Spectrophotometric assessment of the color stability of composite resins polished with different techniques.

This study aimed to use spectrophotometry to assess the color stability of composite resins polished with different polishing techniques and scanning electron microscopy (SEM) to evaluate the surface micromorphology of the specimens. In this in vitro experimental study, a total of 96 disc-shaped specimens were fabricated from microfilled (Renamel Microfill, shade SB3) and nanohybrid (Estelite Sigma Quick, shade BW) composite resins in bright white shades (n = 48). Each group was randomized into 1 control and 2 experimental subgroups (n = 16): no polishing (control), polishing with aluminum oxide discs (experimental), or polishing with diamond-impregnated spiral wheels (experimental). In each subgroup, half of the specimens were immersed in a coffee solution and the other half in a tea solution for 48 hours after finishing (control) or polishing (experimental). Spectrophotometry was used to measure the color of the specimens at baseline, after finishing, after polishing (experimental groups only), and after immersion in tea and coffee. The surface micromorphology of a randomly selected specimen from each subgroup was assessed under SEM. The color change (ΔE*) of the specimens between measurements was calculated and analyzed using 1-way, 2-way, and 3-way analyses of variance (ANOVAs) and the Tukey test. Both tea and coffee caused significant color change in the composite resin specimens, with specimens immersed in coffee undergoing significantly greater color change than those immersed in tea (P < 0.001; 2-way ANOVA). The nanohybrid composite specimens polished with polishing discs had a significantly greater color change than nanohybrid specimens polished with spiral wheels (P = 0.041). The Tukey test revealed that there was no overall significant difference between the 2 polishing techniques (P = 0.505), but both of these subgroups exhibited a significantly lower color change than the control group (P < 0.001). In general, SEM did not reveal substantial differences between the 2 polishing techniques, but specimens polished by spiral wheels appeared to have a smoother surface. All polished specimens demonstrated clinically acceptable mean color change values (ΔE* < 3.5). The type of coloring agent had a greater effect on color stability than either the polishing technique or type of composite resin, with coffee causing a greater color change than tea.

Color stability of three commercial resin cements after accelerated aging.

Purpose: This study aimed to assess the color stability of resin cements subjected to xenon radiation and evaluate their color change (ΔE) during time. Materials and Methods: In this in vitro experimental study, 15 specimens (8 mm in diameter and 2 mm in height) were made from a light-cured resin cement (Choice 2, Bisco, USA) and two dual-cured resin cements (Panavia F2 and V5, Kuraray Co, Ltd, Osaka, Japan). For assessment of color change, ΔE parameters were measured immediately (ΔE1) and 24 h (ΔE2) after polymerization using XRiteCi64 spectrophotometer. Next, they were subjected to xenon lamp radiation (122 h at 35C° and 22% humidity in off mode and 95% in light mode). Then, their color change was measured again (ΔE3). The mean ΔE and standard deviation of all specimens were calculated, and data analysis was done using analysis of variance and Tukey's honestly significant difference. Results: L* values had a tendency to decrease and Panavia F2 and Choice 2 had the highest change after accelerated aging. The comparison of Δa and Δb showed no significant difference between cements except Δa in Panavia F2. All the values were clinically acceptable (ΔE >3.3). The lowest Δ E1 was for Panavia V5 and the highest Δ E1 was measured for Panavia F2. After accelerated aging, there was no significant difference between Panavia V5 and choice 2 (P > 0/05). Conclusions: Following polymerization and under xenon radiation, ΔE of all the specimens was clinically acceptable.

Effect of Wet and Dry Finishing and Polishing Technique on Microhardness and Flexural Strength of Nanocomposite Resins.

Objectives: This in vitro study was aimed to assess the effect of wet and dry finishing and polishing techniques on the flexural strength and microhardness of different commercial nanoparticle contained composite resins. Methods and Materials: The samples were made of Z250 (microhybrid), Z350 XT (nanofilled), and Z550 (nanohybrid) resin composites. Each group was subdivided into 2 subgroups according to polishing protocols. Subgroup 1 for each composite underwent wet polishing, and subgroup 2 was subject to dry polishing technique. Flexural strength and microhardness of the samples were measured at two different times of polishing (T 0 and T 24). The flexural strength test and microhardness test were measured by a 3-point bending test using a universal testing machine, and a Vickers machine, respectively. Data were analyzed by Kolmogorov-Smirnov, two-way ANOVA, and Tukey HSD tests. Results: ANOVA showed that the type of composite has a significant effect on flexural strength. Two-way ANOVA showed that, at T 0, flexural strength of all composites in the dry technique was higher than in the wet technique (p = 0.019). At T 24, Z350 XT had the lowest, and Z250 had the highest flexural strength in both techniques. The time and technique of polishing were also significantly effective on hardness. At T 0, hardness was higher in the wet compared to the dry method (p = 0.008). Tukey test showed that, at T 24, the hardness of Z350 XT was significantly higher than the other materials in both techniques. Conclusion: Immediate wet finishing and polishing presented lower flexural strength. Delayed dry/wet finishing and polishing significantly enhanced the hardness of the samples.

Thermal effect of light irradiation time on the setting time of mineral trioxide aggregate and calcium-enriched mixture cements.

This study aimed to assess the thermal effect of different light irradiation times on the setting time of mineral trioxide aggregate (MTA) and calcium-enriched mixture (CEM) cements. This in vitro experimental study evaluated 40 hydraulic cement specimens, including 20 MTA and 20 CEM specimens, according to the manufacturers'instructions. For each cement, the specimens were divided into 3 test groups light cured with a halogen light-curing unit (n = 5 per group) and 1 control group (n = 5) that was not exposed to irradiation. The specimens in the MTA test groups were light cured for 20, 40, or 60 seconds, and the specimens in the CEM test groups were light cured for 60, 90, or 120 seconds. All test and control groups had 60 seconds of rest time. Setting of the cements was assessed at different timepoints using a Gillmore needle weighing 113.4 g with a 12.2-mm diameter according to ASTM C266-03 standards. The data were analyzed with the Fisher exact test and the Mann-Whitney U test (α = 0.05). The setting of MTA specimens after different curing times was significantly different (P < 0.05). The setting time of MTA control specimens was significantly longer than that of test specimens (P = 0.008). The setting of CEM specimens after different curing times was not significantly different (P > 0.05). However, the setting time for CEM control specimens was significantly longer than that for test specimens (P = 0.008). Light curing with a halogen light-curing unit can significantly decrease the setting time for MTA and CEM cements.

Extract of Propolis on Resin-Modified Glass Ionomer Cement: Effect on Mechanical and Antimicrobial Properties and Dentin Bonding Strength.

This study assessed the effect of addition of aqueous extract of propolis in different concentrations on the mechanical and antimicrobial properties of resin-modified glass ionomer cement (RMGIC). In this in vitro study, powder of Fuji II LC RMGIC was mixed with 25% and 50% aqueous extracts of propolis. Samples (n = 15 for shear bond strength, n = 5 for flexural strength, and n = 20 for the antibacterial activity test) were fabricated using this mixture. The buccal and lingual surfaces of 23 premolars were ground to expose dentin. Tygon tubes were filled with cement, bonded to dentin, and subjected to bond or the flexural strength test in a universal testing machine. Antibacterial activity was assessed using the disc diffusion and well-plate techniques against S. mutans. Data were analyzed using one-way ANOVA and Tukey's test. The three groups showed significant differences (p < 0.001). The 50% propolis group had the lowest flexural and shear bond strength. The control group had the highest flexural and shear bond strength. No growth inhibition zone was noted around any of the discs. It can be concluded that addition of propolis to RMGIC did not confer any antibacterial activity against S. mutans and decreased the flexural and shear bond strength of RMGIC.

Shade reproduction and the ability of lithium disilicate ceramics to mask dark substrates.

OBJECTIVES: This study aimed to evaluate the ability of lithium disilicate ceramics to reproduce the A2 shade and to mask A4 substrates. MATERIALS AND METHODS: Twenty-four discs (8 mm in diameter, shade A2) of high translucency (groups 1-3) and low translucency (groups 4-6) of IPS e.max ceramic with different thicknesses (0.5, 0.75, and 1 mm) were fabricated as monolithic structures. In addition, discs of medium opacity (group 7-8) with different core/veneer combinations (0.3 mm/0.7 mm and 0.5 mm/0.5 mm) were fabricated as bilayer structures. Specimens were superimposed on an A4 substrate (complex). The color changes of the complex were measured using a spectrophotometer on a black background, and the ΔE values of the complex were compared with either the A4 substrate or the A2 shade tab. One-way analysis of variance, the Tukey honest significant difference test, and the Fisher test were used to analyze the data (p < 0.05). RESULTS: Significant between-group differences were found for comparisons to both the A4 substrate and the A2 shade (p < 0.05). When compared with the A4 substrate, the ΔE values in all groups were in the non-acceptable range. When compared with the A2 shade, the ΔE values in all groups, except groups 2 and 3, were in the clinically acceptable range. CONCLUSIONS: All translucencies and thicknesses masked the underlying dark substrate. However, the low-translucency IPS e.max Press better reproduced the A2 shade.

Effect of topical fluoride on microshear bond strength of primary enamel to composite, microhardness of enamel and its surface morphology: An in vitro study.

Background. This in vitro study aimed to evaluate the microshear bond strength (µSBS), microhardness and morphological characteristics of primary enamel after treating with sodium fluoride (NaF) and acidulated phosphate fluoride (APF). Methods. Forty-eight primary canines were cut into mesial and distal sections and assigned to five groups randomly: group 1 (immersed in saliva as a control), group 2 (treated with NAF and immersed in saliva for 30 minutes), group 3 (treated with APF and immersed in saliva for 30 minutes), group 4 (treated with NAF and immersed in saliva for 10 days), and group 5 (treated with APF and immersed in saliva for 10 days). Composite resin (Filtek Z250) was bonded on the specimens (n=15) for measuring the µSBS. After storage in 37°C artificial saliva for 24 hours, µSBS and Vickers hardness tests (10 readings) were performed. The data were analyzed using one-way ANOVA and Kolmogorov-Smirnov, Levene's and Tukey HSD tests (P<0.05). Morphological analysis of enamel and modes of failure were carried out under a scanning electron microscope (SEM) on two remaining specimens. Results. Significant differences in µSBS were only noted between groups 2 and 4 (P=0.024). Group 3 showed a significant decrease in hardness after storage in artificial saliva (P<0.001), with a significantly lower hardness than the other groups (P<0.001). The SEM observations showed irregular particles in groups 3 and 5; uniform, smooth and thin coats were seen in groups 2 and 4. Conclusion. Fluoride therapy with NaF and APF gels prior to restorative treatments had no adverse effects on the microshear bond strength.

Effect of bleaching on color change of composite after immersion in chlorhexidine and coffee.

BACKGROUND: Since the introduction of resin composites, the staining of resin-based materials by colored solutions such as coffee, tea, chlorhexidine (CHX), and other beverages has become a common concern. AIM: The aim of this study was to evaluate the effect of home and office bleaching as a treatment for discoloration of composite after immersion in coffee or CHX. MATERIALS AND METHODS: A microhybrid composite (Z250), nanohybrid composite (Z550), and nanofill composite (ultimate, body shade) were selected. Forty disk shape specimens (8 mm diameter and 2 mm thickness) for each composite were prepared then divided into two groups according to staining solutions (25 g of coffee in 250 ml water, 20 min/day or 0.2% CHX, 1 min/day). Following 1 month staining, specimens were divided into two groups again. Half of the specimens was bleached with in office bleaching agent (Opalescence Boost 40% hydrogen peroxide concentration) 3 times in one visit for 15minutes and the others subjected to home bleaching agent(Opalescence 10% carbamide peroxide) 6h/day until 2 weeks both from Ultradent Products, Inc., South Jordan, UT, USA. Color of the specimens was measured with a spectrophotometer using CIELAB color space at baseline, after 1 month staining, and after ending the bleaching process. STATISTICAL ANALYSIS: Analysis of variance was used to analyze the data (P < 0.05). RESULTS: Coffee and CHX provided significant color changes in all groups (P < 0.05). Z550 was the material more prone to discoloration in coffee in comparison with Filtek Ultimate (P = 0.003). After bleaching, materials showed significant reduction except stained Z550 by coffee in home bleaching groups. Both home and office bleaching provided significant color changes in all CHX groups (P < 0.05). CONCLUSION: Coffee produced more color changes than CHX. The hydrogen peroxide has the same whitening effect in comparison with carbamide peroxide.

Physiochemical Properties of Experimental Nano-hybrid MTA.

Introduction:The development of new pulp capping agents has paved the way towards the preservation of pulp vitality, which is an important goal in restorative dentistry. This study sought to assess the calcium ion release, pH and setting of mineral trioxide aggregate (MTA) Angelus, an experimental formulation of nano-hybrid MTA containing nano-SiO2, nano-Al2O3 and nano-TiO2 and MTA Angelus plus nano-oxides. Methods:In this experimental study, five specimens from each material were placed in polypropylene tubes and immersed in a flask containing deionized distilled water. The amount of calcium ions released into the solution from each material was measured at 15 minutes, one hour and 24 hours using atomic absorption spectroscopy. The pH of the solutions was measured using a pH meter at the respective time points. Setting time was also assessed using a Gilmore needle. Data were analyzed using the repeated measures ANOVA. Results:The amount of released calcium ions was not significantly different among the groups (P=0.060). All materials were alkaline and the pH at 24 hours was significantly higher than the other two time points in all groups (P<0.001). The experimental group had the shortest and MTA Angelus had the longest setting time. All materials were alkaline and capable of releasing calcium. Addition of nanoparticles to MTA Angelus significantly decreased the setting time but had no effect on the release of calcium ions or pH. Abbreviations: mineral trioxide aggregate (MTA), vital pulp therapy (VPT).

Effect of water storage on flexural strength of silorane and methacrylate-based composite resins.

OBJECTIVES: This study assessed the effect of water storage on the flexural strength (FS) of low shrinkage composites. MATERIALS AND METHODS: A total of 165 bar-shaped specimens (2 × 2 × 25 mm) were fabricated of 2 low shrinkage composites (Filtek P90 [3M ESPE], GC Kalore [GC International]) and a conventional methacrylate-based composite (Filtek Z250 [3M ESPE]). The specimens were subjected to 3-point bending test at 6 time intervals, namely: immediately after curing, at 24 hours, 1 week, 1 month, 6 months, and 1 year following storage in wet and dry conditions. The FS of the specimens were measured by applying compressive load at a crosshead speed of 1.0 mm/min. Data was analyzed using 3-way analysis of variance (ANOVA) and Tukey's test. RESULTS: Three-way ANOVA revealed significant interactions between time, type of composite, and storage condition (p = 0.001). Tukey's multiple comparison test revealed significant reductions in FS of all composites after 6 months and 1 year of storage in distilled water compared to dry condition. CONCLUSIONS: Filtek P90 showed the highest and GC Kalore showed the lowest FS after 1 year storage in distilled water. The immediate high strength of Filtek Z250 significantly decreased at 1 year and its final value was lower than that of Filtek P90.

Effect of water storage on ultimate tensile strength and mass changes of universal adhesives.

BACKGROUND: The aim of the present study was to evaluate the influence of water storage on micro tensile strength (µTS) and mass changes (MC) of two universal adhesives. MATERIAL AND METHODS: 10 disk-shaped specimens were prepared for each adhesive; Scotchbond Universal (SCU) All-Bond Universal (ABU) and Adper Single Bond 2 (SB2). At the baseline and after 1 day and 28 days of water storage, their mass were measured and compared to estimate water sorption and solubility. For µTS test, 20 dumbbell shaped specimens were also prepared for each adhesive in two subgroups of 1 day and 28 days water storage. RESULTS: MC was significantly lower for SCU and ABU than SB2 (P < 0.05) at both time intervals. In all three adhesives, the MC was significantly lower at 28 days compared to that at 1 day (P < 0.05). Similarly, µTS was significantly higher for SCU and ABU than SB2 at both storage intervals (P < 0.05). After 28 days, µTS increased significantly for universal adhesives (P < 0.05). CONCLUSIONS: MC and µTS of adhesives were both material and time dependent when stored in water; both universal adhesives showed less water sorption and higher values of µTS than the control group. Key words:Absorption, dental adhesives, dentin-bonding agents, solubility, tensile strength.

Effect of decontamination on micro-shear bond strength of silorane-based composite increments.

AIM: The aim of the present study was to evaluate the micro-shear bond strength of silorane-based composites after saliva/blood decontamination. METHODS: A transparent mold (1 × 2 × 1 cm) was used to make 11 flat, silorane-based composite blocks. One block served as the control. After contamination, the blocks were treated as follows: group 1: 10-s air spray; group 2: 10-s water spray + 10-s air spray; group 3: 10-s water spray + 10-s air spray + 10-s etching with phosphoric acid; group 4: 10-s air spray + 10-s etching + bonding; group 5: 10-s water spray + 10-s air spray + 10-s etching + bonding; and groups 6-10: treated the same as groups 1-5, the only difference being that blood was used instead of saliva. Ten tubes (0.7 mm × 1 mm) containing silorane-based composites were attached to each decontaminated block and light cured for 40 s. After 24-h storage in distilled water, specimens were tested under micro-shear loading at a cross-head speed of 0.5 mm/min. Data were analyzed using one-way anova and Tukey's honest significant difference (HSD) test (P < 0.05). RESULTS: One-way anova showed significant differences in the micro-shear bond strength among the experimental groups (P < 0.001). Tukey's HSD test revealed that the bond strengths in groups 5, 9, and 10 were similar to the control group (P > 0.05). CONCLUSION: Decontamination by water and air spray, etching, and bonding was effective in restoring the bond strength of silorane-based composite increments.

Color Stability of the Bulk-Fill Composite Resins with Different Thickness in Response to Coffee/Water Immersion.

We aimed to evaluate the color stability of bulk-fill and conventional composite resin with respect to thickness and storage media. Twenty specimens of a conventional composite resin (6 mm diameter and 2 mm thick) and 40 specimens of the bulk-fill Tetric EvoCeram composite resin at two different thicknesses (6 mm diameter and 2 mm thick or 4 mm thick, n = 20) were prepared. The specimens were stored in distilled water during the study period (28 d). Half of the specimens were remained in distilled water and the other half were immersed in coffee solution 20 min/d and kept in distilled water between the cycles. Color changes (ΔE) were measured using the CIE L (⁎) a (⁎) b (⁎) color space and a digital imaging system at 1, 7, 14, and 28 days of storage. Data were analyzed using Two-way ANOVA and Tukey's HSD post hoc test (P < 0.05). Composite resins showed significant increase in color changes by time (bulk-fill > conventional; P < 0.001). Coffee exhibited significantly more staining susceptibility than that of distilled water (P < 0.001). There was greater color changes with increasing the increment thickness, which was significant at 14 (P < 0.001) and 28 d (P < 0.01). Color change of bulk-fill composite resin was greater than that of the conventional one after coffee staining and is also a function of increment thicknesses.

Temperature Rise Induced by Light Curing Unit Can Shorten Enamel Acid-Etching Time.

OBJECTIVES: The aim of this in-vitro study was to assess the thermal effect of light emitting diode (LED) light curing unit on the enamel etching time. MATERIALS AND METHODS: Three treatment groups with 15 enamel specimens each were used in this study: G1: Fifteen seconds of etching, G2: Five seconds of etching, G3: Five seconds of etching plus LED light irradiation (simultaneously). The micro shear bond strength (µSBS) of composite resin to enamel was measured. RESULTS: The mean µSBS values ± standard deviation were 51.28±2.35, 40.47±2.75 and 50.00±2.59 MPa in groups 1, 2 and 3, respectively. There was a significant difference between groups 1 and 2 (P=0.013) and between groups 2 and 3 (P=0.032) in this respect, while there was no difference between groups 1 and 3 (P=0.932). CONCLUSION: Simultaneous application of phosphoric acid gel over enamel surface and light irradiation using a LED light curing unit decreased enamel etching time to five seconds without compromising the µSBS.

The Influence of Composite Thickness with or without Fibers on Fracture Resistance of Direct Restorations in Endodontically Treated Teeth.

INTRODUCTION: This in vitro study evaluated the influence of composite thickness (with or without fiber reinforcement) on fracture resistance of direct restorations in endodontically treated teeth. METHODS AND MATERIALS: Fifty-six intact human premolars were chosen and randomly divided into four groups (n=14). After preparation of a mesio-occluso-distal (MOD) cavities and cusp reduction, the teeth were endodontically treated. Subsequently, the samples were restored with composite resin using the following protocols: group 1; composite onlay with cusp coverage of 1.5 mm, group 2; composite onlay with cusp coverage of 2.5 mm, group 3; composite onlay (including resin-impregnated fiber) with cusp coverage of 1.5 mm and group 4; composite onlay (including resin-impregnated fiber) with cusp coverage of 2.5 mm. The fracture resistance of teeth in all test groups was calculated by subjecting them to a progressively increasing compressive axial force in the universal testing machine with the cross-head speed of 1 mm/min to the point of fracture. The data were analyzed using the Kruskal-Wallis test. RESULTS: The mean fracture strengths and obtained standard error were 1263.85±74.03 N, 1330.26±128.01 N, 1344.92±64.40 N and 1312.54±75.63 N for groups 1 to 4, respectively. Statistical analysis revealed no significant difference between groups. CONCLUSION: Cusp coverage of 1.5 and 2.5 mm in MOD access cavities with or without insertion of resin impregnated fiber had similar fracture rates in the endodontically treated teeth.