Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-05-15
2002-06-18
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S115000, C106S035000, C522S908000, C433S228100
Reexamination Certificate
active
06407148
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a metal-free dental filling system for filling therapy or root filling therapy, respectively, as well as to its use as a substitute for amalgam.
BACKGROUND ART
For tooth restoration in dentistry, three hierarchically ordered goals are pursued, whereby each higher standard is based on the fulfillment of the lower standard or the lower standards.
The partial goal of the lowest standard 1 consists in the conservation of the dental hard tissue and the protection of the pulpa.
Standard 2 is further aiming at restoring the tooth's shape and function.
The purpose of standard 3 is to design the restoration in such a way that it is imperceptible at conversation distance and remain so throughout the stipulated service life.
Amalgams, i.e. mixtures of a silver-tin alloy with liquid mercury, have been used for more than 150 years as standard filling material, in particular for posterior, permanent teeth. When used with adequate operative techniques, amalgam restorations are able to protect the dental hard tissue for years and to restore the tooth's shape as well it's functionality. Thus, amalgam restorations fully satisfy standard 2. In filling therapy with amalgam, a comparatively simple operative technique has evolved that relies on steel matrices and wooden wedges for giving the filling its correct, preferably overhang-free contour at its outer surfaces. Occlusal shaping is carried out by carving. Amalgam fillings are furthermore comparatively cheap. The medium survival rate of amalgam fillings can be 10 years and more.
In recent years, however, amalgams have lost quite some ground as a standard restorative material. The main reasons of this decline are, among others, its controversial toxic and allergenic potential, its environmental impact and its lack of tooth color. As a consequence, it was necessary to search for materials or material systems that could be used to replace amalgam for posterior teeth, in particular for permanent teeth and stress-bearing restorations. This resulted in two material or system groups differing in their purpose, namely amalgam alternatives and amalgam substitutes.
Amalgam alternatives have to suffice standard 3 and not only have to guarantee the conservation of the dental hard tissue as well as shape and function of the restored tooth over a long time, but they also must be and remain imperceptible at normal conversation distance. This group of materials in particular comprises composite fillings and composite or ceramic work-pieces. This not only requires tooth color, but also a stress resistant, perfect marginal adaptation. With fillings, the latter is achieved by using a rather complex operative technique, with work-pieces by high accuracy in conjunction with efficient adhesive or combined adhesive/luting systems.
In contrast to this, an amalgam substitute has to satisfy standard 2 just as amalgam does; in addition to this, the operative technique should be simple for cost reasons and be as close as possible to the known amalgam technique, i.e. it should be possible to work with steel matrices and wooden wedges, to use a simple incremental technique and, if light curing materials are used, irradiation from an occlusal direction should suffice.
Various amalgam substitute systems are known:
DE-196 03 577 A1 relates to an adhesive system, wherein a gap free connection between the plastic filling material and the dental hard tissue is aimed at. In such a system, the bond between dental hard tissue and filling material is excellent, such that in case of adhesive failures, continuity fractures occur in the dental hard tissue or in the restorative material. This means that no caries protection is provided along these marginal openings if they run in the dental hard tissue.
DE 195 44 670 describes an adhesive system that does not harden by radical polymerization but rather as a product of condensation. In this way, an oxygen-inhibited surface layer is to be avoided. Thus, however, the adhesive may be better suited than usual, radically polymerizing sealants for sealing caries. In the application as an adhesive, where, according to the inventor, the prevention of margin gap formation is again aimed at, cohesive failure results in the dentin and in the enamel. Hence, this system is unable to reliably protect the dental hard tissue. With comparatively frequent adhesive failure, the enamel is not protected at all in the area of the marginal openings, which are therefore not desired at all. In dentin, a partial, erratic, unpredictable protection is to be expected where the bond happens to break between the adhesive and the filling material and adhesive islands remain on the dental hard tissue. The described system therefore provides no safe and complete protection of the enamel or dentin, and it also belongs to the category of the adhesive systems aiming at a total bond between the dental hard tissue and the restorative material.
EP 0 423 430 describes a dentin-adhesive system using a primer and a bond on dentin. Again, it is aimed at a total leakage-free bond between dental hard tissue and restorative material.
EP 0 088 527 describes an enamel conditioner designed to generate a better bond between the enamel and the restorative material than it used to be the case upon the usual etching process by means of phosphoric acid.
DE 34 14 163 relates on a dentin primer and describes a dentin bonding system working with a primer and a bond on dentin, wherein again a total leakage-free bond between dental hard tissue and restorative material is desired.
None of the adhesive systems according to the state of the art, however, uses enamel and dentin bonding selectively for protection and adhesive sealing of the dental hard tissue, while selectively eliminating the requirement of a bond between the shrinking restorative material and the sealed dental hard tissue.
The adhesive systems according to the state of the art are fully unsatisfactory when being used in combination with amalgam substitutes and the corresponding operative techniques, because unpredictably located fractures in the restorative material, the interface between restorative material and adhesive, within the adhesive, at the interface between the adhesive and the dental hard tissue and/or within the dental hard tissue can occur. Fractures at the interface between the adhesive and the dental hard tissue and within the dental hard tissue are particularly damaging. A reliable protection cannot be achieved using the required simple placement techniques and currently available adhesive systems.
Investigations have shown that fillings made of materials presently used as amalgam substitutes are visible after a short period of time especially when occlusally loaded. Such materials include amalgam substitutes in combination with an adhesive system such as composite-adhesive or compomer adhesive systems, i.e., polyacid-modified composites, as well as composite adhesive systems specifically developed as amalgam substitutes. Sometimes within months, from 60% to 95% of the total margin length of the filling is visible resulting in both marginal discoloration and a high risk for secondary caries in medium time range caries diagnostics.
While marginal discoloration may be acceptable within the requirements of operative standard 2, the high risk for secondary caries with fillings of the known material combinations mentioned above, cannot satisfy operative standard 1, i.e., tooth conservation can not be achieved over a medium time range. Thus, materials presently used as amalgam substitutes should only be used as temporary fillings.
The reason for the failure of the amalgam substitute materials according to the state of the art lies in the fact that such materials usually shrink by 2.5 to 4.5 volume percent during the curing process. The resulting stress build-up damages the bonds as generated by the adhesive systems according to the state of the art and exceeds the cohesive strength of the dental hard tissue, especially in the enamel, and of the filling materi
Krejci Daniela
Krejci Ivo
Lutz Felix
3M Espe AG
Crowell & Moring LLP
Szekely Peter
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