Compositions – Etching or brightening compositions – Inorganic acid containing
Reexamination Certificate
1999-01-26
2001-03-06
Mills, Gregory (Department: 1763)
Compositions
Etching or brightening compositions
Inorganic acid containing
C433S216000, C433S226000, C433S228100
Reexamination Certificate
active
06197212
ABSTRACT:
The present invention relates to a process for the conditioning of dental cavities by etching in preparation for bonding restorations to enamel and dentin, and the invention also covers a kit for use in such conditioning process.
BACKGROUND OF THE INVENTION
Enamel is the hardest biologic tissue found in the body and it forms a protective layer covering the crowns of teeth. It is composed of interlocking rods which, to more than 96%, are constituted by hydroxyapatite. The rods are deposited in keyhole shapes each of which comprise a head and a tail surrounded by a sheath (cf.
FIG. 1
as enclosed). Enamelin, a protein unique to enamel, can be found in minute amounts surrounding individual hydroxyapatite crystallites predominantly in the sheath (for a review see Avery J K. Essentials of Oral Histology and Embryology. A Clinical Approach. St. Louis, Mosby, 1992).
The body of the tooth, both the crown and the root thereof, is constituted by dentin. Dentin is composed of an organic matrix of collagen fibers (on average 20% by weight), in which hydroxyapatite crystallites (on average 70% by weight) are dispersed. The remaining 10% of the dentin is constituted by water. Dentin tubules, approximately 1 &mgr;m in diameter and of a density amounting to 30 000 to 50 000 tubules per mm2, run from the centrally located pulp to the periphery of the body of dentin (cf.
FIG. 2
as enclosed). The walls of the tubules are made up of peritubular dentin which is approximately 40% more highly mineralized than the intertubular dentin in between the tubules. The water component of dentin is mainly found in the dentin tubules (for a view, see Avery 1992, above).
The bonding of dental restorations to dental mineralized tissues is the last step in filling therapy (for details, see Heymann, H., Bayne, S. Current Concepts in dentin bonding. Journal of the American Dental Association 1993, 124, 27-35). The process starts with mechanical removal of carious enamel and dentin followed by cavity preparation. The cavity walls are subsequently pretreated before insertion of the filling material in order to increase adherence of the material to the walls and to minimize gap formation. This process is generally referred to as bonding and relies on two principles:
Mechanical interlocking of the resin-based restoration to irregularities in the mineralized surface.
Chemical bonding of the resin-based restoration to exposed collagen.
The bonding usually involves an initial step of surface etching using ortho-phosphoric acid, such etching having for its purpose to:
remove the debris, such as smear and bacteria, resulting from the mechanical cavity preparation;
maximize the surface area of the enamel cavity walls by eroding the more heavily mineralized enamel rod heads. This produces protruding ridges of rod sheaths for mechanical interlocking with resin-based restorations;
expose collagen in the dentin surface to make the fibers accessible for chemical bonding to resin-based restorations.
Etching is, by definition, the selective removal of parts or components from a solid surface through the action of an etching agent, such as solutions of acids or other substances. Etching does not, however, implicate erosion of the surface to remove a complete surface layer. The purpose of the etching of exposed dental mineralized tissues after cavity preparation is not the same for all tissues involved. Thus, in regard to a dentin surface the purpose is to selectively remove smear and hydroxyapatite leaving an exposed layer of collagen. With regard to an enamel surface the purpose is to increase the surface area available for bonding by removing hydroxyapatite from the more highly mineralized enamel rods.
SUMMARY OF THE INVENTION
The principle object of the present invention is to provide a process for the conditioning of dental cavities by etching considering the different tissues involved in such etching.
Another object of the invention is to selectively remove smear and hydroxyapatite from a dentin surface so as to form an exposed layer of collagen.
A further object of the invention is to increase the surface area available for bonding to an enamel surface, such increase residing in the removal of hydroxyapatite from the more highly mineralized enamel rods.
Yet another purpose of the invention is to provide a kit for use in such conditioning of dental cavities by etching.
For these and other objects that will be clear from the following disclosure the invention provides for a process for the conditioning of dental cavities by etching in preparation for bonding restorations to enamel and dentin, said process comprising the following steps:
a) etching the dentin part of a dental cavity using an aqueous composition containing, as an active constituent, EDTA in an effective amount, and
b) etching the enamel part of said cavity using a conventional etching acid.
Although any conventional etching acid can be used in step b) of the process it is preferred to use an acid selected from phosphoric and citric acids. The etching under step b) above is performed for a fairly short period of time, such as less than about 25 seconds.
With regard to the etching agents used in steps a) and b) above the EDTA-containing agent is suitably in the form of an aqueous solution having a pH of about neutral. The etching acid used in step b) has suitably a pH of about 1 and is also suitably constituted by an aqueous solution, such as a saturated citric acid solution or a phosphoric acid solution having a concentration of about 37%.
The invention also provides for a kit for use in such conditioning of dental cavities by etching in preparation for bonding restorations to enamel and dentin, said kit comprising the following items:
a) a first container holding an aqueous composition containing EDTA;
b) a second container holding an aqueous composition containing a conventional etching acid; and
c) instructions for the use of the kit.
A preferred embodiment of such kit contains as a composition of the first container (based on the water contents of the composition):
EDTA in an amount of about 22 to 27% by weight;
sodium hydroxide as a pH-controlling agent in an amount resulting in a pH within the range about 6.5 to about 7.5; and
a viscosity-increasing agent constituted by carboxymethyl cellulose (CMC) or a salt thereof in an amount of from about 1% by weight to about 5% by weight.
A particularly preferred embodiment of such kit is one wherein:
the amount of EDTA is about 25% by weight;
the pH of the composition is around neutral pH7; and
the viscosity-increasing agent is sodium carboxymethyl cellulose in an amount of about 3 to 5% by weight.
As explained above the etching of the dentin part of a dental cavity is performed by using ethylene-diamino-tetraacetic acid (EDTA), said substance being present in an aqueous environment in combination with an aqueous matrix. EDTA is an agent which chelates divalent cations, such as Ca2
+
, Mg2
+
, Fe2
+
and Pb2
+
. It has found use in infusion solutions for detoxification and as an anticoagulant in vivo. In vitro it has found a variety of uses, such as to detach cells from solid substrata (Paul J. Cell and Tissue Culture. London: Churchill, 1975; Adams R L P. Cell Culture for Biochemists, Amsterdam: Elsevier, 1980), decalcify tissue specimens before sectioning and staining (Brain, E B. The Preparation of Decalcified Sections. Springfield: Charles C Tomas Publisher, 1966; Dickson G R. Methods of Calcified Tissue Preparation. Amsterdam: Elsevier, 1984) and as a detergent in biochemical analysis.
By the use of conventional etching agents operating at about pH 1, such as phosphoric or citric acid, not only the mineral component of exposed dentin surfaces is dissolved but also the collagenous matrix. Accordingly, collagen is dissolved at acid pH's by acids, such as citric acid, already at low concentrations (Trelstad, R T. Native collagen fractionation. In: Immunochemistry of the Extracellular Matrix. Volume 1. Methods. Ed: Furthmayr H. Boca Raton: CRC Press, 1982:31-41). It is true that EDTA can
Blomlof Leif
Lindskog Sven
Burns Doane , Swecker, Mathis LLP
Mills Gregory
Peridoc AB
Powell Alva C
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