Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-08-17
2001-04-24
Szekely, Peter A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S220000, C524S493000, C524S494000, C524S560000, C428S404000
Reexamination Certificate
active
06221931
ABSTRACT:
BAKCGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to a dental restorative composition from which restorations having surface smoothness and transparency similar to natural teeth, having superior esthetics and superior physical properties such as bending strength and bending strain energy characteristics, and being provided with easy polishing properties can be obtained.
2. Description of the Related Art:
Dental restorative compositions are basically constructed by a combination of a polymerizable monomer, a filler, and a polymerization initiator. In order to impart capacities close to natural teeth, various improvements have been made.
Hitherto, inorganic powders having a maximum particle size of from 10 to 50 &mgr;m were used as the filler of dental restorative compositions. However, in case where such filler having a relatively large particle size is used, a surface of the resulting restoration is rough and a finished surface having smoothness similar to natural teeth could not be obtained in the clinical use.
Then, as a dental restorative composition intended to compensate this defect and to improve the surface smoothness, a dental restorative composition using particulate inorganic powders having a mean particle size of from 5 to 50 nm was developed. However, since this particulate inorganic filler has a relative large specific surface area, a large amount of the monomer should be used in the dental restorative composition. Accordingly, the proportion that the filler accounts for in the composition is low as from 30 to 60% by weight, resulting in increasing the polymerization shrinkage. Thus, the resulting restoration tended to be inferior in the physical properties.
As a means for compensating this polymerization shrinkage, an organic-inorganic composite filler prepared by curing a mixture of the monomer with a particulate inorganic powder having a mean particle size of from 5 to 50 nm and pulverizing the cured mixture. Since a dental restorative composition having this organic-inorganic composite filler compounded therewith is suppressed in the specific surface area, the amount of the monomer to be compounded can be small. Accordingly, this dental restorative composition has such characteristics that it compensates the polymerization shrinkage and that the surface smoothness of the resulting restoration is superior. However, the binding between a surface of the organic-inorganic composite filler and the matrix is weak. Thus, the resulting restoration tended to be inferior in the physical properties.
In addition, in recent years, a dental restorative composition using, as a filler, a glass powder having a maximum particle size of about 2 &mgr;m was developed. Although a restoration obtained by using this dental restorative composition has clinically superior surface smoothness, it has a high surface hardness. For this reason, it is difficult to achieve the polishing, so that it requires a lot of skill to obtain a smooth surface. Also, since in this dental restorative composition, the proportion that the glass powder accounts for is relatively high, though the resulting restoration has a high bending strength, it is low in bending energy and has brittle properties, leading to problems from the clinical point of view, such as marginal fracture.
SUMMARY OF THE INVENTION
An object of this invention is to overcome the above-described defects of the conventional dental restorative compositions and to provide a dental restorative composition from which restorations having surface smoothness and transparency similar to natural teeth, having superior esthetics and superior physical properties such as bending strength and bending strain energy characteristics, and being provided with easy polishing properties can be obtained.
In order to achieve the above-described object, we, the present inventors made extensive and intensive investigations. As a result, it has been found that a dental restorative composition which fulfills the above-described object can be obtained by combining a novel organic-inorganic composite filler with a particulate filler as the filler to be used in the dental restorative composition and further with a glass powder, if desired, leading to accomplishment of the invention.
Specifically, the dental restorative composition according to this invention has a great characteristic in using a novel organic-inorganic composite filler as the filler. We studied a combination of the viscosity of a matrix monomer constituting the organic-inorganic composite filler with the particle size of the particulate filler. As a result, in case where a matrix monomer having a specific viscosity is selected and kneaded with a particulate filler having a specific particle size, it has been successful in obtaining an organic-inorganic composite filler in which the matrix monomer is mixed without completely wetting the entire surfaces of primary particles of the particulate filler, and in the organic-inorganic filler prepared by polymerizing the kneaded material as it stands, followed by pulverizing, the surface of the inorganic powder is not entirely covered with the resin segment, but the inorganic segment is partially exposed, whereby the resulting organic-inorganic composite filler has a portion having high surface activity.
Further, when this organic-inorganic composite filler is contained in a dental restorative composition, a binding strength to the monomer segment in the dental restorative composition increases, the resulting dental restorative composition is superior in toughness to the dental restorative composition using the conventional inorganic-organic composite filler and becomes a tough material having in particular, a high bending strain energy, resulting to enabling to obtain a restoration which is less in fracture, etc.
Also, since the dental restorative composition according to this invention contains such organic-inorganic composite material, it has a low surface hardness as compared with the conventional dental restorative composition comprising a large amount of the glass powders (a mean particle size: 2 &mgr;m or lower) filled therein, and therefore, it has a characteristic that a smooth surface is readily obtained without using a special polishing material.
In addition, we studied the transparency similar to natural teeth, which is an indispensable characteristic to the dental restorative composition. In the resin material, a difference in the refractive index between the particulate filler and the cured matrix monomer caused turbidity inherent to the resin. In this case, it has been found that when the particle size of the particulate filler to be used is controlled to a certain particle size or less, the turbidity inherent to the resin is mitigated, a generally called opalescence can be suppressed.
That is, the dental restorative composition of this invention comprises:
(a) a methacrylate or acrylate monomer,
(b) an organic-inorganic composite filler prepared by curing a mixture of a particulate filler having a mean particle size of 20 nm or less with a methacrylate or acrylate monomer having a viscosity of 60 cP or more and pulverizing the cured mixture,
(c) a particulate filler having a mean particle size of 20 nm or less, and
(d) a polymerization initiator, and further, if desired,
(e) a glass powder having a maximum particle size of 5 &mgr;m or less and having a mean particle size of from 0.5 to 2 &mgr;m.
DETAILED DESCRIPTION OF THE INVENTION
This invention is described below in more detail with respect to each of the constitutional components.
The component (a), methacrylate or acrylate monomer, is a component which is used as a matrix monomer of the dental restorative composition, and also, a monomer having a specific viscosity is a component as a matrix monomer used in order to obtain the component (b), organic-inorganic composite filler.
The methacrylate or acrylate monomer includes various methacrylates or acrylates having an unsaturated double bonds. Specifically, examples of monomers having a viscosity of less t
Katsu Makoto
Kumagai Tomohiro
Nakagaki Norikazu
Sakuma Tetsuro
Ueno Takayuki
GC Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Szekely Peter A.
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