Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1981-07-22
1983-06-21
Bleutge, John C.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
523212, 523216, 524493, 524560, 524786, 524789, 524790, 524847, A61K 506, C08K 336
Patent
active
043894976
DESCRIPTION:
BRIEF SUMMARY
As it is known from the U.S. Pat. No. 3,066,112, to the hardenable dental materials on the basis of ethylenically unsaturated, polymerizable monomers of which especially the mono-functional and di-functional as well as poly-functional esters of the acrylic acid and methacrylic acid have achieved considerable practical use, higher amounts of inoganic fillers are added for the reduction of the shrinkage during polymerization, decrease of the thermal expansion coefficient and increase of hardness of the obtained polymerisates. The fraction of inert inorganic fillers can amount up to more than 80% of the total material in such dental permanent filling materials. As fillers e.g. quartz, quartz glass or silicate glasses like lithiumaluminium silicate or barium silicate glass are used as fine powder. The particle sizes of these fillers are within the range of 1 .mu.m to approximately 100 .mu.m, the average particle diameter being generally in the magnitude of approximately 10 .mu.m.
Disadvantageous upon use of these fillers is the fact that the dental materials produced therefrom do not yet have a satisfying abrasion resistance and have surface roughness upon utilisation as tooth fillings. Due to the mediocre abrasion resistance, the tooth filling materials could not be used with the mentioned fillers in the molar field where the amalgam fillings are still predominant despite the toxicologically critical mercury.
The surface roughness of the mentioned materials leads additionally to problems upon use in the anterior tooth area since the depositing of dental plaque is promoted, thereby causing discolorations as well as marginal secondary caries.
From the DE-OS No. 24 03 211, there is known that very finely divided fillers, like micro-fine silicic acid (silicon dioxide gel) or aluminium oxide, having particle sizes within the range of 5-700 nm, yield well-polishable shaped bodies after curing of the dental material produced therewith. As can be seen from the articles of R. Schafer in "Dental Echo", Vol. 49, 136 (1979) and A. Gro.beta. in "Chemie in unserer Zeit", 13th Annual Set, page 142 (1979), no workable pastes having high contents of fillers as required for the dental application in the dental practice can be obtained with these micro-fine fillers which have a very large specific surface. It has been shown that upon blending of the micro-fine silicic acid, e.g. of the pyrolitically produced silicon dioxide gel, into the liquid monomer, a thickening of this monomer to a honey-like, stringy and adhesive mass is firstly obtained and then is suddenly converted into a bittle mass upon continuous addition of silicic acid which mass finally dissolves in a freely flowing powder. Thus, only masses of salve-like or powdery consistency can be produced. In these references, it is now pointed out that the micro-fine filler shall be firstly premixed and prepolymerised with a polymerizable monomer. The solid product so obtained is crushed and finely ground. This pulverized splinter polymerisate is then used as actual filler in the hardenable dental material.
In this manner, however, very high fractions of inorganic fillers are not achievable in the dental materials since, according to this known method the splinter polymerisate to be incorporated in the monomer consists considerably of organic substance, already.
Therefore, upon utilisation of this filler, a higher thermal expansion coefficient must be accepted thereby partly compensating the aspired advantage of having a high filler fraction within the polymerizable dental material. In case the filling material and the tooth substance have a considerably different thermal expansion coefficient, the so-called "pump effect" is obtained caused by the change of temperature e.g. by ingestion. Through the formed marginal gap, bacteria can penetrate and lead to secondary caries or to damages of the pulp in deep cavities. In addition, the micro-fine silicic acid must be mixed very intensively with the monomer fluid during the production of the pre-polyfmerisate in order to achieve
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Hubner Heinz-Joachim
Jochum Peter
Purrmann Robert
Schmitt Werner
Bleutge John C.
Espe Fabrik Parmazeutischer Praparate GmbH
Lilling Herbert J.
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