Journal Article•
New-generation curing units and short irradiation time: the degree of conversion of microhybrid composite resin.
TL;DR: This in vitro study investigated the depth of cure of a microhybrid composite resin when cured with reduced times of exposure to three commercially available curing lights, showing the degree of conversion was not influenced by the curing light employed but was significantly influences by the thickness of composite resin.
Abstract: This in vitro study investigated the depth of cure of a microhybrid composite resin when cured with reduced times of exposure to three commercially available curing lights. Different sample thicknesses (1, 2, and 3 mm) were light cured in high intensity polymerization mode (2,400 mW/cm2 for 5, 10, 15, and 20 seconds; 1,100 mW/cm2 for 10, 20, 30, and 40 seconds; and 1,100 mW/cm2 for 10, 20, 30, and 40 seconds, respectively). The degree of conversion (%) at the bottom of each sample was measured by Attenuated Total Reflection Fourier Transform Infrared (ATR F-TIR) analysis after each polymerization step. Data were analyzed by ANOVA for repeated measures, showing the degree of conversion was not influenced by the curing light employed (P = .622) but was significantly influenced by the thickness of composite resin (P < .05). Variations in the degree of conversion vs the shorter irradiation time permitted (T1) were not significant among different lamps but were significant among different thicknesses. The depth of cure of microhybrid composite resin appears not to be influenced by the curing light employed. Increased irradiation time significantly increases the degree of conversion. Thickness strongly influences depth of cure.
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TL;DR: DC and microhardness of high-viscosity bulk-fill resin composites in depths up to 6 mm can be safely used up to at least 4-mm incremental thickness, however, with respect to hardness, only XF and QF achieved acceptable results at 4 mm depth with 30 s of irradiation.
Abstract: To evaluate the influence of irradiation time on degree of conversion (DC) and microhardness of high-viscosity bulk-fill resin composites in depths up to 6 mm. Four bulk-fill materials (Tetric EvoCeram Bulk Fill—TECBF; x-tra fil—XF; QuixFil—QF; SonicFill—SF) and one conventional nano-hybrid resin composite (Tetric EvoCeram—TEC) were irradiated for 10, 20, or 30 s at 1,170 mW/cm2. DC and Knoop microhardness (KHN) were recorded after 24-h dark storage at five depths: 0.1, 2, 4, 5, and 6 mm. Data were statistically analyzed using ANOVA and Bonferroni’s post-hoc test (α = 0.05). With increasing bulk thickness, DC and KHN significantly decreased for TEC. TECBF and SF showed a significant decrease in DC and KHN at 4-mm depth after 10-s irradiation, but no decrease in DC after 30-s irradiation (p > 0.05). XF and QF demonstrated no significant DC decrease at depths up to 6 mm after irradiation of at least 20 s. At 4-mm depth, all materials tested achieved at least 80 % of their maximum DC value, irrespective of irradiation time. However, at the same depth (4 mm), only XF and QF irradiated for 30 s achieved at least 80 % of their maximum KHN value. Regarding DC, the tested bulk-fill resin composites can be safely used up to at least 4-mm incremental thickness. However, with respect to hardness, only XF and QF achieved acceptable results at 4-mm depth with 30 s of irradiation. Minimum irradiation times stated by the manufacturers cannot be recommended for placement of high-viscosity bulk-fill materials in 4-mm increments.
125 citations
TL;DR: This study evaluated the effect of using three commercial light curing units (LCUs) delivering a range of irradiance values, but delivering similar radiant exposures on the depth of cure of two different resin-based composites (RBCs).
Abstract: Clinical Relevance For both RBCs, rapid photocuring using a PAC light for five seconds resulted in a shallower depth of cure than when the same radiant exposure of (37 J/cm2) was delivered by a QTH...
35 citations
TL;DR: The distance between light-curing tip and adhesive surface does not significantly influence either the cytotoxicity or the DC of the tested adhesives.
Abstract: The degree of conversion (DC) of resin based materials depends, beside other factors, on the light-intensity applied during light curing. A lower DC might be correlated with an increased cytotoxicity of the respective materials. Therefore, aim of the present study was to investigate the influence of the distance between light-curing tip and adhesives on their cytotoxicity and degree of conversion (DC). For the cytotoxicity assay, a total of 98 bovine dentine samples were prepared, distributed to seven groups (G1-G7; n = 14) and treated as follows: G1: untreated; G2-G4: OptiBond FL; G5-G7: OptiBond All-In-One. Adhesives were light-cured (1200 mW/cm2) at 1 mm (G2;G5), 4 mm (G3;G6) or 7 mm (G4;G7) distance. Samples were stored in culture media for 24 h and extracts were added to cell cultures (dental pulp cells and gingival fibroblasts) for a further 24 h. Finally, released lactate dehydrogenase activity (LDH) was photometrically determined, as measure for the cytotoxic effects of the extracts. The cytotoxicity assay was performed three times. Additionally, the DC of the adhesives was determined by FTIR spectroscopy. DC measurements were performed five times. For both cell types, no significant difference of LDH release was observed between untreated control group (G1) and treated groups G2-G7 (p > 0.05, respectively), between the groups treated with same adhesive and light-cured at different distance (p > 0.05, respectively), as well as between groups treated with different adhesives and light-cured at the same distance (p > 0.05, respectively). Within the respective adhesive, no significant difference in the DC was observed when light-cured at different distance (p > 0.05, respectively), while OptiBond FL showed significantly higher DCs compared to OptiBond All-In-One when light-cured at same distances (p < 0.05, respectively). The distance between light-curing tip and adhesive surface does not significantly influence either the cytotoxicity or the DC of the tested adhesives.
32 citations
TL;DR: High-intensity light-curing showed a complex material-dependent effect on micromechanical properties of conventional and bulk-fill resin composites, including two composites specifically designed for high-intensity curing.
Abstract: Rapid high-intensity light-curing of dental resin composites is attractive from a clinical standpoint due to the prospect of time-savings This study compared the effect of high-intensity (3 s with 3,440 mW/cm2) and conventional (10 s with 1,340 mW/cm2) light-curing on micromechanical properties of conventional and bulk-fill resin composites, including two composites specifically designed for high-intensity curing Composite specimens were prepared in clinically realistic layer thicknesses Microhardness (MH) was measured on the top and bottom surfaces of composite specimens 24 h after light-curing (initial MH), and after subsequent immersion for 24 h in absolute ethanol (ethanol MH) Bottom/top ratio for initial MH was calculated as a measure of depth-dependent curing effectiveness, whereas ethanol/initial MH ratio was calculated as a measure of crosslinking density High-intensity light-curing showed a complex material-dependent effect on micromechanical properties Most of the sculptable composites showed no effect of the curing protocol on initial MH, whereas flowable composites showed 11–48% lower initial MH for high-intensity curing Ethanol/initial MH ratios were improved by high-intensity curing in flowable composites (up to 30%) but diminished in sculptable composites (up to 15%) Due to its mixed effect on MH and crosslinking density in flowable composites, high-intensity curing should be used with caution in clinical work
28 citations
TL;DR: The post-curing period played a fundamental role in reaching higher DC values with the low-shrinkage composite resin tested in this study, and both the irradiation time and the composite thickness strongly influenced the DC.
Abstract: Objective: This study evaluated the variation of conversion degree (DC) in the 12 hours following initial photoactivation of a low-shrinkage composite resin (Venus Diamond). Material and Methods: The conversion degree was monitored for 12 hours using Attenuated Total Reflection (ATR) F-TIR Spectroscopy. The composite was placed in 1 or 2 mm rings and cured for 10 or 20 seconds with a LED lamp. ATR spectra were acquired from the bottom surface of each sample immediately after the initial photoactivation (P=0), 30 minutes (P=0.5) and 12 hours after photoactivation (P=12) in order to obtain the DC progression during the post-curing period. Interactions between thickness (T), irradiation time (I) and post-curing (P) on the DC were calculated through ANOVA testing. Results: All the first order interactions were statistically significant, with the exception of the T-P interaction. Furthermore, the shift from P=0 to P=0.5 had a statistically higher influence than the shift from P=0.5 to P=12. The post-curing period played a fundamental role in reaching higher DC values with the low-shrinkage composite resin tested in this study. Moreover, both the irradiation time and the composite thickness strongly influenced the DC. Conclusions: Increased irradiation time may be useful in obtaining a high conversion degree (DC) with a low-shrinkage nano-hybrid composite resin, particularly with 2 mm composite layers.
21 citations
References
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TL;DR: Four commonly used methods for evaluating depth of cure in light-activated composites were compared and degree of conversion appears to be the most sensitive test of depth of cures.
Abstract: Four commonly used methods for evaluating depth of cure in light-activated composites were compared Optical and scraping methods correlate well, but severely overestimate depth of cure as compared with hardness testing or degree of conversion analysis Degree of conversion appears to be the most sensitive test of depth of cure
366 citations
TL;DR: The relationships between polymer property development and the physical evolution of the network structures associated with dental polymers as well as the interrelated kinetics of the photopolymerization reaction process are examined here.
253 citations
TL;DR: Pre-heating composite prior to photoactivation provides greater conversion requiring reduced light exposure than with room-temperature composite, and both hypotheses were accepted.
Abstract: The potential for maximizing conversion of room-temperature, photoactivated resin composite in the oral environment is limited. Pre-heating composite prior to light-curing is hypothesized to increase monomer conversion and reduce the duration of light exposure. Composite temperature was controlled at between 3°C and 60°C prior to exposure with a conventional quartz-tungsten-halogen curing unit: 5, 10, 20, or 40 sec. Monomer conversion was calculated from infrared spectra at 0 mm (top) and 2-mm-deep surfaces 5 min after light initiation. A strong, positive correlation existed between temperature and monomer conversion: top r2 = 0.999, 2 mm r2 = 0.998. Conversion ranged from 31.6% (3°C) to 67.3% (60°C). The duration of light exposure, reduced by 50 to 75% with pre-heated composite, yielded the same or significantly higher conversion (p = 0.001) than with control (22°C, 20 sec). Both hypotheses were accepted: Pre-heating composite prior to photoactivation provides greater conversion requiring reduced light e...
252 citations
TL;DR: The results demonstrate that commercially available composite materials exhibit different degrees of conversion 24 hours after the start of polymerization, which can be correlated to the different monomer compositions of the composite restorative resins.
Abstract: The quantity of the remaining unreacted methacrylate groups in polymerized composite materials has been determined. Six proprietary composites were investigated by infrared multiple internal reflection spectroscopy. Infrared reflectance measurements were made before polymerization and refeated after the composites were subjected to polymerization at 37 C for 24 hours. The quantities of remaining unreacted methacrylate groups were determined and the data expressed as percentages of the total amount of methacrylate groups in the unpolymerized materials. The specimens were specially prepared to ensure that the surface properties simulated the bulk properties of the polymerized composites. The quantities of remaining methacrylate groups in the six composites determined by this surface measuring technique ranged from 25 to 48 %. The results demonstrate that commercially available composite materials exhibit different degrees of conversion 24 hours after the start of polymerization. These differences can be cor...
240 citations
TL;DR: Composite depths of cure is investigated using a variety of light-curing units and exposure protocols to find similar composite cure characteristics to those achieved with conventional QTH technique when used according to manufacturer's recommendations.
Abstract: Purpose: This research investigated composite depths of cure using a variety of light-curing units and exposure protocols.
Materials and Methods: Composite (Herculite XRV, shade A2, Kerr, Orange, California) was exposed in opaque compules to conventional quartz tungsten halogen (QTH) units, soft-start units, high-intensity QTH and plasma arc (PAC) curing lights, and one argon laser. Cured compules were sonicated to remove uncured composite and were sectioned and polished along the long axis to expose cured composite. Knoop hardness was measured 0.5 mm from the irradiated, top surface and then at 1.0 mm and in 1.0-mm increments until reliable readings could no longer be obtained. Hardness values were compared by analysis of variance at similar depths within a specific curing-light classification, using the hardness of the standard 40-second conventional QTH exposure as comparison (Dunnett's t-test). Depth of cure was defined as the deepest hardness value found equivalent to that at 0.5-mm depth for a specific curing light and scenario.
Results: Conventional QTH lights provided similar hardness profiles. At 2-mm depth, use of a different unit or curing tip made no difference in hardness compared with the standard. At this depth, soft-start (pulse-delay and step-cure) methods yielded hardness similar to that of the standard. High-intensity QTH lights provided similar hardness at 2-mm depth in 10 seconds to that of the standard 40-second exposure. Plasma arc exposure for less than 10 seconds produced inferior hardness compared with the standard. A 10-second PAC and a 5-second laser exposure gave hardness at 2-mm depth equivalent to that of the 40-second standard. Depth of cure for almost all curing scenarios was not greater than 2 mm.
CLINICAL SIGNIFICANCE
Similar-type conventional QTH lights with different tip diameter (8 and 12 mm) provide similar composite cure characteristics. Soft-start techniques provide similar cure profiles to those achieved with conventional QTH technique when used according to manufacturer's recommendations. High-intensity QTH units and the argon laser can reduce exposure time while providing composite with similar hardness to that of conventional QTH curing. Plasma arc exposure should be at least of 10 seconds duration to provide hardness equivalent to that achieved with conventional 40-second QTH exposure. Even with consideration of high-intensity curing units, composite increments should still be no greater than 2 mm to provide homogeneous hardness.
129 citations