Abstract
This study compared two resin composites with similar filler systems and different matrix compositions. The depth of cure (DoC), polymerization shrinkage, and marginal leakage were evaluated. A Filtek Bulk Fill resin composite (FB) and a Filtek Supreme resin composite (FS) were used. For the DoC and polymerization shrinkage, cylindrical specimens with different thicknesses were prepared. The DoC was attributed to the bottom/top ratios of Vickers microhardness numbers. For polymerization shrinkage, each specimen was firstly scanned using micro-computed tomography (µCT) then cured for 20 s, then for 10 s, and then for 10 s, and they were rescanned between each curing time. Data were processed using the Mimics software. For marginal leakage, standardized 5 mm cavities were prepared in 90 molars. After etching and bonding, materials were packed according to groups: FB-bulk, FB-incremental, and FS-incremental, which were cured for 20, 30, and 40 s, respectively. After thermo-cycling, teeth were stored in 1% methylene blue dye for 24 h and then sectioned and observed for dye penetration. The results showed insignificant differences in the shrinkage and leakage between the different packing techniques and curing times of both materials. In conclusion, the introduction of a novel matrix into resin composite composition enabled bulk-filling in one layer up to 5 mm deep while keeping a tolerable polymerization shrinkage.
Highlights
Polymerization reactions of most resin composites involve the rupture of the covalent aliphatic double bonds C=C in the reacting monomers and formation of single covalent bonds C–C
The results of the depth of cure (DoC) in the present study revealed that the hardness bottom/top ratio of both tested materials in all groups fulfilled a minimum value of 0.9
The polymerization shrinkage value range was between −1.4% (FB-bulk— cured for 20 s) and −1.9% (FS-incremental—cured for 40 s)
Summary
Polymerization reactions of most resin composites involve the rupture of the covalent aliphatic double bonds C=C in the reacting monomers and formation of single covalent bonds C–C. This is mostly accompanied by the shrinkage and reduction of the intermolecular distances by 0.3–0.4 nm between polymer chains [1]. If the adhesion quality is not adequate, adhesive failure and microleakage may occur. Problems like recurrent caries, discoloration, sensitivity, and pulpal irritation may occur [3,4]. The technology of bulk-fill resin composites is based on a huge dental industry that has experienced new types of monomers, such as expanding monomers [9] and ring-opening monomers [10], as well as innovative mechanisms of polymerization reactions [11]
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