Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1997-03-21
1998-05-19
Zemel, Irina S.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525299, 525309, 525311, C08F29702
Patent
active
057537658
DESCRIPTION:
BRIEF SUMMARY
In recent years, a large number of new and optimized bio-materials for synthetic dental/medical restorative use have been developed. The improvements were initiated by the need for materials which are very similar to the natural tooth substance with regard to esthetic-cosmetic criteria and, nevertheless, are unobjectionable from the medical point of view. Therefore, as a result of the intrinsic color of amalgam, substitution of this commonly used material for dental cements began very early whenever front teeth had to be restored.
Conventional dental cements usually consist of finely ground metal oxides, metal hydroxides, or other ion-leachable materials, e. g. glasses, plus an aqueous acid. The best known cements of this type are phosphate cement (zinc oxide+phosphoric acid) and silicate cement (powdered glass+phosphoric acid). Said cements are strictly inorganic materials, have poor adhesion to the tooth substance, and are relatively brittle. For these reasons and due to their strongly irritating effect to dental pulp, said materials have almost completely disappeared from the market.
From the discovery of polyacrylic acid, i. e. from the middle of this century, modified organic or semi-organic cements have gained increasing importance. Said materials consist of a metal oxide or metal hydroxide and a relatively high-molecular organic acid component. Among these materials, particularly carboxylate cements (zinc oxide+polyacrylic acid) are of interest. They are used as root fillers or pulp-capping materials. Owing to their high pH-value, said materials act as barriers protecting against acids and other toxic substances that may be included in several fillers. However, the main disadvantages associated with these cements are that they set very slowly, that their mechanical strength is poor, and that said materials may be leached by aqueous media.
As a result of the serious shortcomings, dental cements have largely been replaced by more durable, insoluble composites that withstand higher stress and have higher edge strength. Said composites mainly consist of a polymerizable binder reinforced with an organic or inorganic filler. Suitable polymerizable binders are especially those compounds comprising olefinically unsaturated groups, preferably (meth)acrylic acid esters of mono- and polyhydric alcohols. Suitable inorganic fillers are finely powdered quartz, micronized silicic acids, alumina, barium glasses, or other mineral particles covered with polymerizable silane to improve their adhesion. An essential feature of composites is that they cure through free-radical polymerization of the olefinic double bonds and that no water is required to achieve curing. Besides amalgams, composites are mainly used today for dental restorative purposes, but said materials, too, have limited applications because they may cause tissue irritation and intoxication in case of deep tooth cavities, undergo polymerization shrinkage, and have insufficient adhesion to the tooth.
In the late sixties, the discovery of glass ionomer cements, more precisely termed glass polyalkenoate cements, represented a major breakthrough in dental research. Said glass polyalkenoate cements, too, are mixtures of organic components, e. g. polyalkenoic acids or hydroxycarboxylic acids, and inorganic components, such as aluminum silicate glasses or quartzes. The reaction medium required for the cement reaction is water. The reaction is the same as with other cements, namely an acid-base reaction, herein the polycarboxylic acid acts as a proton donor, while the aluminosilicate glass is the proton acceptor.
This reaction may be divided into three steps, the boundaries between the steps being fluid: displacement of cations (first Ca.sup.2+, then Al.sup.3+) out of the glass. causing gelation and/or precipitation of the salt. and improving the mechanical properties. The cement becomes insoluble.
In 1971, glass polyalkenoate cements were described in literature (Wilson, A. D., J. Appl. Chem. Biotechnol., 21 (1971), p. 313) and, from that time, have been used i
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Ernst Muhlbauer KG
Mossman David L.
Zemel Irina S.
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