Microtensile bond strength of one- and two-step self-etching adhesives on sclerotic dentin: the effects of thermocycling.

This study evaluated the effects of thermocycling on the microtensile bond strength (microTBS) of one- and two-step self-etch adhesives (SEAs) to sclerotic dentin. Two adhesives, Clearfil S3 Bond (S3), a one-step self-etch adhesive (1-SEA), and Clearfil SE Bond (SE), a two-step self-etch adhesive (2-SEA), were applied on cervical lesions in human premolars with sclerotic or normal dentin. After adhesive application, the lesions were restored and built up using a resin composite (Clearfil AP-X). After 24 hours in water storage, the restored teeth were sectioned into 0.7 x 0.7 mm composite-dentin beams. The beams were then aged with 0, 5,000 or 10,000 thermocycles. The use of two adhesives, two substrate types and three thermocycling regimens yielded 12 experimental groups of 14-19 beams each. The beams were subsequently subjected to microTBS testing at a crosshead speed of 1 mm/minute and statistical analyses were computed with three-way ANOVA and Tukey's post hoc test at p < 0.05. Three-way ANOVA showed statistically significant effects on bonding effectiveness by lesion type, adhesive system, thermocycling or combinations of the adhesive system and thermocycling (p < 0.05). With sclerotic dentin, although S3 and SE provided comparable microTBS after 24 hours of water storage, S3 showed significantly lower microTBS than SE after thermocycling (p < 0.05). Regardless of lesion type, the microTBS for S3 decreased significantly after 5,000 or 10,000 thermocycles, while the microTBS for SE showed a significant decrease only after 10,000 thermocycles. Regardless of the extent of thermocycling, the microTBS values for either SE or S3 bonded to sclerotic dentin were significantly lower than to normal dentin (p < 0.05). The results suggested that thermocycling had a significant negative effect on the bond strength of the two SEAs tested. In contrast to 2-SEA, 1-SEA might not be a good choice for sclerotic dentin when seeking durability of the resin-dentin bond.

Pb inhibits hippocampal synaptic transmission via cyclin-dependent kinase-5 dependent Synapsin 1 phosphorylation.

Lead (Pb) exposure impairs the nervous system, of which the injury of cognitive development is obvious. But the mechanism of Pb induced disorders of neuro-transmission remain elusive. In this study, primary hippocampal neurons were exposed to Pb at the dosage of 5 µM from days in vitro (DIV) 3 to DIV14 and the electrophysiological recordings were performed at DIV14. Sprague-Dawley (SD) rat pups were exposed to Pb from parturition to weaning indirectly from their mothers whose drinking water containing 250 ppm Pb, then directly exposed to Pb at the dosage of 250 ppm from postnatal day (PND) 21 to PND30. The results showed that Pb significantly decreased the frequency of both miniature excitatory postsynaptic current (mEPSC) and miniature inhibitory postsynaptic current (mIPSC) in cultured hippocampal neurons. Paird-pulse facilitation (PPF) recordings showed there was significant increase in Pb-exposed group. The increase of the magnitude of PPF (the ratio of second to first response amplitude) further confirmed that Pb reduced presynaptic neuro-transmission. By transmission electron microscope, it found that Pb disarranged presynaptic vesicles distribution and decreased the density of presynaptic vesicles. Moreover, it was interestingly found that phosphorylation of Synapsin1, which was phosphorylated by CDK5, has been decreased upon Pb exposure. With the treatment of R-Roscovitine (Ro), an inhibitor of CDK5, it was detected that Pb induced mEPSC and mIPSC frequency reduction have been reversed. Together, our results suggested that Pb disrupted the distribution of synaptic vesicles and impaired the neurotransmitter release, which was dependent on the phosphorylation level of Synapsin 1 via CDK5. This study will help for elucidation of environmental Pb-induced neuronal disorders.

Effect of Pb Exposure on Synaptic Scaling Through Regulation of AMPA Receptor Surface Trafficking.

Homeostatic synaptic plasticity (HSP) helps to stabilize the neuronal network activity, which is essential for optimal information coding. Synaptic scaling is a form of homeostatic plasticity that stabilizes neuronal firing in response to activity blockade. Lead (Pb) is a ubiquitous environmental neuro-toxicant and can impair the input-specific Hebbian type synaptic plasticity, but whether Pb exerts effects in HSP remains unknown. We previously reported that blocking L-type calcium channel induces synaptic scaling, which stimulates the synthesis of all-trans retinoic acid (RA) and the expression of GluA2-lacking α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor. Given Pb is a potent blocker of calcium channel, we hypothesized Pb may participate in synaptic scaling accompanied by RA synthesis and AMPA receptor trafficking. In this study, cultured hippocampal neurons were treated with Pb (1 µM 5 min, 15 min, 4 h, 24 h, and 10 µM 24 h) alone or in combination with tetrodotoxin (TTX, 1 µM, 24 h). The results showed that Pb alone, either at 1 µM or 10 µM, cannot induce synaptic scaling. But Pb participated in synaptic scaling when concurrent with TTX (10 µM Pb + 1 µM TTX, 24 h). Further results showed that surface heteromeric GluA1 and GluA2 AMPA receptors were increased in TTX+ Pb-induced synaptic scaling. In addition, RA was proved not to participate in TTX+ Pb-mediated synaptic scaling. Taken together, our work supported that TTX+ Pb could induce synaptic scaling and enhance synaptic accumulation of AMPAR GluA1 and GluA2 during synaptic up scaling. Our study would help for elucidation of the Pb-induced neuronal network instability mechanism.

[Effect of carbamide peroxide bleaching agents on micro-leakage of composite resin interface in vitro].

OBJECTIVE: 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. METHODS: 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. RESULTS: 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. CONCLUSION: Thickening carriers and the concentration of CP (20% or below) have no significant effect on micro-leakage of composite resin.

[Two-dimensional morphology of microleakage between dentin and adhesives].

OBJECTIVE: To observe the two-dimensional morphology of microleakage between dentin and adhesives. METHODS: 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. RESULTS: The planar contour of all the silver leakage was various branching, treelike shape, spreading from the border of section to the center. CONCLUSION: The planar contour of microleakage is treelike shape and its extent is influenced by adhesives and thermal cycling.

[Structural characteristics of laser-welded cast pure titanium joints by different gap distance].

OBJECTIVE: To measure the microstructure of laser-welded cast pure titanium by different gap distance. METHODS: 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. RESULTS: 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. CONCLUSION: The effects of the joint gap were not significant.

[Effects of laser welding on bond of porcelain fused cast pure titanium].

OBJECTIVE: To investigate the influence of the laser welding on bond of porcelain fused to cast pure titanium. METHODS: 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. RESULTS: 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. CONCLUSIONS: Laser welding does not affect low-fusing porcelain fused to pure titanium.