Effect of carbamide peroxide bleaching agents on micro-leakage of composite resin interface in vitro / 南方医科大学学报

<p><b>OBJECTIVE</b>To evaluate the effect of carbamide peroxide (CP) bleaching agents at different concentrations and with different carriers on the micro-leakage of composite resin interface.</p><p><b>METHODS</b>Class V cavity (2 mm in diameter and 2 mm in depth) preparations were made at the enamelo-cemental junction on the buccal and lingual surfaces of 35 extracted human premolars. The cavities were filled with hybrid composite resin. The teeth were stored for 24 h in distilled water at 37 degrees celsius; before thermocyling for 500 times between 5 and 55 degrees celsius;. The teeth were then randomly assigned into 7 groups, and in groups 1-6, the bleaching gels containing 10% or 20% of CP were applied on the buccal and lingual surface of the teeth for two weeks (6-8 h/day, 37 degrees celsius;, 100% relative humidity) using Carbopol, PVP or Poloxamer as the thickening carriers, respectively. The seventh group served as the control without bleaching treatment. Nail polish was applied to the surface of the tooth, and all the teeth were immersed in ammoniacal silver nitrate solution followed by developing solution. The teeth were finally sectioned through the midline of the restoration and observed under stereomicroscope. SEM micrographs were also made to observe the interface.</p><p><b>RESULTS</b>With the same bleaching agent, the micro-leakage in the gingival wall was slightly greater than in the occlusive wall, but the difference was not significant. Only 20% CP with Poloxamer as the thickening agent significantly increased the leakage of dentine-resin composite interface, and 10% and 20% CP with Carbopol or PVP as the thickening agents and 10% CP with Poloxamer produced minimal effects on filling the micro-leakage.</p><p><b>CONCLUSION</b>Thickening carriers and the concentration of CP (20% or below) have no significant effect on micro-leakage of composite resin.</p>

Two-dimensional morphology of microleakage between dentin and adhesives / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To observe the two-dimensional morphology of microleakage between dentin and adhesives.</p><p><b>METHODS</b>The occlusal enamel of human third molar was cut out and the dentin exposed, followed by the application of dental adhesive (Prime & Bond NT, Contax and Adper Prompt), then a composite resin crown was built up. After storage in water (37 degrees C) for 24 h, all teeth were vertically serially sectioned into matchstick-shaped specimens through the bond interfaces. Half of the specimens from one tooth were subjected to thermal cycling and another half was stored in water (37 degrees C). All specimens were then immersed in ammoniacal silver nitrate solution, followed by developing solution. At last all specimens were subjected to microtensile test at a cross-head speed of 1.0 mm/min and their fractured surfaces were observed under scanning electron microscope.</p><p><b>RESULTS</b>The planar contour of all the silver leakage was various branching, treelike shape, spreading from the border of section to the center.</p><p><b>CONCLUSION</b>The planar contour of microleakage is treelike shape and its extent is influenced by adhesives and thermal cycling.</p>

Structural characteristics of laser-welded cast pure titanium joints by different gap distance / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To measure the microstructure of laser-welded cast pure titanium by different gap distance.</p><p><b>METHODS</b>Forty specimens were sectioned and welded at four gaps (0.00 mm, 0.25 mm, 0.50 mm and 1.00 mm). Took microhardness test and metallographic examination of welded zone surface.</p><p><b>RESULTS</b>There were no difference in microhardness value and metallographic observation between welded specimens. The width of heat-effected zone was different. The smaller grains and needle-like alphamartensitic structure were found in the heat-affected zone.</p><p><b>CONCLUSION</b>The effects of the joint gap were not significant.</p>

Effects of laser welding on bond of porcelain fused cast pure titanium / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the influence of the laser welding on bond of porcelain fused to cast pure titanium.</p><p><b>METHODS</b>Twenty cast titanium plates were divided into two groups: laser welded group and control group. The low-fusing porcelain was fused to the laser welded cast pure titanium plates at fusion zone. The bond strength of the porcelain to laser welded cast pure titanium was measured by the three-point bending test. The interface of titanium and porcelain was investigated by scanning electron microscopy (SEM) and energy depressive X-ray detector (EDX). The non-welded titanium plates were used as comparison.</p><p><b>RESULTS</b>No significant difference of the bond strength was found between laser-welded samples [(46.85 +/- 0.76) MPa] and the controls [(41.71 +/- 0.55) MPa] (P > 0.05). The SEM displayed the interface presented similar irregularities with a predominance. The titanium diffused to low-fusing porcelain, while silicon and aluminum diffused to titanium basement.</p><p><b>CONCLUSIONS</b>Laser welding does not affect low-fusing porcelain fused to pure titanium.</p>