Dentistry – Apparatus – Broach
Reexamination Certificate
1999-04-08
2001-10-09
Lucchesi, Nicholas D. (Department: 3732)
Dentistry
Apparatus
Broach
C433S224000
Reexamination Certificate
active
06299445
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to endodontic instruments, such as files and reamers and, more specifically, to those instruments especially useful in root canal procedures.
BACKGROUND OF THE INVENTION
Endodontists use various types of instruments for cleaning and enlarging the root canals of the teeth. In a typical root canal procedure, an endodontist first makes an opening in the surface of the tooth to provide access to the interior. The endodontist then utilizes small instruments, such as hand held files and reamers, to clean and enlarge the narrow, tapered root canals. In a conventional procedure, the endodontist fills the prepared root canals with gutta percha, which is a rubber-like substance, and then seals the tooth with protective cement. The endodontists may sometimes apply a crown to the tooth as a final step.
Typically, the endodontist uses a series of delicate, flexible files to clean out and shape the root canals. Each file includes a proximal and typically including a handle to be gripped between the fingers of the endodontist and a distal end or tip. A working length with helical flutes and cutting edges is located between the proximal and distal ends. The endodontist uses files of increasingly larger diameter to sequentially increase the diameter of the root canal and achieve the desired diameter and shape.
Endodontic root canal files and reamers have been formed from twisted blanks in generally three different configurations. One type is formed by twisting a ground blank having a square cross section to create four helical cutting edges per revolution. Another type consists of a twisted blank of triangular cross section having three cutting edges per revolution. The third type, often referred to as a K-flex type, is formed from a blank having a parallelogram-shaped cross section, such as a rhomboid-shaped cross section. After twisting this type of blank, two cutting edges and two debris removal edges will be formed per revolution. All three of these types of instruments have a tapered major diameter or cross-sectional dimension and a tapered minor diameter or cross-sectional dimension in which the taper angles are generally the same. Also, the angles formed between the surfaces that define the cutting and debris removal edges are constant along the length of the instrument. In other words, a given grind angle of an edge on the instrument remains the same along the entire working length of that instrument.
Existing endodontic files and reamers formed from twisted blanks are designed in such a manner that the minor diameter is purely a function of the major diameter. The undesirable consequences of this type of design become significant for instruments that have a greater taper along the working length. In particular, these instruments become much stiffer toward the proximal end or handle of the instrument. This can cause the instrument to be difficult to maneuver within curved root canals because the instrument may not flex enough to conform to the shape of the canal. Although certain helically fluted endodontic instruments have been formed completely by grinding to achieve more constant flexibility along the length, these instruments have significant drawbacks. First, instruments formed completely by grinding are more costly to manufacture. Also, twisted instruments may be formed in a wide variety of cross-sectional shapes, depending on the shape of a initially ground wire blank.
In view of problems in this field, including those problems noted above, it would be desirable to provide an endodontic instrument, such as a file or reamer formed from a twisted blank, in which the size of one diameter or cross-sectional dimension is formed independent of the other to optimize flexibility, strength and other operating characteristics of the instrument. In this manner, instruments of greater taper may be formed with greater flexibility for maneuvering within curved root canals, while also retaining sufficient strength to resist breakage during use.
SUMMARY OF THE INVENTION
The present invention provides an endodontic instrument, such as a file or reamer or other cutting, shaping or cleaning instrument, comprising an elongate member with optimal flexibility, strength and other operating characteristics. The elongate member includes a longitudinal axis, which is preferably straight when not in use, and a proximal end, a distal end and a working length generally between the proximal and distal ends. The working length is formed with an outer surface comprising a plurality of twisted or curved surface portions defining at least one cutting edge formed at a junction between adjacent surface portions. The adjacent surface portions are preferably both cut from the outer surface along paths extending along and at least partially around the longitudinal axis. There may be only one twisting surface portion or multiple twisting surface portions on a blank ground according to the invention. These cut surface portions are further physically twisted to form helical cutting edges extending around the longitudinal axis.
The adjacent surface portions define a cutting edge or debris removal edge having an angle which, in accordance with one aspect of the invention, varies along the working length. Preferably, the angle defined at each edge decreases in a direction from the distal end to the proximal end. This inventive aspect benefits the instrument in several ways. For example, even at larger tapers, the instrument will be more flexible than conventional instruments of the same taper. Also, one or more cutting edges will be sharper at the proximal end of the working length because of the reduced angle between adjacent surface portions at this location. This allows the proximal end to be a more efficient cutter at that portion of the tooth having the greatest amount of material needing removal. Finally, this inventive aspect also provides an increased area for debris removal at the proximal end.
The invention also enables the minor and major diameters of the instrument to be sized independent of one another. This aspect allows the minor diameter or cross-sectional dimension to be maintained substantially constant along the working length, while the major diameter or cross-sectional dimension includes a taper. Thus, a twisted instrument according to this aspect of the invention will have a more constant flexibility along the working length notwithstanding a significant taper existing along the major diameter. Other embodiments of this general aspect are also possible and include forming the minor and major diameters with different tapers.
Endodontic instruments of this invention may be formed with many different cross sectional shapes. Typically, the elongate member of the finished instrument will have three or four longitudinally extending surface portions and a corresponding number of longitudinal, helically-shaped edges. The elongate member may be formed from materials having superelastic properties and/or other materials, such as titanium, carbon steel or stainless steel.
A preferred method of making endodontic instruments according to the invention includes removing material from an outer surface of a wire blank in at least a first path extending along and twisting at least partially around the longitudinal axis of the wire blank, and then twisting one end of the wire blank with respect to the other and about the longitudinal axis to form at least one helical cutting edge along the working length. Preferably, at least two adjacent surface portions are cut or ground from the outer surface of the wire blank in first and second paths extending along and twisting at least partially around the longitudinal axis of the wire blank. For example, a three-sided endodontic instrument may be formed from a blank ground to have two partially twisting outer surface portions and one straight or axially extending outer surface portion. As another example, a four-sided instrument may be formed with four longitudinally extending, partially twisting ground flats. It w
Lucchesi Nicholas D.
Ormco Corporation
Wood Herron & Evans L.L.P.
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