Abstract
Abstract 
 Objective: To assess the in vitro effect of bulkfill and incremental application techniques on the microleakage of class II dental cavities filled with three different bulkfill composite materials at occlusal and cervical margins.
 Methods: Standardized class II cavities were prepared on 120 human premolar teeth extracted for orthodontic treatment, which were randomly divided into two main groups of 60 teeth, corresponding to the two application techniques. Each group wasthen sub-dividedrandomly into three sub-groups based on the type of bulkfill restorative materials as follows: Tetric®N-Ceram BulkFill, Filtek™BulkFill flowable restorative material and X-trafil®BulkFill. All cavities were prepared and etched, and the corresponding self-etch bond adhesive systems were applied. A stereomicroscope was used to assess microleakage after thermocycling and immersion of the specimens in 0.1% methylene blue for 24 hours. Mann-Whitney U test was then used to analyze data.
 Results: No statistically significant difference was found in the marginal microleakage between the incremental and bulkfill techniques using the three types of composite materials at both occlusal and cervical margins. The X-trafil®BulkFill showed the lowest score of microleakage with both application techniques compared to other bulkfill composite materials.
 Conclusion: Both incremental and bulkfill application techniques using Tetric®N-Ceram BulkFill, Filtek™BulkFill flowable restorative material and X-trafil®BulkFill composite materials have a comparable effect on the marginal microleakage at occlusal and cervical margins of human teeth extracted from dental clinics in Sana’a city. Further studies are recommended to assess the clinical success of bulkfill composite materials using SEM or confocal microscope.
Highlights
The stability and success of resin composite restorations depend on their marginal seal and the absence of microleakage
An increased marginal leakage could when the cervical finishing line is positioned below the cemento-enamel junction (CEJ).[10,11] To overcome this leakage, the use of flowable composites is recommended because of the increased elasticity, wettability, and low viscosity that improve the marginal adaptation of composite restorations.[6] flowable composites are not suitable filling materials for all types of restorations due to their lower physical and wear resistance properties
Scanning electron microscope (SEM) and stereomicroscope have been used to assess the marginal seal and microleakage of direct and indirect composite inlays in cavities with cervical margin set in enamel or dentin.[19]No significant differences were found between both techniques when the cervical margin was in enamel
Summary
The stability and success of resin composite restorations depend on their marginal seal and the absence of microleakage. Several techniques have been developed to avoid the effect of polymerization shrinkage and microleakage, including incremental layering application, light curing of the composite restoration of less than 2 mm thickness,(1,2) and the use of indirect and semi-direct restorations.[7] nonear highly successful in reducing the occurence of polymerization shrinkage. The incremental filling remains the “gold standard” technique to restore dental cavities exceeding 2 mm in depth. This technique minimizes gap formation and polymerization stress, allows adequate bonding of composite to tooth tissue and ensures complete polymerization of resin-based composites.[8] the incremental application of composite filling material can reduce C-factor and, ,the shrinkage stress at the tooth restoration margin by allowing the stress-relieving flow of composite restoration from the unbonded surface to the bonded one.[9]. Most conventional composite filling materials exhibit lower polymerization shrinkage when compared to flowable composites
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