the initial level at 37 degrees C and in the unloading stage, the load became higher than the initial load. The largest load change in the unloading stage was measured with the 13 degrees C Af point wire. Care must be taken when handling Ni-Ti wire with an Af point of less than 1 degree C in order to prevent it from reaching the limit of critical stress of slip deformation when the temperature in the mouth rises to above 40 degrees C. (+info)
Adhesion of a new commercial self-etching/self-priming bonding resin to human caries-infected dentin.
(45/1852)
We have examined the adhesive properties of a new commercial self-etching/self-priming bonding resin (Unifil Bond, UB) to normal and caries-infected dentin of human extracted molars using scanning electron microscopy (SEM) and a micto-tensile bonding strength (MTBS) test. In this study, 7 human extracted molars with moderate occlusal caries were used, and flat surfaces including occlusal dentin caries were prepared from the teeth. After the application of UB to the surfaces, a composite resin was built up, and subjected to the measurement of MTBS and SEM observation of the interfacial morphology between UB and dentin. The MTBS of UB to normal dentin was 33.4 MPa, but that to caries-infected dentin was 11.0 MPa. There was a significant difference between the MTBS to normal and carious dentin. SEM observation revealed that the typical hybrid layer was not formed in caries-infected dentin. These results suggested that resin infiltration into caries-infected dentin was not sufficient to allow perfect sealing of the restoration. (+info)
An evaluation of the stresses generated in a bonded orthodontic attachment by three different load cases using the Finite Element Method of stress analysis.
(46/1852)
The objective of the investigation was to develop a clinically valid three-dimensional computer model of the orthodontic bracket-cement-tooth continuum, and determine the magnitude and distribution of stresses generated by three different load cases. A three-dimensional finite element model of the bracket-cement-tooth system was constructed consisting of 15,324 nodes and 2,971 finite elements. The stresses induced in the bracket-tooth interface by a masticatory load, a peel force and a twisting couple were recorded. The maximum principal stresses resulting from occlusal and 'twisting' forces are distributed toward the lute periphery. Peel forces, applied to the bracket tie wing, are concentrated beneath the bracket stem. Twisting forces result in the highest enamel stresses. The quality of orthodontic attachment can be explained by the magnitude and distribution of major principal stresses within the cement and impregnated bracket base. Shear and shear/peel forces are most likely to induce crack propagation within the adhesive layer. However, when a twisting action is used to remove orthodontic brackets, enamel failure is most likely. A clearer insight into the complexity of the bracket-cement-tooth system has been provided by numerical and finite element investigations. Further investigations, evaluating the influence of bracket base designs and orthodontic cement physical and geometric properties are indicated. Refereed Scientific Paper (+info)
Decreased passive stiffness of cardiac myocytes and cardiac tissue from copper-deficient rat hearts.
(47/1852)
Passive stiffness characteristics of isolated cardiac myocytes, papillary muscles, and aortic strips from male Holtzman rats fed a copper-deficient diet for approximately 5 wk were compared with those of rats fed a copper-adequate diet to determine whether alterations in these characteristics might accompany the well-documented cardiac hypertrophy and high incidence of ventricular rupture characteristic of copper deficiency. Stiffness of isolated cardiac myocytes was assessed from measurements of cellular dimensional changes to varied osmotic conditions. Stiffness of papillary muscles and aortic strips was determined from resting length-tension analyses and included steady-state characteristics, dynamic viscoelastic stiffness properties, and maximum tensile strength. The primary findings were that copper deficiency resulted in cardiac hypertrophy with increased cardiac myocyte size and fragility, decreased cardiac myocyte stiffness, and decreased papillary muscle passive stiffness, dynamic stiffness, and tensile strength and no alteration in aortic connective tissue passive stiffness or tensile strength. These findings suggest that a reduction of cardiac myocyte stiffness and increased cellular fragility could contribute to the reduced overall cardiac tissue stiffness and the high incidence of ventricular aneurysm observed in copper-deficient rats. (+info)
Do high impact exercises produce higher tibial strains than running?
(48/1852)
BACKGROUND: Bone must have sufficient strength to withstand both instantaneous forces and lower repetitive forces. Repetitive loading, especially when bone strain and/or strain rates are high, can create microdamage and result in stress fracture AIM: To measure in vivo strains and strain rates in human tibia during high impact and moderate impact exercises. METHODS: Three strain gauged bone staples were mounted percutaneously in a rosette pattern in the mid diaphysis of the medial tibia in six normal subjects, and in vivo tibial strains were measured during running at 17 km/h and drop jumping from heights of 26, 39, and 52 cm. RESULTS: Complete data for all three drop jumps were obtained for four of the six subjects. No statistically significant differences were found in compression, tension, or shear strains with increasing drop jump height, but, at the 52 cm height, shear strain rate was reduced by one third (p = 0.03). No relation was found between peak compression strain and calculated drop jump energy, indicating that subjects were able to dissipate part of the potential energy of successively higher drop jumps by increasing the range of motion of their knee and ankle joints and not transmitting the energy to their tibia. No statistically significant differences were found between the principal strains during running and drop jumping from 52 cm, but compression (p = 0.01) and tension (p = 0.004) strain rates were significantly higher during running. CONCLUSIONS: High impact exercises, as represented by drop jumping in this experiment, do not cause higher tibial strains and strain rates than running and therefore are unlikely to place an athlete who is accustomed to fast running at higher risk for bone fatigue. (+info)