Dual Crosslinked Methacrylated Alginate Hydrogel Micron Fibers and Tissue Constructs for Cell Biology.

As an important natural polysaccharide biomaterial from marine organisms, alginate and its derivatives have shown great potential in the fabrication of biomedical materials such as tissue engineering, cell biology, drug delivery, and pharmaceuticals due to their excellent biological activity and controllable physicochemical properties. Ionic crosslinking is the most common method used in the preparation of alginate-based biomaterials, but ionic crosslinked alginate hydrogels are prone to decompose in physiological solution, which hinders their applications in biomedical fields. In this study, dual crosslinked alginate hydrogel microfibers were prepared for the first time. The ionic crosslinked methacrylated alginate (Alg-MA) hydrogel microfibers fabricated by Microfluidic Fabrication (MFF) system were exposed to ultraviolet (UV) light and covalent crosslink between methacrylate groups avoided the fracture of dual crosslinked macromolecular chains in organizational environment. The chemical structures, swelling ratio, mechanical performance, and stability were investigated. Cell-encapsulated dual crosslinked Alg-MA hydrogel microfibers were fabricated to explore the application in tissue engineering for the first time. The hydrogel microfibers provided an excellent 3D distribution and growth conditions for cells. Cell-encapsulated Alg-MA microfibers scaffolds with functional 3D tissue structures were developed which possessed great potential in the production of next-generation scaffolds for tissue engineering and regenerative medicine.

Hollow Capsules with Multiresponsive Valves for Controlled Enzymatic Reactions.

The current challenge for polymeric nanoreactors is to precisely control the membrane permeability between permeable, impermeable, and semipermeable at defined pH. Additionally, the synthetic methods are obstructed by tedious purification processes, especially when polymer multiblocks are required in the membrane of capsules to achieve different responsiveness and functions. Here, we report a rapid one-pot synthesis of ABA-type triblock copolymer brushes on silica template via surface-initiated single electron transfer living radical polymerization (SI-SET-LRP). It is worth noting that there is no purification between the successive block formation steps, since each step is taken to full translation within 20 min. After removing the template, hollow capsules with cross-linked membrane are obtained and have been used as multiresponsive nanoreactors for enzymatic reactions. Their membrane permeability is triggered primarily by temperature and secondarily by pH to allow controlled enzymatic reactions to be reversibly addressable between "permeable", "semipermeable", and "impermeable" valve-like membrane status. These valve-like features highlight the significant potential of hollow capsules, for example, in the fields of synthetic biology and enzyme-deficient disease therapeutic applications.

Photochemically Induced ATRP of (Meth)Acrylates in the Presence of Air: The Effect of Light Intensity, Ligand, and Oxygen Concentration.

Well-defined poly(methyl methacrylate) (PMMA) and poly(methyl acrylate) (PMA) are prepared via photochemically induced atom transfer radical polymerization (photoATRP) using ppm amounts of CuBr2 /tris(2-pyridylmethyl)amine and CuBr2 /tris[2-(dimethylamino)ethyl]amine catalyst complexes, respectively, without degassing of polymerization mixture and with no need to introduce an external reducing agent to the system. The effect of ligand to CuBr2 ratio on kinetic and induction period during the polymerization of MMA and MA is investigated. The induction period is influenced also by the amount of oxygen in the polymerization system. Both the kinetics of MA polymerization and the induction period are affected by light intensity. Finally, the high livingness and initiation efficiency of the photoATRP system in the presence of air are proved by chain extension polymerizations. The presented system is valuable from an industrial point of view, since after optimization, well-defined and high-molar-mass poly(meth)acrylates can be prepared without the necessity of degassing the system, while the polymerization can be proceeded quickly and without an induction period.

Radiopacity of Methacrylate and Silorane Composite Resins Using a Digital Radiographic System.

The aim of this study was to evaluate the radiopacity of silorane and methacrylate resin composites, comparing them to the enamel, dentin, and aluminum penetrometer using a digital image. From six resin composites (Filtek™ P90, Filtek Z350, Filtek Z350 XT flow, Tetric Ceram, TPH Spectrum, and SureFil SDR flow) cylindrical disks (5 × 1 mm) were made and radiographed by a digital method, together with a 15-step aluminum step-wedge and a 1 mm slice of human tooth. The degree of radiopacity of each image was quantified using digital image processing. The mean values of the shades of gray of the tested materials were measured and the equivalent width of aluminum was calculated for each resin. The results of our work yielded the following radiopacity values, given here in descending order: Tetric Ceram > TPH > SDR > Z350 > Z350 flow > P90 > enamel > dentin. The radiopacity of the materials was different both for the enamel and for the dentin, except for resin P90, which was no different than enamel. In conclusion, silorane-based resin exhibited a radiopacity higher than dentin and closest to the enamel; a large portion of the methacrylate-based flow and conventional resins demonstrated greater radiopacity in comparison to dentin and enamel.

Degradation of Kresoxim-Methyl in Water: Impact of Varying pH, Temperature, Light and Atmospheric CO2 Level.

In the present investigation, persistence of kresoxim-methyl (a broad spectrum strobilurin fungicide) was studied in water. Results revealed that kresoxim-methyl readily form acid metabolite. Therefore, residues of kresoxim-methyl were quantified on the basis of parent molecule alone and sum total of kresoxim-methyl and its acid metabolite. In water, influence of various abiotic factors like pH, temperature, light and atmospheric carbon dioxide level on dissipation of kresoxim-methyl was studied. The half life value for kresoxim-methyl and total residue varied from 1 to 26.1 and 6.1 to 94.0 days under different conditions. Statistical analysis revealed the significant effect of abiotic factors on the dissipation of kresoxim-methyl from water.

Effects of prolonged light exposure times on water sorption, solubility and cross-linking density of simplified etch-and-rinse adhesives.

PURPOSE: This study evaluated the effects of light exposure times on water sorption, solubility, and polymer cross-linking density of simplified etch-and-rinse adhesives. MATERIALS AND METHODS: Four commercial adhesives (XP Bond, Adper Single Bond 2, Tetric N-Bond, and Ambar) were selected, and resin disks 5 mm in diameter and 1.0 mm thick were prepared and light cured for 20, 40, or 80 s using an LED light-curing unit at 1200 mW/cm2. Water sorption and solubility were evaluated over a 28-day period. For polymer cross-linking density, additional specimens were prepared and their Knoop hardness measured before and after immersion in 100% ethanol. The data from each test were evaluated using a two-way ANOVA and Tukey's test (α = 0.05). RESULTS: The XP Bond adhesive showed higher water sorption (similar to Adper Single Bond 2) and solubility (p < 0.05) than did the other materials. Prolonged exposure times did not reduce the water sorption but did reduce the solubility of all tested materials (p < 0.05). For Ambar, the increase in the exposure time resulted in a significantly lower percent reduction in hardness. CONCLUSION: Water sorption, solubility, and cross-linking density of the materials selected in this study seem to be mainly influenced by the adhesive composition. Prolonged light exposure times reduced the solubility of the materials.

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.

Influence of activation mode of resin cement on the shade of porcelain veneers.

PURPOSE: The aim of this study was to evaluate the influence of resin luting cement's activation mode in the final shade of porcelain veneers after accelerated artificial aging (AAA). MATERIALS AND METHODS: Porcelain veneers (IPS Empress Esthetic) were produced using a standardized shade (ET1) and thickness (0.6 mm). Twenty bovine teeth were collected, prepared, and divided into two groups: group I (n = 10)-light-cured group, only base paste was applied to the veneers; group II (n = 10)-dual-cured group, in which the same base paste used in group I and a transparent catalyst were proportionally mixed for 20 seconds and then applied to the veneers. The specimens were light-cured for 60 seconds each and were next subjected to AAA. They were submitted to color readings with a spectrophotometer in three instances: in the tooth surface (only the substrate), after the cementation and polymerization of the veneers, and after the AAA. The values of L*, a*, and b* were obtained and the total color change was calculated (∆E*). Values obtained were subjected to statistical analysis, with a significance of 0.05. RESULTS: There were no significant differences between dual- and light-cured modes considering ∆E*, L*, a*, and b* values obtained after aging (p > 0.05). Within the dual-cured mode there were no significant differences in ∆E*, L*, a*, and b* values (p > 0.05). CONCLUSION: No relevant differences were found between the two activation modes in color change. When submitted to aging, dual- and light-cured modes of the resin cement showed visually perceptible (∆E* > 1.0) color changes; however, within the threshold of clinical acceptance (∆E* > 3.3).

Shear bond strength of denture teeth to two chemically different denture base resins after various surface treatments.

PURPOSE: Debonding of acrylic teeth from the denture base remains a major problem in prosthodontics. The objective of this study was to evaluate the effect of various surface treatments on the shear bond strength of the two chemically different denture base resins-polymethyl methacrylate (PMMA) and urethane dimethacrylate (UDMA). MATERIALS AND METHODS: Two denture base resins, heat-cured PMMA (Meliodent) and light-activated UDMA (Eclipse), were used in this study. A total of 60 molar acrylic denture teeth were randomly separated into four groups (n = 15), according to surface treatment: acrylic untreated (group AC), Eclipse untreated (group EC), treated with eclipse bonding agent (group EB), and Er:YAG laser-irradiated eclipse (group EL). Shear bond strength test specimens were prepared according to the manufacturers' instructions. Specimens were subjected to shear bond strength test by a universal testing machine with a 1 mm/min crosshead speed. The data were analyzed with one-way ANOVA and post hoc Tukey-Kramer multiple comparison tests (α = 0.05). RESULTS: The highest mean bond strength was observed in specimens of group EB, and the lowest was observed in group EC specimens. A statistically significant difference in shear bond strength was found among all groups (p < 0.001), except between groups EC and EL (p = 0.61). CONCLUSION: The two chemically different denture base polymers showed different shear bond strength values to acrylic denture teeth. Laser-irradiation of the adhesive surface was found to be ineffective on improving bond strength of acrylic denture teeth to denture base resin. Eclipse bonding agent should be used as a part of denture fabrication with the Eclipse Resin System.

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.

The impact of polymerization method on tensile bond strength between denture base and acrylic teeth.

Failure of the bond between acrylic teeth and the denture base resin interface is one of the major concern in prosthodontics. The new generation of denture bases that utilize alternate polymerization methods are being introduced in the market. The aim of the study is to evaluate the influence of polymerization methods on bonding quality between the denture base and artificial teeth. Sixty test specimens were prepared (20 in each group) and were polymerized using heat, microwave and visible light curing. The tensile strength was recorded for each of the samples, and the results were analyzed statistically. The light-activated Eclipse™ System showed the highest tensile strength, followed by heat curing. The microwave-cured samples exhibited the least bonding to the acrylic teeth. Within the limitations of this study, it can be concluded that the new generation of light-cured denture bases showed significantly better bonding to acrylic teeth and can be used as an alternative to the conventional heat-polymerized denture base.

Comparison of hardness of three temporary filling materials cured by two light-curing devices.

AIM: Polymerization ability of light-curing devices can affect the light-cured material hardness. The purpose of the present study was to evaluate and compare the hardness of three temporary filling materials that had been light-cured by either a light emitting diode (LED) or a halogen light-curing unit. METHODS: The temporary filling materials, First Fill, Voco Clip and Bioplic, were placed in wells in a Teflon plate. The 24 specimens of each material were divided into two groups (N.=12/group) for photo-activation by either of the two light-curing units. The LED or halogen device was applied for 40s to the top surface of each specimen. A Knoop hardness test was performed on the top and bottom surface of each specimen, with five measurements per specimen. RESULTS: The highest hardness values for both the LED and halogen treated groups were observed for First Fill and the lowest values were for Voco Clip in top and bottom surfaces. The hardness obtained for the three materials with the halogen unit were significantly higher than the values obtained with the LED unit in both surfaces (P<0.05). CONCLUSION: First Fill light-cured temporary material exhibited the highest hardness values on the top and bottom surfaces than Voco Clip and Bioplic temporary materials. The hardness of light-cured temporary filling materials can be affected by the type of light-curing unit.

Effect of photoactivation mode on the hardness and bond strength of methacrylate- and Silorane monomer-based composites.

PURPOSE: To evaluate the Knoop hardness (KH) and the bond strength (BS) at the tooth/restoration interface of conventional methacrylate- (Filtek Supreme) and silorane-based (Filtek P90) composites photoactivated by different methods using an LED Freelight 2. MATERIALS AND METHODS: Bond strength was tested in a universal testing machine by the "push-out" test in restored cavities measuring 2 × 1.5 × 2 mm with a C-factor of 2.2, prepared in 60 bovine teeth. To restore the cavities, the respective adhesive system of each composite was used (Single Bond 2 and P90 system adhesives). The composites were photoactivated by 3 different methods: continuous light: 40 s at 1000 mW/cm²; soft-start: 10 s at 150 mW/cm² + 38 s at 1000 mW/cm²; pulse delay: 5 s at 150 mW/cm², followed by a 3-min wait (without photoactivation) and 39 s at 1000 mW/cm². Before the push-out test was performed, the KH was analyzed at the top and bottom of the restorations. Data were statistically anaylzed using ANOVA and Tukey's test. RESULTS: The photoactivation methods produced no differences in BS or KH in the same composite, while Filtek P90 (28.0 MPa) showed higher BS values than Filtek Supreme (22.3 MPa) and a lower KH. CONCLUSION: The composite Filtek P90 was capable of increasing bond strength, but presented lower Knoop hardness.

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.

Degree of conversion of nano-hybrid resin-based composites with novel and conventional matrix formulation.

OBJECTIVES: This study aimed to determine the degree of conversion (DC) of two nano-hybrid resin-based composites (RBCs) with novel monomer composition based on dimer acid derivates (hydrogenated dimer acid) and tricyclodecane-urethane structure compared to three nano-hybrid materials containing conventional matrices. DC was evaluated at 0.1, 2, and 6 mm depth at varying irradiation times (10, 20, and 40 s) and layering techniques (bulk and incremental). MATERIALS AND METHODS: DC was measured in real time by a Fourier transform infrared spectroscopy (FTIR) spectrometer with attenuated total reflectance accessory. The FTIR spectra were recorded on the bottom of the samples in real time for 5 min from photoinitiation. Results were compared using one- and multiple-way ANOVA, Tukey's HSD post hoc test (α = 0.05), and partial eta-squared statistic. RESULTS: After 5 min of measurement, DC showed no significant difference by varying cure time for specimens of 0.1 mm thickness. At 2 mm depth, the DC significantly increased after a cure time of 20 s compared to 10 s, remaining equal after 40 s of irradiation. At 6 mm depth, bulk curing showed significantly lower DC compared to incremental curing for all polymerization times. Specimen geometry revealed a strong effect on DC (η (2) = 0.90) followed by curing time (η (2) = 0.39). CONCLUSIONS: The RBCs containing the dimer acid and tricyclodecane-urethane structure showed a relatively low decrease of DC with increasing incremental thickness compared to the conventionally formulated materials. The former reached the highest DC among the tested materials. CLINICAL RELEVANCE: For the tested RBCs, increments of 2 mm and irradiation time of at least 20 s may be recommended for clinical practice. The two materials containing novel monomer composition might be applied for enlarged increments because of the low decrease of DC they demonstrated for 6-mm increments.

Influence of curing light power and energy on shrinkage force and acoustic emission characteristics of a dental composite restoration.

PURPOSE: To evaluate the density effects of light power and energy on the volumetric polymerization shrinkage and acoustic emission (AE) characteristics of a dental resin composite in the cavities of human teeth. METHODS: Two experiments were performed at different power levels (1,000 and 4,000 mW/cm2) using a light curing unit: (1) cylindrical cavities with diameters of 4 mm and depths of 2 mm were constructed using two symmetric steel molds. The cavities were filled with resin, and the shrinkage force during polymerization was measured using a load cell attached to the mold. Polymerization shrinkage forces were measured under four conditions (1,000 mW/cm2 x 10 seconds, 1,000 mW/cm2 x 20 seconds, 4,000 mW/cm2 x 3 seconds, and 4,000 mW/cm2 x 5 seconds); (2) tooth specimens with cavity diameters of 6 mm and depths of 2 mm were made from human molars. AE signals during polymerization shrinkage were monitored in real time for 10 minutes after irradiation and two AE factors (amplitude for defect size and hit number for defect number) were assessed in the examination of defects. Two levels of light energy (20 J/cm2 = 1,000 mW/cm2 x 20 seconds and 12 J/cm2 = 4,000 mW/cm2 x 3 seconds) were used. RESULTS: Shrinkage occurred more quickly at 4,000 mW/cm2 than at 1,000 mW/cm2 during the initial phase. The shrinkage force became almost the same for equivalent light energy as time increased. Higher light energy (20 J/cm2) under low-power conditions (1,000 mW/cm2) caused larger cumulative numbers of AE hits than did lower light energy (12 J/cm2) under high-power conditions (4,000 mW/cm2). At 4,000 mW/cm2 and 12 J/cm2 (i.e., high power, low energy), the average amplitude of the AE signals was larger than at 1,000 mW/cm2 and 20 J/cm2 (low power, high energy).

Temperature changes in the pulpal chamber and the sealing performance of various methods of direct pulp capping of primary teeth.

AIM: To compare changes in pulpal chamber temperature during the visible-light curing of direct pulp capping compounds and various modes of diode laser irradiation without prior placement of a pulp capping compound and the resultant seals. MATERIALS AND METHODS: Pulp exposure holes were made in 100 extracted human primary first molars, which were randomly assigned to ten equal groups. The holes were sealed by (a= Group 1, 2, 3, 4, 5, 6 and 7) different pulp capping compounds which were cured using various types of visible-light curing units or (b=Group 8, 9 and 10) diode laser irradiation without prior application of a pulp capping compound. Pulpal chamber temperatures were recorded during the procedure, and the resultant seals were examined under a scanning electron microscope. RESULTS: Visible-light curing of the pulp capping compounds and diode laser irradiation at a 0.7 W output power can cause non-injurious temperature rises in the pulpal chamber. At higher output powers of the diode laser, the temperature rises are sufficient to cause thermal injury. The seals were complete when pulp capping compounds were used for direct pulp capping, but were incomplete when laser irradiation without prior placement of a pulp capping compound was used for the identical purpose. CONCLUSION: The visible-light curing of pulp capping compounds is not harmful to vital pulp, and provides an effective seal of the pulp exposure hole. Laser irradiation is not an effective sealant, and can cause thermal injury to vital pulp at high output powers.

Influence of different photo-activation distances on cytotoxicity of a dental adhesive model resin.

AIM: This study evaluated the cytotoxicity of a dental bonding model resin (DBMR) submitted to different photo-activation distances. METHODS: A monomer mixture based on Bis-GMA and HEMA was used to assess the cytotoxicity in a mouse fibroblast-cell line. To promote different photo-activation distances glass slides were interposed between DBMR surface and halogen light curing unit (LCU) tip. Afterwards, the specimens were immersed in RPMI culture medium for 24 h to obtain extracts. The extracts were incubated in contact with the cells for 24 h. Finally, an MTT colorimetric assay was used to assess the cytotoxicity. The cell viability data (absorbance) were analyzed by one way ANOVA followed by Tukey's test (P<0.05). RESULTS: The light output decreased according to the increase in the number of glass slides between the halogen LCU tip and DBMR surface. Yet, the distance between the tip of the curing light system and the specimens had significant influence on the cytotoxicity. All extracts produced by groups submitted to different photo-activation distances showed cytotoxic effect after 24h of incubation. CONCLUSION: The photo-activation distance and the interposition of glass slides between LCU tip and DBMR was shown to play an important role in the cytotoxic effect.

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.