Does the Period of Air-Drying Affect Dentin Bond Strength of Different Adhesive Systems.

Aims: To evaluate the effect of air-drying time of adhesives on shear bond strength of different adhesive systems. Methodology: The occlusal surfaces of 175 mandibular third molars were ground to obtain flat dentin surfaces and then divided into three groups according to three adhesive systems used: (1) Conventional three-step adhesive (Scotchbond Multi-purpose Plus); 2) Self-etch adhesive (Adper Easy Bond) and 3) Single bottle self-etch adhesive (Scotchbond Universal adhesive). Regarding the application of adhesives before resin composite application, it was gently air-dried for 3 s in Groups 1, whereas, the adhesive was left wet in Group 2. The group 3, that was air-dried until the liquid did not move (5 s), was served as control. Following bonding of resin cement (Filtek Supreme) to dentin, the specimens were light cured for 20s with a LED. After storage in water at 37ºC for one week, the strength measurements were accomplished with universal testing machine (Lloyd LRX) until the failure occurs. Failure modes were examined using a stereomicroscope and scanning electron microscope. The data were analyzed with two-way analysis of variance Original Research Article British Journal of Medicine & Medical Research, 4(27): 4523-4532, 2014 4524 (ANOVA) and TukeyHSD tests (α=0.05). Results: The two-way ANOVA revealed that adhesive systems had a significant effect on shear bond strength values (p<0.001). However, air-drying time did not influence shear bond strength (p=0.442). Additionally, there was no interaction effect between adhesive systems and air-drying time (p=0.835). Conclusion: The data suggests that increased air-drying time of adhesives does not significantly affect bond strength.

In vitro cytotoxicity of indirect composite resins: Effect of storing in artificial saliva.

Aim: The aim of this study was to compare the cytotoxic effects of two indirect composite resins (Artglass and Solidex) on the viability of L-929 fibroblast cells at different incubation periods by storing them in artificial saliva (AS). Materials and Methods: Disk-shaped test samples were prepared according to manufacturers' instructions. Test materials were cured with light source (Dentacolor XS, Heraus Kulzer, Germany). The samples were divided into two groups. The first group's samples were transferred into a culture medium for 1 hour, 24 hours, 72 hours, 1 week and 2 weeks. The other group's samples were transferred into a culture medium for 1 hours, 24 hours, 72 hours, 1 week, and 2 weeks after being stored in AS for 48 hours. The eluates were obtained and pipetted for evaluation onto L-929 mouse fibroblast cultures incubated for 24 hours. Measurements were performed by MTT (3-(4,5)-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay. The degree of cytotoxicity for each sample was determined according to the reference values represented by the cells with a control group. Results: Statistical significance was determined by ANOVA. Both groups presented lower cell viability in comparison to the control group at all periods. Storing in artificial saliva reduced cytotoxicity significantly (P < 0.05). Stored Artglass and Solidex showed similar effects on cytotoxicity. Nonstored Solidex samples were found more cytotoxic than Artglass samples. The cell survival rate results of 24-hour incubation period were significantly lower than those of the other experimental periods (P < 0.05). Conclusion: Storing indirect composite resins in AS may reduce cytotoxic effects on the fibroblast cells. However, resin-based dental materials continue to release sufficient components to cause cytotoxic effects in vitro after 48 hours of storing in AS.

Effect of different light curing methods on mechanical and physical properties of resin-cements polymerized through ceramic discs

OBJECTIVE: The aim of this study was to compare the polimerization ability of three different light-curing units (quartz tungsten halogen, light-emitting diodes and plasma arc) and their exposure modes (high-intensity and soft-start) by determination of microhardness, water sorption and solubility, and diametral tensile strength of 5 dual-curing resin cements. Material and methods: A total of 720 disc-shaped samples (1 mm height and 5 mm diameter) were prepared from different dual-curing resin cements (Duolink, Nexus, Bifix-QM, Panavia F and RelyX Unicem). Photoactivation was performed by using quartz tungsten halogen (high-power and soft-up modes), light-emitting diode (standard and exponential modes) and plasma arc (normal and ramp-curing modes) curing units through ceramic discs. Then the samples (n=8/per group) were stored dry in the dark at 37°C for 24 h. The Vickers hardness test was performed on the resin cement layer with a microhardness tester (Shimadzu HMV). For sorption and solubility tests; the samples were stored in a desiccator at 37°C and weighed to a constant mass. The samples were weighed both before and after being immersed in deionized water for different periods of time (24 h and 7 days) and being desiccated. The diametral tensile strength of the samples was tested in a universal testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed statistically by nonparametric Kruskal Wallis and Mann-Whitney U tests at 5 percent significance level. RESULTS: Resin cement and light-curing unit had significant effects (p<0.05) on microhardness, diametral tensile strength, water solubility and sorption. However, no significant differences (p>0.05) were obtained with different modes of LCUs. Conclusion: The study indicates that polymerization of resin cements with different light-curing units may result in various polymer structures, and consequently different mechanical and physical properties.

Effect of reduced exposure times on the cytotoxicity of resin luting cements cured by high-power led

OBJECTIVE: Applications of resin luting agents and high-power light-emitting diodes (LED) light-curing units (LCUs) have increased considerably over the last few years. However, it is not clear whether the effect of reduced exposure time on cytotoxicity of such products have adequate biocompatibility to meet clinical success. This study aimed at assessing the effect of reduced curing time of five resin luting cements (RLCs) polymerized by high-power LED curing unit on the viability of a cell of L-929 fibroblast cells. MATERIAL AND METHODS: Disc-shaped samples were prepared in polytetrafluoroethylene moulds with cylindrical cavities. The samples were irradiated from the top through the ceramic discs and acetate strips using LED LCU for 20 s (50 percent of the manufacturer's recommended exposure time) and 40 s (100 percent exposure time). After curing, the samples were transferred into a culture medium for 24 h. The eluates were obtained and pipetted onto L-929 fibroblast cultures (3x10(4) per well) and incubated for evaluating after 24 h. Measurements were performed by dimethylthiazol diphenyltetrazolium assay. Statistical significance was determined by two-way ANOVA and two independent samples were compared by t-test. RESULTS: Results showed that eluates of most of the materials polymerized for 20 s (except Rely X Unicem and Illusion) reduced to a higher extent cell viability compared to samples of the same materials polymerized for 40 s. Illusion exhibited the least cytotoxicity for 20 s exposure time compared to the control (culture without samples) followed by Rely X Unicem and Rely X ARC (90.81 percent, 88.90 percent, and 83.11 percent, respectively). For Rely X ARC, Duolink and Lute-It 40 s exposure time was better (t=-1.262 p=0,276; t=-9.399 p=0.001; and t=-20.418 p<0.001, respectively). CONCLUSION: The results of this study suggest that reduction of curing time significantly enhances the cytotoxicity of the studied resin cement materials, therefore compromising their clinical performance.