Dentistry – Prosthodontics – Impression taking or bite determination
Reexamination Certificate
2002-03-01
2003-05-13
Dawson, Robert (Department: 1712)
Dentistry
Prosthodontics
Impression taking or bite determination
C525S478000, C528S031000, C528S015000, C528S032000, C528S039000, C523S109000, C264S016000, C106S035000, C524S493000, C524S588000
Reexamination Certificate
active
06561807
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is directed to improvements in room temperature polymerizable polyorganosiloxanes having good dimensional stability upon curing or hardening and having improved flow characteristics. 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. In one embodiment, the inventive material has a high tear strength, low viscosity and is highly hydrophilic.
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 hard and soft tissue to support subsequent elaboration of crowns, bridges, dentures and 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 notes that an elastomer with small elastic deformation having a higher tenacity and hardness results. However, 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.
As stated above, all silicone material are known to have highly hydrophobic properties. Therefore, these materials are usually not able to wet the surface of the teeth properly, especially under moist conditions. Hydrophilic properties can be achieved in a silicone with the addition of dipoler surfactants. These additives are usually not soluble in the silicone matrix, but rather form an emulsion together with the silicon system. The rheological properties of such materials are characterized by a typical non-Newtonian flow behavior with a high yield stress and a highly sheer stress-dependent viscosity. Non-dipolar surfactants include for example, polyether modified silicones, and do not build proper micelles. The resulting emulsions are therefore not stable and tend to separate. However, the resulting multiple phase systems have a high yield stress which avoids the flow on the tooth surface when no or low stress is applied. Hydrophilic silicones therefore usually have poor flow characteristics under low stress.
Conventional “light bodies” formed from a two component system are usually applied in one of two forms. The first is a handmixed form in the case when the two components have to be mixed by hand. Second is an automixed form when the two components have to be released through a static mixer out of a cartridge. In both cases, the mixablility of the two components are strongly influenced by the rheological properties of the individual components making up the light body. Especially in the most common automixed form, the force to release the material out of the cartridge is influenced by the yield stress of the pastes.
Because of the rheological sub-structures, most conventional hydrophilic silicones have high yield stresses. To take advantage of low forces for releasing the material, large static mixers have to be employed. This leads to a high rate of waste because much of the material often remains in the mixer. Therefore, it is desired to achieve a low yield stress of both the single paste component and the mix in order to minimize the force which is necessary to remove the paste from the cartridge.
With conventional light body formulations a high stress has to be applied to obtain a flow of the impression material into the sulcus and into the other details of the preparation. Low viscosity type materials (“light bodies”) are therefore always used in combination with a high viscosity type material in the so called “putty/wash” technique or in the “double mix” technique. To improve the mixablility of the putties, the viscosity of these products must be low. Even in the case where machine mixed heavy bodies are used the stress for releasing is limited by the technical properties of the machine. Higher viscosities lead to longer release times. In cases where these so-called soft putties or heavy bodies are used together with low viscosity silicones, the high yield stress and the highly stressed viscosity of the light body causes problem because it is impossible to generate su
Bieber James B.
Dawson Robert
Dentsply Research & Development Corp.
Hura Douglas J.
Peng Kuo-Liang
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