###### Abstract  
The objective of this work was to investigate the advantages of using dichloro bisphenol A-glycidyll methacrylate (dCl-BisGMA) as a potential matrix for dental resin composites. A series of model composites containing 65 wt% resin (urethane dimethacrylate/triethylene glycol dimethacrylate/BisGMA as 13:1) and 35 wt% silanated silica were prepared. Thus, BisGMA was replaced by dCl-BisGMA as 0, 25, 50, and 100 wt% to obtain UTBC0, UTBC25, UTBC50, and UTBC100, respectively. The composites' rheological properties, degree of double-bond conversion (DC), water sorption (WSP), and water solubility (W\({}_{\text{SL}}\)) were examined. The data revealed a statistically significant reduction in the complex viscosity of composites containing dCl-BisGMA, compared with UTBC0. No significant differences between DCs were detected (\(p<0.05\)). A significant enhancement in the reduction of the dCl-BisGMA composite W\({}_{\text{SP}}\) was also detected, and conversely, W\({}_{\text{SL}}\) was increased. Although the viscosity, DC, and W\({}_{\text{SP}}\) characters were enhanced, a W\({}_{\text{SL}}\) increase is an undesirable development. However, W\({}_{\text{SL}}\) is supposedly caused by cyclization of small flexible chains, which is more likely to occur in the presence of hydrophobic monomers such as dCl-BisGMA and more prone to leaching than are crosslinked networks. We concluded that dCl-BisGMA is a monomer that could potentially be used as an alternative or in combination with traditional monomers, including BisGMA, in resin-based dental composites, and it deserves further investigation. dichloro-BisGMA; resin matrix; dental composite; degree of conversion; water uptake; water solubility +
Footnote †: journal: Applied Sciences  
viscosity raises handling issues, decreases the degree of vinyl double-bond conversion (DC) upon curing, and restricts the addition of an adequate amount of reinforcing materials required for better mechanical properties of the restoratives [1,4]. To deal with viscosity issues, the incorporation of reactive, low-viscosity dimethacrylate monomers (diluents) within the resin matrices of dental composites is necessary. The most commonly used diluent is triethylene glycol dimethacrylate (TEGDMA); however, some other dimethacrylates, including ethovylated bisphenol A dimethacrylate (BisEMA), urethane dimethacrylate (UDMA), and ethylene glycol dimethacrylate (EGDMA), are used in combination with BisGMA [4]. Owing to the linear structure associated with triethylene oxide spacers, the addition of TEGDMA commonly enhances the hydrophilicity characteristics of the resins and increases water sorption and microcavities, which further affect the longevity of the composites. Indeed, the viscosity issue of BisGMA necessitates material development; thus, BisGMA structural modification including the replacement of its OH groups with low hydrophilic substituents may be one solution. In this context, various derivatives of BisGMA have been synthesized by different researchers, in which the OH functional groups were partially or fully replaced with targeted substituents, including alkyls, aryls, ethers, and esters with small or bulky groups [3,5,6,7,8,9,10,11,12]. Regardless of the type of substituent used, the viscosity of BisGMA was greatly reduced after modification, confirming that H-bonding is the major cause of its high viscosity character [2,6,10,12,13]. Adversely, substitution may affect the hygroscopic, mechanical, DC, and some other critical physicochemical properties of the composites. For example, modification of the BisGMA structure with less hydrophilic, small-sized substituents, such as methyl [14], methoxy [6], and chloride [2], resulted in low viscous analogs (\(\eta\) = 8.4, 3.6, and 7.2 Pa-s, respectively, at -22-25 \({}^{\circ}\)C). The incorporation of modified-BisGMA resin in dental composites showed enhanced properties, e.g., lower volumetric shrinkage, better mechanical properties, and lower water uptake [6,14].