• Journal of the korean academy of Pediatric Dentistry
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• v.43 no.4
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• pp.365-373
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• 2016

Composites are the most useful restorative material. However, composites have some disadvantages such as polymerization shrinkage, long working time, and susceptibility to water and contamination, which are stood out more especially when treating children. To solve these problems, bulk-fill composites have been developed. The aim of this study is to compare mechanical properties of bulk-fill and conventional composites. Bulk-fill composites (SureFil SDR flow (SDR), Tetric N-Ceram bulk fill (TBF)) and conventional composites (Filtek Z-350 (Z-350), Unifil Flow (UF), Unifil Loflo Plus (UL)) were used. The Vickers hardness tester was used to measure the microhardness of materials, and Fourier transform infrared spectroscopy was used to measure the degree of conversion. Polymerization shrinkage was measured by using a linometer. Flexural and compressive properties were measured by using the universal testing machine. Data were statistically analyzed by ANOVA and Scheffe's post hoc test. The level of significance was set to p < 0.05. Most conventional composites showed higher microhardness than bulk-fill composites. However, bulk-fill composites showed a higher top/bottom microhardness ratio than conventional composites. Bulk-fill composites showed a higher top/bottom degree of conversion ratio than conventional composites. The polymerization shrinkage was highest in UL and lowest in Z-350. The polymerization shrinkage of flowable composites was higher than that of non flowable composites. The compressive properties were highest in Z-350 and lowest in SDR and UL. In terms of flexural properties, Z-350 was the highest. However, none of the bulk-fill composites exhibited mechanical properties as good as those of conventional composites. Nonetheless, the ratio of microhardness and degree of conversion, which are important properties of bulk filling, were higher in bulk-fill composites. Therefore, the bulk-fill composites might be considered suitable restorative materials in pediatric dentistry.

• Journal of dental hygiene science
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• v.13 no.1
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• pp.13-19
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• 2013

This study evaluated the change of color and the microhardness according to time-out using the office bleaching with in vitro test after bleaching one time 1 day per week, total three times, for the control group and three times per 1day for the experimental group. $L^*$ was increased in both groups. Group 1 showed a significant increase statistically between before and after tooth whitening (p<0.05). Group 2 showed a significant increase statistically between before and after tooth whitening (p<0.05). ${\Delta}E^*$ was huge in both groups. In group 1, it was great in terms of statistical significance between 1 day and 7 days after tooth whitening (p<0.05). In group 2, it was the greatest between before and 1 day after tooth whitening and was significant statistically as well (p<0.05). Vickers hardness number (VHN) decreased in both groups. In group 1, VHN decreased over time and the difference was significant statistically (p<0.05). In group 2, VHN decreased over time and the difference was significant statistically (p<0.05). Percentage microhardness loss was great in both groups. In group 1, it was the greatest between 1 day and 7 days after the treatment, and it was significant statistically (p<0.05). In group 2, it was the greatest between before and 1 day after the treatment, and it was significant statistically (p<0.05). Put together, the more frequent tooth whitening a day is, the longer the period of tooth whitening when applying the same frequency, the greater color change was, however the microhardness decreased, in regard to the results over time using 15% hydrogen peroxide tooth whitening product for professionals.