Influence of Thickness on the Translucency Parameter and Whiteness Index of Single-Shade Resin Composites

The study aimed to evaluate the effect of thickness on the translucency parameter (TP) and whiteness index for dentistry (WID) of single-shade resin composites compared with a multi-shade resin composite after thermocycling. A total of 100 resin composite samples of five brands (Filtek Z250, Omnichroma, Vittra APS Unique, Zenchroma, and Charisma Diamond One) with thicknesses of 2 mm and 4 mm were prepared (n=10). CIE L*a*b* coordinates were obtained using a spectrophotometer. The resin composite samples were subjected to 10,000 thermocycles. Before and after thermocycling, TP values were calculated with the CIEDE2000 formula, and whiteness values were calculated using the WID. The influence of thickness, resin composite, and aging on these variables was analyzed using the generalized linear model (p<0.05). Omnichroma and Filtek Z250 exhibited, respectively, the highest and the lowest TP00 values compared with the other resin materials (p<0.001). The TP00 values of Zenchroma and Diamond One were similar (p>0.05). Vittra APS Unique had a lower TP than Zenchroma and Diamond One (p<0.001). Before thermocycling, the highest WID showed the combination of Vittra APS Unique with thicknesses of 2 mm (48.33±1.18). After thermocycling, the highest WID was shown in the combination of Vittra APS Unique with thicknesses of 2 mm (45.33±0.55) and 4 mm (46.23±0.94) (p<0.001). After thermocycling, the lowest WID was for the combination of Filtek Z250 with thicknesses 2 mm (21.16±0.93) and 4 mm (20.70±0.91) (p<0.001). The TP and WID values of the resin composites varied across different composites and thicknesses. Single-shade resin composites of different thicknesses demonstrated higher translucency and whiteness values than multi-shade resin composite, both before and after thermocycling.

Effect of different polymerization times on color change, translucency parameter, and surface hardness of bulk-fill resin composites

BACKGROUND

Polymerization plays an important role in the optical and mechanical properties resin composite materials.

AIM

The current study aimed to evaluate the effect of different polymerization times on the color change, translucency parameter (TP), and surface hardness of resin composites after thermocycling.

MATERIALS AND METHODS

Microhybrid resin composite (Filtek Z250; used in the control group) and bulk-fill resin composites (Filtek One Bulk-Fill Restorative, Tetric EvoCeram Bulk-Fill, and Tetric N-Ceram Bulk-Fill) were used. Each bulk-fill composite was placed as a single layer. Polymerization of the bulk-fill composites in the first group was completed in 20 s, and that in the second group was completed in 40 s (n = 10). Filtek Z250's polymerization was completed with 2 mm (20 s) + 2 mm (20 s). The color change (ΔE₀₀) and translucency parameter (TP₀₀) were calculated using the CIEDE2000 formula. Before and after thermocycling, the TP and surface hardness values were measured. The data were analyzed using one- and two-way analysis of variance, paired-samples t-test, and Tukey's test (P < 0.05).

RESULTS

After thermocycling, the ΔE₀₀ values of the resin composite samples were 1.66-2.56. Compared to the control group, the Filtek One Bulk-Fill 20 s group exhibited the lowest color change values. The Filtek Z250 group exhibited lower TP and significantly higher microhardness values than the other bulk-fill resin groups before and after thermocycling (P < 0.05). There were no observed differences in the Tetric N-Ceram and Tetric EvoCeram groups before and after thermocycling.

CONCLUSION

Under the conditions of 10,000 thermal cycles, different curing times did not affect the color change and hardness values of the bulk-fill materials. However, differences were observed among the composite materials. After thermocycling, the surface hardness and TP values decreased in all the resin composites. Depending on the material content, effective results can be obtained from the 20 s polymerization of bulk-fill resin composites.

Synthesis, crystal structure, spectroscopic, fluorescent, thermal properties and EPR spectra of doped Cu2+ ions in [Cd(sac)2(H2O)2(meim)2] single crystal

The crystal structures of the six-coordinate complexes [Cd(sac)2(H2O)2(meim)2] (complex 1) formed by reaction of 4-methylimidazole(meim) with [Cd(sac)2(H2O)4]·2H2O (saccharinate=sac), was synthesized and characterized by elemental analysis, infrared (IR) and electron paramagnetic resonance (EPR) spectroscopy, thermal analysis and X-ray single crystal diffraction. X-ray diffraction analysis revealed that complex 1 crystallized in the monoclinic crystal system with space group P21/c. The Cd(II) center was six-coordinated with four nitrogen atoms from two sac and two 4-meim ligands, two oxygen atoms from two aqua ligands. Spectral and thermal analysis data for complex 1 was in agreement with the crystal structures. In addition complex 1 displayed blue fluorescent emission in the solid state at room temperature. Single crystal EPR spectra at room temperature are resolved and have exhibited that two different Cu(2+) complexes were located in different chemical environments which contained two magnetically nonequivalent Cu(2+) sites. In low temperature EPR spectra down to 110 °C did show no considerable change. At higher temperatures, however, both thermo gravimetric analyses (TGA) and EPR spectra showed detectable changes around 140 °C; the causes and the mechanisms of changes are discussed.

Thermal and EPR spectroscopic studies of novel coordination compound trans-bis(acesulfamato)tetraaquazinc(II) with Mn(II) impurity

The thermogravimetric analysis (TGA) and electron paramagnetic resonance (EPR) studies of powder and single crystals of bis(acesulfamato)tetraaquazinc(II), Zn(acs)(2)(H(2)O)(4), a novel coordination compound, are carried out. Previously synthesized bis(acesulfamato) tetraaquamanganese(II), Mn(acs)(2)(H(2)O)(4), is included into the host in trace amount as a paramagnetic probe for EPR analysis. Single crystal EPR spectra at room temperature are resolved and discussed. Low temperature EPR spectra down to 90K do not show remarkable change. At higher temperatures, however, the TGA and EPR spectra show changes around 335 K and 395 K; the causes and the mechanisms of changes are discussed.

Point mutant mice with hypersensitive alpha 4 nicotinic receptors show dopaminergic deficits and increased anxiety

Knock-in mice were generated that harbored a leucine-to-serine mutation in the alpha4 nicotinic receptor near the gate in the channel pore. Mice with intact expression of this hypersensitive receptor display dominant neonatal lethality. These mice have a severe deficit of dopaminergic neurons in the substantia nigra, possibly because the hypersensitive receptors are continuously activated by normal extracellular choline concentrations. A strain that retains the neo selection cassette in an intron has reduced expression of the hypersensitive receptor and is viable and fertile. The viable mice display increased anxiety, poor motor learning, excessive ambulation that is eliminated by very low levels of nicotine, and a reduction of nigrostriatal dopaminergic function upon aging. These knock-in mice provide useful insights into the pathophysiology of sustained nicotinic receptor activation and may provide a model for Parkinson's disease.

Oxidative stress and Ca2+ influx upregulate calpain and induce apoptosis in PC12 cells

Calpain, a Ca2+-dependent cysteine protease, has previously been implicated in apoptosis or programmed cell death (PCD) in immune cells. Although oxidative stress and intracellular free Ca2+ are involved in neurodegenerative diseases, the mechanism of neuronal cell death in the central nervous system (CNS) due to these agents has not yet been defined. To explore a possible role for calpain in neuronal PCD under oxidative stress and Ca2+ influx, we examined the effects of H2O2 and A23187 on PC12 cells. Treatments caused PCD (light microscopy and TUNEL assay) with altered mRNA expression (RT-PCR) of bax (pro-apoptotic) and bcl-2 (anti-apoptotic) genes, resulting in a high bax/bcl-2 ratio. Control cells expressed 1.3-fold more microcalpain (requiring microM Ca2+) than mcalpain (requiring mM Ca2+). Expression of mcalpain was significantly increased following exposure to oxidative stress and Ca2+ influx. The mRNA levels of calpastatin (endogenous calpain inhibitor) and beta-actin (house-keeping) genes were not changed. Western analysis indicated degradation of 68 kDa neurofilament protein (NFP), a calpain substrate. Pretreatment of cells with MDL28170 (a cell permeable and selective inhibitor of calpain) prevented increase in bax/bcl-2 ratio, upregulation of calpain, degradation of 68 kDa NFP, and occurrence of PCD. These results suggest a role for calpain in PCD of PC12 cells due to oxidative stress and Ca2+ influx.

Analgesic and anti-inflammatory effects of some benzanilides

Analgesic and anti-inflammatory effects of N-(p-ethoxyphenyl)-2,6-dihydroxybenzamide (1), N-(p-ethoxyphenyl)-2,6-diacetoxybenzamide (2), N-(p-ethoxyphenyl)-2,5-dihydroxybenzamide (3), and N-(p-ethoxyphenyl)-2,5-diacetoxybenzamide (4) have been investigated in mice and rats. The analgesic effect of 2 on acetic acid-induced writhing was found to be stronger than that of aspirin, whereas that of 1, 3, and 4 was weaker than that of aspirin. In inflammatory studies, 1-4 showed inhibition of formaldehyde-induced paw swelling (edema). The effects of 1-3 were more potent than that of aspirin, 1 being the most potent. The potency of 4 was almost equal to that of aspirin.

Regulation of thromboxane A2 biosynthesis in platelet-free human monocytes and the possible role of polypeptide growth factor(s) in the induction of cyclooxygenase system

It has previously been shown that platelet-free human monocytes, when properly incubated in the presence of animal and human sera, became capable of producing large amounts of thromboxane A2 and prostaglandin E2. The characteristics of these processes are reported here. Prostaglandin biosynthesis was time and cell concentration dependent; 24 h of incubation at 37 degrees C and 0.5 X 10(6) cells per ml medium were found to give the most reproducible results. Human monocytes produced thromboxane A2 and prostaglandin E2 in a typical ratio which ranged from 2.0 to 5.0 (28 experiments). Animal and human sera were similarly effective, while serum obtained from platelet-free blood was much less active. The activity of all sera tested was stable to heating (100 degrees C for 2-10 min) and extreme pH values (pH 2 and 11). It was unstable when the serum was heated at pH 11 and after 2-mercaptoethanol treatment. These observations prompted us to check the effect of polypeptide growth factors having properties similar to those reported above, such as platelet-derived growth factor, fibroblast growth factor, epidermal growth factor as well as insulin and transferrin. None of these, alone or in various combinations, was capable of eliciting a stimulation comparable with that of serum. Stimulation due to sera was, as expected, dose dependently inhibited by acetylsalicylic acid and more efficiently by indomethacin; unexpectedly it was also inhibited by protein synthesis inhibitors such as actinomycin D and cycloheximide in conditions under which no toxic effect of the drugs was evident. On the basis of these results we conclude that: (a) polypeptide growth factor(s) with a molecular weight at least 30 000 (as judged by Amicon ultrafiltration) is involved in the regulation of prostaglandin biosynthesis); (b) such a factor(s) acts by inducing rather than by activating the cyclooxygenase system.