Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-10-22
2002-03-05
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C433S228100, C523S117000, C523S118000
Reexamination Certificate
active
06353041
ABSTRACT:
FIELD OF THE INVENTION
The invention is directed to dental compositions, particularly for filling and sealing a root canal.
BACKGROUND OF THE INVENTION
When treating an infected root canal, the infected dentin is removed and the pulp and canal are then cleaned and disinfected. The disinfected canal is shaped and filled with a filling material that is cemented with a sealer.
The desirable properties for a root canal filling material include ease of removal from the canal if rework is needed, ease of manipulation with ample working time, dimensional stability (minimal shrinkage or change of form after insertion), ability to seal the canal laterally and apically (conforming and adapting to the various shapes and contours of individual canals), lack of irritation to periapical tissues, inertness and insolubility in tissue fluids. A desirable root canal filling material also provides bacteriostatic properties and is radiopaque.
Gutta percha is currently the root canal filling material of choice because, with careful manipulation, gutta percha can fulfill many of the above requirements. Gutta percha is available in cone shapes with different sizes. Its composition is gutta percha (a natural rubber) as a thermoplastic resin matrix, zinc oxide as a filler, one or more barium- or strontium-containing compounds as a filler and radiopacifier, waxes or resins, pigments and plasticizers.
The most common sealing material is a zinc oxide-eugenol type in a powder and liquid configuration. The powder is composed of zinc oxide and other additives such as a radiopacifier and colloidal silica, and the liquid is composed of eugenol and other resinous material and additives such as a plasticizer. When the powder and liquid are mixed in the presence of moisture, zinc oxide and eugenol undergo a setting reaction and the pasty material slowly becomes a solid. The sealer is used to fill any gaps between the gutta percha cones as well as in the lateral canal branches. The gutta percha filler needs to be softened by heat and then condensed into the canal, forcing the sealer to have an intimate contact with the canal wall and to fill the lateral canal branches.
The above method of filling and sealing the canal is, however, rather complicated. Separate sealing and filling materials are used. The gutta percha cone needs to be softened by heat in order to compact it inside the canal, and has a rather limited working time once the heat source is removed. Also, there are some other drawbacks associated with both materials. The zinc oxide-eugenol mixture is brittle, fragile, not very coherent and can easily disintegrate under a small stress. The zinc oxide-eugenol sealer is quite soluble in oral fluids, slowly dissolving away and leaving gaps between the filling material and the canal wall. Bacteria or other microorganisms can multiply in such gaps, causing infection and inflammation inside the canal and surrounding tissues. The gutta percha filling materials are quite hard and difficult to remove whenever rework is needed; removal often requires the application of a toxic organic solvent to soften the material. The gutta percha filling materials are also quite brittle and prone to breakage during insertion into root canals due to their intricate shape.
Therefore, there is a need to improve existing canal filling and/or sealing materials.
SUMMARY OF THE INVENTION
The invention is directed to a dental composition that may be used as a root canal sealing material, a root canal filling material, or a root canal filling and sealing material in one. The composition may be a two-part system of a powder/liquid or a paste/paste. The inventive composition provides a tight and effective seal in the root canal, yet is easily removed from the tooth structure if rework is needed. The composition also has a desirable flowable consistency and exhibits good adhesiveness with a tooth substrate.
The composition has at least one elastomeric acrylate (acrylate, as used herein, means either acrylate or methacrylate and may be abbreviated as (meth)acrylate) oligomer, at least one diluent comonomer that has at least one ethylenically unsaturated group, at least one filler and at least one polymerization initiator system.
The elastomeric (meth)acrylate oligomer may be a urethane (meth)acrylate oligomer or a polyalkyleneglycol (meth)acrylate oligomer. The concentration of the elastomeric (meth)acrylate oligomer may be 0.5-50% by weight. The filler may be inorganic metal, salt, inorganic oxide, silicate, aluminosilicate, aluminoborosilicate, fluoroaluminosilicate, colloidal silica, precipitated silica, polymeric solid, or mixtures of the above. The polymerization initiator system may be a redox initiator system.
The composition may optionally contain one or more antimicrobial agents. The antimicrobial agent may be, for example, benzalkonium chloride, iodoform, eugenol, zinc oxide, triclosan, butyl parahydroxybenzoate or mixtures of the above. The inventive compositions may also contain calcium hydroxide, one or more adhesion promoters, a plasticizer, and a wetting agent or surfactant.
The invention also includes a method of sealing and/or filling a root canal by preparing the inventive composition and providing the prepared composition to fill and/or seal a root canal.
These and other embodiments of the inventive composition will be apparent in light of the following detailed description and examples.
DETAILED DESCRIPTION
A two part composition for use in filling and sealing root canals is disclosed. One or more elastomeric acrylate (acrylate, as used herein, means either acrylate or methacrylate and may be abbreviated as (meth)acrylate) oligomers are mixed with one or more diluent comonomers, one or more radiopaque fillers and one or more polymerization or curing initiator systems. In one embodiment, one or more antimicrobial agents may be included in the composition. The elastomeric (meth)acrylate oligomer provides soft or elastomeric materials upon setting. The diluent comonomer controls the viscosity and optimizes the physical properties of the composition. The radiopaque filler facilitates detection of gaps or voids. The optional antimicrobial agent controls infection.
In use, the components are mixed and undergo a setting reaction. The set components are subsequently cured. The composition, upon curing, has a low modulus and is therefore flexible, which facilitates easy removal from the tooth structure should dental rework be needed. The composition exhibits only a small amount of shrinkage upon curing and may even slightly expand upon water absorption. This produces a tight and effective seal in the root canal. The composition also has a desirable flowable consistency and exhibits good adhesiveness with a tooth substrate.
Thus, the composition is an endodontic material that can function as a sealing and/or a filling material, and thereby eliminate the need for separate filling and sealing materials.
The invention is also directed to a root canal sealing and/or filling material that, when hardened, remains soft and flexible so that it can be easily removed from the canal if rework becomes necessary. This is achieved by utilizing a special (meth)acrylate oligomer that is flexible upon hardening. The composition, when applied, does not require the application of heat to compact it inside the canal.
The composition is antibacterial in some embodiments, is radiopaque, exhibits minimal volumetric shrinkage during curing, is dimensionally stable in oral fluids and has limited solubility in oral fluids. It has good adhesive properties and adapts well to canal walls and irregularities.
The root canal sealing and/or filling compositions of the invention comprise one or more elastomeric (meth)acrylate oligomers that have a low elastic modulus and that remain soft and flexible upon curing through free radical polymerization. “Acrylate” as used herein is a monomer, oligomer or prepolymer that contains one or more acrylate or methacrylate functional groups and may be abbreviated as (meth)acrylate. “Elastomeric” as used herein means that the (
Kerr Corporation
Michl Paul R.
Wood Herron & Evans LLP
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