Light-curing Times Research Articles

Influence of Light-Curing Time and Increment Thickness on the Properties of Bulk Fill Composite Resins With Distinct Application Systems.

The objective of this study was to evaluate the influence of light-curing time and increment thickness on the microhardness and degree of conversion (DC) of bulk fill composite resins with different application systems. Translucency parameter (TP) was also measured. Specimens of resin composites were prepared in a circular matrix using a single increment with different thicknesses (2, 4, and 6 mm) and light-cured with distinct times (10, 20, and 40 s). The materials tested (n = 5 pergroup) were Filtek One (FO) bulk fill, Tetric N-Ceram (TC) bulk fill, SonicFill 3 (SF), VisCalor (VC) bulk. After 24 h, Knoop microhardness (KN) was measured, and the bottom/top ratio (B/Tratio) was calculated. The DC was measured using Fourier transformed infrared (FTIR) spectroscopy. The TP was assessed in additional specimens with 1 mm thick (n = 5). The data were statistically analyzed with analysis of variance (ANOVA) and Tukey's tests (5%). Significant differences were observed for all factors, for both B/Tratio and DC (p < 0.05). The higher increment thickness and the lower curing times resulted in lower B/Tratio and DC means. The VC and TC resins exhibited the overall higher B/Tratio, and the highest TP. SF presented the lowest values of B/Tratio and DC, with compromised polymerization at 6 mm depth. TP (means ± SD) were FO (12.85 ± 1.0)1, SF (15.62 ± 0.73)2, TC (20.32 ± 0.49)3, and VC (20.53 ± 0.73)3. We concluded that the greater the thickness of the increment, the lower the DC. Higher light curing times resulted on increased DC of the tested composites. The higher translucent materials VC and TC showed the greater B/Tratio; and FO resin exhibited the higher DC values.

Influence of medium-translucency monolithic zirconia thicknesses and light-curing time on the polymerization of dual-cure resin cements

Aim: To investigate and compare the effects of different thicknesses of medium-translucency monolithic zirconia and light curing times on the polymerization of two types of dual-cured resin cement. Methods: A total of 200 cement specimens were prepared from TheraCem and RelyX U200 cement. The specimens were divided into 5 groups: Group I, without interposing zirconia; Group II, 0.50 mm thickness; Group III, 1.00 mm; Group IV, 1.50 mm; and Group V, 2.00 mm thickness. Each group was subdivided into (1) RelyX U200 and (2) TheraCem. Each subgroup was subdivided according to the light-curing time into (a) 20 s and (b) 40 s (n =5). The polymerization was tested using Fourier-transform infrared (FTIR) spectroscopy and a Vickers microhardness tester. The data were statistically analyzed using ANOVA, an independent sample t-test, and Tukey’s test at a significance level of 0.05. Results: The control group had the highest values of DC and VMH, followed by 0.50, 1.00, and 1.50 mm, respectively, while the 2.00 mm group showed the lowest values. The specimens irradiated for 40 s had greater DC and VMH than those irradiated for 20 s. RelyX U200 revealed higher values for both parameters compared to TheraCem cement. Conclusion: The polymerization of selfadhesive cement depends on the thickness of the monolithic zirconia, the light curing time, and the composition of the cement. The cement should be irradiated for a longer period than recommended to overcome the light attenuation of zirconia. TEGDMA-based self-adhesive cement showed a higher DC and VMH than BISGMA-based cement.

The relationship between light curing time, shear bond strength (SBS) and remanence index of adhesive (ARI)

The objective of this study is to investigate the effect of different light curing times on the shear strength and remanence index of the adhesive. The light curing intensity was presented by Woodpecker LED light curing unit (2500 mw/cm2). The study was performed on groups of extracted premolars: The first and second groups had a light-curing time of 3 seconds, and the third and fourth groups had a light-curing time of 6 seconds. However, the first and third groups were tested after 24 hours, and the second and fourth groups after 14 days. The study showed that increasing the light curing intensity, exposure time and the time after the brackets bonding will increase SBS and will decrease ARI on the other hand, using light curing unit (2500 mw/cm2) with 6 seconds light exposer will produce sufficient SBS, and 3 seconds light cure exposer (2500 mw/cm2) will produce insufficient SBS.

The influence of light-curing time on fluoride release, surface topography, and bacterial adhesion in resin-modified glass ionomer cements: AFM and SEM in vitro study.

Reinforced glass ionomer cements have been widely used in pediatric dentistry to prevent dental caries. However, the influence of biomaterial light-curing and its anti-cariogenic effects remain unclear. This study evaluates the influence of the light-curing time on fluoride release, surface topography, and bacterial adhesion in two types of resin-modified glass ionomer cements (RMGICs). One hundred disks were made, and samples were divided into two groups (n=50 per group), according to each dental material (Vitremer™ and Ketac™ N100), and also divided into different light-cured times (10, 20, 30, 40, and 60 s). They were placed in phosphate-buffered saline solution (PBS) to measure the fluoride release. Subsequently, an independent sample of RMGICs per group was examined using atomic force microscopy (AFM). Four disks per group were incubated in a brain heart infusion (BHI) medium that was inoculated with Streptococcus mutans GS5 to evaluate the bacterial adhesion by 3-4, [5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide cell viability assay (MTT assay). The fluoride release was related to the light-curing time and gradually decreased as the light-curing time increased in both materials. Surface topography in Vitremer™ presents more irregular surfaces than Ketac™ N100. For S. mutans adhesion, the smallest number of cells per milliliter (cell/ml) was found at 40 s for Vitremer™ and at 30 s for Ketac™ N100. Thus, the shorter light-curing times allowed for major fluoride release in both materials. However, the RMGICs showed different patterns of bacterial adhesion according to the brand and light-curing time.

Marginal and Internal Adaptation Evaluation of Dental Composites Using Micro-CT

The aim of the study was to determine the marginal and internal adaptation after curing of different composite resin restorations, using a nondestructive X-ray micro-computed tomography (micro-CT). Forty previously extracted human molars, kept in 10% formalin to preserve the bonding capabilities of the tooth structures, were divided into four groups based on the composite system used and different light-curing times. Class II (vertical slot) cavities were prepared on one proximal side and restored with dental composite using a Tofflemire matrix, with a bulk-fill composite resin (Venus Bulk Fill, Heraeus Kulzer) and a universal posterior composite (G-ænial Posterior, GC). A curing lamp (Kerr Demi Ultra) was used with different curing times. Micro-CT scanning was performed by using Nikon XTH 225ST to reveal any defects in adaptation or gaps at the tooth restoration interface. The 3D images of the adaptation around the restorations were reconstructed using VG Studio Max 2.2 and myVGL 2.2.6 64-bit software. All samples from the G-ænial group showed marginal and internal gaps, with G-ænial Posterior having higher polymerization shrinkage and marginal gap values. In the Venus Bulk Fill group, there were fewer restorations with internal and external gap formation. Micro-CT is a three-dimensional imaging technique that can nondestructively detect adaptation around the resin composite restorations at every level of the sample.

Effect of light-curing time on light-cure/post-cure volumetric polymerization shrinkage and regional ultimate tensile strength at different depths of bulk-fill resin composites.

The aim of this study was to investigate volumetric polymerization shrinkage (VS), using swept-source optical coherence tomography (SS-OCT), of bulk-fill composites with different light-curing strategies; immediately after light-irradiation and after 24 h, and to evaluate their regional ultimate tensile strength (UTS) at different curing depths. The immediate VS after photo-polymerization decreased when the curing light-curing time was reduced from 20 to 10 to 5 s. On the other hand, their VS values after 24 h significantly increased due to the post-cure polymerization, resulting in similar VS values at all the light-curing times. Five seconds light-curing decreased the regional UTS of resin composites after the 24 h period compared with the 10 and 20 s light-curing regimes; therefore, the remarkable progress of post-cure polymerization after light-curing for a short time would not lead to an improvement in the mechanical properties of resin composites. The influence of the light-curing time on the curing depth was dependent upon the bulk-fill composite material.

Effects of Cusp Inclination and Light-curing Time on Microshear Bond Strength of a Dual-cure, Self-adhesive Composite Cement to Zirconia.

To evaluate the effect of cusp inclination and light-curing time on the microshear bond strength (μSBS) between zirconia and a dual-cure self-adhesive composite cement and zirconia. Forty U-shaped specimens with angled surfaces, simulating different cusp inclinations (0 degrees, 20 degrees, and 30 degrees), were fabricated from zirconia blocks (Zenostar, Wieland). The specimens were randomly divided into two groups (n = 20) according to different light-curing times of the adhesive composite cements (20 s and 40 s). Three polyethylene tubes filled with a dual-curing self-adhesive composite cement (Multilink Speed, Ivoclar Vivadent) were bonded to the surfaces of each specimen with light-curing times of 20 s and 40 s. The μSBS was tested using a universal testing machine with a crosshead speed of 0.5 mm/min. Failure analysis was performed. Two-way ANOVA (cusp inclination and light-curing time) followed by two independent samples t-test were used for statistical analyses (α = 0.05). The composite cement showed various bond strengths to angled zirconia surfaces (7.07 ± 1.69 to 13.91 ± 3.11 MPa). The μSBS between composite cement and 0-degree zirconia surfaces was statistically higher than that of 20- and 30-degree zirconia surfaces. The composite cement light cured for 40 s showed nonsignificantly higher μSBS than did the composite cement cured for 20 s. Adhesive failure was the most common failure mode. Cusp inclination affected bond strength between the dual-curing self-adhesive composite cement and zirconia.

Influence of Shortened Light-curing Duration on the Potential of Resin-based Surface Sealants to Prevent Erosion.

To determine whether reducing the light-curing time of resin-based surface sealants influences their potential to prevent erosion, as well as their mechanical stability and degree of conversion. 240 bovine dentin samples were randomly divided into 10 groups (1-10). The 24 samples of one group remained unsealed and served as control. Three groups were sealed with Seal&Protect, another three groups with K-0184 (experimental sealant), and the remaining three groups with Syntac Classic. One group of each sealant was light cured for 10 s, another group of that sealant for 5 s, and the last group of the respective sealant for 2 s at 1014 mW/cm2. After 7-day water storage, the first measurement of sealant permeability was performed. The samples were stored in hydrochloric acid (pH 2.3) for 24 h and the dentin calcium release was measured by atomic absorption spectroscopy. Following thermomechanical loading (5000 cycles, 5°/50°C, 12,000 brushing strokes), the second measurement of sealant permeability was performed. Additionally, the sealants' degrees of conversion (DC) were determined by FTIR spectroscopy. For the first and second measurements, no significant difference in the permeability of the sealants was observed when the light-curing duration was shortened. Additionally, no significant difference in the stability of the respective sealants was observed when light cured for different durations. Regarding DC, a significant influence of the light-curing duration was observed (p = 0.000). Shortening the light-curing time has no influence on permeability and stability of the investigated sealants. However, short light-curing times (2 s or 5 s) decrease the DC of the tested sealants.

Impact of light-curing time and aging on dentin bond strength of methacrylate- and silorane-based restorative systems

AIM: To evaluate the impact of different light-curing times on dentin microtensile bond strength of two restorative systems after 24 h and 6 months of water storage. METHODS: Standardized Class II preparations were performed in 56 freshly-extracted human molars (n = 7), restored with methacrylate- or silorane-based restorative systems, and light-cured using a light-emitting diode at 1390 mW/cm2 by the recommended manufacturers' time or double this time. After storage for 24 h at 37 oC, the teeth were sectioned to yield a series of 0.8-mm thick slices. Each slab was trimmed into an hourglass shape of approximately 0.64 mm2 area at the gingival dentin-resin interface. Specimens were tested using universal testing machine at crosshead speed of 0.5 mm/min until failure, after 24 h and 6 months of storage. Data were statistically analyzed by three-way ANOVA and Tukey's test (α = 0.05). RESULTS: The highest bond strength values were recorded for the groups restored with methacrylate system (p<0.001) as well as for extended light-curing time (p = 0.0034). There was no statistically significant difference between 24 h and 6 months storage on bond strength (p>0.05). CONCLUSIONS: Bond strength was influenced by the material and light-curing time, but the 6-month storage did not affect the bond strength of restorations.

Application of the water subtraction algorithm in determining the degree of conversion of self-etching adhesives.

This study evaluated the effect of residual water included within the FT-IR spectra on the calculation of the degree of conversion (DC) of a self-etching adhesive (SEA). FT-IR spectra of a SEA (Adper Prompt SE, 3M ESPE) were obtained for different amounts of dentin powder, agitation times, and light-curing times. The measured DC (mDC) obtained from the IR spectra was compared to the apparent DC (aDC) from the adjusted IR spectra using the water subtraction algorithm (WSA), by which the water absorption band was subtracted from the obtained IR spectrum. When the SEA was mixed with 10 mg of dentin powder, the aDC was significantly higher than the mDC immediately after light curing (paired t-test, p < 0.001). With the increase in the amount of dentin powder, the mDC immediately after curing and the difference between the mDC and the aDC gradually increased. The amount of dentin powder, light-curing time, square of light-curing time, and time until measurement were the variables that significantly affected the aDC (linear mixed model, p < 0.05). However, the agitation time did not affect the aDC or the difference between the mDC and the aDC, except at 20 s. When the DC of SEA itself is measured with FT-IR, the mDC needs to be adjusted with the water subtraction algorithm. Clinically, SEA needs to be applied under conditions of prolonged contact with the dentin substrate and vigorous and prolonged drying.

Microhardness of nanofilled composite resin light-cured by LED or QTH units with different times

Aim: To evaluate the influence of light-curing units and light-curing time on the microhardness of a nanofilled composite resin. Methods: Forty-five composite resin (Z350 - 3M) specimens were randomly prepared using Teflon ring molds (4.0 mm internal diameter and 2 mm depth) and divided into nine experimental groups (n=5): three polymerization units (conventional - 450 mW/ cm2 ; 2nd generation LED - 1100 mW/cm2 ; and 3rd generation LED - 700 mW/cm2 ) and three lightcuring times (20 s, 40 s, and 60 s). All specimens were polymerized with the light-curing tip positioned 8 mm far from the top surface of the specimen. After 24 h, Knoop microhardness measurements were made on the top and bottom surfaces of the specimen, with a load of 10 g for 10 s. Five indentations were made on each surface. All results were analyzed statistically by subdivided parcel ANOVA (Split-Plot) and Tukey’s tests (p<0.05). Results: There were no statistically significant differences for the polymerization unit and light-curing time factors in either top or bottom surface. For all experimental conditions, the top surfaces showed greater hardness than the bottom surfaces (p<0.0001). Conclusions: The mode of polymerization and the lightcuring time did not affect the hardness of the nanofilled composite resin, and increasing the lightcuring time did not improve the hardness of the bottom surface of the composite resin.

Evaluation of different light-curing lamps

The aim of this study has been to evaluate light-curing composites polymerization quality carried out by halogen and new-diode lamps through the thermal analysis (TG–DTA). Samples have been polymerized at 3–20–40–60 s by halogen lamp and 1–3–6–9 s by new-diode lamp. The TG/DTA analysis shows that different light-curing times affect the degree of conversion of the composite, since by increasing the curing time the quantity of the monomer that has not reacted (residual) decreases. The new-diode lamp, according to the manufacturer, can cure composite restorations in few seconds; but at the conditions used in this study, the samples cured by the halogen lamp at the standard times of exposure, compared to the samples cured in few seconds by the new-diode lamp, show a lower mass loss.

Evaluation of composites light-curing at different times and distances of irradiation

The aim of this study is to evaluate light-curing composites polymerization quality (monomer/polymer) carried out at different times and distances of irradiation through the thermal analysis (TG-DTA). Samples have been polymerized at 20, 40 and 60 s (0-2-4-6-8 mm) through a constant polymerization and subsequently analysed by TG-DTA. The TG/DTA analysis shows that different light-curing times and different distance of irradiation affect the quality of polymerization; it is necessary to increase the curing time when the irradiation distance is longer than 2 mm.

Diode-pumped solid-state laser for bonding orthodontic brackets: effect of light intensity and light-curing time

This study evaluated the shear bond strength (SBS) of orthodontic brackets bonded to teeth using a diode-pumped solid state (DPSS) laser of 473 nm with various light intensity and light-curing settings. For the study, a total of 150 extracted human teeth were divided into ten groups. In the control group, the brackets were bonded to the teeth using a quartz-tungsten-halogen (QTH) light with an intensity of 900 mW/cm(2). In the experimental groups, the brackets were bonded using a DPSS laser with three different light intensities and light-curing times. The same bracket type and adhesive were used in all groups throughout the study. Statistical analysis was performed to compare the SBS, and adhesive remnant index (ARI) among the groups. As results, brackets bonded using the DPSS laser with an intensity of 700 mW/cm(2) for 40 s (totally) showed a slightly higher SBS (12.2 ± 1.8 MPa) than that of those bonded using a QTH light (control; 11.6 ± 1.6 MPa). The SBS values linearly increased with increasing energy density (light intensity × light-curing time) of the DPSS laser (R = 0.95, p < 0.001). However, the SBS values among the test groups were similar regardless of the difference in light-curing conditions. A comparison of the ARI scores among the groups suggested a similar bracket failure mode.

Thermal analysis of light-curing composites

The aim of this study has been to evaluate light-curing composites polymerization quality (monomer/polymer) with an halogen and diode lamp through the thermal analysis (TG-DTA). Samples have been polymerized at 20, 40 and 50 s through a constant and a soft start polymerization and, subsequently, analyzed by TG-DTA. The TG/DTA analysis shows that different light-curing times affect the degree of conversion of the composite, since by increasing the curing time the quantity of the monomer that has not reacted (residual) decreases. The halogen lamp, compared to the diode lamp, produces a lower mass loss at 20 s, while for 40 and 50 s the results are overlapping. The soft start polymerization (20 s) initially produces a higher mass loss, if compared to the constant intensity, but, by performing a polymerization for at least 40 s, the results can be overlapped.

Effect of etching and light-curing time on the shear bond strength of a resin-modified glass ionomer cement

The aim of this study was to assess the influence of etching and light-curing time on the shear bond strength (SBS) and adhesive remnant index (ARI) of a resin-modified glass ionomer cement (RMGIC) upon debonding of orthodontic brackets. Sixty-eight bovine permanent incisors were obtained and embedded in acrylic resin. Edgewise metallic brackets were bonded to the teeth with Fuji Ortho LC RMGIC. The specimens were randomly assigned to 4 groups, using the following etching and light-curing times: G1: 10% polyacrylic acid and 40 s (control); G2: 37% phosphoric acid and 40 s; G3: 10% polyacrylic acid and 50 s; and G4: 37% phosphoric acid and 50 s. Shear test was performed at 0.5 mm/min and the ARI was assessed. G2 (3.6 ± 0.98 MPa) presented significantly higher (p<0.05) SBS than G1 (2.76 ± 0.86 MPa) and G4 (2.86 ± 0.68 MPa), and there was no statistically significant difference (p>0.05) between G2 and G3 (2.94 ± 0.67 MPa). ARI presented prevalence of scores 2 and 3 in all groups. RMGIC SBS enhanced with 37% phosphoric acid etching and 40 s light-curing time, but this did not occur when the light-curing time was increased, regardless of the acid used. RMGIC presented prevalence of failures at the adhesive/bracket interface.

Bond Strength of Fiber Posts to Weakened Roots After Resin Restoration With Different Light-Curing Times

Introduction This study evaluated the bond strength of translucent fiber posts to experimentally weakened radicular dentin restored with composite resin and polymerized with different light-exposure time. Methods Roots of 60 maxillary incisors were used. Twenty-four hours after obturation, the filling materials of root canals were removed to a depth of 12 mm, and 4 groups were randomly formed. In 3 groups, root dentin was flared to produce a space between fiber post and canal walls. In the control group, the roots were not experimentally weakened. The flared roots were bulk restored with composite resin, which was light-activated through the translucent post for 40, 80, or 120 seconds. Posts were cemented, and after 24 hours, all roots were sectioned transversely in the coronal, middle, and apical regions, producing 1-mm-thick slices. Push-out test was performed, and failure modes were observed. Results The quantitative analysis showed significant statistical difference only among groups ( P < .001). Comparing the weakened/restored groups, composite light-exposure time did not influence the results. Overall, adhesive failures occurred more frequently than other types of failures. Cohesive failures occurred only in the weakened/restored roots. Conclusions Intracanal root restoration with composite resin and translucent fiber posts provided similar or higher bond strength to dentin than the control group, regardless of the light-exposure time used for polymerization.

Shear bond strength of metallic brackets photo-activated with light-emitting diode (LED) at different exposure times

The purpose of this study was to compare the shear bond strength of orthodontic metallic brackets photo-activated with two different light-curing sources at different exposure times: halogen light (XL 1500, 3M ESPE) and LED light (Ortholux, 3M Unitek). Sixty bovine permanent lower incisors were inserted into PVC tubes containing plaster. The buccal surfaces were cleaned with pumice and water, and then etched with 37% phosphoric acid gel. The XT Primer bonding agent (3M Unitek) was applied to the enamel surfaces and the metallic pre-coated brackets (Transbond APC II system, 3M Unitek) were attached to upper central incisors. The teeth were randomly divided into four groups (n=15). In Group I (Control), halogen light was used for 40 seconds, while in Groups II, III, and IV were light-cured with LED light unit for 40, 10, and 5 seconds, respectively. The teeth were stored in distilled water at 37°C for 24 hours. The brackets were submitted to shear bond strength test in universal testing machine (Instron) at a crosshead speed of 0.5 mm/minute. Shear bond strength means (MPa) were 4.87 for Group I; 5.89 for Group II; 4.83 for Group III, and 4.39 for Group IV. Tukey's test detected no statistically significant differences among the groups regarding the shear bond strength (p>0.05). Neither of the types of light-curing sources or exposure times influenced the shear bond strength of metallic brackets.

Effect of Light Curing Modes and Light Curing Time on the Microhardness of a Hybrid Composite Resin

The aim of this in vitro study was to evaluate the influence of light curing modes and curing time on the microhardness of a hybrid composite resin. Forty-five Z250 composite resin specimens (3M-ESPE Dental Products, St. Paul, MN, USA) were randomly divided into nine groups (n=5): three polymerization modes (conventional-550 mW/cm2; light-emitting diodes (LED)-360 mW/cm2, and high intensity-1160 mW/cm2) and three light curing times (once, twice, and three times the manufacturer's recommendations). All samples were polymerized with the light tip 8 mm from the specimen. Knoop microhardness measurements were obtained on the top and bottom surfaces of the sample. Conventional and LED polymerization modes resulted in higher hardness means and were statistically different from the high intensity mode in almost all experimental conditions. Tripling manufacturers' recommended light curing times resulted in higher hardness means; this was statistically different from the other times for all polymerization modes in the bottom surface of specimens. This was also true of the top surface of specimens cured using the high intensity mode but not of conventional and LED modes using any of the chosen curing times. Top surfaces showed higher hardness than bottom surfaces. It is important to increase the light curing time and use appropriate light curing devices to polymerize resin composite in deep cavities to maximize the hardness of hybrid composite resins.

Effect of the increase of energy density on knoop hardness of dental composites light-cured by conventional QTH, LED and xenon plasma arc

The aim of this study was to evaluate the effect of the increase of energy density on Knoop hardness of Z250 and Esthet-X composite resins. Cylindrical cavities (3 mm in diameter X 3 mm in depth) were prepared on the buccal surface of 144 bovine incisors. The composite resins were bulk-inserted and polymerized using different light-curing units and times: conventional QTH (quartz-tungsten-halogen; 700 mW/cm(2); 20 s, 30 s and 40 s); LED (light-emitting diode; 440 mW/cm(2); 20 s, 30 s and 40 s); PAC (xenon plasma arc; 1700 mW/cm(2); 3 s, 4.5 s and 6 s). The specimens were stored at 37 degrees C for 24 h prior to sectioning for Knoop hardness assessment. Three measurements were obtained for each depth: top surface, 1 mm and 2 mm. Data were analyzed statistically by ANOVA and Tukey's test (p<0.05). Regardless of the light source or energy density, Knoop hardness of Z250 was statistically significant higher than that of Esthet-X (p<0.05). Specimens cured with PAC had lower hardness than those cured with QTH and LED (p<0.05). Higher Knoop hardness was obtained when the energy density was increased for LED and PAC (p<0.05). No statistically significant differences (p>0.05) were found for QTH. Knoop hardness values decreased with the increase of depth. The increase of energy density produced composites with higher Knoop hardness means using LED and PAC.