Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-08-13
2003-07-29
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S493000, C524S543000, C524S612000, C524S430000, C524S436000, C524S435000, C528S031000, C528S032000, C528S901000, C528S012000, C528S015000, C528S019000, C528S041000, C556S444000, C525S478000, C106S038200
Reexamination Certificate
active
06599974
ABSTRACT:
Subject matter of the present invention is an impression material for use with an impression spoon.
WO-A-97/32536 and WO-A-98/52491 describe an impression spoon and an impression material for said impression spoon.
There, the impression material is fed from the rear ends of the impression spoon into the mold cavity confined and sealed between the impression spoon and the jaw and drawn through the groove of the mold to the front end of the impression spoon under the influence of reduced pressure. An introduction of deflector elements in the form of skeleton foams results in a flow component of the impression material parallel to the tooth center promoting the complete impression of undercut and deeper areas.
Using such impression spoons, one obtains highly precise impressions which—as compared to impressions obtained by conventional impression techniques—do not contain any trapped liquids (sulcus liquid, blood) or air bubbles and which do not have any defective wetting, distortions, or elastic recovery of shape after the deformation of the plastic impression material under pressure.
The low-viscous impression materials used in the conventional impression techniques are not or only restrictedly usable with the new impression spoon due to the kinetic and rheological properties thereof.
The impression materials usually used in the conventional impression techniques consist of a multicomponent system:
&agr;) di- and polyalkenylsiloxanes;
&bgr;) polyhydrogensiloxanes;
&ggr;) a precious metal catalyst of the 8th side group of the periodic system;
&dgr;) reinforcing fillers;
&egr;) non-reinforcing fillers.
The technical problem forming the basis of the invention is the provision of an impression compound which can be used in the novel impression spoons according to WO-A-97/32536 and WO-A-98/52491. Another problem is the provision of a formulation which does not sedimentate and separate during storage, the rheological properties of which remain almost unchanged and which results in a cured impression material having mechanical properties which correspond to the features of DIN 24823 (ISO 4823) as well as the required tear resistance and tear propagation resistance.
Said problem is solved by an impression material for use with an impression spoon, wherein the impression material comprises curable components and at least one first filler, characterized in that said at least one filler has a BET surface of from 20 to 50 m
2
/g, preferably from 30 to 40 m
2
/g, whereby the impression material becomes slightly thixotropic and attaining a viscosity of from 1 to 350 Pas.
The impression material of the invention is advantageous in that it meets the demands made on the use thereof in the novel impression spoon, in particular the demands made on the impression material with regard to viscosity, reaction kinetics, elastic properties and thixotropy during the flow of the material through the impression spoon. These are in particular:
a) Viscosity
The impression materials of the invention used in the novel impression spoon according to WO-A-97/32536 and WO-A-98/52491 ensure a very good flow behavior which results in an optimal impression. Studies have revealed that the impression results of said novel impression technique are the better the lower the mixed viscosity of the employed impression material is.
Preferably, low-viscous formulations having a mixed viscosity in the range of from 1 to 40 Pas are employed; especially preferred are mixed viscosities of from 1 to 10 Pas.
Low-viscous formulations in this viscosity range have been known in the art (see table 3).
The tooth impression materials having the lowest viscosity (DIN 24823, ISO 4823) obtainable on the market have a mixed viscosity of from 27 to 1100 Pas. The mixed viscosities of the impression materials having the lowest viscosity (Permadyne Garant 2:1, Provil L Panasil contact plus, and Lastic Xtra superfine) exceed the ideal viscosity range of from 1 to 10 Pas. Therefore, said materials used for the conventional impression techniques such as the correction and sandwich impressions have only unsatisfactory impression results in this novel impression technique.
b) Elastic Properties During the Flow Through the Impression Spoon (Reaction Kinetics)
In the novel impression technique according to WO-A-97/32536 and WO-A-98/52491 the impression spoon is filled from the rear to the front. An important criterion is that the mixed viscosity of the inventive impression material during the flow through the impression spoon has to remain almost constant, i.e., no or only very weak elastic properties by chemical crosslinking may be generated. Also here, the marketable products used for the conventional impression techniques (Aquasil LV, Xantopren XL, Coltene President light) have drawbacks. These products are disadvantageous in that they crosslink too fast during the flow through the impression spoon according to WO-A-97/32536 and WO-A-98/52491 and thus generate elastic properties already during the flow through the impression spoon.
When employing the conventional impression materials as such in the novel impression spoon, also this kinetic effect results in unsatisfactory impression results.
c) Thixotropy
The impression materials of the invention employed in the novel impression spoon according to WO-A-97/32536 and WO-A-98/52491 ensure that the thixotropy is as low as possible, which considerably contributes to an optimum impression. Studies have revealed that the impression results obtained with the use of this novel impression technique are the better the lower the thixotropy of the employed impression material is. Usually, the impression materials employed in accordance with prior art have thixotropic properties (e.g., Panasil contact plus, thixotropic index: 1.7).
In the novel impression technique, said impression materials revealed only unsatisfactory impression results since said impression materials form flow trails in the shadow area of the flow direction when flowing through the impression spoon from the rear to the front around the teeth.
In addition to the above-mentioned properties, the inventive impression material for the novel impression technique meets further demands which will be explained below:
Mechanical Properties of the Cured Impression Material
The inventive impression materials for the novel impression technique according to WO-A-97/32536 and WO-A-98/52491 meet the demands of type 3 of DIN 24823 and ISO 4823, resp., with regard to the compression set in the range of from 2 to 20% and the recovery of shape after the compression in the range of from 96.5 to 100%, a linear dimensional change (polymerization shrinkage) in the range of from 0 to 1.5%, and an accuracy of reproduction of 0.02 mm.
The Shore hardness (DIN 53505, ISO 868) of the cured impression material of the invention is between a Shore A of from 30 to 50, preferably from 35 to 45, which is advantageous for the novel impression technique according to WO-A-97/32536 and WO-A-98/52491.
Some impression materials in accordance with prior art used for the conventional impression techniques have Shore A hardnesses of >50. (Aquasil LV: Shore A of 58, Coltene, President light body: a Shore A of 59). High Shore A hardnesses render the removal of the cured impression material from the mouth more difficult.
In the novel impression technique according to WO-A97/32536 and WO-A-98/52491, inventive impression materials having minimum tear resistance and tear propagation resistance values (according to DIN/EN 53504 and DIN 53515) in the cured state of from 150 N/cm
2
to 250 N/cm
2
and 0.5 to 2.5 N/mm, resp., are employed.
In the novel impression technique according to WO-A97/32536 and WO-A-98/52491 the teeth are reproduced faithfully in every detail, Gaps between the teeth and fissures between crowns and tooth stamps are completely filled with impression material. After the curing of the impression material, the tear resistance and tear propagation resistance values have to be so high that the impression can be removed from the mouth and the impression spoon without being des
Bublewitz Alexander
Hahn Rainer
Reber Jens-Peter
Dawson Robert
Jacobson & Holman PLLC
Kettenbach GmbH & Co. KG
Peng Kuo-Liang
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