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Fracture resistance of teeth restored with packable and hybrid composites
M. Ghavam , M. Ataee , F. Fallahzade ,
Volume 19, Issue 1 (4-2006)
Abstract

Background and Aim: With recent introduction of packable composites, it is claimed that they apply less stress on tooth structure because of reduced polymerization shrinkage, and similarity of coefficient of thermal expansion to tooth structure. However, the high viscosity may in turn cause less adaptation, so it is not clearly known whether these materials strengthen tooth structure or not. The aim of this study was to evaluate fracture resistance of maxillary premolars, receiving hybrid or packable composite restorations with different methods of application and curing.

Materials and Methods: In this experimental study, seventy five intact premolars were randomly assigned to five groups of 15 teeth each. One group was maintained intact as the control group. Similar MOD cavities were prepared in the other teeth. The teeth in group two were restored with Spectrum in incremental layers and light cured with 500 mw/cm2 intensity. The third group were filled with Surefil and cured with light intensity of 500 mw/cm2. The groups four and five were restored with Surefil in bulk technique with two different modes: 500 mw/cm2 intensity and a ramp mode (100-900 mw/cm2) respectively. After thermocycling, force to fracture was assessed and degree of conversion (DC) at the bottom of cavities was evaluated for different modes and methods. The curing and placement methods in groups tested for DC (A to D) were the same as fracture resistance groups (2 to 5). Data were analyzed using one way ANOVA and Tukey HSD tests with p<0.05 as the limit of significance.

Results: All the restored groups showed significantly less fracture resistance than the control group, but had no significant difference among themselves. DC of Spectrum was higher than Surefil. Bulk method with 500 mw/cm2 light intensity, significantly decreased DC. DC in bulk method with high light intensity was not significantly different from incremental method with 500 mw/cm2 light intensity.

Conclusion: Placement techniques, light intensity and type of composite had no influence on the fracture resistance. The use of packable composite with bulk technique and 500 mw/cm2 intensity or less is not recommended in 4 mm depth cavities due to insufficient DC.


Evaluation and comparison the effect of different polishing methods on surface roughness of two types of nano-hybrid composites
Abdolrahim Davari, Farnaz Farahat, Marjan Mehravaran, Alimohammad Doosthosseini, Negar Etminan,
Volume 38, Issue 0 (4-2025)
Abstract
Background and Aims: Finding an appropriate method for polishing that can be used in dental practices to improve the longevity and ease of dental restorations is of great importance. The aim of this study was to evaluate the effect of different polishing methods on the surface roughness of two types of nano-hybrid composites, an in vitro study.
Materials and Methods: In this study, 42 samples in the form of discs (6 mm in diameter and 3 mm in thickness) of two nano-hybrid composites (Charisma Kulzer and EvoCeram Tetric IPS) were prepared. Each group had 21 samples (polymerized in a mold made of polyfluorohalide material) and were all shaded (A2 color). To prevent mirror-like reflections, each sample was covered. A 2 kg load was applied for 30 seconds on each sample, after which the composites were removed. The samples were stored for 7 days in deionized water at room temperature and in the dark. After this period, the samples underwent finishing and polishing procedures. Seven random samples from each composite group were polished using different methods: System Gloss Composite LUCIDA, EVE polishing discs, and EVE polishing discs + Cosmedent polish. The surface roughness was measured using a profilometer, and observations were made under a microscope. Data were analyzed using SPSS 25 software with t-tests, ANOVA, and the Bonferroni post hoc test.
Results: The two-stage method using EVE polishing discs showed significantly the lowest surface roughness in both types of composites (P<0.0001). The type of composite did not have a significant effect on initial surface roughness (P=0.067), but the polishing method had a significant effect on the surface roughness (P<0.0001). The difference in the mean surface roughness was statistically significant among different polishing methods for either type of composites (P<0.0001). The t-test analysis showed no significant difference in the surface roughness between the two types of composites with different polishing methods (P>0.05), except in the LUCIDA polishing system where a significant difference was observed in both groups.
Conclusion: The results showed that the polishing method had a significant effect on the surface roughness and not the type of composte. The use of EVE polishing discs effectively reduced the surface roughness in both types of nano-hybrid composites used in the present study.

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