Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-04-22
2001-08-28
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S116000, C523S117000, C523S118000, C522S071000, C522S083000, C524S786000, C524S789000, C524S790000, C524S853000
Reexamination Certificate
active
06281271
ABSTRACT:
The invention relates to two- and multi-component, radically polymerizable dental materials which are particularly suitable as cements and filling materials.
Cements and filling materials can be divided roughly into glass ionomer cements and composites (cf. for example R. Hickel, Stomatologie (1997) 94/7:363-382). Glass ionomer cements are aqueous, two-component cements based on polymeric organic acids such as for example poly(acrylic acid) and powdery solid bases such as calcium-fluorine-aluminium silicate glasses. The cement is cured by ionic reaction between polymer-bonded carboxyl groups and calcium or aluminium ions emerging from the filler. Glass ionomer cements are characterized by a high fluoride release which reduces the danger of secondary caries, but are not suitable for occlusion-bearing fillings because of their poor flexural strength.
The term composites describes compositions which consist essentially of a polymerizable binder and an organic or inorganic filler. Composites have a clearly higher flexural strength than glass ionomer cements, but do not generally release fluoride ions and also require the use of dentive adhesives and completely dry conditions during application.
Recently, it has been attempted to combine the positive properties of glass ionomer cements and composites. To do this, aqueous, plastics-modified glass ionomer cements (hybrid ionomers) and anhydrous compomers were suggested, whose curing is based on both an acid-base reaction and a radical polymerization.
The curing of composites, hybrid ionomers and compomers generally comprises a radical polymerization which is initiated chemically, by light or heat. Light- or heat-curing has the advantage that the materials remain processable up to irradiation with a suitable light source, and can as a rule be preserved over long periods of time when stored in opaque containers. The use of photoinitiators is however restricted to light-permeable materials and for deep cavities, a step-by-step processing and curing is necessary. In addition, the use of photopolymerizable materials is restricted to areas which are accessible for the polymerization lamp. Heat-curable materials cannot be used in the patient's mouth.
Chemical curing is carried out by using redox systems as polymerization initiators. These have the advantage that they can also be used with opaque materials and deep cavities. However, their restricted storage stability is disadvantageous.
Redox-initiator systems for chemical polymerization contain initiators such as peroxide or azo-compounds which can form free radicals (oxidizing substance) and a reducing substance which serves as an activator. The polymerization is triggered by mixing initiator and activator.
U.S. Pat. No. 3,991,008 discloses polymerizable dental materials with improved colour and storage stability, which contain substituted thiourea derivatives as reducing agents.
U.S. Pat. No. 5,554,665 describes the use of oxygen-permeable containers for storing chemically curable dental materials. The polymerization of the components is said to be inhibited by the incoming atmospheric oxygen.
U.S. Pat. No. 5,367,002 discloses dental materials which contain a curable liquid composition and a powdery component. The curing of the materials takes place on the one hand by the ionic reaction of polyalkene acids with an ion-releasing filler and on the other hand by radical polymerization. The materials can contain a redox-initiator system, the constituents of the redox system being distributed over different components of the dental material. Because of hydrolytic and/or undesired redox reactions in the liquid phase, the systems have a limited durability only. The use of strongly acidic monomers is not possible due to possible reactions with the constituents of the redox system.
According to U.S. Pat. No. 5,154,762, the constituents of the redox system are microencapsulated so that both components can be worked into the solid phase. In this way, reactions in the liquid phase can be avoided and the durability of the materials increased. However, to initiate the polymerization, initiator and activator must be released by dissolving the microcapsules or by their mechanical destruction. This requires either a relatively long activation period or the use of strong mechanical forces. In addition, microencapsulation is a laborious and thus cost-intensive process.
The object of the present invention is the preparation of a two- or multi-component dental material polymerizable at room temperature, in which the constituents of the redox-initiator system are contained in a single solid component, which can be manufactured easily and is polymerizable without the disadvantages described.
The object is achieved by dental materials with at least one polymerizable binder and at least one filler, the material containing a redox-initiator system for the radical polymerization, which comprises an initiator and an activator. The dental material is characterized in that the filler contains a homogeneous mixture of a first part of the filler, which is mixed with the initiator, a second part of the filler, which is mixed with the activator, and a third part of the filler, which does not contain a component of the initiator system.
With the dental materials according to the invention, the third filler portion functions as a thinner for the two initiator- or activator-containing filler portions so that, during conventional storage of the filler, no reaction takes place between initiator and activator. When the filler is mixed with the binder, the constituents of the redox-initiator system are dissolved by the binder and the redox-reaction initiated. By mixing initiator and activator with a part of the filler each, a uniform distribution of the constituents and thus a uniform polymerization of the dental material is ensured.
The filler preferably contains 20 to 90 wt.-%, particularly preferably 50 to 90 wt.-% and most preferably 70 to 90 wt.-% of the third filler part. The first and second filler parts are preferably used in the same amount.
The initiator is preferably mixed with the filler in a ratio such that the first filler part contains 1 to 20 wt.-%, preferably 7 to 15 wt.-% of the initiator, relative to the sum of the masses of initiator and filler. Similarly, the activator is preferably mixed with the filler in a ratio such that the second filler part contains 1 to 20 wt.-%, preferably 7 to 15 wt.-% of the activator, relative to the sum of the masses of activator and filler.
The ratio of the individual filler parts is selected such that the amount of each redox component is preferably 0.01 to 10 wt.-%, particularly preferably 0.02 to 5 wt.-%, quite particularly preferably 0.1 to 5 wt.-%, relative to the overall mass of the filler. The most preferred ranges are 0.2 to 1 wt.-%, and in particular 0.5 to 1 wt.-% relative to the overall mass of the filler.
Suitable redox-initiator systems are described in “Redox Polymerization”, G. S. Misra and U. D. N. Bajpai, Proc. Polym. Sci., 8, 61-131 (1982).
Preferred initiators (oxidizing substances) are cobalt(III) chloride, tert.-butyl hydroperoxide, iron(III) chloride, hydroxylamine (depending on the activator selected), perboric acid and its salts, and salts of permanganate anions or per-sulphate anions. Hydrogen peroxide can also be used, although if a photoinitiator is used simultaneously, interactions can take place.
Preferred activators (reducing substances) are ascorbic acid, cobalt(II) chloride, iron(II) chloride, iron(II) sulphate, hydrazine, hydroxylamine (depending on the initiator selected), oxalic acid, thiourea and salts of dithionite or sulphite anions.
Particularly preferred activators are ascorbic acid and benzyl-phenyl barbituric acid (BPBS), particularly preferred initiators are benzoyl peroxide (BPO) and lauroyl peroxide. The most preferred redox system is BPO/BPBS.
Besides the redox initiator, the dental materials according to the invention can additionally contain one or more photoinitiators. Preferred photoinitiators are benzoin ether, dialkylbe
Gianasmidis Alexandros
Moszner Norbert
Rheinberger Volker
Rumphorst André
Salz Ulrich
Ivoclar AG
Nixon & Peabody LLP
Szekely Peter
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