BackgroundThe use of composites in dental restoration has been commonly criticized, due to their underwhelming mechanical properties. This problem may be solved partially by preheating. The present research aims to determine the effect of preheating on the mechanical properties of two different classes of composites. Material and Methods A Silorane-based (Silorane) and a Methacrylate-based (Z250) composite were preheated to different temperatures (25, 37, and 68 °C) and afterwards were tested with the appropriate devices for each testing protocol. The material’s flexural strength, elastic modulus, and Vickers microhardness were evaluated. Two-way ANOVA, and Tukey’s post hoc were used to analyze the data. Results Microhardness and elastic modulus increased with preheating, while flexural strength values did not increase significantly with preheating. Furthermore the methacrylate-based composite (Z250) showed higher values compared to the Silorane-based composite (Silorane) in all the tested properties. Conclusions Preheating Silorane enhances the composite’s microhardness and elastic modulus but does not affect its flexural strength. On the other hand, preheating Z250 increases its microhardness but does not change its flexural strength or elastic modulus. In addition, the Z250 composite shows higher microhardness and flexural strength than Silorane, but the elastic modulus values with preheating are similar. Therefore Z250 seems to have better mechanical properties making it the better choice in a clinical situation.
Key words:Composite, elastic modulus, flexural strength, microhardness, preheating.
Objectives: Plaque and stains are removed by prophylaxis methods from tooth surfaces. Since prophylaxis methods can have a detrimental effect on the surface finish of restorations, the aim of this in vitro study was to investigate the effect of three prophylaxis methods, including pumice with rubber cup, pumice with brush, and air-powder polishing device (APD) on the surface roughness of giomer. Study design: Sixty four cylindrical giomer (Beautifil II, Shofu) samples with a diameter of 6 mm and a height of 2 mm were used. Subsequent to a 3-month period of storage in distilled water at 37ºC, the samples were randomly divided into four groups of 16. In group 1 (control), no prophylaxis procedure was carried out. In groups 2 to 4 the samples were exposed to pumice with rubber cup, pumice with brush, and APD prophylaxis methods, respectively. The surface roughness of the samples was measured using a profilometer and the effect of different prophylaxis methods on surface topography was characterized by atomic force microscopy (AFM). All data were analyzed by one-way ANOVA and Duncan's post hoc test at a significance level of P < 0.05. Results: There were statistically significant differences in surface roughness among the groups (P < 0.0005). Furthermore, in pairwise comparisons there were statistically significant differences between all the groups (P < 0.05). The roughest surfaces, in descending order, were observed with the use of APD, pumice with brush, and pumice with rubber cup. Conclusions: The use of different prophylaxis methods resulted in an increased surface roughness of giomer compared with the control group. APD prophylaxis exerted the most detrimental effects on the surface of giomer.
Background. Bulk-fill composite resins are a new type of resin-based composite resins, claimed to have the capacity to be placed in thick layers, up to 4 mm. This study was carried out to evaluate factors affecting gap formation in Cl II cavities restored using the bulk-fill technique.
Methods. A total of 60 third molars were used in this study. Two Cl II cavities were prepared in each tooth, one on the mesial aspect 1 mm coronal to the CEJ and one on the distal aspect 1 mm apical to the CEJ. The teeth were divided into 4 groups: A: The cavities were restored using the bulk-fill technique with Filtek P90 composite resin and its adhesive system and light-cured with quartz tungsten halogen (QTH) light-curing unit. B: The cavities were restored similar to that in group A but light-cured with an LED light-curing unit. C: The cavities were restored using the bulk-fill technique with X-tra Fil composite resin and Clearfil SE Bond adhesive system and light-cured with a QTH curing unit. D: The cavities were restored similar to that in group C but light-cured with an LED light-curing unit. The gaps were examined under a stereomicroscope at ×60. Data were analyzed with General Linear Model test. In cases of statistical significance (P<0.05), post hoc Bonferroni test was used for further analyses.
Results. The light-curing unit type had no effect on gap formation. However, the results were significant in relation to the composite resin type and margin location (P<0.001). The cumulative effects of light-curing unit*gingival margin and light-curing unit*composite resin type were not significant; however, the cumulative effect of composite rein type*gingival margin was significant (P=0.04)
Conclusion. X-tra Fil composite exhibited smaller gaps compared with Filtek P90 composite with both light-curing units. Both composite resins exhibited smaller gaps at enamel margins.
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.
Aim: This study evaluated the effect of three different contamination removal methods on bond strength of one-step self-etching adhesive to dentin contaminated with an aluminum chloride hemostatic agent.
Materials and methods:One hundred noncarious adult molars were used in this study; 2-mm-thick dentin disks were prepared and randomly assigned to 5 groups (n = 20). Group I: control; group II: hemostatic agent-contaminated; group III: hemostatic agent-contaminated and rinsing with water; group IV: hemostatic agent-contaminated and ethylene diamine tetraacetic acid (EDTA) application; and group V: hemostatic agent-contaminated and phosphoric acid application. Clearfil S3 Bond was used to bond composite to dentin surfaces. Subsequent to adding composite cylinders the shear bond strength test was performed. Data were analyzed by one-way ANOVA and Tukey test. Two additional specimens from each group were prepared and evaluated under scanning electron microscope (SEM).Results: There were statistically significant differences in bond strength among the groups (p < 0.001). In two-by-two comparisons statistically significant differences were observed in bond strength values between all the groups (p < 0.001) except for groups I and IV (p = 0.933).
Conclusion:Aluminum chloride hemostatic agent adversely affected the bond strength of self-etch adhesive to dentin. However, application of EDTA increased the bond strength to the level of normal dentin.Clinical significance: EDTA and phosphoric acid removed aluminum chloride hemostatic agent contamination of dentin surfaces. However, unlike EDTA phosphoric acid failed to increase the bond strength of self-etch adhesive to dentin to the level of the control group.
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