Gamma-irradiation-induced micro-structural variations in flame-retardant polyurethane foam using synchrotron X-ray micro-tomography.

Flame-retardant polyurethane foams are potential packing materials for the transport casks of highly active nuclear materials for shock absorption and insulation purposes. Exposure of high doses of gamma radiation causes cross-linking and chain sectioning of macromolecules in this polymer foam, which leads to reorganization of their cellular microstructure and thereby variations in physico-mechanical properties. In this study, in-house-developed flame-retardant rigid polyurethane foam samples were exposed to gamma irradiation doses in the 0-20 kGy range and synchrotron radiation X-ray micro-computed tomography (SR-µCT) imaging was employed for the analysis of radiation-induced morphological variations in their cellular microstructure. Qualitative and quantitative analysis of SR-µCT images has revealed significant variations in the average cell size, shape, wall thickness, orientations and spatial anisotropy of the cellular microstructure in polyurethane foam.

Characterization of Ivoclar Vivadent Dental Restoration Material for 137CS Retrospective Radiation Dosimetry.

Retrospective dosimetry is the method of using materials on or near a person who is exposed to ionizing radiation to determine the amount of radiation received by the person. A possible candidate material for retrospective dosimetry is Ivoclar Vivadent IPS e.max® CAD ceramic dental restoration material, which exhibits radiation-induced thermoluminescence when exposed to gamma- and x-ray radiation from a Cs source. The purpose of this paper is to characterize the material and study the behavior of the thermoluminescence signal with radiation dose and with delay time between radiation exposure and thermoluminescence measurement. The first glow peak is well-modeled by a first-order glow curve deconvolution formula. The height of the first glow peak is approximately linear with dose. The fading of the signal with time is approximately described by a power law curve with cutoff. The material appears to be suitable for retrospective radiation dosimetry.

The Effect of Postmastectomy Radiation Therapy on Breast Implants: Material Analysis on Silicone and Polyurethane Prosthesis.

INTRODUCTION: The pathogenic mechanism underlying capsular contracture is still unknown. It is certainly a multifactorial process, resulting from human body reaction, biofilm activation, bacteremic seeding, or silicone exposure. The scope of the present article is to investigate the effect of hypofractionated radiotherapy protocol (2.66 Gy × 16 sessions) both on silicone and polyurethane breast implants. METHODS: Silicone implants and polyurethane underwent irradiation according to a hypofractionated radiotherapy protocol for the treatment of breast cancer. After irradiation implant shells underwent mechanical, chemical, and microstructural evaluation by means of tensile testing, infrared spectra in attenuated total reflectance mode, nuclear magnetic resonance, and field emission scanning electron microscopy. RESULTS: At superficial analysis, irradiated silicone samples show several visible secondary and tertiary blebs. Polyurethane implants showed an open cell structure, which closely resembles a sponge. Morphological observation of struts from treated polyurethane sample shows a more compact structure, with significantly shorter and thicker struts compared with untreated sample. The infrared spectra in attenuated total reflectance mode spectra of irradiated and control samples were compared either for silicon and polyurethane samples. In the case of silicone-based membranes, treated and control specimens showed similar bands, with little differences in the treated one. Nuclear magnetic resonance spectra on the fraction soluble in CDCl3 support these observations. Tensile tests on silicone samples showed a softer behavior of the treated ones. Tensile tests on Polyurethane samples showed no significant differences. CONCLUSIONS: Polyurethane implants seem to be more resistant to radiotherapy damage, whereas silicone prosthesis showed more structural, mechanical, and chemical modifications.

LED Curing Lights and Temperature Changes in Different Tooth Sites.

Objectives. The aim of this in vitro study was to assess thermal changes on tooth tissues during light exposure using two different LED curing units. The hypothesis was that no temperature increase could be detected within the dental pulp during polymerization irrespective of the use of a composite resin or a light-curing unit. Methods. Caries-free human first molars were selected, pulp residues were removed after root resection, and four calibrated type-J thermocouples were positioned. Two LED lamps were tested; temperature measurements were made on intact teeth and on the same tooth during curing of composite restorations. The data was analyzed by one-way analysis of variance (ANOVA), Wilcoxon test, Kruskal-Wallis test, and Pearson's χ (2). After ANOVA, the Bonferroni multiple comparison test was performed. Results. Polymerization data analysis showed that in the pulp chamber temperature increase was higher than that without resin. Starlight PRO, in the same condition of Valo lamp, showed a lower temperature increase in pre- and intrapolymerization. A control group (without composite resin) was evaluated. Significance. Temperature increase during resin curing is a function of the rate of polymerization, due to the exothermic polymerization reaction, the energy from the light unit, and time of exposure.

Differences in the intensity of light-induced fluorescence emitted by resin composites.

BACKGROUND: The aims of this study were to compare the intensities of fluorescence emitted by different resin composites as detected using quantitative light-induced fluorescence (QLF) technology, and to compare the fluorescence intensity contrast with the color contrast between a restored composite and the adjacent region of the tooth. METHODS: Six brands of light-cured resin composites (shade A2) were investigated. The composites were used to prepare composite discs, and fill holes that had been prepared in extracted human teeth. White-light and fluorescence images of all specimens were obtained using a fluorescence camera based on QLF technology (QLF-D) and converted into 8-bit grayscale images. The fluorescence intensity of the discs as well as the fluorescence intensity contrast and the color contrast between the composite restoration and adjacent tooth region were calculated as grayscale levels. RESULTS: The grayscale levels for the composite discs differed significantly with the brand (p<0.001): DenFil (10.84±0.35, mean±SD), Filtek Z350 (58.28±1.37), Premisa (156.94±1.58), Grandio (177.20±0.81), Charisma (207.05±0.77), and Gradia direct posterior (211.52±1.66). The difference in grayscale levels between a resin restoration and the adjacent tooth was significantly greater in fluorescence images for each brand than in white-light images, except for the Filtek Z350 (p<0.05). However, the Filtek Z350 restoration was distinguishable from the adjacent tooth in a fluorescence image. CONCLUSIONS: The intensities of fluorescence detected from the resin composites varied. The differences between the composite and adjacent tooth were greater for the fluorescence intensity contrast than for the colors observed in the white-light images.

Effect of a broad-spectrum LED curing light on the Knoop microhardness of four posterior resin based composites at 2, 4 and 6-mm depths.

OBJECTIVE: To measure the Knoop microhardness at the bottom of four posterior resin-based composites (RBCs): Tetric EvoCeram Bulk Fill (Ivoclar Vivadent), SureFil SDR flow (DENTSPLY), SonicFill (Kerr), and x-tra fil (Voco). METHODS: The RBCs were expressed into metal rings that were 2, 4, or 6-mm thick with a 4-mm internal diameter at 30°C. The uncured specimens were covered by a Mylar strip and a Bluephase 20i (Ivoclar Vivadent) polywave(®) LED light-curing unit was used in high power setting for 20s. The specimens were then removed and placed immediately on a Knoop microhardness-testing device and the microhardness was measured at 9 points across top and bottom surfaces of each specimen. Five specimens were made for each condition. RESULTS: As expected, for each RBC there was no significant difference in the microhardness values at the top of the 2, 4 and 6-mm thick specimens. SureFil SDR Flow was the softest resin, but was the only resin that had no significant difference between the KHN values at the bottom of the 2 and 4-mm (Mixed Model ANOVA p<0.05). Although the KHN of SureFil SDR Flow was only marginally significantly different between the 2 and 6-mm thickness, the bottom at 6-mm was only 59% of the hardness measured at the top. CLINICAL SIGNIFICANCE: This study highlights that clinicians need to consider how the depth of cure was evaluated when determining the depth of cure. SureFil SDR Flow was the softest material and, in accordance with manufacturer's instructions, this RBC should be overlaid with a conventional resin.

Can Increasing the Manufacturer's Recommended Shortest Curing Time of High-intensity Light-emitting Diodes Adequately Cure Sealants?

PURPOSE: To investigate sealant depth of cure after increasing the curing times of high-intensity light-emitting diode units (LEDs). METHODS: Three sealants (opaque-unfilled, opaque-filled, and clear-filled) were light cured in a covered-slot mold with: (a) three LEDs (VALO, SmartLite, Fusion) for six to 15 seconds; and (b) a quartz-tungsten halogen (QTH) light for 40 seconds as a control (N=10). Twenty-four hours after light curing, microhardness was measured at the sealant surface and through the depth at 0.5 mm increments. Results were analyzed via analysis of variance followed by the Student-Newman-Keuls test (significance level 0.05). RESULTS: The opaque-filled and clear-filled sealants cured with VALO for six or nine seconds had hardness values that were statistically equivalent to or better than the QTH to a depth of 1.5 mm. Using Fusion for 10 seconds (exposure limit) did not adequately cure the three sealants beyond one mm. SmartLite at 15 seconds (maximum exposure period without overheating) did not adequately cure the sealants beyond 0.5 mm. CONCLUSIONS: Among the tested high-intensity LEDs, only VALO at double or triple the manufacturers' shortest curing time (six or nine seconds) provided adequate curing of opaque-filled and clear-filled sealants at 1.5 mm depth compared to the 40-second QTH light.

Effect of post-curing treatment on mechanical properties of composite resins.

The aim of this study is to assess the effect of additional curing procedures on the flexural strength and modulus of elasticity of indirect and direct composite materials. Twenty-four rectangular prism-shaped 2 mm x 2 mm x 25 mm samples of Belleglass, Premisa (Kerr), Adoro and Heliomolar (Ivoclar Vivadent) were prepared. Each composite was packed in an ad-hoc stainless steel device with a TeflonR instrument. A mylar strip and a glass slab were placed on top to obtain a flat surface. Polymerization was activated for 20 seconds with a halogen unit (Astralis 10, Ivoclar - Vivadent) with soft start regime and an output with a 350 to 1200 mw/cm2 range at four different points according to the diameter of the end of the guide. The specimens obtained were then randomly divided into two different groups: with and without additional treatment. In the group with additional treatment, the samples adorro were submitted to 25 minutes in Lumamat 100 (Ivoclar Vivadent) and the rest to 20 minutes in BelleGlass HP (Kerr). After the curing procedures, all samples were treated with sandpapers of decreasing grain size under water flow, and stored in distilled water for 24 h. Flexural strength was measured according to the ISO 404920 recommendations and elastic modulus was determined following the procedures of ANSI/ADA standard No. 27. Statistical differences were found among the different materials and curing procedures employed (P<0.01). The elastic modulus was significantly higher after the additional curing treatment for all materials except Premisa. Further work is needed to determine the association between the actual monomers present in the matrix and the effect of additional curing processes on the mechanical properties of both direct and indirect composites, and its clinical relevance.

Evaluation of microleakage of class II dental composite resin restorations cured with LED or QTH dental curing light; Blind, Cluster Randomized, In vitro cross sectional study.

BACKGROUND: The aim of this study is to compare the microleakage of Class II dental composite resin restorations which have been cured by three different LED (light emitting diode) light curing modes compared to control samples cured by QTH (quartz tungsten halogen) light curing units (LCUs), to determine the most effective light curing unit and mode of curing. RESULTS: In this experimental study, class II cavities were prepared on 100 sound human premolars which have been extracted for orthodontic treatment. The teeth were randomly divided into four groups; three experimental and one control group of 25 teeth each. Experimental groups were cured by either conventional, pulse-delay, or ramped curing modes of LED. The control group was cured for 20 seconds by QTH. The restorations were thermocycled (1000 times, between 5 and 55°C, for 5 seconds dwell time), dyed, sectioned mesio-distally and viewed under stereo-microscope (40×) magnification. Teeth were then scored on a 0 to 4 scale based on the amount of microleakage. The data were analyzed by Chi-square test.No significant difference was demonstrated between the different LCUs (light curing units), or modes of curing, at the enamel side (p > 0.05). At the dentin side, all modes of LED curing could significantly reduce microleakage (p < 0.05). The results suggest that slow start curing improves marginal integrity and seal. High intense curing endangers those aims. CONCLUSIONS: Comparison between the three LED mode cured composite resin restorations and QTH curing showed LED curing in all modes is more effective than QTH for reducing microleakage. Both LED and QTH almost completely eliminate the microleakage on the enamel side, however none of them absolutely eliminated microleakage on the dentin side.

Effect of ultraviolet light irradiation period on bond strengths between fiber-reinforced composite post and core build-up composite resin.

The aim of the present study was to characterize the effects of the ultraviolet light (UV) irradiation period on the bond strength of fiber-reinforced composite (FRC) posts to core build-up resin. Three types of FRC posts were prepared using polymethyl methacrylate, urethane dimethacrylate, and epoxy resin. The surfaces of these posts were treated using UV irradiation at a distance of 15 mm for 0 to 600 s. The pull-out bond strength was measured and analyzed with the Dunnett's comparison test (α=0.05). The bond strengths of the post surfaces without irradiation were 6.9 to 7.4 MPa; those after irradiation were 4.2 to 26.1 MPa. The bond strengths significantly increased after 15 to 120-s irradiation. UV irradiation on the FRC posts improved the bond strengths between the FRC posts and core build-up resin regardless of the type of matrix resin.

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.

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 use of light-cured resin as an alternative method of occlusal splints manufacturing--in vitro study.

BACKGROUND: Temporomandibular disorders are very common nowadays. One of the methods to treat these problems is occlusal splint therapy. Modern materials should be introduced to this treatment. OBJECTIVES: The aim of this paper was to evaluate the properties of light-activated urethane dimethacrylate and the quality of the bonds it creates with thermoforming foils. MATERIAL AND METHODS: Thermoforming foils were covered with light-cured resin. A bond was formed between the materials using an adhesive. A coating lacquer was used on the resin as a final preparatory step. Three laboratory tests were run: dye penetrant inspection, a Vickers microhardness test and a linear polymerization shrinkage test. The materials were layered and then cured with a polymerizing lamp emitting light of a wavelength of 400 Nm, according to the manufacturer's instructions. All the occlusal splints were fitted to upper dental arch. The devices had been made in an articulator on specially prepared gypsum models. The results were analyzed statistically using a one-sided binomial test, Spearman's rank-order correlation coefficient and the Friedman ANOVA (p=0.05). RESULTS: In the dye penetrant inspection, only one sample out of sixty showed the effects of color penetration to the adhesive connection. The dye only penetrated the layer of lacquer coating the resin. The average value of the Vickers microhardness test with a load of F=50 g applied to the material surface for 30 s was HV0.05=7.43 N/mm2. The average linear shrinkage of the resin observed after polymerization was 1.175%. CONCLUSIONS: Light-cured resin and an adhesive connection between the resin and thermoforming foil do not show susceptibility even to strong dye. The maximum polymerization shrinkage occurs immediately after curing. The light-cured resin that was tested seems to be a good alternative method for occlusal splints manufacturing.

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.

EFFECT OF LIGHT CURING UNIT CHARACTERISTICS ON LIGHT INTENSITY OUTPUT, DEPTH OF CURE AND SURFACE MICRO-HARDNESS OF DENTAL RESIN COMPOSITE.

BACKGROUND: Modern dental composite restorations are wholly dependent on the use of Visible Light Curing devices. The characteristics of these devices may influence the quality of composite resin restorations. OBJECTIVE: To determine the characteristics of light curing units (LCUs) in dental clinics in Nairobi and their effect on light intensity output, depth of cure (DOC) and surface micro-hardness (SMH) of dental resin composite. DESIGN: Laboratory based, cross-sectional analytical study. SETTING: Public and private dental clinics in Nairobi, Kenya. SUBJECTS: Eighty three LCUs which were in use in private and public dental health facilities in Nairobi, Kenya and resin composite specimens. RESULTS: Of the 83 LCUs studied, 43 (51.8%) were Light Emitting Diodes (LEDs) and 39(47.0%) were Quartz-Tungsten-Halogen (QTH) and 1 (1.2%) was Plasma Arc Curing (PAC) light. Mean light intensity for QTH and LED lights was 526.59 mW/cm2 and 493.67 mW/cm2 respectively (p=0.574), while the mean DOC for QTH lights was 1.71 mm and LED was 1.67 mm (p=0.690). Mean Vickers Hardness Number (VHN) for LED was 57.44 and for QTH was 44.14 (p=0.713). Mean light intensity for LCUs < or = 5 years was 596.03 mW/cm2 and 363.17 mW/cm2 for units > 5 years old (p=0.024). The mean DOC for the two age groups was 1.74 mm and 1.57 mm respectively (p=0.073). For SMH, the < or = 5 years and >5 years age groups gave a mean VHN of 58.81 and 51.46 respectively (p=0.1). On maintenance history, the frequency of routine inspection, duration since the last repair/replacement of a part or other maintenance activity and the nature of the last maintenance activity were determined and were not found to have influenced the light intensity, DOC and SMH. CONCLUSION: The LCU age has a statistically significant influence on its light intensity (p=0.024) while the type and maintenance history have no significant influence on its light intensity and composite DOC and SMH (p=0.574, p=0.690, p=0.713 respectively).

Preheating of resin-based flowable materials in a microwave device: a promising approach to increasing hardness and softening resistance under cariogenic challenge.

This study aimed to evaluate whether preheated resin-based flowable restoratives would show increased hardness and softening susceptibility after an early cariogenic challenge. Fluroshield- Yellowed, Bioseal, Wave, Master Flow, Fluroshield-White, Conseal F, Filtek Z350 Flow, and Opallis Flow were tested. Preheating was performed using a microwave device. Five specimens of each preheated or room temperature material (n = 5) were fabricated. Hardness was assessed before and after a cariogenic challenge. The analysis was done by two-way analysis of variance (ANOVA) with repeated measures (cariogenic challenge) and Tukey's test for multiple comparisons (

Simultaneous determination of polymerization shrinkage, exotherm and thermal expansion coefficient for dental resin-composites.

OBJECTIVES: To measure shrinkage strain, exotherm, and coefficient of thermal expansion (CTE), simultaneously for a set of representative resin-composites. METHODS: Six commercially available resin-composites with different filler loadings were selected. A modified bonded-disk instrument that includes temperature-monitoring apparatus was used to measure simultaneously: shrinkage strain, exotherm, and CTE. Shrinkage strain and temperature of disk specimens (n=3/materials) were monitored for 1h after irradiation for 20s at 1200mW/cm(2) (energy density=24J/cm(2)). Disks were irradiated for a second time 60min after the first irradiation. Axial expansion strain and temperature were monitored for 3min. Exotherm was obtained from differences between temperature rise during 1st and 2nd irradiations. CTE was calculated from disk axial expansion due to irradiation heat (ΔL) and rise in temperature (ΔT) during the second irradiation. RESULTS: The final shrinkage strain values ranged from 1.7% to 2.34%, exotherm values ranged from 4.66 to 9.43°C, and CTE ranged from 18.44 to 24.63 (10(-6)/°C). Negative correlations were found between filler loading and shrinkage strain, exotherm, and CTE. Positive correlation was apparent between shrinkage strain and CTE. SIGNIFICANCE: The modified bonded-disk instrument could be used to measure simultaneously shrinkage strain, exotherm, and CTE of resin-composites.

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.

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.

Scanning electron microscopy and roughness study of dental composite degradation.

Our aim was to test the hypothesis that the use of mouthwashes, consumption of soft drinks, as well as the type of light curing unit (LCU), would change the surface roughness (Ra) and morphology of a nanofilled composite resin (Z350® 3M ESPE). Samples (80) were divided into eight groups: Halogen LCU, group 1, saliva (control); group 2, Pepsi Twist®; group 3, Listerine®; group 4, Colgate Plax®; LED LCU, group 5, saliva; group 6, Pepsi Twist®; group 7, Listerine®; group 8, Colgate Plax®. Ra values were measured at baseline, and after 7 and 14 days. One specimen of each group was prepared for scanning electron microscopy analysis after 14 days. The data were subjected to multifactor analysis of variance at a 95% confidence followed by Tukey's honestly significant difference post-hoc test. All the treatments resulted in morphological changes in composite resin surface, and the most significant change was in Pepsi Twist® groups. The samples of G6 had the greatest increase in Ra. The immersion of nanofilled resin in mouthwashes with alcohol and soft drink increases the surface roughness. Polymerization by halogen LCU (reduced light intensity) associated with alcohol contained mouthwash resulted in significant roughness on the composite.