Composite resins that are typical examples of dental compositions usually contain polymerizable monomer compositions including polymerizable monomers and additives such as a filler, a polymerization initiator, a polymerization inhibitor and a dye. In a composite resin including such components, a filler usually has the largest weight fraction followed by a polymerizable monomer composition and these two components represent a major proportion of the weight of the composite resin. The polymerizable monomer composition serves as a binder for the filler. The properties of the monomers, and the properties of cured products of the monomers are significantly influential on the properties and performance of the composite resin containing the monomer composition, and cured products thereof.
From the points of view of aspects such as the biological safety of monomers and the mechanical strength and wear resistance of cured products, the polymerizable monomer compositions frequently include radically polymerizable polyfunctional methacrylates. Typically, the polyfunctional methacrylate compositions are based on 2,2-bis[4-(3-methacryloyloxy-2-hydroxypropoxy)phenyl]propane (hereinafter, written as Bis-GMA) or 2,2,4-trimethylhexamethylenebis(2-carbamoyloxyethyl) dimethacrylate (hereinafter, written as UDMA), and contain triethylene glycol dimethacrylate (hereinafter, written as TEGDMA) to control the viscosity.
In the dental clinical practice, the use of composite resins in the restoration of tooth defects has a long history and is still expanding. However, the mechanical properties of cured composite resins are still insufficient. In particular, the poor strength obstructs the application of the resins to sites subjected to a high stress, for example, the use as molar tooth crowning materials.
In recent years, clinical experts strongly demand the expansion of the use of composite resins to such high-stress sites. Therefore, the development of composite resins having higher mechanical properties is an urgent necessity. As mentioned above, the properties of cured products of polymerizable monomer compositions used for composite resins significantly affect the properties of cured products of the composite resins containing the compositions.
Techniques have been reported in which Bis-GMA and UDMA that are widely used as main components of polymerizable monomer compositions are replaced by other monomers so as to enhance the mechanical strength of cured products of composite resins (Patent Literature 1 and Patent Literature 2).
Further, techniques aiming to improve main component monomers have been reported. For example, main component monomers are improved so as to enhance the refractive index of cured products of polymerizable monomer compositions (Patent Literature 3), and main component monomers are improved so as to enhance the degree of polymerization shrinkage between before and after the curing of polymerizable monomer compositions (Patent Literature 4).