are made up of an organic matrix and silanized inorganic fillers. The organic matrix typically contains a mixture of different dimethacrylates and additives (photoinitiator system, stabilizer, etc.). Polymerization shrinkage is one of the main drawbacks associated with the use of dental composites. [3] The resulting shrinkage stress generated during the curing of the material may result in marginal leakage between the restoration and the tooth. As a consequence, marginal staining, postoperative sensitivity, or the formation of secondary caries can arise.2,2-Bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (bis-GMA) and bis-[(2-methacryloyloxyethoxy-carbonyl)-amino]-2,2,4-trimethylhexane (UDMA) are the most frequently used crosslinking monomers in dental composites. These monomers are highly reactive in free-radical polymerization, exhibit a relatively low polymerization shrinkage, and enable the formation of polymer networks with excellent mechanical Polymerization shrinkage of dental composites remains a major concern. Free-radically polymerizable cyclic monomers can be a conceivable alternative to methacrylates for the development of low-shrinkage composites. In this study, the one-step synthesis of the novel low viscosity difunctional vinylcyclopropanes 1-4 is described. Photopolymerization kinetics of these monomers are investigated by photo-differential scanning calorimeter, using bis(4methoxybenzoyl)diethylgermane as photoinitiator. Real-time near-infrared photorheology measurements are performed to evaluate rheological behavior (i.e., time of gelation, polymerization-induced shrinkage force) and chemical conversion (i.e., double bond conversion at the gel point, final double bond conversion) of the vinylcyclopropanes in situ. The potential of these monomers as reactive diluents in dental restorative materials is evaluated. Composites based on vinycyclopropanes 1-4 show good mechanical properties and exhibit significantly lower volumetric shrinkage and shrinkage stress than corresponding dimethacrylate-based materials. The results indicate that such monomers are promising candidates for the replacement of commonly used low viscosity dimethacrylates such as triethylene glycol dimethacrylate in dental composites.
Polymerization shrinkage of methacrylate-based dental composites remains a major concern in restorative dentistry. Cyclic monomers that undergo ring-opening polymerization are known to exhibit reduced polymerization shrinkage compared to methacrylates. In this article, the synthesis of four crosslinking 1,1-disubstituted 2-vinylcyclopropanes bearing rigid spacers is described. These monomers were synthesized by esterification of 1-ethoxycarbonyl-2-vinylcyclopropane-1-carboxylic acid with the corresponding diols. The photopolymerization kinetics of these monomers was investigated by photo-differential scanning calorimeter using bis(4-methoxybenzoyl)diethylgermane as the photoinitiator. The synthesized vinylcyclopropanes (VCPs) were shown to be more reactive than the frequently used reactive diluent triethylene glycol dimethacrylate. Composites based on these VCPs showed good mechanical properties and exhibited a significantly reduced volumetric shrinkage and shrinkage stress compared to a corresponding dimethacrylatebased restorative material. This work highlights the excellent potential of VCPs as alternatives to methacrylates in the development of low-shrinkage dental composites.
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