Abstract
The aim of this study was to evaluate the Knoop microhardness and the microtensile bond strength of a second-generation of bulk-fill (BF) and a nanohybrid composite resins (NH) in different thicknesses of increments. For this, ninety disks of composite resin were made for Knoop microhardness, being divided into six groups (n = 15). The Knoop microhardness obtained in each millimeter of the internal face. For microtensile bond strength, ninety restored in third molars were used, divided into six groups (n = 15). For Knoop microhardness, the Wilcoxon and Friedman test was used. For the microtensile bond strength were used the Two-way Anova test and Tukey's post-test (p <0.05). The NH resin showed higher Knoop micro hardness than BF and it was observed that hardness value decreases as increases the thickness of the resin. There was no significant difference in microtensile bond strength comparing NH and BF. However, there was a significant difference between G2 and G4 for the NH groups, with the highest and lowest bond strength values, respectively. Thus, the new generation of the bulk-fill composite resin provided lower microhardness values as the thickness of the increments increases in comparison with the nanohybrid composite resin. The microtensile bond strength does not appear to have been influenced by the type of resin, or the thickness of the increment.
Highlights
Nowadays, the conventional composite resins have many desirable characteristics that making it useful for use in anterior and posterior teeth, mainly because the ability to mimic tooth natural shades, the adhesion to enamel and dentin, the satisfactory mechanical properties and clinical longevity
3.1 Microhardness The results of microhardness (Table 2) show that there was a significant difference between the depths of each thickness of both composite resins (p
When comparing the composite resins, it showed that the groups referring to the NH showed higher hardness values compared to BF (p
Summary
The conventional composite resins have many desirable characteristics that making it useful for use in anterior and posterior teeth, mainly because the ability to mimic tooth natural shades, the adhesion to enamel and dentin, the satisfactory mechanical properties and clinical longevity. The conventional resin composites are inserted using the incremental technique (Aggarwal et al, 2019). Thesissues are usually observed as the depth and extension of the cavity increases. In order to minimize or avoid the above negative effects conventional resin, the bulk-fill composite resins were developed (Chesterman, Jowett, Gallacher, & Nixon, 2017; Kim et al, 2015). The bulk -fill resins usually are inserted by means of a single thick increment of 4 to 6 mm thick. To make and effective light-cured and improve the depth of cure, manufacturers increased the translucency of this materials and added alternative photo-initiators, increasing the light absorption in deep restorations (Behery, El-Mowafy, El-Badrawy, Saleh, & Nabih, 2016; Tauböck, Tarle, Marovic, & Attin, 2015)
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