For the dual-polymerizing resin cements, the self-cure mode should ensure the high level of conversion, especially in the cervical proximal areas, the root canal and in the internal and deep areas of the cavity preparations. The restorative resin-based materials must reach a high degree of monomer conversion in order to present better clinical performance and longevity and also to reduce the early failures. The filler loading and the viscosity of composites may interfere in the monomer conversion, since they could restrict the mobility of monomers and the propagation of polymerization reaction. Vinyl groups (e.g., ethylene glycol dimethacrylate) are added as a thinner or diluent monomer for uncured pastes, which are considered another approach to change the viscosity of resin-based materials. Most direct dental restorative composites use bisphenol-A-diglycidylether dimethacrylate (Bis-GMA), which is considered a very viscous monomer, and when mixed with higher filler loadings, it becomes a nearly solid mass and unusable product. 7, 8 Low viscosity or flowable resins and resin cements present lower filler loading than regular restorative materials. High volume fraction of fillers can increase the viscosity and the elastic modulus and strength of composites. 5, 6 The difference in the cement formulations that change the viscosity is related to the proportion between resin matrix and filler particle content. The lowest film thickness generates smaller polymerization shrinkage, reducing the possibility of gaps formation and premature marginal leakage. The option for low viscosity versions offer some benefits, such as minor thickness of the pellicle that was formed following the restoration placement. Modifications in the viscosity of the resin cements allow their use in different clinical situations. ![]() ![]() In some clinical situations, such as in dark zones at the apical region and during the cementation of indirect restorations, the severe light attenuation results in low degree of conversion (DC), which can compromise the mechanical properties and consequently the longevity of the indirect restorations. ![]() The dual-polymerizing materials were developed to compensate for the lack of polymerization in the absence of light and to represent a combination of auto- and light-polymerizing components. Dual-polymerizing resin cements have been extensively used for placement of indirect restorations and posts.
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