Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2001-04-12
2003-09-16
Yoon, Tae H. (Department: 1714)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C523S116000, C523S219000, C433S218000, C433S219000, C433S226000, C433S228100
Reexamination Certificate
active
06620232
ABSTRACT:
This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/SE99/01803 which has an International filing date of Oct. 8, 1999, which designated the United States of America and was published in Swedish.
TECHNICAL FIELD
The present invention relates to a chemically bound ceramic material, the binder phase of which essentially consisting of a cement based system. The primary use for the material is as a dental filling material.
BACKGROUND OF THE INVENTION
The present invention relates to binding agent systems of the cement system type, especially the system CaO—Al
2
O
3
—(SiO
2
)—H
2
O. This system is used in the building industry for exceptionally hard and tough environments, i.e. acid environments with a high mechanical stress (R J Mangabhai, Calcium Aluminate Cements, Conference volume, E & F N Spon, London 1990). By applying rupture mechanical methods and advanced powder technique on the system, the generally good properties profile of the base system can be considerably improved. Studies in connection with the invention and previous work (SE patent 463 493 and 502 987) have given results which point at a great potential for the system for strong and acid resistant materials as dental filling materials. No dental filling material existing today fulfills all the requirements as to bio-compatibility, aesthetics and function, which may be posed by patients and dental care personnel. The situation for different dental filling materials may be concluded according to the following. Amalgam exhibits a generally good strength, but exhibits flaws when it comes to bio-compatibility and aesthetics. Plastic composites exhibit a good workability, but exhibit flaws when it comes to erosion and corrosion and in handling for the personnel (allergy problems arisen). Plastic composites shrink at the hardening, which leads to a risk of formation of gaps and, over a time period, carries attack. Glass ionimers exhibit a good binding to dentine, and enamel, but exhibit flaws when it comes to corrosion and strength. Silicate cement exhibits a good compression strength and aesthetics, but suffers from corrosion and strength problems. Different types of inserts exhibit good mechanical properties, but are work demanding and require gluing.
In the following there is given a description of the requirements which generally should be posed for a new practical dental filling material; A good manageability with easy applicability in cavities, a workability which permits a good ability of modelling, a hardening/solidification which is fast enough for the filling work and functioning directly after the dentist appointment. Furthermore, there is required a high level of strength and corrosion resistance, which exceeds the one for existing filling materials, a good bio-compatibility, good aesthetics and a secure handling for the personnel, without additives in the materials which may cause allergies or which are toxic. Also, there is required good long time properties in the form of dimension stability. Especially it is a problem if the material expands over time, which may result in fatal tooth bursts.
It has been previously shown, in Swedish patent 502 987, that a complete hydration (which was believed to lower the risk of dimension changes) in a cement system, may take place if a complete soaking and a thereafter following compaction of the cement system is made by aid of a specially designed stopper. The method does however not prevent dimension changes which take place later on and which are related to phase transitions in hydrates or reactions with the surrounding environment (as for example exhalation air with an increased content of carbon dioxide), or other reactions. These reactions and related dimension changes are more noticeable in cases where a high compaction degree is used in the production of the material. A higher compaction degree is however normally desired, since it generally leads to a better strength.
In Yan et al, Characteristics of shrinkage compensation expansive cement containing pre-hydrated high alumina cement-based expansive additive, Cement and Concrete Research, Vol. 24, p 267-276 (1990), the use of the tendency of calcium aluminates to expand, is described. This article and related work on expansive cements describe the possibilities to get standard cement to expand or shrink less, with the use e.g. calcium aluminates, but does not discuss the problems of long time expansion of highly compacted systems or controlling of the expansion of calcium aluminates to very low levels, which is necessary for the use of these binding agent systems in applications according to the present invention.
Other related work and patents, which however do not discuss the basic ideas of the present invention, are for example SE-B-381 808, EP-A-0 024 056 and EP-A-0 115 058, DE 5 624 489 and U.S. Pat. No. 4,689,080.
DESCRIPTION OF THE INVENTION
It is an object of the present invention to provide a material of the type described in the introduction, which material exhibits dimension stable long time properties. The material should also, for dental applications, fulfill the requirements which according to the above are posed for such materials.
This is accomplished according to the invention by the material comprising one or more expansion compensating additives adapted to give the material dimension stable long time properties.
Chemical properties are, besides good mechanical properties, important for dental applications. In one important aspect of the invention, calcium aluminates, i.e. double oxides of CaO (calcium oxide) and Al203 (aluminium oxide)—here and below denoted the CA system, which react with water under formation of calcium aluminate hydrates, are used as the main binder phase. This hydration reaction constitutes the setting and hardening process itself To the calcium aluminate cements there are conventionally added some type of aggregates (filler particles), essentially for economic reasons. According to the invention, the choice of the CA cement system, combined with some other cement system or a phase which interacts with the aluminate cements, or combined with an addition of porous aggregates or soft particles, enables a dimension change which is below about 0.20% linearly, often below 0.10%. In special cases, the dimension change may be close to zero expansion.
According to a first embodiment of the invention, the CA system may be used as the sole main binder phase, or with an addition of another cement binder phase in contents decreasing 30 vol-%. Advantageously, there is used additions of ordinary Portland cement (OPC cement) or fine grain silica. While calcium aluminate cements have a tendency to expand seriously at more dense compaction, the combination of CA cement and other phases of the above mentioned type, with the tendency to shrink, may give decreased dimension changes. The CA cements should, in dental applications, be the main phase in the binder phase, since the CA phase contributes to a good strength and acid resistance.
It has become clear that the theories relating to causes for dimension changes, which theories were put forward in connection with SE patent 502 987, i.e. incomplete hydration, do not seem to fully explain the reasons behind the problems in dimension stability. The background of the present invention is more an apprehension that the dimension changes are connected with hydrate phase transitions. This statement, which should not be seen as limiting for the invention, means that calcium aluminate, when it is beginning do be dissolved at the addition of water, forms a gel which thereafter crystallizes and forms hydrate phases, By subsequent hydration reactions and hydrate transitions, different pure Ca-aluminate hydrates as 10-phase, 8-phase, other less defined hydrate phases or transition phases, and finally 6-phase (katoit) may exist, and in the case of silicon containing additives, Ca—Si-aluminate hydrates. By 10-phase, 8-phase and 6-phase it is hereby meant Ca-aluminate phases with 10, 8 and 6 crystal waters re
Hermansson Leif
Kraft Lars
Birch & Stewart Kolasch & Birch, LLP
Doxa Aktiebolag
Yoon Tae H.
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