Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-03-27
2003-04-22
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C528S015000, C528S031000, C528S032000, C528S039000, C525S478000, C106S035000, C106S038220, C264S016000, C433S214000, C524S493000, C524S588000
Reexamination Certificate
active
06552104
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is directed to improvements in room temperature polymerizable polyorganosiloxanes having very high viscosity (putty) and good dimensional stability upon curing or hardening. More particularly, this invention is directed to improvements in compositions that are generally of the type comprising two components, one component comprising organopolysiloxanes having vinyl groups, capable of undergoing addition reactions with organopolysiloxanes having silicone-bonded hydrogen atoms. The second component comprises a catalyst capable of promoting the addition of hydrogen atoms bonded to silicone atoms across the vinyl groups.
A major field for the use of certain of these room temperature curable polyorganosiloxane compositions is dentistry. Such materials are typically employed as impression materials for securing an analog representation of oral bard and soft tissue to support subsequent elaboration of crowns, bridges, dentures, an other oral prostheses. For dental use, extraordinary fidelity of structural reproduction is required in order to ensure good fidelity of oral prosthetic fit and the like. In this regard, changes in the dimensions of the impression material during curing are to be avoided. Moreover, the surface of the reproductions or oral prosthetics and the like must be exceptionally free from irregularities, blemishes, pits, and other imperfections. This is so because castings and prostheses derived from such impressions must have good surface qualities and be free from pits and irregularities in order to have proper fit, to achieve good adhesion, and to avoid irritation of sensitive mouth structures. These polyorganosiloxanes will also be useful in other fields where detailed reproductions are important such as in the science of metrology, laboratory processing of SEM and even jewelry fabrication and the like.
In employing polyorganosiloxanes as dental impression materials, a number of difficulties have arisen. First of all, tear strength tends to be low. It is necessary, in effectively taking an impression, to be able to easily remove the impression, from the dentition without tearing, particularly at thin marginal areas, to preserve fine detail. In the past, fillers of various types have been added to improve tear strength. Such additions may result in some improvement, on the order of about 10%, but such improvements have proved inadequate.
Paradiso in WO 93/17654 describes improving tear strength by incorporating multi-functional, including quadri-functional, polysiloxane components into the impression material, to add increased cross-linking to the resulting cured impression material matrix, particularly along the length of the linear vinyl end-stopped polysiloxane principal component. The Paradiso composition comprises SiOH groups capped off with Me
3
Si units that form pendants from the molecule. These pendants provide only mechanical or physical interlinking between the linear polysiloxane chains. This solution is deficient, being non-chemical and low in cross-linking density.
Voigt et al in EP 0 522 341 A1 describes very short processing times of 35-45 seconds for forming dentition bite registration devices, utilizing a “QM” resin as a means of speeding and increasing cross-linking. These resins comprise as Q, the quadri-functional SiO
4/2
and as M, building blocks such as monofunctional units R
3
SiO
1/2
wherein R is vinyl, methyl, ethyl or phenyl, or similar tri or bi-functional units. Voigt also notes that an elastomer with small elastic deformation having a higher tenacity and hardness results. However, hydrophobic poor wetting, such material lacks flexibility, having a low strain value, and is unsuitable for impression taking. The increased cross- linking rate of the QM resin also results in very limited processing times that are unsatisfactory.
The other major, well-known difficulties with polyorganosiloxane impression materials are caused by its inherent hydrophobic character. Such characteristics make reproduction of hard and soft oral tissue difficult since the oral cavity environment is wet and often contaminated with saliva or blood. The hydrophobicity of the impression material can result in loss of surface detail often at critical surfaces of the dentition.
A number of improvements of polyorganosiloxane impression materials focus upon adding a surfactant component to the dental impression material in order to reduce the hydrophobic nature of the polysiloxanes and make the composition more hydrophilic. Thus, Bryan et al in U.S. Pat. No. 4,657,959 describes adding an ethoxylated nonionic surface active agent containing siloxane or perfluoroalkyl solubilizing groups to achieve a three minute water contact angle below about 65°. While surfactants including hydrocarbyl groups, for rendering the surfactant soluble or dispersible in silicone prepolymer, are mentioned, including ethyleneoxy groups, the results achieved appeared to be less than optimal. Wetting but low tear strength.
In sum, polyorganosiloxane impression materials still need improvement in tear strength and wettability in order to provide improved use of these compositions for taking impressions of oral hard and soft tissues such that adequate working time, tear strength and wettability are provided. Also, sweating occurs as a result of the plasticizer that is in the composition migrating to the surface of the impression forming oily droplets of liquid. Sweating has been reported to cause melting of polystyrene impression trays and loss of impression detail.
Sweating as used herein refers to droplet formation of plasticizer formed on the outer surface of cured elastermeric impression material at 23° C. within 24 hours of curing the cured material.
Non-sweating as used herein refers to elastomeric impression material which does not form visible droplets (and/or a film) of plasticizer on the outer surface- thereof at 23° C. within 24 hours of curing the impression material.
Low liquid mass loss as used herein refers to elastomeric impression material which has less than 0.05 percent mass loss after 12 days at 23° C. from the start of curing the impression material. A specimen is made of the putty using ADA 19 detail reproduction mold. The specimen is placed on top of an absorbent paper towel in a labeled crystallization dish and covered with a watch glass. 12 days after mixing the putty, the surface of the putty is observed, a record of the readability of the detail reproduction is made. The specimen is gently touched (blotted) with the paper towel to absorb any “sweat” or oil from the surface. Then the specimen reweighed and the weight recorded. The results for the impression material of Example 1 and some commercially available dental impression materials are shown in the following Table I.
TABLE I
Material
EXAMPLE 1
REPROSIL
EXAFLEX
EXPRESS
EXTRUDE
PRESIDENT
Initial detail readability
20 Micron
20 Micron
75 Micron
75 Micron
75 Micron
50 Micron
Initial weight (+/−0.00001 Grams)
4.09034
3.59762
5.00262
5.18539
4.28017
4.15028
Final detail readability
20 Micron
20 Micron
75 Micron
75 Micron
failed 75
50 Micron
Final weight (+/−0.00001 Grams)
4.08984
3.58888
4.99765
5.18025
4.27401
4.14442
Difference between initial and
−0.00050
−0.00874
−0.00497
−0.00514
−0.00616
−0.00586
final weights
% Mass loss
−0.01222
−0.24294
−0.09935
−0.09912
−0.14392
−0.1412
Non-sweating preferably refers to elastomeric impression material which after storage at 23° C. for 24 hours has less than 10% by weight of the placticizer in the starting material separated from the stored impression material to form droplets (or a film) on the outer surface of the stored material. More preferably, there is less than 5% by weight of placticizer separated from material in accordance with the invention and most preferably, there is less than 1% by weight of placticizer separation from material in accordance with the inventio
Bieber James B.
Dentsply Research & Development Corp.
Lovercheck Dale R.
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