فهرست مطالب نازنین آرین

Failure of restored teeth after endodontic treatment is one of the challenges faced in restorative dentistry. Premolar teeth are more likely to fracture due to exposure to tensile stress and inappropriate anatomical shape. Therefore, the aim of this study was the comparison of the fracture resistance of maxillary premolars which were restored with composite resin, composite resin with glass ionomer lining and composite resin reinforced with fiber post. In this experimental study, 60 extracted human maxillary premolars were randomly divided into 4 groups of 15: Composite resin without bonding (1), Composite resin+ glass ionomer lining (2), Composite resin+ single bond 2 (3) and Composite resin+ Fiber post (4). The teeth were prepared by MOD design with palatal cusp reduction. The samples were placed in a chewing simulator and went under a 30 N force for 1200000 cycles. The threshold of compressive resistance was measured in MPa. Also, fracture patterns were assessed divided by restorability and non-restorability. ANOVA test was used for statistical analysis of data in all groups and post-hoc TUKEY test was used for two by two comparisons. The threshold of force resistance significantly increased from group 1 to 4 and the difference among all groups was strongly significant (p = 0.000). Restorable fracture pattern followed an ascending order from group 1 to 4 which was reversed for unrestorable pattern with no significance. (P> 0.05) Composite resin restoration reinforced with fiber post can increase the fracture resistance of endodontically treated premolars but the number of unrestorable fractures also increases with the use of these posts. Fracture strength and fracture patterns obtained through usage of composite resin restorations in endodontically treated teeth are appropriate.

Discoloration of composite restorations over time is among common factors causing their replacement, which weakens the tooth structure and causes pulpal injury. Since tea is a common drink among Iranians, the current study aimed to evaluate the discoloration effect of tea on Kalore and Gradia composite resins. This experimental study was performed on 20 disc-shaped specimens of two composites, Kalore and Gradia. Ten specimens of each composite type with subgroups of 5 were stored in tea and distilled water for 72 Hours. Color measurements were obtained using Spectrophotometer (Minolta, Japan) before and after immersion in solutions. Final spectrophotometry was done after polishing. The results were analyzed using Kruskal-Wallis test. The discoloration value of both composites increased significantly after being immersed in tea (P<0.001). Discoloration in Kalore was higher than Gradia (P<0.014); and amount of discoloration was clinically unacceptable for both composites. (ΔE >3/3) After final polishing of the samples kept in tea, amount of discoloration decreased for both composites (P<0.001) and (P=0.002) respectively; this reduction was more prominent in Kalore (P=0.008). Nonetheless, discoloration value was yet clinically unacceptable. Immersing the composites in tea caused clinically unacceptable amount of discoloration in both Gradia and Kalore and polishing had more corrective effect on Kalore.