Catalytic-adsorptive stripping voltammetric determination of molybdenum in plant foodstuffs.

In acetate buffer solution (pH 3.5) containing oxine and chlorate, ultratrace amounts of molybdenum can be determined after adsorptive accumulation of the Mo(VI)-oxine complex on a hanging mercury drop electrode, coupled with the catalytic effect on the reduction of chlorate. Under optimized conditions, the catalytic-adsorptive stripping voltammetric procedure gives excellent selectivity and an extremely low detection limit of 1.7 pM molybdenum (60 s accumulation). The stripping peak current increases linearly with molybdenum concentration between 10 pM and 5.0 nM. The procedure is applied to determine traces of molybdenum in plant foodstuffs.

Determination of trace amounts of iron by catalytic-adsorptive stripping voltammetry.

A highly sensitive and selective voltammetric procedure is described for the determination of trace amounts of iron. The procedure is based on the adsorptive collection of an iron-thiocyanate-nitric oxide complex on a hanging mercury drop electrode. The adsorbed complex catalyzes the reduction of nitrite in solution, which gives a detection limit of 40 ppt iron (30 s accumulation). The stripping current increases linearly with iron concentration up to 80 ppb. The relative standard deviations are 4.2% and 1.6% at 0.5 ppb and 40 ppb respectively. Most of the common ions, except cobalt, do not interfere with the determination of iron. The procedure is applied to determine iron in biological samples, natural waters and analytical-grade chemicals.

Effectiveness of composite cure with pulse activation and soft-start polymerization.

The study investigated the effectiveness of composite cure with pulse activation and soft-start polymerization. A light-cure unit (BISCO VIP, BISCO Dental Products, Schaumburg, IL 60193, USA) that allowed for independent command over time and intensity was used. The six light-curing modes examined were: Control (C)-400 mW/cm2 [40 seconds]; Pulse Delay I (PDI) -100 mW/cm2 [3 seconds] --> delay [3 minutes] --> 500 mW/cm2 [30 seconds]; Pulse Delay II (PDII) - 200 mW/cm2 [20 seconds] --> delay [3 minutes] --> 500 mW/cm2 [30 seconds]; Soft-start (SS) - 200 mW/cm2 [10 seconds] --> 600 mW/cm2 [30 seconds]; Pulse Cure I (PCI) - 400 mW/cm2 [10 seconds] --> delay [10 seconds] --> 400 mW/cm2 [10 seconds] --> delay [10 seconds] --> 400 mW/cm2 [20 seconds]; and Pulse Cure II (PCII) - 400 mW/cm2 [20 seconds] --> delay [20 seconds] --> 400 mW/cm2 [20 seconds]. Effectiveness of cure with the different modes was determined by measuring the top and bottom surface hardness of 2 mm thick composite (Z100) specimens using a digital microhardness tester (load=500 gf; dwell time=15 seconds). The effectiveness of cure of the bottom surface of the composite was also established by Fourier Transform Infrared (FTIR) spectroscopy using the KBr technique. Data obtained was analyzed using one-way ANOVA/Scheffe's post-hoc test (p<0.05). No significant difference in top Knoops Hardness Number KHN wa s observed except for PDIand PDII. At the bottom surfaces, KHN obtained with the control was significantly greater than with PDII, SS and PCII. FTIR results ranked well with the hardness of the bottom surfaces. The absorbance ratio of carbon double bonds to aromatic ring obtained with the control group was significantly greater than with PDII and PCII. Effectiveness of the cure at the bottom surfaces of composites may be reduced by some pulse activation and soft-start polymerization regimens.

Post-gel shrinkage with pulse activation and soft-start polymerization.

This study investigated the influence of pulse activation and soft-start polymerization regimens on the post-gel shrinkage of a visible light-activated composite resin (Z100). A light-cure unit (BISCO VIP) that allowed for independent command over time and intensity was used. The six light-curing modes that were examined include: Control (C)-400 mW/cm2 [40 seconds]; Pulse Delay I (PDI)-100 mW/cm2 [3 seconds], delay [3 minutes], 500 mW/cm2 [30 seconds]; Pulse Delay II (PDII)-200 mW/cm2 [20 seconds], delay [3 minutes], 500 mW/cm2 [30 seconds]; Soft-start (SS)-200 mW/cm2 [10 seconds], 600 mW/cm2 [30 seconds]; Pulse Cure I (PCI)--two 400 mW/cm2 [10 seconds] and one 400 mW/cm2 [20 seconds] pulses with 10 seconds interval between; and Pulse Cure II (PCII)-two 400 mW/cm2 [20 seconds] pulses with 20 seconds interval between. A strain-monitoring device measured the linear polymerization shrinkage associated with the various cure modes during and post light polymerization up to 60 minutes. Five specimens were made for each cure mode. Data was analyzed using one-way ANOVA and Scheffe's post-hoc test at significance level 0.05. Post-gel shrinkage associated with PDI was significantly lower than with PDII, SS and PCI immediately post light-polymerization. At one-minute post light polymerization, PDI had significantly lower shrinkage compared to PDII and SS. Significant differences in shrinkage were observed between PDI and SS only at 10, 30 and 60 minutes. At all time intervals, no significance in post-gel shrinkage was observed between the control and all-pulse activation/soft-start polymerization regimens.

Post-gel shrinkage with different modes of LED and halogen light curing units.

This study compared the post-gel shrinkage of two LED (light-emitting diodes) lights (Elipar FreeLight [FL], 3M ESPE; GC e-Light [EL], GC), a high intensity (Elipar TriLight [TL], 3M ESPE) and a very high intensity (Astralis 10 [AS], Ivoclar Vivadent) halogen light to a conventional (Max [MX] (control), Dentsply-Caulk) halogen light. Ten light curing regimens were investigated. These included continuous (FL1, EL2, MX, TL1 and AS1), soft-start (FL2, EL4, TL2), pulse activation (EL1) and turbo (EL3) modes. A strain-monitoring device and test configuration was used to measure the linear polymerization shrinkage of a composite restorative (Z100, [3M ESPE]) during and post-light polymerization up to 60 minutes when cured with the different modes. Five specimens were made for each cure mode. Results were analyzed using ANOVA/Scheffe's post-hoc test and independent sample t-tests at significance level 0.05. Shrinkage associated with the various modes of EL was significantly lower than MX immediately after light polymerization and at one-minute post-light polymerization. No significant difference between MX and the various lights/cure modes was observed at 10, 30 and 60-minutes post-light polymerization. At all time intervals, post-gel shrinkage associated with continuous light curing mode was significantly higher than the soft-start light curing mode for FL and TL.

Composite cure and shrinkage associated with high intensity curing light.

This study investigated the effectiveness of cure and post-gel shrinkage of three visible light-cured composite resins (In Ten-S [IT], Ivoclar Vivadent; Z100 [ZO], 3M-ESPE; Tetric Ceram [TC], Ivoclar Vivadent) when polymerized with a very high intensity (1296 +/- 2 mW/cm2) halogen light (Astralis 10, Ivoclar Vivadent) for 10 seconds. Irradiation with a conventional (494 +/- 3 mW/cm2) halogen light (Spectrum, Dentsply) for 40 seconds was used for comparison. The effectiveness of cure was assessed by computing the hardness gradient between the top and bottom surfaces of 2-mm composite specimens after curing. A strain-monitoring device was used to measure the linear polymerization shrinkage associated with the various composites and curing lights. A sample size of five was used for both experiments. Data was analyzed using ANOVA/Scheffe's post-hoc and Independent Samples t-tests at significance level 0.05. Results showed that the effect of the curing method on the effectiveness of cure and shrinkage was material-dependent. Polymerization of IT and TC with Spectrum for 40 seconds resulted in significantly more effective cure than polymerization with Astralis for 10 seconds. Polymerization of ZO with Spectrum for 40 seconds resulted in significantly more shrinkage than polymerization with Astralis for 10 seconds. In view of the substantial time saving, using high intensity lights may be a viable method to polymerize composites.

Effectiveness of composite cure associated with different curing modes of LED lights.

This study compared the effectiveness of cure of two LED (light-emitting diodes) lights (Elipar FreeLight [FL], 3M-ESPE; GC e-Light [EL], GC) to conventional (Max [MX], Dentsply-Caulk [control]), high intensity (Elipar TriLight [TL], 3M-ESPE) and very high intensity (Astralis 10 [AS], Ivoclar Vivadent) halogen lights. The 10 light-curing regimens investigated were: FL1 400 mW/cm2 [40 seconds], FL2 0-400 mW/cm2 [12 seconds] --> 400 mW/cm2 [28 seconds], EL1 750 mW/cm2 [10 pulses x 2 seconds], EL2 350 mW/cm2 [40 seconds], EL3 600 mW/cm2 [20 seconds], EL4 0-600 mW/cm2 [20 seconds] --> 600 mW/cm2 [20 seconds], TL1 800 mW/cm2 [40 seconds], TL2 100-800 mW/cm2 [15 seconds] --> 800 mW/cm2 [25 seconds], AS1 1200 mW/cm2 [10 seconds], MX 400 mW/cm2 [40 seconds]. Effectiveness of cure with the different modes was determined by measuring the top and bottom surface hardness (KHN) of 2-mm thick composite (Z100, [3M-ESPE]) specimens using a digital microhardness tester (n=5, load=500 g; dwell time=15 seconds). Results were analyzed using one-way ANOVA/Scheffe's post-hoc test and Independent Samples t-test (p<0.05). At the top surface, the mean KHN observed with LED lights ranged from 55.42 +/- 1.47 to 68.54 +/- 1.46, while that of halogen lights was 62.64 +/- 1.87 to 73.14 +/- 0.97. At the bottom surface, the mean KHN observed with LED and halogen lights ranged from 46.90 +/- 1.73 to 66.46 +/- 1.18 and 62.26 +/- 1.93 to 70.50 +/- 0.87, respectively. Significant differences in top and bottom KHN values were observed between different curing regimens for the same light, and between LED and halogen lights. Although curing with most modes of EL resulted in significantly lower top and bottom KHN values than the control, no significant difference was observed for the different modes of FL. Hence, the effectiveness of composite cure with LED LCUs is product dependent.

Comparative depths of cure among various curing light types and methods.

This study evaluated the depth of cure associated with commercial LEDs (light-emitting diodes) (Elipar FreeLight [FL], 3M-ESPE; GC e-Light [EL], GC), high intensity (Elipar TriLight [TL], 3M-ESPE) and very high intensity (Astralis 10 [AS], Ivoclar Vivadent) Quartz Tungsten Halogen (QTH) curing lights. Depth of cure of the various lights/curing modes were compared to a conventional QTH light (Max [Mx], Dentsply-Caulk). Ten exposure regimens were investigated: FL1 - 400 mW/cm2 [40 seconds]; FL2 - 0-400 mW/cm2 [12 seconds] --> 400 mW/cm2 [28 seconds]; EL1 - 750 mW/cm2 [10 pulses x 2 seconds], EL2 - 350 mW/cm2 [40 seconds]; EL3 - 600 mW/cm2 [20 seconds]; EL4 - 0 - 600 mW/cm2 [20 seconds] --> 600 mW/cm2 [20 seconds]; TL1 - 800 mW/cm2 [40 seconds]; TL2 - 100- 800 mW/cm2 [15 seconds] --> 800 mW/cm2 [25 seconds]; AS1 - 1200 mW/cm2 [10 seconds]; MX - 400 mW/cm2 [40 seconds]. Depth of cure was determined by penetration, scraping and microhardness techniques. The results were analyzed using one-way ANOVA/Scheffe's post-hoc test and Pearson's correlation at significance level 0.05 and 0.01, respectively. All light curing regimens met the ISO depth of cure requirement of 1.5 mm with the exception of EL1-EL3 with the microhardness technique. Curing with most modes of EL resulted in significantly lower depths of cure than the control [MX]. No significant difference in depth of cure was observed among the control and the two modes of FL. Curing with TL1 resulted in significantly greater depth of cure compared to MX with all testing techniques. No significant difference in depth of cure was observed between the control and AS1 for all testing techniques except for the penetration technique. The depth of composite cure is light unit and exposure mode dependent. Scraping and penetration techniques were found to correlate well but tend to overestimate depth of cure compared to microhardness.

Soft-start polymerization: influence on effectiveness of cure and post-gel shrinkage.

This study investigated the influence of soft-start polymerization on the effectiveness of cure and post-gel shrinkage of a visible light cured resin composite (Z100). Three cure modes (LH-high intensity; LA-soft-start polymerization involving step-wise modulation of light intensity and LL-low intensity) of a commercial light-cure unit (Kavo PolyLUX II) were examined and compared to another light-cure unit (Spectrum). The effectiveness of cure with the different cure modes was assessed by computing the hardness gradient between top and bottom surfaces of 2 mm composites specimens after different light exposure times. A strain-monitoring device was used to measure the linear polymerization shrinkage associated with the different cure modes and exposure times over 180 minutes. A sample size of five was used for both experiments. Data was analyzed using one-way ANOVA and Scheffe's post-hoc test at significance level 0.05. Results showed that effectiveness of cure generally increased with increase cure time. Although modulation of light energy intensity (LA 40/80 seconds) resulted in lower polymerization shrinkage compared to LH 40 seconds, no significant difference was observed between these three cure regimes. Curing with the Spectrum curing light resulted in the lowest polymerization shrinkage.

The effectiveness of cure of LED and halogen curing lights at varying cavity depths.

This study compared the effectiveness of cure of two LED (light-emitting diodes) lights (Elipar FreeLight [FL], 3M-ESPE and GC e-Light [EL], GC) to conventional (Max [MX] (control), Dentsply-Caulk), high intensity (Elipar TriLight [TL], 3M-ESPE) and very high intensity (Astralis 10 [AS], Ivoclar Vivadent) halogen lights at varying cavity depths. Ten light curing regimens were investigated. They include: FL1-400 mW/cm2 [40 seconds], FL2-0-400 mW/cm2 [12 seconds] --> 400 mW/cm2 [28 seconds], EL1-750 mW/cm2 [10 pulses x 2 seconds], EL2-350 mW/cm2 [40 seconds], EL3-600 mW/cm2 [20 seconds], EL4-0-600 mW/cm2 [20 seconds] --> 600 mW/cm2 [20 seconds], TL1-800 mW/cm2 [40 seconds], TL2-100-800 mW/cm2 [15 seconds] --> 800 mW/cm2 [25 seconds], AS1-1200 mW/cm2 [10 seconds], MX-400 mW/cm2 [40 seconds]. The effectiveness of cure of the different modes was determined by measuring the top and bottom surface hardness (KHN) of 2-mm, 3-mm and 4-mm thick composite (Z100, [3M-ESPE]) specimens using a digital microhardness tester (n = 5, load = 500 g; dwell time = 15 seconds). Results were analyzed using ANOVA/Scheffe's post-hoc test and Independent Samples t-Test (p < 0.05). For all lights, effectiveness of cure was found to decrease with increased cavity depths. The mean hardness ratio for all curing lights at a depth of 2 mm was found to be greater than 0.80 (the accepted minimum standard). At 3 mm, all halogen lights produced a hardness ratio greater than 0.80 but some LED light regimens did not; and at a depth of 4 mm, the mean hardness ratio observed with all curing lights was less than 0.80. Significant differences in top and bottom KHN values were observed among different curing regimens for the same light and between LED and halogen lights. While curing with most modes of EL resulted in significantly lower top and bottom KHN values than the control (MX) at all depths, the standard mode of FL resulted in significantly higher top and bottom KHN at a depth of 3 mm and 4 mm. The depth of composite cure with LED LCUs was, therefore, product and mode dependent.

Polymerization shrinkage of visible-light-cured composites.

This study investigated the long-term dimensional changes of a conventional and a polyacid-modified composite resin and the effects of hydration on polymerization shrinkage. A strain-monitoring device was used to measure the linear polymerization shrinkage of the composites in the free state when stored in water at 37 degrees C or air at 26 degrees C over a one-month period. Results showed that the polymerization reaction of both conventional and polyacid-modified composite resins was accompanied by a dimensional shrinkage change. The rate of shrinkage for both composites was greatest during the polymerization reaction and continued after removal of the curing light. When stored in water, the greatest shrinkage was noted at one hour for both materials. This was followed by a slow uptake of water and expansion from one day to one month. The polyacid-modified composite had significantly less polymerization shrinkage than the conventional composite after one month of storage in water.

Influence of curing lights and modes on cross-link density of dental composites.

This study investigated the influence of curing lights and modes on the cross-link density of dental composites. Four LED/halogen curing lights (LED-Elipar Freelight [FL], 3M-ESPE and GC e-light [EL], GC; high intensity halogen-Elipar Trilight [TL], 3M-ESPE; very high intensity halogen-Astralis 10 [AS], Ivoclar Vivadent) were selected for this study. Pulse (EL1), continuous (FL1, EL2, TL1), turbo (EL3, AS) and soft-start (FL2, EL4, TL2) curing modes of the various lights were examined. A conventional, continuous cure halogen light (Max [MX], Dentsply-Caulk) was used for comparison. Six composite (Z100, 3M-ESPE) specimens were made for each light-curing mode combination. After polymerization, the specimens were stored in air at 37 degrees C for 24 hours and subjected to hardness testing using a digital microhardness tester (load=500 g; dwell time=15 seconds). The specimens were then placed in 75% ethanol-water solution at 37 degrees C for 24 hours and post-conditioning hardness was determined. Mean hardness (HK)/change in hardness (deltaHK) was computed and the data subjected to analysis using one-way ANOVA/Scheffe's test and Independent Samples t-test (p<0.05). Softening upon storage in ethanol (deltaHK) was used as a relative indication of cross-link density. Specimens polymerized with AS, TL2 and all modes of both LED lights were significantly more susceptible to softening in ethanol than specimens cured with MX. No significant difference in cross-link density was observed among the various modes of EL and FL. For TL, curing with continuous mode resulted in specimens with significantly higher cross-link density than curing with the soft-start mode.

Elution of leachable components from composites after LED and halogen light irradiation.

This study investigated the influence of curing lights and modes on the elution of leachable components from dental composites. Four LED/halogen curing lights (LED-Elipar Freelight [FL], 3M-ESPE and GC e-light [EL], GC; high intensity halogen-Elipar Trilight [TL], 3M-ESPE; very high intensity halogen-Astralis 10 [AS], Ivoclar Vivadent) were selected for this study. Pulse (EL1), continuous (FL1, EL2, TL1), turbo (EL3, AS) and soft-start (FL2, EL4, TL2) curing modes of the various lights were examined. A conventional continuous cure halogen light (Max [MX], Dentsply-Caulk) was used for comparison. Three composite (Z100, 3M-ESPE) specimens (6.5 mm in diameter and 1-mm thick) were made for each curing light-mode combination. After polymerization, the specimens were stored in air at 37 degrees C for 24 hours and incubated in acetonitrile at 37 degrees C for 24 hours. BisGMA and TEGDMA extracts were isolated by high performance liquid chromatography (HPLC). Data were subjected to analysis using one-way ANOVA/Scheffe's post-hoc test and Independent Samples t-test at significance level 0.05. The total monomer (BisGMA and TEGDMA) eluted ranged from 8.75 to 27.97 ppm for FL1 and AS, respectively. Significantly more unreacted monomers were leached from composites cured with all modes of EL and AS when compared to MX. No significant difference in the total monomer eluted was observed between the two modes of FL/TL and MX Although composites cured with EL2 released significantly less monomer than EL1, 3 and 4, no significant difference in the total monomer eluted was observed between the continuous and soft-start modes of FL and TL. The elution of leachable components from composites appears to be curing light specific rather than light source (LED or halogen) and curing mode specific.