Dentistry – Method or material for testing – treating – restoring – or... – Endodontic
Reexamination Certificate
2000-01-21
2001-04-24
Wilson, John J. (Department: 3732)
Dentistry
Method or material for testing, treating, restoring, or...
Endodontic
C523S116000
Reexamination Certificate
active
06220863
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a root canal filling material that is used for dental remedies and to a method for filling a root canal upon heat softening during the root canal treatment. In particular, the invention relates to a root canal filling material with improved filling operability and adhesion to root canal walls.
2. Description of the Background
As to the matter of remedies for dental pulp disease and apical periodontitis, normally in root canal treatment, a root canal filling material is employed which is a substance which is not only materially safe, but which is also safe to living bodies upon filling a root canal after extirpation of the dental pulp, thereby keeping a tooth root harmless against periodontal tissue. There are many variations of root canal filling material. Of these, most frequently used is a thin needle-like root canal filling material called a guttapercha point. In general, a guttapercha point is comprised of guttapercha as a natural resin and zinc oxide as the major components. A root canal is filled with the material after extirpation of dental pulp.
In order to fill a root canal with a guttapercha point, a method known as the lateral condensation method is usually conducted. This method utilizes two types of guttapercha points of different thickness from each other (a master point and an accessory point). The master point has a thickness which is the same as a reamer or a file which is used for the root canal preparation and is first filled in the root canal. The thin accessory point is then placed in the root canal under pressure in the gap between the root canal wall and the master point. In order to seal the inside of the root canal to a good state by the guttapercha points according to this method, it is necessary to minutely fill the root canal with the guttapercha points. However, since the guttapercha points have extremely low plasticity, it is difficult to completely seal the inside of the root canal. In the event the filling is incomplete, tissue fluid from the root apex is liable to penetrate into the root canal, resulting in inflammation. Also, depending on the case, the guttapercha points protrude out from the root apex, leading to the generation of inflammation. Moreover, in order to achieve lateral condensation, it is necessary to implant a few guttapercha points, so that the operation is very complicated.
In order to overcome the complication of the lateral condensation with guttapercha points, a method has been developed in which a root canal filling material having a relatively low softening temperature is heat softened and then a root canal is filled using a syringe, or the like. However, although the root canal filling material that is presently used for this method has a relatively low softening temperature, when filled in the root canal, it rapidly cools, which decreases its fluidity within an extremely short period of time. For this reason, the root canal filling material hardens before completely filling the root canal, and is thereby likely to result in incomplete filling. Also, drawback occurs which is the inside of the root canal cannot be completely sealed by the root canal filling material because of its low adhesion to the root canal wall and large heat shrinkage.
SUMMARY OF THE INVENTION
In order to overcome the above-described defects of the related art technologies, an object of this invention is to provide a root canal filling material for filling root canals after heat softening and which adheres to root canal walls and presents simple operability for filing. In order to attain these objectives, the present invention provides a root canal filling material whose characteristics are that it can be softened at a relatively low temperature, it is not readily hardened after softening, and that it provides a sufficient working time so that the filling operation can be carried out in a root canal.
As a result of study, a root canal filling material has now been discovered that has good adhesion to root canal walls, can be softened at a relatively low temperature (from about 40 to 70° C.), can be filled into a root canal leaving a sufficient working time after the softening and that has less shrinkage and sufficient hardness during hardening in the root canal.
Specifically, the root canal filling material according to the present invention is one in which polybutene and ester gum having a prescribed number average molecular weight are present in a guttapercha which is a natural resin generally used in guttapercha points and/or in trans-polyisoprene which is the major component of the guttapercha for the purpose of improving the adhesion of the material to a root canal wall while minimizing the shrinkage during hardening in a root canal. Further a paraffin wax is present for the purpose of lowering the viscosity after heat softening. Further one or more than two inorganic fillers selected from zinc oxide, barium sulfate and calcium hydroxide are present for the purpose of maintaining an adequate hardness of the filling material in the root canal.
More specifically, the invention is a root canal filling material comprising (A) from 1 to 50% by weight of guttapercha and/or trans-polyisoprene, (B) from 0.1 to 10% by weight of polybutene having a number average molecular weight of from 600 to 4,000, (C) from 0.1 to 10% by weight of ester gum, (D) from 0.1 to 20% by weight of paraffin wax, and (E) from 10 to 95% by weight of one or more than two inorganic fillers selected from zinc oxide, barium sulfate and calcium hydroxide.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The guttapercha and/or trans-polyisoprene as component (A) is the basic component of the root canal filling material according to the present invention and imparts the basic strength and moldability to the root canal filling material. Of these, guttapercha is a natural resin which contains various compounds as impurities; and the trans-polyisoprene is a resin that is the major component of the guttapercha and is prepared by synthesis and used in place of the natural guttapercha. It is necessary that component (A) be present in an amount of from 1 to 50% by weight in the root canal filling material according to the present invention. If the amount of component (A) is less than 1% by weight, not only is sufficient strength not imparted to the root canal filling material, but also the resulting product is very brittle, whereby the stability in the root canal is lowered. On the other hand, when the amount of component (A) exceeds 50% by weight, the viscosity during heat softening is too high, so that the filling operation becomes very difficult, and likely results in incomplete root canal filling. The amount of component (A) is preferably from 3 to 40% by weight. This is because the viscosity of the material during filling of the root canal in a heat softened state is proper in order to simplify the filling operation.
The polybutene having a number average molecular weight of from 600 to 4, 000 as the component (B), when used together with the ester gum as component (C), can improve the adhesion to a root canal wall and has an effect for minimizing the shrinkage generated during filling in a root canal in a heat softened state. Further, it has an effect of prolonging the working time during heat softening and filling the root canal. The polybutene is a liquid polymer comprising isobutylene as the major component having a small amount of 1-butene copolymerized therewith and properly has a number average molecular weight of from 600 to 4,000. If the number average molecular weight of the polybutene is 600 or less, the tackiness is so low that the adhesion to the root canal wall is insufficient when used together with the component (C). Further, during filling of the root canal with filling material after heat softening, the fluidity is rapidly lost, which extremely shortens the time in which the filling operation can be conducted. On the other hand, if the number average molecular weight of the polybutene excee
Abiru Masao
Kamohara Hiroshi
Watanabe Nobutaka
Bumgarner Melba
GC Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wilson John J.
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