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Root canal treatment tool and method for manufacturing the sameRelated Patent Categories: Dentistry, Apparatus, BroachRoot canal treatment tool and method for manufacturing the same description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070037118, Root canal treatment tool and method for manufacturing the same. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a root canal treatment tool for dental treatment and a method for manufacturing this root canal treatment tool. [0003] 2. Description of the Related Art [0004] Tools for treating the root canal of a tooth includes various kinds of tools: for example, a reamer and a file that cut and form a root canal; a compactor, a filler, a spreader, and a plugger that fill the root canal with thermoplastic resin; a cleanser that removes remainders in the root canal; and a broach that fills the root canal with cotton. [0005] The above-described root canal treatment tool is constructed of a slender tapered rod having a work portion provided with a cutting blade or piercing protrusion appropriate for a treatment object or a member having a work portion formed by forming a tapered rod in a spiral shape. Moreover, some kind of tool is constructed of a handle or a grip integrated with the end of the member so that it is gripped or operated by a dentist, or is constructed of a shank so that it is griped by a chuck of a hand piece and the like, or is directly operated by the dentist. [0006] The root canal is excessively thin and has a variety of shapes and sizes and is very different between persons. For this reason, many tools of different sizes are provided even for the same kind of root canal treatment tools. For example, in the case of cutting and forming a root canal by use of a reamer, the reamer is required to be deformed along the shape of the root canal, that is, to have appropriate elasticity so that it should not hurt the surrounding of the root canal. [0007] A technology disclosed in Japanese Patent No. 3375765 is proposed as a root canal treatment tool having extremely high elasticity and shape restoration property as described above. This technology relates to a root canal treatment tool having a work portion formed and manufactured by applying a removing work to a rod-shaped raw material that is subjected to shape memory heat treatment and has a superelastic characteristic while holding it under a memory treatment temperature. [0008] In the above root canal treatment tool, the rod having the work portion formed thereon is flexibly deformed in response to an external force applied thereto and is quickly restored to an original shape when the external force is removed. For this reason, this tool can extremely follow up the shape of the root canal with extremely high fidelity and form the root canal with high accuracy. [0009] In the root canal treatment tool relating to the Japanese Patent No. 3375765, the work portion has the superelastic characteristic uniformly along the whole length and hence when the work portion is bent, a tip portion of a free end also has an action of returning to an original shape. Hence, when the tip portion is inserted into the root canal for the treatment of the root canal and is bent, a repulsive force is generated to act on the wall of the root canal. For this reason, there is a problem of possibility that in the vicinity of a root sharp mouth (tip of the work portion), the work portion might cut the outside of a bent portion more heavily and might cut the inside in the center of the bent portion more heavily to go out of the root canal. [0010] Moreover, since the root canal treatment tool is rotated in a state where the work portion is bent almost along the whole length from the tip at the time of forming the root canal, a repeated bending stress is applied to the work portion. This increases the possibility of breaking a slender tip portion of the work portion. For this reason, although the root canal treatment tool relating to the Japanese Patent No. 3375765 has sufficiently high durability as compared with a root canal treatment tool made of stainless steel, it is required to further enhance the hi-her durability. SUMAMRY OF THE INVENTION [0011] The object of the invention is to provide a root canal treatment tool that is improved in a point of being apt to go out of the root canal and that is enhanced in durability by weakening the action of returning to an original shape of the tip portion of the work portion, and a method for manufacturing the root canal treatment tool. [0012] In order to solve the above problems, a root canal treatment tool according to the present invention is a root canal treatment tool that is formed in the shape; of a rod and has a work portion formed in a predetermined length from a tip and a shank formed in a manner continuous with the work portion, and is such that the work portion has a shape memory characteristic in the range of a predetermined length from the tip and a superelastic characteristic in a remaining portion. [0013] In the root canal treatment tool, the work portion has the shape memory characteristic in the range of a predetermined length from the tip and the superelastic characteristic in the remaining portion. For this reason, in a state where the tip does not recover a memory shape, even when a small force is applied to the tip from the outside, it is easily deformed in response to this force. That is, the tip having the shape memory characteristic can be freely deformed by a small force as compared with the other portion having the superelastic characteristic. [0014] Therefore, the tip of the work portion loses an action of returning to an original shape and hence well follows up the shape of the root canal and does not deviates from the root canal at the time of forming the root canal. Furthermore, the tip portion becomes soft to improve durability when the work portion is rotated at the time of forming the root canal. [0015] Further, a method for manufacturing a root canal treatment tool according to the present invention is characterized in that: a portion of a wire provided with a superelastic characteristic by a memory heat treatment is subjected to a working of removing metal; and then a portion of the portion subjected to the working of removing metal is again subjected to heat treatment to provide the portion with a shape memory characteristic or a portion of the wire provided with the superelastic characteristic by the memory heat treatment is again subjected to heat treatment to provide the portion with the shape memory characteristic; and then the portion having the shape memory characteristic and the portion that is continuous with the portion having the shape memory characteristic and that has the superelastic characteristic is subjected to the working of removing metal. [0016] According to the above method for manufacturing a root canal treatment tool, the wire provided with the superelastic characteristic is previously subjected to the working of removing metal, thereby being formed into the shape of an objective root canal treatment tool, and then the tip portion of the work portion is again subjected to heat treatment. In this manner, it is possible to manufacture the root canal treatment tool having the work portion that is provided with the shape memory characteristic in the tip and the superelastic characteristic in the remaining portion. Moreover, a portion of the wire provided with the superelastic characteristic is previously again subjected to heat treatment, thereby being provided with the shape memory characteristic, and then is subjected to the working of removing metal, thereby being formed into the shape of the objective root canal treatment tool. In this manner, it is possible to manufacture the root canal treatment tool having the work portion that is provided with the shape memory characteristic in the tip and the superelastic characteristic in the remaining portion. BRIEF DESCRIPTION OF THE DRAWINGS [0017] FIG. 1 is an illustration to show a reamer as a typical example of a root canal treatment tool. [0018] FIGS. 2A, 2B, and 2C are illustrations to show a method for manufacturing a reamer. [0019] FIG. 3 is a schematic view to illustrate a construction when a fatigue fracture test is conducted on the tip portion of a reamer. [0020] FIGS. 4A, 4B, 4C, 4D, and 4E illustrate a method for heating a wire. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Continue reading about Root canal treatment tool and method for manufacturing the same... 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