Technical Field
The present invention relates to a curable composition, a curable composition for dental use, and an organic-inorganic composite particle for dental use.
Related Art
A curable composition formed of a polymerizable monomer and a filler is used in various fields from the viewpoints of mechanical strength and simplicity of work.
In the curable composition, selection of the filler is important, and the curable composition is formed by selecting, for example, the material, shape, particle diameter, and filling amount of the filler to be used. Through appropriate selection thereof, various properties, such as mechanical strength, physical characteristics, optical characteristics, and workability, of a final product are optimally adjusted.
For example, a curable composition for dental use generally includes a polymerizable monomer, a filler, and a polymerization initiator as main components, and is applied as a composite resin, a hard resin, an artificial tooth, cement, a resin material for machining processing, or the like. The curable composition for dental use is widely used as a dental material because of its ease of handling and low harmfulness to a living body. However, as compared to other materials, such as a metal and a ceramic, the curable composition for dental use can be hardly said to be sufficient yet in terms of mechanical strength required in order to function in a severe oral environment, and still needs to be improved also from the viewpoint of simultaneously achieving the mechanical strength and other physical properties, such as aesthetics and workability.
Under such situation, organic-inorganic composite particles are often used as the filler. For example, according to JP 2000-80013, when the organic-inorganic composite particles are used, a curable composition for dental use having a paste form and having excellent workability can be obtained while excellent surface smoothness and wear resistance are maintained, and moreover, its polymerization shrinkage rate is small. The organic-inorganic composite particles are composite particles each containing fine inorganic particles in an organic resin. The organic-inorganic composite particles have a smaller specific surface area than that of the fine inorganic particles. Therefore, the curable composition for dental use having a paste form can be produced by blending a sufficient amount of the organic-inorganic composite particles without expressing a thickening action. The curable composition for dental use produced by this method has had the following problem: in a cured body obtained by curing the composition, bonding at an interface between each of the organic-inorganic composite particles and its surrounding matrix is weak, and hence strength of the cured body is low.
In WO 2013/039169, there is a proposal of using organic-inorganic composite particles having aggregation gaps and having a micropore volume measured by a mercury intrusion method (in this case, the micropore refers to a pore having a micropore diameter in the range of from 1 nm to 500 nm) of from 0.01 cm3/g to 0.30 cm3/g. According to WO 2013/039169, when the organic-inorganic composite particles having aggregation gaps are used, a polymerizable monomer of a curable composition penetrates the organic-inorganic composite particles due to capillarity and is then cured, and hence an anchoring effect occurs to retain the organic-inorganic composite particles in a cured body of the curable composition with high interlocking strength, resulting in an improvement in mechanical strength.
In addition, in JP 2015-105254 A, it is described that, in a curable composition for dental use having blended therein organic-inorganic composite particles having aggregation gaps, when an organic resin component of each of the organic-inorganic composite particles is one obtained by polymerizing a polymerizable monomer component containing a certain amount or more of a polymerizable monomer having a hydrogen-bonding functional group, and a certain amount or more of a polymerizable monomer having a hydrogen-bonding functional group is blended as a polymerizable monomer component constituting an organic matrix, there is obtained a curable composition for dental use capable of providing a cured body having even higher mechanical strength.
As a typical method of evaluating the mechanical strength of a final product, there is given bending strength that is a stress value calculated on the basis of the maximum load applied to the product in a bending test. In the case of an organic-inorganic composite material obtained by curing a curable composition formed of a polymerizable monomer and an inorganic filler, in general, as the content of the inorganic filler is increased, the maximum load tends to increase, i.e., the bending strength tends to increase. However, as the amount of the inorganic filler increases, brittleness resulting from a decrease in amount of a resin serving as a binder also tends to increase. Therefore, it is considered that the bending strength and resistance to fracture do not necessarily coincide with each other. Meanwhile, total energy applied to a material until its fracture is called fracture energy. The fracture energy is a numerical value obtained on the basis of an integrated value up to fracture in a stress-strain curve, and may be rather important in evaluating the mechanical strength of an organic-inorganic composite material in which some degree of strain is generated.
The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a curable composition capable of providing a cured product having high fracture energy, a curable composition for dental use using the curable composition, and an organic-inorganic composite particle for dental use to be used for the curable composition for dental use.