Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-08-11
2002-09-24
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S116000, C523S117000, C433S228100
Reexamination Certificate
active
06455608
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to dental compositions. In particular, this invention relates to dental compositions comprising degradable copolymers which are suitable for use as root canal sealants, root canal filling materials, implant materials, and in pulp capping.
2. Description of the Related Art
Endodontic therapy for a diseased or otherwise compromised tooth generally involves the dental practitioner accessing the root canal, debriding and disinfecting the root canal to clean and remove all of the soft tissue (the pulp) therein, and then enlarging the canal to remove irregularities or rough surfaces within the canal. A pre-formed “cone” or “point” is then inserted into the canal, and the cone is laterally or vertically condensed into the canal so that the point of the cone terminates at the apex of the canal. A commonly used cone material is gutta percha, which is a thermoplastic rubber. Because of the many irregularities which remain in the surface and shape of the canal even after treatment, it is difficult to achieve a satisfactory seal between the apex of the root canal and the cone without use of a root canal filler or sealant. Numerous sealants have been described, for example swellable hydrophilic acrylates and methacrylates such as 2-hydroxyethyl methacrylate (HEMA), as disclosed in U.S. Pat. No. 3,925,895 to Kliment et al. The monomers are mixed with polymerization initiator immediately prior to use and delivered to the root where polymerization occurs in situ. U.S. Pat. No. 4,986,754 discloses an injectable endodontic filling material comprising a mixture of balata or gutta percha with a liquid plasticizer. U.S. Pat. No. 4,449,938 discloses use of a two-component, room temperature setting organopolysiloxane compositions used for dental impression materials.
Despite these advances, the most commonly used root canal sealants remain compositions comprising a mixture of zinc oxide with eugenol (ZOE), and mixtures comprising calcium hydroxide. ZOE in particular is irritating to some patients, and has low adhesion to the walls of the root canal. Root canal sealants should be non-toxic, non-irritating, radiopaque, and have no or minimal shrinkage. They should also set within a reasonable period of time. They must be biologically compatible with tooth structure, and are preferably inert to moisture and to the pH conditions found in the mouth. Ideal preparations have low viscosity to facilitate insertion into the root canal, and even more preferably, are thixotropic. In the case of overflow of root canal sealant from the apex into the surrounding tissue or structure during a filling process, the overflowed excess should be desirably absorbed by the surrounding body tissue and cause tissue growth and recovery.
In contrast to endodontic procedures, in certain other dental procedures the pulp of the tooth is left intact. Where the pulp is exposed, a “pulp capping” compound is required which will preserve the vitality of the pulp. Pulp capping compounds must also be non-toxic, and cannot result in any irritation to the pulp. Ideal pulp capping compounds also allow for regrowth of the surrounding tissue and dentine. Calcium hydroxide-based pulp capping compounds are therefore common, as described in U.S. Pat. No. 3,047,400, and in U.S. Pat. No. 4,240,832, which discloses use of condensates of alkyl salicylates with aldehydes reacted with calcium hydroxide or calcium oxide. Despite these advances in the art, there remains a need for pulp capping materials which are biocompatible, non-toxic, and which have advantageous handling properties.
SUMMARY OF THE INVENTION
The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by compositions comprising degradable macromonomers having biodegradable segments selected from the group consisting of poly(lactide), poly(glycolide), and poly(caprolactone), together with terminal acrylate or methacrylate functionality, a curing composition, and optionally a co-polymerizable acrylate or methacrylate monomer. Degradable macromonomers are manufactured by the polymerization of cyclic lactide, glycolide, or caprolactone in the presence of a compound having at least one active hydrogen and at least one acrylate or methacrylate functionality. Preferred active hydrogen containing acrylate or methacrylate compounds comprise 2-hydroxyethyl methacrylate, hydroxypolyethyl methacrylate, phenoxy-2-hydroxypropyl methacrylate, and the like. Preferred co-polymerizable acrylate or methacrylate monomers include diluent monomers such as 1,6-hexanediol dimethacrylate, triethylene glycol trimethacrylate and 2-hydroxyethyl methacrylate. Degradable macromonomers can also be manufactured by the esterification of hydroxyl-group(s) terminated macromonomers of the above-mentioned hydroxy acids with acrylic acid, methacrylic acid and their derivatives. Depending on their use, the degradable macromonomer compositions further comprise one or more organic or inorganic fillers and one or more radiopacity-imparting agents. A degradable macromonomer means degradation by means of hydrolysis and/or biodegredation.
The present compositions are expected to be biocompatible and biodegradable, which advantageously allows for tissue regrowth. The degradable macromonomer compositions therefore find particular utility as root canal sealants, implant materials, and as pulp capping compositions. The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present compositions comprise degradable macromonomers having terminal acrylate or methacrylate groups, a curing agent, and optionally one or more co-polymerizable acrylate or methacrylate monomer. Depending on their use, the degradable macromonomer compositions further comprise optional organic or inorganic filler and a radiopacity-imparting agent.
Degradable macromonomers having terminal acrylate or methacrylate groups are obtained by the polymerization and copolymerization of lactide, glycolide or caprolactone in the presence of a compound having at least one active hydrogen, such as an amine or a hydroxyl group, and at least one acrylate or methacrylate functionality. Such compounds include but are not limited to hydroxyalkyl acrylates and methacrylates wherein the alkyl group has from 1 to 12 carbons, such as 2-hydroxyethyl methacrylate (HEMA), 2-hydroxyethyl acrylate, diethylene glycol monomethacrylate, diethylene glycol monoacrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, tetraethyleneglycol monomethacrylate, tetraethyleneglycol monoacrylate, pentaethyleneglycol monomethacrylate, pentaethyleneglycol monoacrylate, dipropyleneglycol monomethacrylate, dipropyleneglycol monoacrylate, hydroxy polyethyl methacrylates, phenoxyhydroxyphenyl methacrylate and the like. HEMA is preferred. Degradable macromonomers having terminal acrylate or methacrylate groups can also be manufactured by the esterification of hydroxyl-group(s) terminated macromonomers of the above mentioned hydroxy acids with acrylic acid, methacrylic acid and their derivatives.
Lactide is the cyclic dimer of lactic acid, and is available as both L-lactide ((3S)-cis-3,6-dimethyl-1,4-dioxane-2,5-dione) and D,L-lactide (3,6-dimethyl-1,4-dioxane-2,5-dione). Polymerization of lactide with HEMA, for example, yields a poly(lactide-HEMA) (hereinafter PLAMA) macromonomer having the following structure (I), wherein m=1, n≧1, and G is hydroxyl, or acrylate or methacrylate containing terminal non-polymerizable esters:
Synthesis of suitable poly(lactic acid) macromonomers having terminal acrylate or methacrylate groups is described by S. J. Huang and J. M. Onyari, in “Multicomponent Polymers of Poly(Lactic) Acid Macromonomers With Methacrylate Terminal and Copolymers of Poly(2-Hydroxyethyl Methacrylate)”, in
Journal of Macromolecular Science—Pure and Applied Chemistry
, Volume A33, No. 5, pp. 571
Huang Samuel Jien-shek
Jia Weitao
Jin Shuhua
Cantor & Colburn LLP
Jeneric Pentron Incorporated
Yoon Tae H.
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