Biodegradable Polymersomes with Structure Inherent Fluorescence and Targeting Capacity for Enhanced Photo-Dynamic Therapy.

Biodegradable nanostructures displaying aggregation-induced emission (AIE) are desirable from a biomedical point of view, due to the advantageous features of loading capacity, emission brightness, and fluorescence stability. Herein, biodegradable polymers comprising poly (ethylene glycol)-block-poly(caprolactone-gradient-trimethylene carbonate) (PEG-P(CLgTMC)), with tetraphenylethylene pyridinium-TMC (PAIE) side chains have been developed, which self-assembled into well-defined polymersomes. The resultant AIEgenic polymersomes are intrinsically fluorescent delivery vehicles. The presence of the pyridinium moiety endows the polymersomes with mitochondrial targeting ability, which improves the efficiency of co-encapsulated photosensitizers and improves therapeutic index against cancer cells both in vitro and in vivo. This contribution showcases the ability to engineer AIEgenic polymersomes with structure inherent fluorescence and targeting capacity for enhanced photodynamic therapy.

Molecular environment and reactivity in gels and colloidal solutions under identical conditions.

A PEG-Tyr block copolymer forms a kinetically stable colloidal solution in water at room temperature which undergoes an irreversible conversion to a gel phase upon heating. A micellar solution and a gel can therefore be studied under identical experimental conditions. This made it possible to compare physical properties and chemical reactivity of micelles and gels in identical chemical environments and under identical conditions. EPR spectra of the spin-labelled copolymer showed that tyrosine mobility in gels was slightly reduced compared to micelles. Chemical reactivity was studied using photochemical degradation of tyrosine and tyrosine dimerization, in the absence and in the presence of an Fe(iii) salt. The reactivity trends were explained by reduced tyrosine mobility in the gel environment. The largest reactivity difference in gels and micelles was observed for bimolecular dityrosine formation which was also attributed to the reduction in molecular mobility.

IR-780-loaded polymeric micelles enhance the efficacy of photothermal therapy in treating breast cancer lymphatic metastasis in mice.

Cancer metastasis is responsible for over 90% of breast cancer-related deaths, and inhibiting lymph node metastasis is an option to treat metastatic disease. Herein, we report the use of IR-780-loaded polymeric micelles (IPMs) for effective photothermal therapy (PTT) of breast cancer lymphatic metastasis. The IPMs were nanometer-sized micelles with a mean diameter of 25.6 nm and had good stability in simulated physiological solutions. Under 808-nm laser irradiation, IPMs exhibited high heat-generating capability in both in vitro and in vivo experiments. After intravenous injection, IPMs specifically accumulated in the tumor and metastatic lymph nodes and penetrated into these tissues. Moreover, a single IPMs treatment plus laser irradiation significantly inhibited primary tumor growth and suppressed lymphatic metastasis by 88.2%. Therefore, IPMs are an encouraging platform for PTT applications in treatment of metastatic breast cancer.

Longevity of bond strength of resin cements to root dentine after radiation therapy.

AIM: To evaluate the bond strength and adhesive interface between several resin cements and root dentine immediately and 6 months after radiotherapy. METHODOLOGY: Sixty maxillary canines were selected and randomly assigned to two groups (n = 30): one group was not irradiated and the other one was subjected to a cumulative radiation dose of 60 Gy. The teeth were sectioned to obtain roots 16 mm long and the canals were prepared with the Reciproc system (R50) and filled using a lateral condensation technique with an epoxy resin sealer. Each group was divided into three subgroups (n = 10) according to the resin cement used for fibreglass fibre post cementation: RelyX-U200, Panavia-F2.0 and RelyX ARC. The posts were cemented in accordance with the manufacturer's recommendations. Three 1-mm-thick dentine slices were then obtained from each root third. The first two slices in the crown-apex direction of each third were selected for the push-out test. The failure mode after debonding was determined with a stereo microscope. The third slice from each root third was selected for scanning electron microscopy (SEM) analyses to examine the resin cement-dentine interface with 100, 1000, 2000 and 4000× magnification. Bond strength data were analysed by anova and Tukey's test (α = 0.05). RESULTS: Significantly lower bond strength (P < 0.0001) was obtained after irradiation compared to nonirradiated teeth. RelyX-U200 cemented fibre posts had the higher bond strength (15.17 ± 5.89) compared with RelyX ARC (P < 0.001) and Panavia-F2.0 (P < 0.001). The evaluation after 6 months revealed lower bond strength values compared to the immediate values (P < 0.001) for irradiated and nonirradiated teeth. Cohesive failures occurred in the irradiated dentine. SEM revealed fractures, microfractures and fewer collagen fibres in irradiated root dentine. RelyX-U200 and Panavia-F2.0 were associated with a juxtaposed interface of the cement with the radicular dentine in irradiated and nonirradiated teeth, and for RelyX ARC, hybrid layer formation and tags were observed in both irradiated and nonirradiated teeth. CONCLUSION: Radiation was associated with a decrease in the push-out bond strength and with lower resin cement/root dentine interface adaptation. Self-adhesive resin cement was a better alternative for fibre post cementation in teeth subjected to radiation therapy. The bond strength decreased after 6 months.

Experimental and simulation studies of unusual current blockade induced by translocation of small oxidized PEG through a single nanopore.

Detection of a single macromolecule based on the use of artificial nanopores is an attractive and promising field of research. In this work, we report a device based on a 5 nm single nanopore with a high length/diameter ratio, tailored by the track etching and atomic layer deposition techniques. The translocation of neutral polyethylene glycol (PEG) and charged polyethylene glycol-carboxylate (PEG-carboxylate) molecules of low molar masses (200 and 600 g mol(-1)) through this nanodevice was studied. It was shown that charged PEG-carboxylate molecules, which permeate through the pore, promote an unusual blockade of ionic current whereas the neutral PEG molecules do not show such behaviour. The molecular dynamics simulation shows that both neutral and charged PEGs permeate through the nanopore close to its inner surface. The main difference between the two macromolecules is the existence of a structured shell of cations around the charged PEG, which is likely to cause the observed unusual current blockade.

Residual HEMA and TEGDMA release and cytotoxicity evaluation of resin-modified glass ionomer cement and compomers cured with different light sources.

The purpose of this study was first to evaluate the elution of 2-hydroxyethyl methacrylate (HEMA) and triethylene glycol dimethacrylate (TEGDMA) monomers from resin-modified glass ionomer cement (RMGIC) and compomers cured with halogen and light-emitting diode (LED) light-curing units (LCUs). The effect of cured materials on the viability of L929 fibroblast cells was also evaluated. One RMGIC (Ketac N100) and two compomers (Dyract Extra and Twinkystar) were tested. Materials were prepared in teflon disks and light-cured with LED or halogen LCUs. The residual monomers of resin materials in solution were identified using high-performance liquid chromatography. The fibroblast cells' viability was analyzed using MTT assay. The type of LCU did not have a significant effect on the elution of HEMA and TEGDMA. A greater amount of HEMA than TEGMDA was eluted. The amount of TEGDMA eluted from Twinkystar was greater than Dyract Extra (P < 0.05) when cured with a halogen LCU. All material-LCU combinations decreased the fibroblast cells' viability more than the control group (P < 0.01), except for Dyract Extra cured with a halogen LCU (P > 0.05). Curing with the LED LCU decreased the cells' viability more than curing with the halogen LCU for compomers. For Ketac N100, the halogen LCU decreased the cells' viability more than the LED LCU.

Effect of gamma irradiation on structural and biological properties of a PLGA-PEG-hydroxyapatite composite.

Gamma irradiation is able to affect various structural and biological properties of biomaterials In this study, a composite of Hap/PLGA-PEG and their ingredients were submitted to gamma irradiation doses of 25 and 50 KGy. Various properties such as molecular weight (GPC), thermal behavior (DSC), wettability (contact angle), cell viability (MTT assay), and alkaline phosphatase activity were studied for the composites and each of their ingredients. The results showed a decrease in molecular weight of copolymer with no change in the glass transition and melting temperatures after gamma irradiation. In general gamma irradiation can increase the activation energy ΔH of the composites and their ingredients. While gamma irradiation had no effect on the wettability of copolymer samples, there was a significant decrease in contact angle of hydroxyapatite and composites with increase in gamma irradiation dose. This study showed an increase in biocompatibility of hydroxyapatite with gamma irradiation with no significant effect on cell viability in copolymer and composite samples. In spite of the fact that no change occurred in alkaline phosphatase activity of composite samples, results indicated a decrease in alkaline phosphatase activity in irradiated hydroxyapatites. These effects on the properties of PLGA-PEG-hydroxyapatite can enhance the composite application as a biomaterial.

The effect of time between handling and photoactivation on self-adhesive resin cement properties.

PURPOSE: To evaluate the degree of conversion, absorption, and solubility in water of self-adhesive resin cements subjected to different time intervals between material preparation and the photoactivation procedure. MATERIALS AND METHODS: Two dual self-adhesive resin cements were tested: RelyX Unicem and SmartCem2. The degree of conversion as a function of time was evaluated by Fourier-transformed infrared spectroscopy using the attenuated total reflectance technique. Three time intervals between handling and photoactivation were applied: Group 1 = immediately; Group 2 = a 1-minute interval; Group 3 = a 4-minute interval. All specimens were irradiated with a light-emitting diode source for 40 seconds. Thirty discs of each cement (1 mm thick × 6 mm diameter, n = 10) were prepared for the absorption and solubility tests. These specimens were stored in distilled water at 37°C for 90 days. The results were subjected to ANOVA with two factors (material and activation time intervals) and Tukey's test (95% significance). RESULTS: The 4-minute interval significantly reduced the degree of conversion of SmartCem2 (30.6% ± 8.3%). No other significant changes were observed for the degree of conversion; however, the time intervals before photoactivation interfered significantly in the water absorption of the RelyX Unicem specimens but not the SmartCem2 specimens. The time intervals did not affect the solubility of either cement. In all cases, SmartCem2 had higher solubility than RelyX Unicem. CONCLUSION: The time interval between handling and photoactivation significantly influenced the degree of conversion and water sorption of the resin-based cements. In general, one can say that the self-adhesive resin cements should be photoactivated as soon as possible after the material handling process.

Effect of artificial aging on the bond durability of fissure sealants.

PURPOSE: To evaluate the effect of artificial aging on the bond durability of fissure sealants in vitro. MATERIALS AND METHODS: Twenty bovine incisors received 4 different sealant treatments and were divided into four groups: 1. Ultraseal XT plus (UX); 2. Enamel Loc (EL); 3. 35% phosphoric acid plus Enamel Loc (PEL); 4. Adper Prompt L-Pop plus Clinpro (PPC). Beam-shaped specimens were prepared and randomly divided into three subgroups. One subgroup underwent the microtensile bond strength (µTBS) test after 24-h storage in 37°C water. The other two subgroups were also subjected to the microtensile bond strength test after 5000 and 10,000 thermal cycles, respectively. Another twelve intact human third molars were sealed using 1 of 3 methods and were divided into 3 groups of 4 each: 1. Ultraseal XT plus; 2. Adper Prompt L-Pop plus Clinpro; and 3. Enamel Loc. Two specimens from each group were immersed in a 50% silver nitrate solution for 24 h, followed by exposure to fluorescent light for 8 h, before being scanned in a micro-CT (microcomputer tomography) machine. The other two were handled in the same way after undergoing 10,000 thermal cycles. The CT images obtained were evaluated. RESULTS: All samples from the EL group were broken during preparation, so no µTBS results were available. After 5000 thermal cycles, the bond strengths of the three other groups (UX, PEL, PPC) decreased significantly (p < 0.05). Longer thermocycling (10,000 cycles) resulted in more decreases in µTBS for group PEL and PPC, while the strength of the UX group remained relatively unchanged. After thermocycling, considerable silver penetration could be seen at the sealant/enamel interface of the EL group in micro-CT images. CONCLUSIONS: The etch-and-rinse procedure for sealant application promotes higher bond strength under artificial aging. Micro-CT, a nondestructive analytical tool, may be used to evaluate the sealant/enamel interface effectively.

Effect of curing mode on the micro-mechanical properties of dual-cured self-adhesive resin cements.

Light supplying to luting resin cements is impeded in several clinical situations, causing us to question whether materials can properly be cured to achieve adequately (or adequate) mechanical properties. The aim of this study was therefore to analyse the effect of light on the micro-mechanical properties of eight popular dual-cured self-adhesive resin cements by comparing them with two conventional, also dual-cured, resin cements. Four different curing procedures were applied: auto-polymerisation (dark curing) and light curing (LED unit, Freelight 2, 20 s) by applying the unit directly on the samples' surface, at a distance of 5 and 10 mm. Twenty minutes after curing, the samples were stored for 1 week at 37°C in a water-saturated atmosphere. The micro-mechanical properties-Vickers hardness, modulus of elasticity, creep and elastic/plastic deformation-were measured. Data were analysed with multivariate ANOVA followed by Tukey's test and partial eta-squared statistics (p < 0.05). A very strong influence of the material as well as filler volume and weight on the micro-mechanical properties was measured, whereas the influence of the curing procedure and type of cement-conventional or self-adhesive-was generally low. The influence of light on the polymerisation process was material dependent, with four different behaviour patterns to be distinguished. As a material category, significantly higher micro-mechanical properties were measured for the conventional compared to the self-adhesive resin cements, although this difference was low. Within the self-adhesive resin cements group, the variation in micro-mechanical properties was high. The selection of suitable resin cements should be done by considering, besides its adhesive properties, its micro-mechanical properties and curing behaviour also.

Effect of light activation on resin-modified glass ionomer shear bond strength.

OBJECTIVE: Recent studies confirmed that resin-modified glass ionomers (RMGIs) set on the basis of two competing mechanisms, an acid-base reaction and a light-activated resin polymerization. This study evaluated the effect of the setting mechanism on bond strength by measuring the shear bond strength of three RMGIs to dentin with and without light activation. METHODS: Sixty human molars were ground to midcoronal dentin and randomly divided into six even groups: 1) Ketac Nano (KN), 2) KN without light cure (woLC), 3) Fuji Filling LC (FF), 4) FF woLC, 5) Fuji II LC (FII), and 6) FII woLC. The dentin surfaces of the specimens were conditioned/primed according to the manufacturers' instructions. A 1.54-mm diameter plastic tube was filled with RMGI material and affixed to the dentin surface. Groups 1, 3, and 5 were light cured for 20 seconds, and groups 2, 4, and 6 were immediately placed in a damp dark box with no light curing at 37°C for 24 hours. Shear bond strength testing was performed in an Instron device at 1 mm/min. Data were analyzed with a one-way analysis of variance (ANOVA) and Tukey/Kramer test (α=0.05). RESULTS: Mean ± standard deviation shear bond strength values (MPa) are: 7.1 ± 4.2 (KN), 11.7 ± 3.9 (FF), 10.2 ± 3.2 (FF woLC), 12.5 ± 5.1 (FII), and 0.3 ± 0.4 (FII woLC). Two KN, all KN woLC, and seven FII woLC specimens debonded before testing. Tukey/Kramer analysis revealed no significant differences in bond strength between the three light-cured RMGIs. KN and FII showed significantly lower bond strength without light cure, but no significant difference was observed between FF and FF woLC. CONCLUSIONS: The results of this study strongly suggest that light activation is necessary to obtain optimal bond strength between RMGI and dentin. FF may contain components that chemically activate resin polymerization. Clinically, KN and FII need to be light cured after placement of these RMGIs.

Influence of shade and light-curing distance on the degree of conversion and flexural strength of a dual-cure core build-up resin composite.

PURPOSE: To investigate the influence of shade and light-curing distance on the degree of conversion (DC) and flexural strength (FS) of a dual-cure core build-up resin composite. METHODS: 135 specimens were prepared and divided into three main groups according to the shade of the composite core material; dentin, blue and white shades. Each group was further subdivided into three subgroups according to the light-curing distance; 0 mm, 3 mm and 5 mm. The DC was measured using FTIR spectrometer. For testing the FS, the mini flexural test specimens were prepared and subjected to three point bending test in a universal testing machine. The results were analyzed using two-way and one-way ANOVA followed by Duncan's Multiple Range Test. The significance level was set at P = 0.05. RESULTS: Both the DC and FS of the dual-cure core build-up material used in this study were influenced by the shade of the material and the light-curing distance. The blue shade exhibited the highest percentage DC values while the white shade revealed the lowest percentage DC. The dentin shade at 0 mm light-curing distance exhibited the highest mean FS value; however the 3 mm and 5 mm light-curing distance of the white shade showed the lowest mean FS values.

Single-injection HPLC method for rapid analysis of a combination drug delivery system.

Developing combination drug delivery systems (CDDS) is a challenging but necessary task to meet the needs of complex therapy regimes for patients. As the number of multi-drug regimens being administered increases, so does the difficulty of characterizing the CDDS as a whole. We present a single-step method for quantifying three model therapeutics released from a model hydrogel scaffold using high-performance liquid chromatography (HPLC). Poly(ethylene glycol) dimethacrylate (PEGDMA) hydrogel tablets were fabricated via photoinitiated crosslinking and subsequently loaded with model active pharmaceutical ingredients (APIs), namely, porcine insulin (PI), fluorescein isothiocyanate-labeled bovine serum albumin (FBSA), prednisone (PSE), or a combination of all three. The hydrogel tablets were placed into release chambers and sampled over 21 days, and APIs were quantified using the method described herein. Six compounds were isolated and quantified in total. Release kinetics based on chemical properties of the APIs did not give systematic relationships; however, PSE was found to have improved device loading versus PI and FBSA. Rapid analysis of three model APIs released from a PEGDMA CDDS was achieved with a direct, single-injection HPLC method. Development of CDDS platforms is posited to benefit from such analytical approaches, potentially affording innovative solutions to complex disease states.

Effect of immediate or delayed light activation on curing kinetics and shrinkage stress of dual-cure resin cements.

OBJECTIVES: This study evaluated the effect of light activation (absence, immediate, or delayed) on conversion kinetics and polymerization stress of three commercial dual-cured resin cements (Enforce, RelyX ARC, and Panavia F). METHODS: Degree of conversion (DC) was monitored for 30 minutes using real-time near­Fourier transform infrared spectroscopy. The cement was mixed, placed on the spectrometer sample holder, and light activated either immediately or after five minutes (delayed light activation). When no light activation was performed, the materials were protected from light exposure (control). DC was evaluated at five and 30 minutes postmixture. Maximum rates of polymerization (Rp(max)) were obtained from the first derivative of the DC vs time curve. Polymerization stress was monitored for 30 minutes in 1-mm-thick specimens inserted between two cylinders attached to a universal testing machine. Data were submitted to analysis of variance/Tukey tests (α=0.05). RESULTS: Immediate light activation promoted the highest DC at five minutes. At 30 minutes, only RelyX ARC did not present a significant difference in DC between activation modes. Enforce and Panavia F presented higher Rp(max) for immediate and delayed light-activation, respectively. RelyX ARC showed similar Rp(max) for all activation modes. The absence of light activation resulted in the lowest stress followed by delayed light activation, while immediate light activation led to the highest values. RelyX ARC showed higher stress than Enforce, while the stress of Panavia F was similar to that of the others. CONCLUSION: Delayed light activation reduced the polymerization stress of the resin cements tested without jeopardizing DC.

Evaluation of the light energy transmission and bottom/top rate in silorane and methacrylate-based composites with different photoactivation protocols.

AIM: This study investigated the influence of different composite resin organic matrix (methacrylate - Filtek Z350 XT and silorane - Filtek P90) on light energy transmission through the composite and bottom/top rate. MATERIALS AND METHODS: A light-emitting diode (New Blue Phase), light-curing unit was used with different photoactivation protocols (high-continuous mode - HCM, 1400 mW/cm2 for 20 seconds; low-continuous mode - LCM , 700 mW/cm2 for 40 seconds; and soft-start mode - SSM, 140 mW/cm2 for 5s followed by 39 seconds for 700 mW/cm2). Twenty specimens were prepared for each composite. The light energy transmission through the composite was calculated (n=10). The bottom/top rate of the same specimen was calculated (n=10). The data were compared by Tukey's test in different tests (light energy transmission through the composite and bottom/top rate). RESULTS: The light energy transmission through the Filtek Z350 XT composite (HCM - 576 mW/cm2, LCM - 238 mW/cm2, SSM - 232 mW/cm2) did not show statistical difference when compared with Filtek P90 composite (HCM - 572 mW/cm2, LCM - 233 mW/cm2, SSM - 230 mW/cm2). The bottom/top rate of the Filtek Z350 XT composite (HCM - 88.98%, LCM - 90.94%, SSM - 89.92%) was statistically higher than that of the Filtek P90 composite (HCM-77.29%, LCM-77.51%, SSM- 77.79%). CONCLUSION: Light energy transmission through the composite was not influenced by the use of different dental composite restoratives. However, the bottom/top rate of the composites was influenced by the use of different dental composite restoratives. CLINICAL SIGNIFICANCE: Insufficiently polymerized composite resin may present a large number of problems. For this reason, dental composite resins should have the similar deep surface polymerization as the top surface in dental restorations.

Microwave-assisted synthesis and characterization of optically active poly (ester-imide)s incorporating L-alanine.

Pyromellitic dianhydride (1) was reacted with L-alanine (2) to result [N,N'-(pyromellitoyl)-bis-L-alanine diacid] (3). This compound (3) was converted to N,N'-(pyromellitoyl)-bis-L-alanine diacyl chloride (4) by reaction with thionyl chloride. The microwave-assisted polycondensation of this diacyl chloride (4) with polyethyleneglycol-diol (PEG-200) and/or three synthetic aromatic diols furnish a series of new PEIs and Co-PEIs in a laboratory microwave oven (Milestone). The resulting polymers and copolymers have inherent viscosities in the range of 0.31-0.53 dl g(-1). These polymers are optically active, thermally stable and soluble in polar aprotic solvents such as DMF, DMSO, NMP, DMAc, and sulfuric acid. All of the above polymers were fully characterized by IR spectroscopy, (1)H NMR spectroscopy, elemental analyses, specific rotation and thermal analyses. Some structural characterizations and physical properties of these optically active PEIs and Co-PEIs have been reported.

Protein patterning by UV-induced photodegradation of poly(oligo(ethylene glycol) methacrylate) brushes.

The UV photodegradation of protein-resistant poly(oligo(ethylene glycol) methacrylate) (POEGMA) bottle-brush films, grown on silicon oxide by surface-initiated atom radical transfer polymerization, was studied using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Exposure to light with a wavelength of 244 nm caused a loss of polyether units from the brush structure and the creation of aldehyde groups that could be derivatized with amines. An increase was measured in the coefficient of friction of the photodegraded polymer brush compared to the native brush, attributed to the creation of a heterogeneous surface film, leading to increased energy dissipation through film deformation and the creation of new polar functional groups at the surface. Exposure of the films through a photomask yielded sharp, well-defined patterns. Analysis of topographical images showed that physical removal of material occurred during exposure, at a rate of 1.35 nm J(-1) cm(2). Using fluorescence microscopy, the adsorption of labeled proteins onto the exposed surfaces was studied. It was found that protein strongly adsorbed to exposed areas, while the masked regions retained their protein resistance. Exposure of the film to UV light from a scanning near-field optical microscope yielded submicrometer-scale patterns. These data indicate that a simple, rapid, one-step photoconversion of the poly(OEGMA) brush occurs that transforms it from a highly protein-resistant material to one that adsorbs protein and can covalently bind amine-containing molecules and that this photoconversion can be spatially addressed with high spatial resolution.

Activation mode effects on the shear bond strength of dual-cured resin cements.

OBJECTIVES: This study evaluated the immediate (10-minute) and delayed (24-hour) bond strength of dual-cured resin cements that are light-activated either immediately or delayed (after five minutes) or chemically-activated only. MATERIALS AND METHODS: Three dual-cured resin cements were evaluated: RelyX ARC, Panavia F and Enforce. Cylinders of resin cement were built up over resin composite blocks following the manufacturers' instructions for each luting agent. The cements were mixed, inserted into the molds and light-activated either immediately or after five minutes (delayed light activation). When no light activation was performed, the materials were protected from light exposure until testing. Half of the samples were tested at 10 minutes; the remaining samples were stored at 100% relative humidity for 24 hours when they were then tested (n = 10). Data were submitted to three-way ANOVA and post-hoc Tukey's tests (alpha = 0.05). The failure mode was evaluated under SEM. RESULTS: RelyX ARC presented the highest values of shear bond strength, followed by Enforce. Panavia F showed the lowest values. Both immediate and delayed light activation caused the cements to present the highest means of shear bond strength. There was an improvement in bond strength after 24 hours of storage. CONCLUSIONS: RelyX ARC produced the highest bond strength, which was improved by light activation and storage for 24 hours.

Effect of light energy density on conversion degree and hardness of dual-cured resin cement.

This study evaluated the effect of different light energy densities on conversion degree (CD) and Knoop hardness number (KHN) of RelyX ARC (RLX) resin cement. After manipulation according to the manufacturer's instructions, RLX was inserted into a rubber mold (0.8 mm x 5 mm) and covered with a Mylar strip. The tip of the light-curing unit (LCU) was positioned in contact with the Mylar surface. Quartz-tungsten-halogen (QTH) and light-emitting diode (LED) LCUs with light densities of 10, 20 and 30 J/cm2 were used to light-cure the specimens. After light curing, the specimens were stored dry in lightproof containers at 37 degrees C. After 24 hours, the CD was analyzed by FT-Raman and, after an additional 24-hours, samples were submitted to Knoop hardness testing. The data of the CD (%) and KHN were submitted to two-way ANOVA and the Tukey's test (alpha = 0.05). QTH and LED were effective light curing units. For QTH, there were no differences among the light energy densities for CD or KHN. For LED, there was a significant reduction in CD with the light energy density set at 10 J/cm2. KHN was not influenced by the light-curing unit and by its light energy density.

Efficiency of light-emitting diode and halogen units in reducing residual monomers.

INTRODUCTION: In this in-vitro study, we aimed to compare the residual monomers in composites beneath brackets bonded to enamel, using a light-emitting diode (LED) or a halogen unit, and to compare the residual monomers in the central to the peripheral areas of the composite. METHODS: Twenty bovine teeth preserved in 0.1% thymol were used in this study. Ten teeth were used to standardize the thickness of the composite film, since different thicknesses would cause different absorbance of light. Brackets were bonded to 10 bovine incisors, with the halogen light (n = 5) and the LED (n = 5). The brackets were debonded, and the remaining composite on the enamel surface was sectioned in 2 regions: peripheral (0.8 mm) and central, resulting in 2 subgroups per group: central halogen (n = 5), peripheral halogen (n = 5), central LED (n = 5), and peripheral LED (n = 5). The spectrometric analysis in the infrared region was used to measure the free monomers with the attenuated total reflectance method. RESULTS: Normal distribution was tested by using the Kolmogorov-Smirnov test. Data were compared by 2-way analysis of variance (ANOVA) at P <0.05. The LED group showed fewer residual monomers than did the halogen group (P = 0.014). No differences were found among the regions (P = 0.354), and there were no interactions between light type and region (P = 0.368). CONCLUSIONS: LED leaves less residual monomer than does the halogen light, even with half of the irradiation time; there were no differences between the central and peripheral regions, and no interaction between light type and region.