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Bulk Fill vs. Incremental Fill: Does It Matter? An Investigation into Porosity and Flexural Strength of Composite Resins


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Bulk fill composites not only offer clinicians a less technique sensitive placement method of direct composite restorations, but also may offer the advantage of lower porosity due to the bulk placement of material. The purposes of this study are threefold: (1) to nondestructively compare the porosities of a conventional, nanofilled resin-based composite (RBC) with bulk-fill and bulk-fill-flowable RBCs using micro-computed tomography (microCT) analysis, (2) to investigate whether incremental and bulk-fill techniques can affect the internal porosities of a restoration, generating void disparities between restorations, and (3) to explore whether the strength of a restoration is related to its internal porosities or voids. 162 specimens were created by injecting the restorative material into stainless steel molds until completely filled using either a bulk fill (filled in one step) or incremental fill (filled in 2 increments). Each sample was then scanned using MicroCT in the middle 5mm of the sample to analyze the porosity and subjected to a 3 point bend test to calculate flexural strength. The combination that yielded the lowest porosity was the Filtek Supreme Ultra incrementally filled (FSU inc.) (0.19%) while the combination that yielded the highest porosity was the Filtek Bulk fill flowable - incrementally filled (FBFF - inc.) (0.33%). Filtek One - bulk filled (F1-B) yielded the highest strength (137.27 MPa), while Filtek Bulk Fill Flowable - bulk filled (FBFF-B) yielded the lowest results (80.08 MPa). A 2-way ANOVA analysis revealed that overall the bulk fill samples had a higher flexural strength while there was no significant difference between porosities of bulk fill and incremental fill groups. RBC restorations that were placed using a bulk fill technique produced a higher flexural strength than those filled by incremental fill despite having a slightly higher porosity.



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