Effects of various light curing methods on the leachability of uncured substances and hardness of a composite resin

Irradiance from 12 LED light curing units measured using 5 brands of dental radiometers

OBJECTIVE

To evaluate the accuracy of five brands of radiometers in reporting the irradiance (mW/cm2 ) from twelve brands of LCUs compared to a 'Gold Standard' (GS) reference obtained from a hand-held laboratory-grade radiometer.

MATERIALS AND METHODS

The irradiance was measured from two examples of twelve brands of previously used LCUs on two examples of five brands of dental radiometers. The emission spectrum was also obtained. Irradiance data from each brand of LCU against each meter was analyzed using the Shapiro-Wilk test for normality. The irradiance values were subjected to a two-way ANOVA followed by Bonferroni tests for each LCU brand. Finally, a descriptive analysis was made using a 95% confidence interval around the mean irradiance.

RESULTS

The power output from the LCUs ranged from 271 mW to 1005 mW. Among the tested radiometers, only the Bluephase Meter II could accurately report the irradiance from 11 out of the 12 brands of LCU evaluated in this study. When measured using the "GS" system, the mean irradiance values from the two examples of nine brands of previously used LCU were not always within ±10% of the irradiance values stated by the manufacturer.

CONCLUSIONS

The mean irradiance values from 9 of the 12 brands of used LCUs were beyond ±10% of the irradiance values stated by the manufacturer. Only the Bluephase Meter II could accurately report the irradiance from 11 out of the 12 brands of LCU evaluated in this study.

CLINICAL SIGNIFICANCE

There was a wide range in the power output from the LCUs tested. It was impossible to accurately measure the irradiance from all the LCUs using the dental radiometers examined. However, dental radiometers should still be used in dental offices to monitor the light output from LCUs and verify that they are working correctly before they are used on patients.

New Resin-Based Bulk-Fill Composites: in vitro Evaluation of Micro-Hardness and Depth of Cure as Infection Risk Indexes

The current in vitro study evaluated the Vickers hardness number (VHN) and hardness ratio of four bulk-fill composites (VisCalor bulk; Admira Fusion x-tra; x-tra fil; and GrandioSO x-tra-Voco, Cuxhaven, Germany) to assess the risk of bacterial colonization in comparison with standard composite materials. Thirty samples were prepared for each group. The VHN of both the external (top) and internal surface (bottom) was determined with a micro-hardness tester (200 g load for 15 s), and the hardness ratio was also calculated for each sample. Subsequently, storage in an acidic soft drink (Coca-Cola, Coca-Cola Company, Milano, Italy) was performed; for each group, 10 samples were stored for 1 day, while another 10 were stored for 7 days and the remaining 10 were kept in water as controls. A significant reduction in VHN was shown for all the groups when comparing the external versus internal side (P < 0.05), although the hardness ratio was greater than 0.80, resulting in an adequate polymerization. Regarding the acid storage, all the groups showed a significant decrease of VHN when compared with the controls, both after 1 day (P < 0.05) and after 7 days (P < 0.001). All the products showed adequate depth of cure without further risk of bacterial colonization. However, acid exposure negatively affected micro-hardness values, which might promote subsequent colonization.

Toxicology of Pre-heated Composites Polymerized Directly and Through CAD/CAM Overlay

Objectives

The aim was to compare cytotoxicity/genotoxicity of pre-heated composites polymerized through CAD/CAM overlays on isolated human peripheral blood lymphocytes.

Material and Methods

A microhybrid (Z100, 3M ESPE) and nanofilled composite (Filtek Supreme Ultra, 3M ESPE) were heated in a heating unit (Calset, AdDent Inc.) at different temperatures: 37 ^oC, 54 ^oC, and 68 ^oC. A small amount of heated composite was placed in a cylindrical mold (6mm diameter; 0.65mm thick), covered with a Mylar sheet, pressed and light-cured directly and through 2 mm thick CAD/CAM ceramic-reinforced polymer (CRP)(LAVA Ultimate, 3M ESPE) or CAD/CAM lithium disilicate ceramic (LDC)(e.max, Ivoclar/Vivadent) overlay. After curing, the specimens were immediately placed in a prepared lymphocyte cell culture. Cytotoxicity was assessed using a dye exclusion method by simultaneous staining with ethidium bromide and acridine orange, aimed to determine percentages of viable, apoptotic and necrotic cells. Genotoxicity was studied using alkaline comet assay.

Results

For Z100, the highest percentage of viable cells is recorded at T1 (93.7%) after direct light curing, followed by light curing through CRP (92.3%) and through LDC (91.7%T1,T3). For Filtek Supreme Ultra, the highest percentage of viable cells is recorded while curing through CRP (91.0% T2), followed by LDC (90% T1,T3) and direct light curing (88.7%T2).

Conclusion

For both tested materials, preheating the procedure at T1 and T2 may be the procedure of choice. In terms of genotoxicity, preheating at T3 may not be suggested.

Efficiency of Dual-Cured Resin Cement Polymerization Induced by High-Intensity LED Curing Units Through Ceramic Material

Objective

This study aimed to evaluate the ability of high-intensity light-emitting diode (LED) and other curing units to cure dual-cured resin cement through ceramic material.

Methods

A halogen curing unit (Jetlite 3000, Morita), a second-generation LED curing unit (Demi, Kerr), and two high-intensity LED curing units (PenCure 2000, Morita; Valo, Ultradent) were tested. Feldspathic ceramic plates (VITABLOCS Mark II, A3; Vita Zahnfabrik) with thicknesses of 1.0, 2.0, and 3.0 mm were prepared. Dual-cured resin cement samples (Clearfil Esthetic Cement, Kuraray Noritake Dental) were irradiated directly or through one of the ceramic plates for different periods (5, 10, 15, or 20 seconds for the high-intensity LED units and 20, 40, 60, or 80 seconds for the others). The Knoop hardness test was used to determine the level of photopolymerization that had been induced in the resin cement. Data were analyzed by one-way analysis of variance and Dunnett's post-hoc test to identify test-control (maximum irradiation without a ceramic plate) differences for each curing unit (p&lt;0.05).

Results

For all curing units, the curing conditions had a statistically significant effect on the Knoop hardness numbers (KHNs) of the irradiated cement samples (p&lt;0.001). In general, the KHN decreased with increasing plate thickness and increased as the irradiation period was extended. Jetlite 3000 achieved control-level KHN values only when the plate thickness was 1.0 mm. At a plate thickness ≥2.0 mm, the LED units (except for PenCure 2000 at 3.0 mm) were able to achieve control-level KHN values when the irradiation time was extended. At a plate thickness of 3.0 mm, irradiation for 20 seconds with the Valo or for 80 seconds with the Demi were the only methods that produced KHN values equivalent to those produced by direct irradiation.

Conclusion

Regardless of the type of curing unit used, indirect irradiation of dual-cured resin cement through a ceramic plate resulted in decreased KHN values compared with direct irradiation. When the irradiation period was extended, only the LED units were able to achieve similar KHN values to those observed under direct irradiation in the presence of plates ≥2.0-mm thick. High-intensity LED units require a shorter irradiation period than halogen and second-generation LED curing units to obtain KHN values similar to those observed during direct irradiation.

Influence of softening test and light-activation protocols on resin composite polymer structure

OBJECTIVE

This study analyzed the influences of the light-activation protocol and softening test on the degree of conversion (DC) and Knoop Hardness (KHN) of a microhybrid resin composite.

MATERIALS AND METHODS

Filtek Z250 (3M ESPE) was light-activated with a third-generation light-emitting diode (Valo Ultradent) by three protocols - standard, high power, and plasma emulation - or with a quartz-tungsten halogen XL 3000 (3M ESPE) in conventional mode. All modes were set to deliver 19 J/cm(2). The DC (N = 20) was determined by Fourier transform infrared spectrometry on the top (T) and bottom (B) surfaces. For the KHN test, samples were subdivided in four groups (n = 5 each) according to the storage media: absolute ethanol, 75% ethanol, distilled water, and air (control group). The KHN values were evaluated on T and B before and 24 h after immersion in the storage media. Data were analyzed by split-plot analysis of variance (ANOVA; for DC) or repeated-measures split-plot ANOVA (for KHN), followed by Tukey's test (α = 0.05).

RESULTS

For the DC, the light-activation protocol did not influence the results and there was no difference between T and B. For the KHN test, the light-activation protocol did not influence the results and T showed higher microhardness values than B for all experimental conditions. There were significant differences in KHN depending on the storage media. Samples immersed in absolute ethanol generally presented lower KHN values, with no differences compared to samples in 75% ethanol.

CONCLUSION

The storage media affected the outcomes of the softening test.

Characterization of heat emission of light-curing units

OBJECTIVES

This study was designed to analyze the heat emissions produced by light-curing units (LCUs) of different intensities during their operation. The null hypothesis was that the tested LCUs would show no differences in their temperature rises.

METHODS

FIVE COMMERCIALLY AVAILABLE LCUS WERE TESTED: a "Flipo" plasma arc, "Cromalux 100" quartz-tungsten-halogen, "L.E. Demetron 1" second-generation light-emitting diode (LED), and "Blue Phase C5" and "UltraLume 5" third-generation LED LCUs. The intensity of each LCU was measured with two radiometers. The temperature rise due to illumination was registered with a type-K thermocouple, which was connected to a computer-based data acquisition system. Temperature changes were recorded in continues 10 and 20 s intervals up to 300 s.

RESULTS

The Flipo (ARC) light source revealed the highest mean heat emission while the L.E. Demetron 1 LED showing the lowest mean value at 10 and 20 s exposure times. Moreover, Cromalux (QTH) recorded the second highest value for all intervals (12.71, 14.63, 14.60) of heat emission than Blue Phase C5 (LED) (12.25, 13.87, 13.69), interestingly at 20 s illumination for all intervals the highest results (18.15, 19.27, 20.31) were also recorded with Flipo (PAC) LCU, and the lowest (6.71, 5.97, 5.55) with L.E. Demetron 1 LED, while Blue Phase C5 (LED) recorded the second highest value at the 1st and 2nd 20 s intervals (14.12, 11.84, 10.18) of heat emission than Cromalux (QTH) (12.26, 11.43, 10.26). The speed of temperature or heat rise during the 10 and 20 s depends on light intensity of emitted light. However, the QTH LCU was investigated resulted in a higher temperature rise than LED curing units of the same power density.

CONCLUSION

The PAC curing unit induced a significantly higher heat emission and temperature increase in all periods, and data were statistically different than the other tested groups (p < .05). LED (Blue Phase C5) was not statistically significant (p < .05) (at 10 s) than QTH units, also LED (Blue Phase C5, UltraLume 5) generates obvious heat emission and temperature rises than QTH units (at 20 s) except for those which have lower power density of LED curing units (first generation). Thus, the null hypothesis was rejected.

Resin-composite cytotoxicity varies with shade and irradiance

OBJECTIVES

The study was aimed at investigating the cytotoxicity of different composites as a function of composite shade and the light curing unit (LCU) employed.

METHODS

Non-polymerized and polymerized samples of the composites Grandio(®) (VOCO, Cuxhaven), Solitaire(®) (Heraeus Kulzer, Hanau) and Filtek Z 250(®) (3M/Espe, Seefeld) in two markedly differing shades (A2, C2) were prepared. Polymerization was performed with two LCUs: Heliolux II (Ivoclar/Vivadent, Ellwangen) and Swiss Master Light (EMS, Nyon, Switzerland). To obtain composite extracts, the samples were immersed in cell culture medium (DMEM--Dulbecco's Modified Eagle Medium), which was replaced daily up to the 7th day of the experiment, and then on the 14th, 21st and 28th day. After incubation of human gingival fibroblasts (HGF) with the extracts obtained, cytotoxicity was determined using the MTT test.

RESULTS

With the non-polymerized samples, essentially no influence of the composite shades investigated on HGF viability was detected, with the exception of the Solitaire material, where a higher cytotoxicity of the shade C2 in the non-polymerized state was found at the end of the observation period. After polymerization of the different composites, the cytotoxic reaction observed for the extracts of shade C2 was stronger than that observed for A2. After polymerization with the Heliolux II (HLX) LCU, the extracts of composites Grandio and Solitaire C2 were significantly more toxic than those of the A2 shade (p<0.01). Polymerization with the Swiss Master Light (SML) reduces this cytotoxic effect. The extracts of the Grandio composite showed the least cytotoxic effect throughout the observation period, irrespective of the LCU used. For the extracts of the Z250 specimens, the cytotoxicity observed was generally higher.

SIGNIFICANCE

The results show that the shade of the composite has an influence on its cytotoxicity and that this cytotoxicity is also influenced by the light curing unit used. It was observed that composites of the darker shade (C2) had a higher cytotoxicity, which varied with the LCU employed.

Curing efficiency of various resin-based materials polymerized through different ceramic thicknesses and curing time

PURPOSE

The aim of this in vitro study was to examine the curing efficiency of various resin-based materials polymerized through ceramic restorations with 3 different thicknesses. Curing efficiency was evaluated by determining the surface microhardness (VHN) of the resin specimens.

MATERIALS AND METHODS

Four kinds of resin materials were used. Z350 (3M ESPE Filtek™ Z350: A2 Shade), Z250 (3M ESPE Filtek™ Z250: A2 Shade) and Variolink® II (VL: Ivoclar vivadent, base: transparent) either with or without a self-curing catalyst (VLC: Ivoclar vivadent, catalyst: low viscosity/transparent) were filled into the silicone mold (10 mm diameter, 1 mm thick). They were cured through ceramic discs (IPS e.max Press MO-0 ingot ivoclar vivadent, 10 mm diameter, 0.5, 1 and 2 mm thicknesses) by LED light-curing units for 20 and 40 seconds. Vicker's microhardness numbers (VHNs) were measured on the bottom surfaces by a microhardness tester. Data were analyzed using a 3- way analysis of variance (ANOVA) at a significance level of 0.05.

RESULTS

The thickness of ceramic disc increased, the VHNs of all four resin types were decreased (P<.05). The mean VHN values of the resins light cured for 40 seconds were significantly higher than that of LED for 20 seconds in all four resin materials (P<.05). VLC showed significantly higher VHN values than VL regardless of other conditions (P<.05). Z350 and Z250 showed higher values than VL or VLC (P<.01).

CONCLUSION

Thinner ceramic disc with increased curing time resulted higher VHN values of all resin materials. The use of a catalyst produced a greater hardness with all polymerization methods. Restorative resin materials (Z350, Z250) showed higher VHN values than resin cement materials (VL, VLC).

Influence of prolonged light-curing time on the shear bonding strength of resin to bleached enamel

This study evaluated the effect of prolonged light-curing time using a light-emitting diode unit (LED) on the shear bond strength of a resin composite to enamel immediately after bleaching. The enamel surfaces of human molars were divided into four groups: one control and three bleaching groups. One bleaching group (CP) was exposed to a 10% carbamide peroxide bleaching agent and bonded after 24 hours. The other two bleaching groups (HP) were bleached with a 38% hydrogen peroxide bleaching agent, then bonded either within one hour (HPA) or after 24 hours (HPB). All groups were subdivided into two subgroups and cured for two different times (20 or 40 seconds) with an LED unit. Shear bond strength (SBS) was tested with a universal-testing machine and the data were analyzed by ANOVA and post-hoc tests. Scanning electron micrographs of representative specimens were taken. A significant difference was seen between the control and HPA groups for both curing times (p = 0.000). However, neither the CP nor HPB groups showed any significant differences compared with the control groups (p > 0.05). Two-way ANOVA showed that a significant effect of the curing time factor was recorded for all groups (p = 0.000). Prolonged curing time, using an LED unit with a light intensity of 500 mW/cm2, increased resin-enamel bonding strengths for the control and bleached groups when bonding was performed after 24 hours of immersion in deionized water. However, the SBS was still compromised when bonding was performed immediately to enamel bleached with 38% HP.

Monomer elution from nanohybrid and ormocer-based composites cured with different light sources

OBJECTIVES

To study monomer elution from four resin-based composites (RBCs) cured with different light sources.

METHODS

Twenty-eight premolars were randomly allocated to four groups. Standardized cavities were prepared and restored with a nanohybrid (Filtek Supreme XT or Tetric EvoCeram), an ormocer (Admira) or a microhybrid RBC (Filtek Z250) which served as control. Buccal restorations were cured with a halogen and oral restorations with an LED light-curing unit. Elution of diurethane dimethacrylate (UDMA), Bisphenol A diglycidylether methacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) was analyzed using high-performance liquid chromatography (HPLC) 1h to 28 days post-immersion in 75% ethanol. Data were analyzed using multivariate and repeated measures analysis of variance (α = 0.05).

RESULTS

The greatest elution of UDMA and BisGMA occurred from Tetric EvoCeram and the least from Filtek Z250 (p < 0.05). LED and halogen light-curing units gave similar results for all RBCs (p > 0.05) except Tetric EvoCeram which showed greater elution for the LED unit (p < 0.05). TEGDMA was below the limit of quantification. HEMA eluted in similar concentrations from Filtek Supreme and Tetric EvoCeram (p > 0.05).

SIGNIFICANCE

The two nanohybrid RBCs eluted more cross-linking monomers than the ormocer and the control microhybrid RBC. Continuous elution over 28 days indicates that RBCs act as a chronic source of monomers in clinical conditions. Light source may affect monomer elution since differences were found for one out of four RBCs. Mathematical models for elution kinetics of UDMA and BisGMA indicated two elution mechanisms.

Post-gel shrinkage strain and degree of conversion of preheated resin composite cured using different regimens

OBJECTIVES

This study investigated the influence of resin composite preheating temperature, light curing regimen (mode and duration) on post-gel shrinkage strain (PGSS) and degree of conversion (DC) of a restorative resin composite.

METHODS

A hybrid resin composite preheated to three different temperatures (37 degrees C, 54 degrees C and 68 degrees C) was cured using a high intensity light emitting diode (LED) curing unit. The light source was used in 40- and 20-second continuous mode as well as soft start mode. The resin composite was monitored for PGSS during curing and 10 minutes following light irradiation using strain gauges. DC was measured using FTIR spectrometer. The results were analyzed using two-way ANOVA followed by the Duncan's Multiple Range Test for pairwise comparisons. The significance level was set at p < or = 0.05.

RESULTS

Preheating of the resin composite significantly increased its PGSS and DC. The soft start groups revealed significantly lower PGSS values compared to the 20- and 40-second groups without altering the DC.

CONCLUSIONS

Preheating of resin composite prior to curing increased its DC but also increased its PGSS. The soft-start mode decreased the PGSS of resin composite without altering the DC.

Effect of Light Energy Density on Conversion Degree and Hardness of Dual-cured Resin Cement

Light energy density can influence the curing of dual-cured resin cement. The ultimate physical properties of dual-cured resin cement depend on light energy delivered from the light-curing unit. It can guide the clinicians to select the appropriate curing unit for curing dual cement.

Effect of thickness of indirect restoration and distance from the light-curing unit tip on the hardness of a dual-cured resin cement

This study evaluated the Knoop hardness and polymerization depth of a dual-cured resin cement, light-activated at different distances through different thicknesses of composite resin. One bovine incisor was embedded in resin and its buccal surface was flattened. Dentin was covered with PVC film where a mold (0.8-mm-thick and 5 mm diameter) was filled with cement and covered with another PVC film. Light curing (40 s) was carried out through resin discs (2, 3, 4 or 5 mm) with a halogen light positioned 0, 1, 2 or 3 mm from the resin surface. After storage, specimens were sectioned for hardness measurements (top, center, and bottom). Data were subjected to split-plot ANOVA and Tukey's test (a=0.05). The increase in resin disc thickness decreased cement hardness. The increase in the distance of the light-curing tip decreased hardness at the top region. Specimens showed the lowest hardness values at the bottom, and the highest at the center. Resin cement hardness was influenced by the thickness of the indirect restoration and by the distance between the light-curing unit tip and the resin cement surface.

In vitro biological response to a self-adhesive resin cement under different curing strategies

Self-adhesive resin cements represents a new approach in indirect restorative dentistry, although little is known about its biological properties. The influence of the curing strategy on the biological response of a self-adhesive resin cement (Rely-X Unicem/3M ESPE) was evaluated through methyltetrazolium (MTT) and nitric oxide (NOx) assays. Cylindrical specimens (n = 48) were prepared and cured according to the following strategies: photoactivation with halogen light-curing unit (LCU) Demetron/Kerr, LED LCU Radii/SDI, and chemical activation. A control group with culture medium and a group with lipopolysaccharide, employed for cells stimulation, were used for comparisons (n = 8). After 24 h of direct contact between specimens and rat alveolar macrophages, the biological response was evaluated. Statistical evaluation of the data was performed with Kruskal-Wallis and Dunn's test (p = 0.05). The MTT test showed that the specimens cured by halogen light and chemical activation provided higher alterations on cell metabolism. For LED-cured specimens, cell viability was compatible to the results observed in the control group. For the NOx assay, all curing methods were cytotoxic to rat macrophages. Rely-X Unicem demonstrated different cytotoxic effects according to the curing strategy employed.

Molecular toxicology of substances released from resin-based dental restorative materials

Resin-based dental restorative materials are extensively used today in dentistry. However, significant concerns still remain regarding their biocompatibility. For this reason, significant scientific effort has been focused on the determination of the molecular toxicology of substances released by these biomaterials, using several tools for risk assessment, including exposure assessment, hazard identification and dose-response analysis. These studies have shown that substances released by these materials can cause significant cytotoxic and genotoxic effects, leading to irreversible disturbance of basic cellular functions. The aim of this article is to review current knowledge related to dental composites' molecular toxicology and to give implications for possible improvements concerning their biocompatibility.

HPLC analysis of eluted monomers from two composite resins cured with LED and halogen curing lights

This study investigated the leaching of monomers (Bis-GMA and TEGDMA) from nano-hybrid (Filtek Supreme) and flowable (Filtek Flow) dental composite resins cured with LED or conventional halogen curing lights, and immersed in saliva or water for 24 h. Nine disc specimens were made for each experimental group. After the polymerization process, the specimens were immersed in either water or saliva and incubated at 37 degrees C for 24 h. Eluted Bis-GMA and TEGDMA monomers were detected using high performance liquid chromatography (HPLC). The data were analyzed using three-way ANOVA (p = 0.05) and the independent samples t test. TEGDMA (53.15-1 microg/L) was leached from the resins at a higher level than Bis-GMA (28-0.5 microg/L) (p < 0.01), regardless of the affecting factors: composite type, solvent (media) and type of curing light. In general, Filtek Flow resin released more TEGDMA than Filtek Supreme (p < 0.05), but the Supreme resin released more Bis-GMA than TEGDMA (p < 0.05). Halogen light induced greater monomer elution than LED light immersion in water. Saliva released more TEGDMA than water (p < 0.05). We conclude that (1) total leached TEGDMA was higher than total Bis-GMA, (2) saliva and halogen light (lower intensity than LED) leached more monomers from the resins, and (3) the flowable composite resin leached more TEGDMA than the nano-hybrid.

Microhardness of a resin cement polymerized by light-emitting diode and halogen lights through ceramic

PURPOSE

This study evaluated the curing efficiency of light-emitting diode (LED) and halogen [quartz tungsten halogens (QTH)] lights through ceramic by determining the surface microhardness of a highly filled resin cement.

MATERIALS AND METHODS

Resin cement specimens (Variolink Ultra; with and without catalyst) (5-mm diameter, 1-mm thick) were condensed in a Teflon mold. They were irradiated through a ceramic disc (IPS Empress 2, diameter 5 mm, thickness 2 mm) by high-power light-curing units as follows: (1) QTH for 40 seconds (continuous), (2) LED for 20 seconds, and (3) LED for 40 seconds (5-second ramp mode). The specimens in control groups were cured under a Mylar strip. Vickers microhardness was measured on the top and bottom surfaces by a microhardness tester. Data were analyzed using analysis of variance (ANOVA) and a post hoc Bonferroni test at a significance level of p < 0.05.

RESULTS

The mean microhardness values of the top and bottom surfaces for the dual-cured cement polymerized beneath the ceramic by QTH or LED (40 seconds) were significantly higher than that of light-cured cement (p < 0.05). The top and bottom surface microhardness of dual-cured cement polymerized beneath the ceramic did not show a statistically significant difference between the LED and QTH for 40 seconds (p > 0.05).

CONCLUSIONS

The efficiency of high-power LED light in polymerization of the resin cement used in this study was comparable to the high-power QTH light only with a longer exposure time. A reduced curing time of 20 seconds with high-power LED light for photopolymerizing the dual-cured resin cement under ceramic restorations with a minimum 2-mm thickness is not recommended.

Effect of veneering materials and curing methods on resin cement knoop hardness

This study evaluated the Knoop hardness of Enforce resin cement activated by the either chemical/physical or physical mode, and light cured directly and through ceramic (HeraCeram) or composite resin (Artglass). Light curing were performed with either conventional halogen light (QTH; XL2500) for 40 s or xenon plasma arc (PAC; Apollo 95E) for 3 s. Bovine incisors had their buccal surfaces flattened and hybridized. On these surfaces a mold was seated and filled with cement. A 1.5-mm-thick disc of the veneering material was seated over this set for light curing. After storage (24 h/37 masculineC), specimens (n=10) were sectioned for hardness (KHN) measurements in a micro-hardness tester (50 gf load/ 15 s). Data were submitted to ANOVA and Tukey's test (alpha=0.05). It was observed that the dual cure mode yielded higher hardness compared to the physical mode alone, except for direct light curing with the QTH unit and through Artglass. Higher hardness was observed with QTH compared to PAC, except for Artglass/dual groups, in which similar hardness means were obtained. Low KHN means were obtained with PAC for both Artglass and HeraCeram. It may be concluded that the hardness of resin cements may be influenced by the presence of an indirect restorative material and the type of light-curing unit.

Effect of LED Light-curing on the Relative Hardness of Tooth-colored Restorative Materials

The use of high intensity LED curing units will result in the polymerization of tooth-colored restoratives using shorter times.

Effects of light curing modes and resin composites on temperature rise under human dentin: an in vitro study

The influence of three curing modes of a high-powered LED curing unit on temperature rise under 2-mm-thick dentin was investigated during the polymerization of resin composite samples of Admira, Filtek P60, Premise, Tetric Flow, Tetric Ceram, and Filtek Z250. Ninety standard specimens were prepared. The bonding agents and resin composites were cured with standard, pulse, or soft-start mode (n=5 for each curing mode). Temperature rise was measured using a type L thermocouple. Data were analyzed by two-way ANOVA and Tukey's test. Soft-start curing led to statistically higher temperature rises compared than the other two modes. The highest temperature rise was observed for Admira and Tetric Flow cured with soft-start mode. The lowest temperature rise was observed for Premise cured with pulse mode. However, temperature rise did not reach the critical value that can cause pulpal damage by virtue of a prominent safety feature of the high-powered LED LCU, which ensures that no excessive heat is produced by all the three curing modes.

Microarray analysis of bisphenol A-induced changes in gene expression in human oral epithelial cells

Bisphenol A (BPA) is a common ingredient in dental materials. However, its potential adverse effects on the oral cavity are unknown. The purpose of this study is to identify the genes responding to BPA in a human oral epithelial cell line using DNA microarray. Of the 10,368 genes examined, changes in mRNA levels were detected in seven genes: five were up-regulated and two were down-regulated. The expression levels of the calcium channel, voltage-dependent, L-type, alpha 1C subunit (CACNA1C), cell death activator CIDE-3 (CIDE-3), haptoglobin-related protein (HPR), importin 4 (IPO4), and POU domain, class 2 and transcription factor 3 (POU2F3) were significantly up-regulated in the cells exposed to 100 mM BPA. The spermatogenesis-associated, serine-rich 2 (SPATS2) and HSPC049 protein (HSPC049) were significantly down-regulated. The detailed knowledge of the changes in gene expression obtained using microarray technology will provide a basis for further elucidating the molecular mechanisms of the toxic effects of BPA in the oral cavity.

Effect of Light-Curing Method and Cement Activation Mode on Resin Cement Knoop Hardness

PURPOSE

To evaluate the Knoop hardness (KHN) of the resin cement Enforce activated by chemical/physical mode or physical mode solely; light-cured directly or through a 1.5 mm thick ceramic disc (HeraCeram) on shade DD2.

MATERIALS AND METHODS

Light-curing was carried out using a conventional quartz tungsten halogen light (QTH) (XL2500) for 40 seconds at 700 mW/cm(2); light-emitting diodes (LED) (Ultrablue Is) for 40 seconds at 440 mW/cm(2); and Xenon plasma arc (PAC) (Apollo 95E) for 3 seconds at 1600 mW/cm(2). Bovine incisors had their buccal faces flattened and hybridized. A mold was seated on these surfaces and filled with cement. A disc of the acid-etched and silanized veneering material was seated over this set for light-curing. After dry storage (24 hours at 37 degrees C), specimens (n= 10) were sectioned for KHN measurements performed in a microhardness tester (50 gf load for 15 seconds). Data were submitted to ANOVA and Tukey's test (alpha= 0.05).

RESULTS

The highest KHN values were obtained with LED, for both dual-cured and light-cured cement. The lowest KHN value was obtained with light-cured PAC. Light-curing with QTH resulted in hardness values similar to PAC in dual-cured groups.

CONCLUSIONS

Light-curing through HeraCeram can influence resin cement hardness.

Effect of photoactivation protocol and radiant exposure on monomer conversion and flexural strength of a resin composite after water and ethanol storage

The use of soft-start photoactivation to reduce shrinkage stress has become widespread in restorative dentistry. However, an increased susceptibility to ethanol degradation of polymers formed by pulse-delay photoactivation was reported. It was hypothesized that reductions in flexural strength after ethanol storage were related not only to low curing rates, but also to the radiant exposure employed. A commercial composite was subjected to different curing protocols (continuous at high irradiance, continuous at low irradiance, and pulse-delay) and radiant exposures (6, 12, and 24 J/cm2). After 48 h, differences in degree of conversion were minimal and no differences in strength were detected among specimens stored in water. Ethanol storage caused significant strength reductions in pulse-delay and low irradiance specimens that received 6 J/cm2. The results suggest that when low irradiances or pulse-delay methods are used, a relatively high radiant exposure is necessary to originate a polymer network structure similar to that obtained by continuous high irradiance photoactivation.

Modulated photoactivation methods: Influence on contraction stress, degree of conversion and push-out bond strength of composite restoratives

OBJECTIVES

Verify the influence of curing methods on contraction stress, stress rate, and degree of conversion (DC) of a restorative composite and on bond strength of composite restoratives.

METHODS

For the stress test, composite (0.84 mm thick) was applied between two 5-mm diameter glass rods, mounted in a servohydraulic machine. Stress rate was taken by the value of stress/time at each second. DC was measured by micro-FTIR. Bond strength testing was performed using a push-out test. The C-factor in all tests was 3.0. Four curing methods were tested: continuous light (CL), soft-start (SS), and two pulse delay methods using different initial irradiances--150 mW/cm(2) (PD150) and 80 mW/cm(2) (PD80). Results were analyzed by ANOVA and Tukey's test (alpha=0.05).

RESULTS

Stress values ranged from 7.9 MPa (PD80) to 10.3 MPa (CL). No statistical difference was verified among CL, SS, and PD150. PD80 presented statistically lower stress values compared to CL and SS. CL presented the highest maximum stress rate, followed by SS, PD150 and PD80. Mean DC values ranged from 54.2% (PD150) to 55.9% (PD80), with no difference observed among the methods. For the bond strength test, values ranged from 26.4 MPa (CL) to 35.5 MPa (PD150). PD150 and PD80 were both statistically superior to SS and CL. SS presented statistically higher bond strength compared to CL.

CONCLUSIONS

Modulated curing methods were shown to be effective in reducing contraction stress rate and improving the strength of the bonded interface, and without compromising the DC of the restorative composite.

Influence of different light curing units on the cytotoxicity of various dental composites

OBJECTIVES

To evaluate the dependence of the toxicity of various dental composites on the use of high- and low-power light curing units (LCUs).

METHODS

The composites Filtek Z 250, Durafill VS, Solitaire 2 and Grandio were polymerized using different light densities from three LCUs, namely Heliolux II, Swiss Master Light (SML) and a prototype LED. The toxicity of polymerized samples was tested by exposing them to the cell culture medium up to 28 days. The extracts of the composites were collected daily and used for incubation in human gingival fibroblasts cultures.

RESULTS

Slow, low-intensity curing using the LED or the Heliolux II showed similar characteristics for all four composites, regarding the cell viability rate of human gingival fibroblasts. After 1 day of storage suboptimal results could be observed for the SML/Durafill and optimal results for SML/Grandio combination (approximately 100% cell viability). In addition, the composite Solitaire the SML yielded significantly better results than the other LCUs (cell viability, p < or = 0.001: SML 60.5%, Heliolux 44.5%, LED 44.2%). Furthermore, the combination of the SML with Z 250 composite showed, after the first day and up to day 28, statistically significantly higher cell viability rates than the combination with the LED or Heliolux II.

SIGNIFICANCE

This study shows that the combination of a high power LCU with some composites positively influences the HGF cell viability effected by the investigated composite extracts. Moreover, there is further indication that a reduction of composite toxicity is possible if the curing mode is adapted to the used composite.

Exposure to bisphenol A from bis-glycidyl dimethacrylate-based dental sealants

BACKGROUND

Bisphenol A (BPA) is a common component of composites and dental sealants. The potential exists for human exposure after sealant placement.

METHODS

The authors prospectively enrolled 15 men in an exposure assessment study; 14 completed the study. After placement of clinically appropriate amounts of one of two sealants, the authors measured BPA in saliva and urine samples collected at prescribed intervals after the sealants were placed. They used selective and sensitive isotope-dilution mass-spectrometry-based methods for BPA measurements, thus providing the most reliable results.

RESULTS

Helioseal F (Ivoclar Vivadent, Amherst, N.Y.) leached negligible amounts of BPA. Urinary and salivary BPA levels in subjects who received these sealants were similar to baseline levels. Delton Light Cure (LC) Opaque pit-and-fissure sealant (Dentsply/Ash, York, Pa.) leached more BPA, resulting in low-level BPA exposures similar to those used in laboratory animal testing. BPA exposure after Delton LC sealant placement was significantly higher than exposure after placement of Helioseal F. Patients treated with Delton LC had significantly higher doses of BPA (110 microg) than did those treated with Helioseal F (5.5 microg) (P < .0001).

CONCLUSIONS

Placement of clinically relevant amounts of Delton LC sealant resulted in low-level BPA exposure; however, exposure was negligible after placement of Helioseal F. Saliva collection after sealant placement likely reduced systemic absorption of BPA from dental sealants. Sealants should remain a useful part of routine preventive dental practice, especially those that leach negligible amounts of BPA.

CLINICAL IMPLICATIONS

Dental sealants may be a point source for low-level BPA exposure at levels that show health effects in rodents. Further research is required to determine whether human exposure to BPA at these levels causes adverse effects.

Influence of heat from light curing units and dental composite polymerization on cells in vitro

OBJECTIVES

The aim of the present study was to test the hypothesis that the use of a light curing unit (LCU) with high light power would result in a higher temperature and therefore a statistically significant lower number of living human gingiva fibroblasts within a pulp chamber model than the use of a light emitting diode (LED) LCU.

MATERIALS AND METHODS

The composites Admira, Grandio, Filtek Supreme and Filtek Z250 were polymerized with the LCUs Swiss Master Light, Optilux 501 and an LED LCU prototype in a mould on top of a pulp chamber model. The temperature was recorded within the pulp chamber with a thermocouple. The cytotoxicity of the polymerized samples was tested by using the MTT test.

RESULTS

In general there was no considerable difference in the temperature increase within the pulp chamber model for the different LCUs and composites. There was no statistically significant difference in the cell number (p=0.3767) when the different LCUs were used.

CONCLUSIONS

Using a high power halogen LCU for a short time or a standard halogen or LED LCU for a longer time did not result in a considerable difference in the temperature increase or the number of living cells within a pulp chamber model. This study indicates not only that the temperature may have an effect on the living cells, but also that cells may be negatively affected by the unpolymerized composite or light of the LCUs.

Time-based Elution of TEGDMA and BisGMA from Resin Composite Cured with LED, QTH and High-intensity QTH Lights

Under the conditions of this study, when compared to standard QTH, both standard LED and high-intensity QTH light curing resulted in lower levels of the elution of TEGDMA, which is suspected to be the prime cause of cytotoxic reactions in resin composite restorations.

Influence of photoactivation method on conversion, mechanical properties, degradation in ethanol and contraction stress of resin-based materials

OBJECTIVES

To investigate the influence of photoactivation method on degree of conversion (DC), flexural strength (FS), flexural modulus (FM) and Knoop hardness (KHN) of a composite and an unfilled resin (Filtek Z250 and Scotchbond multi-purpose plus, 3M ESPE) after storage in water or ethanol, and on composite contraction stress (CS).

METHODS

Specimens 1x2x10 mm were prepared for FS test, photoactivated by 600 mW/cm2 x 40 s (A), 200 mW/cm2 x 120 s (B), or 600 mW/cm2 x1 s +3 min delay +600 mW/cm2 x 39 s (C), and tested after 24 h in water or ethanol. Load and displacement values were used to calculate FM. Specimen fragments were used to measure KHN. DC was determined by FT-Raman spectroscopy. CS was determined by mechanical testing. Data were submitted to ANOVA/Tukey's test (alpha=0.05).

RESULTS

Composite DC was not affected by photoactivation (A: 65+/-1.8%; B: 66+/-3.4%; C: 65+/-2.9%). Unfilled resin DC was statistically higher using method A (79+/-0.3%) than B (74+/-1.0%) and C (73+/-0.9%). Photoactivation did not influence composite properties, regardless of the storage medium (p>0.05). After ethanol storage, FS of the unfilled resin was lower for specimens irradiated by method B (p<0.001). Pulse-delay curing (C) significantly reduced CS (7.7+/-1.3 MPa), compared to A (10.7+/-1.2 MPa) and B (10.1+/-1.3 MPa).

SIGNIFICANCE

Photoactivation method did not affect composite properties or susceptibility to ethanol degradation. For the unfilled resin, DC was lower with the use of low intensity and pulse-curing, while FS after ethanol storage was reduced by low intensity curing. Pulse-delay curing significantly reduced CS.

Effect of high-powered LED polymerization on the shear bond strength of a light-polymerized resin luting agent to ceramic and dentin

STATEMENT OF PROBLEM

A newly introduced high-powered light-emitting diode (LED) light-polymerization unit with various polymerization modes is purported to polymerize dental resins more quickly than standard units. However, there is insufficient information about the effects of this type of light source and its polymerization modes on resin luting agents (RLAs).

PURPOSE

This in vitro study evaluated the effects of different modes of a high-powered LED polymerization unit on the shear bond strength of a light-polymerized RLA to ceramic and dentin.

MATERIAL AND METHODS

Sixty ceramic cylinders (3 x 3 mm) were fabricated from a heat-pressed ceramic (IPS Empress 2). Specimen surfaces were abraded using 600-grit silicon carbide paper and airborne-particle abraded with 50-mum desiccant alumina particles, cleaned ultrasonically, etched using hydrofluoric acid, and treated with a silane coupling agent (Ceramic primer). Sixty noncarious, freshly extracted, permanent human molar teeth were embedded in autopolymerizing acrylic resin, and their dentin surfaces were wet-ground using a grinding and polishing machine fitted with 180-grit abrasive disks. The ground dentin surfaces were then etched with 37% phosphoric acid gel, and an adhesive agent (Single Bond) was applied. Ceramic specimens (n = 15) were bonded to dentin surfaces with a dual-initiated RLA (Rely-X ARC) and individually polymerized by 1 of 4 different modes, as follows: Halogen standard mode (Control) (600 mW/cm2 for 40 seconds); high-powered LED fast mode (1100 mW/cm2 for 10 seconds); high-powered LED pulse mode (1100 mW/cm2 for 10 seconds); and high-powered LED exponential mode (1100 mW/cm2 for 20 seconds). Cemented specimens were subjected to shear loading until fracture using a universal testing machine. A stereomicroscope (x25) was used to identify the mode of fracture. Bond strength (MPa) data were analyzed using 1-way analysis of variance and the Tukey HSD test (alpha = .05).

RESULTS

Specimens polymerized using halogen standard mode (23.9 +/- 1.3 MPa) and LED exponential mode (23.0 +/- 1.1 MPa) had significantly higher ( P < .001) mean shear bond strengths compared with both LED fast (15.1 +/- 1.3 MPa) and pulse (14.6 +/- 1.3 MPa) modes. The Tukey HSD tests showed no significant differences in shear bond strength between specimens polymerized using high-powered LED exponential mode and halogen standard mode. Most failures were adhesive failures at the dentin-RLA interface or the RLA-ceramic interface in specimens polymerized using high-powered LED fast or pulse modes.

CONCLUSION

Within the limitations of this study, the shear bond strength of an RLA to ceramic and dentin was found to be similar when polymerized using halogen light in standard mode and high-powered LED light in exponential mode, whereas shear bond strength was significantly lower when polymerized using LED in fast or pulse mode.