Effect of accelerated aging and double application on the dentin bond strength of universal adhesive system.

BACKGROUND: Despite the many advantages of simplified adhesive systems, there are concerns about the durability of the adhesive layer over time. The aim was to investigate the effects of various aging methods and double application of an adhesive layer on the bond strength of the universal adhesive system using etch-and-rinse (ER) and self-etch (SE) strategies. MATERIALS AND METHODS: In this in vitro study, the occlusal enamel of 120 extracted, intact human third molars was removed to expose the dentin. Then, the samples were randomly divided into four groups of thirty according to All-Bond Universal (ABU) adhesive application strategy (ER and SE) and the number of adhesive layers (1 or 2). Then, each group was subdivided into three subgroups of ten according to aging method (control, thermal cycling, and 10% sodium hypochlorite [NaOCl]). The shear bond strength was measured at the strain rate of 0.5 mm/min. Data were analyzed using three-way ANOVA and Tukey's post hoc tests (P < 0.05). RESULTS: The effect of adhesive application strategy (P < 0.001) and aging method (P < 0.001) on the bond strength was statistically significant, but the effect of the double application was not statistically significant (P > 0.05). In addition, the interactive effect of adhesive application strategy-aging method was significant (P = 0.005). CONCLUSION: Using ABU with ER strategy leads to higher dentin bond strength compared to the SE method in the control and thermal cycling groups. However, no significant differences were observed between ER and SE strategies after aging with the NaOCl. Furthermore, the double application might not have any effect on the bond strength and durability.

Effect of curing method and thermocycling on flexural strength and microhardness of a new composite resin with alkaline filler.

BACKGROUND: Cention N has been introduced as an alternative material for amalgam. The purpose was to investigate the flexural strength and microhardness of this material in self-cure and dual-cure modes before and after thermocycling. MATERIALS AND METHODS: In this experimental study, 40 samples of Cention N were prepared in order to determine and compare the microhardness. Half of the samples were set by self-cure method and the other half with dual-cure method. The Vickers microhardness test was performed once after 24 h and again after 10000 thermocyclings. Three-point flexural test was used to determine and compare the flexural strength of 52 rod-shaped samples. Half of the samples were set by self-cure method and the other half with dual-cure method. Among 26 samples in each group, 13 samples were randomly selected and three-point flexural test was performed after 24 h and for another 13 samples after 10,000 thermocyclings. Data were analyzed using two-way ANOVA and paired samples t-test (P < 0.05). RESULTS: There was a statistically significant difference between the mean of microhardness values in two curing methods (P < 0.001) and in two storage conditions (P < 0.001). The mean of dual-cure microhardness (100.99 ± 7.22) was higher than that of self-cure (64.61 ± 12.51) and the mean value associated with pre-thermocycling (89.75 ± 15.84) was higher than that of the post-thermocycling (76.44 ± 23.56). There was no statistically significant difference between the mean flexural strength in the two curing methods (self-cure [72.85 ± 16.26], dual cure [79.87 ± 23.07]; [P > 0.05]). However, the mean flexural strength without thermocycling (85.98 ± 21.74) was higher than that of the thermocycled group (64.24 ± 6.40) (P < 0.001). CONCLUSION: The microhardness of Cention N in dual-cure mode was higher than that of self-cure mode, but the flexural strength of dual-cure was not significantly different from that of self-cure. Thermocycling had a significant effect on the microhardness and flexural strength.

Effect of Bleaching Method and Curing Time on the Surface Microhardness of Microhybrid Composite Resin.

Objectives: The present study aimed to evaluate the effect of curing time and bleaching agents on microhybrid composite resin surface microhardness. Material and method: A total of 180 microhybrid composite resin disks were divided into two groups in terms of curing time: 40 s, 60 s. Then, each group was divided into three subgroups: control (distilled water), home bleaching (15% carbamide peroxide) and office bleaching (40% hydrogen peroxide). Surface microhardness of the samples was determined by using Vickers hardness test both at baseline and after the completion of the tests. Two-way ANOVA and Tukey HSD tests were used to analyze and compare microhardness changes between groups. Statistical significance was defined at P<0.05. Results: Based on the two-way ANOVA, curing time, bleaching method, and cumulative effect of these two variables significantly affected composite resin microhardness (P<0.001). Tukey HSD tests showed that microhardness had significantly decreased in the bleaching groups, with the highest decrease when the office bleaching method was used (P<0.001). The samples cured for 40 s exhibited lower microhardness than those cured for 60 s and had an increased reduction in microhardness after bleaching (P<0.001). Conclusions: Application of both bleaching methods decreased the surface hardness of microhybrid composite resin. An increase in the curing time was associated with a decrease in adverse effects of bleaching agents on microhardness.

Fracture Resistance of over Flared Endodontically Treated Central Incisors Restored with Multiple Prefabricated and Custom-Made Glass Fiber Posts.

Objectives: This study aimed to evaluate the fracture resistance of over flared endodontically treated bovine central incisors restored with prefabricated and custom-made glass fiber posts, using the multi-post approach. Materials and Methods: Sixty-eight crownless over flared endodontically treated incisors were used for this study. The depth of prepared post space was 10 mm, and the remaining dentin thickness of the roots was 1 mm. The samples were randomly divided into four groups (n=17): Group 1: two prefabricated glass fiber posts; group 2: prefabricated glass fiber post + braided glass fiber; group 3: braided glass fiber; group 4: no post. Static load was applied at a crosshead speed of 0.5 mm/min at 135° angle relative to the root longitudinal axis until fracture. The data were analyzed using one-way ANOVA and post hoc Tukey's test at a significance level of P<0.05. Results: Groups 3 and 4 exhibited the maximum (981 N) and minimum (461 N) fracture strength values, respectively. The differences between group 4 and other groups were significant (P<0.001), but the differences between groups 1, 2, and 3 were not significant (P>0.05). Conclusion: Multiple prefabricated and custom-made glass fiber posts significantly increased the fracture resistance of crownless endodontically treated central incisors with over flared root canals.

Effect of Galardin and its Solvents on the Microtensile Bond Strength of Different Adhesive Systems to Dentin

Objective: To evaluate the effect of a synthetic inhibitor of MMPs (Galardin) and its solvents [ethanol and dimethyl sulfoxide (DMSO)] on the microtensile bond strength (µTBS) of adhesive systems to dentin. Material and Methods: Sound human third molars (n=180) were randomly assigned into 5 based on solution type: DMSO; ethanol; Galardin + DMSO; Galardin + ethanol; and distilled water as control. Then were further subdivided into 6 based on the adhesive system, i.e. 3-step and 2-step etch-and-rinse (ER), one-step and 2-step self-etch (SE) and universal in ER and SE strategies. The samples underwent a 500-round thermocycling procedure at 5±5/55±5°C and were sectioned into 1-mm2 pieces perpendicularly in a cutting machine. The µTBS was measured at a strain rate of 1 mm/min. Data were analyzed with two-way ANOVA and post hoc Games-Howell tests (p<0.05). Results: The adhesive system and the solution had significant effects on the µTBS (p<0.001). The universal adhesive in the SE mode resulted in a significant decrease in µTBS compared to the other adhesives (p<0.05). Ethanol, too, resulted in a significant decrease in µTBS compared to other solutions (p<0.05). Conclusion: Galardin and its solvents, except for ethanol, had no detrimental effects on the immediate µTBS.

Effects of surface treatments of conventional glass-ionomer on shear bond strength to giomer.

BACKGROUND: An appropriate bond between glass-ionomer and the superficial resin materials is very important for the success of sandwich technique. The aim of the present in vitro study was to evaluate the effect of three surface treatments of conventional glass-ionomer on its shear bond strength to giomer. MATERIALS AND METHODS: Sixty cylindrical specimens of a conventional glass-ionomer (GC Fuji II) were prepared and randomly divided into three groups (n = 20). The specimens in groups 1 and 2 were treated with total-etch adhesive resin (Single Bond) along with acid etching, and self-etch adhesive resin (FL-Bond II) on the set glass-ionomer, respectively. Specimens in group 3 were treated with self-etch adhesive resin (FL-Bond II) before initial setting of the glass-ionomer was complete. Then a giomer restorative (Beautifil II) was added to the specimens. Subsequent to thermocycling, the specimens were subjected to shear bond strength test. Failure modes were evaluated under a stereomicroscope. Data were analyzed by one-way analysis of variance and a post hoc Tukey test at a significance level of P < 0.05. RESULTS: There were statistically significant differences in bond strengths between the groups (P < 0.0005). Differences in bond strengths between group 2 and other groups were significant (P < 0.0005) while the differences between groups 1 and 3 were not significant. Failures were predominantly of the cohesive type in all the groups. CONCLUSION: Based on the results of this study, the use of self-etch adhesive resin (FL-Bond II) on the set glass-ionomer yielded the highest bond strength in the glass-ionomer/giomer sandwich technique.

Effect of two types of composite fibers on fracture resistance of endodontically treated maxillary premolars: an in vitro study.

AIM: The aim of the present study was to evaluate the effect of the use of composite fibers (glass fiber and polyethylene fiber) at the gingival third of mesio-occlusodistal (MOD) cavities on the fracture resistance of endodontically treated premolars. MATERIALS AND METHODS: A total of 45 extracted premolars underwent endodontic treatment. MOD cavities, 2.5 ± 0.2 mm thick at the buccal and lingual heights of contour, were prepared, with the gingival cavosurface margin 1.5 mm coronal to the cementoenamel junction. Then the teeth were randomly divided into three groups. In group 1, the cavities were restored with Z250 composite resin without the use of any fibers. In groups 2 and 3, the teeth were restored in the same manner as that in group 1 after placement of glass fiber and polyethylene fiber at the gingival third of the cavities, respectively. Subsequent to thermocycling, fracture resistance of the specimens was measured in Newton (N). STATISTICAL ANALYSIS: Data were analyzed with one-way ANOVA and a post hoc Tukey test at a significance level of p < 0.05. RESULTS: There were significant differences in the means of fracture resistance values between the three groups (p = 0.001). Statistically significant differences were observed in the fracture resistance between group 2 and groups 1 and 3 (p < 0.05). However, the differences between groups 1 and 3 were not significant (p = 0.25). CONCLUSION: The type of fiber influenced the fracture resistance of endodontically treated human premolars. CLINICAL SIGNIFICANCE: Using glass and/or polyethylene fibers in the gingival third of composite restorations leads to different results in fracture resistance of endodontically treated maxillary premolars.

Comparison of microleakage of three adhesive systems in class V composite restorations prepared with Er,Cr:YSGG laser.

OBJECTIVE: This study compared microleakage of three adhesives in class V (CI V) composite restorations prepared with Er,Cr:YSGG laser. BACKGROUND DATA: Changes produced on enamel and dentin surfaces subsequent to laser irradiation influence microleakage of composite restorations. MATERIALS AND METHODS: CI V cavities were prepared in 80 sound extracted human premolars with Er,Cr:YSGG laser. The teeth were randomly divided into 4 groups (n = 20). In group 1, a total-etch adhesive was used, and two-step and one-step self-etch adhesives were used in groups 2 and 3, respectively. Group 4 was the control group with no adhesives. Following restoration and thermocycling, microleakage was evaluated. To compare microleakage in occlusal and gingival margins in each group, the Wilcoxon test was used. Kruskal-Wallis analysis was used for comparison of occlusal and gingival microleakage, and two-by-two comparisons were made using the Mann-Whitney U test. RESULTS: There were significant differences in microleakage between occlusal and gingival margins in each group except for the control group. Significant differences were observed in occlusal and gingival microleakage among all the groups. Two-by-two comparisons revealed significant differences in occlusal microleakage between the control group and the other groups. There were significant differences in gingival microleakage between groups 1 and 2 and groups 1 and 3; however, differences in gingival microleakage between groups 2 and 3 were not significant. CONCLUSION: With all the adhesives, microleakage was significantly higher in gingival margins compared with occlusal margins. In occlusal margins, there were no significant differences in microleakage among the three adhesives. In gingival margins, self-etch adhesives revealed less microleakage than the total-etch adhesive.