Endodontic instrument

An endodontic instrument includes a plurality of flutes and a plurality of lands extending helically around a working portion. Each flute includes a curved concave flute surface, a pair of flute shoulders at the peripheral edges of the flute surface, a flute width defined by a distance between the flute shoulders, and a flute depth defined by a point of maximum depth between the flute shoulders. Each land is positioned between a pair of axially adjacent flutes and includes a curved concave land surface, a pair of land shoulders at the peripheral edges of the land surface, a land width defined by a distance between the land shoulders, and a land depth defined by a point of maximum depth between the land shoulders. The land width is less than the flute width and the land depth is less than the flute depth in the upper region of the working portion.

FIELD

This disclosure relates to the field of endodontics. More particularly, this disclosure relates to instruments used for enlarging and obturating an extirpated root canal.

BACKGROUND

In the field of endodontics, one of the most important and delicate procedures is that of cleaning or extirpating a diseased root canal to provide a properly dimensioned cavity while essentially maintaining the central axis of the canal for filling of the canal void and capping of the tooth. When done properly, this step enables substantially complete filling of the canal with biologically inert or restorative material without entrapping noxious tissue in the canal that could lead to failure of the therapy.

In a root canal procedure, the dentist removes diseased tissue and debris from the canal prior to filling the canal with a biologically inert or restorative filling material. Many tools and techniques have been designed in an effort to enable dentists to perform the difficult task of cleaning and shaping root canals. Historically, dentists have used endodontic files to remove the soft and hard tissues in and adjacent the root canal. These endodontic files are typically made by grinding helical flutes into a working portion of a small elongate tapered rod to create a curvilinear, abrasive file with a helical cutting edge.

Conventional endodontic instruments with helical cutting/abrading edges have certain endemic problems which, to some degree, have been tolerated and approached from a management perspective rather than an elimination perspective. For example, conventional endodontic instruments may only cut when rotated in one direction. Further, the instruments typically must be backed off after rotating in a first direction to unload the instrument before advancing the instrument further into the root canal. Conventional endodontic instruments also may begin to screw into the wall of the canal rather than continuing down the canal toward the apical tip of the root. In some cases, this “screwing in” can cause the instrument to break through the side of the root canal and into surrounding tissue or bone. Or, it may begin to “drift” or displace laterally relative to the center axis of the canal as it is moved roto-axially.

These and other problems continue to plague practitioners and designers alike in their efforts to enlarge and prepare for filling the varied tooth root canal configurations in a manner substantially concentric with the natural or original canal curvature/shape to enable successful, effective and permanent treatment therapies. Accordingly, there is a need for improved endodontic instrument designs and methods that will avoid, minimize or eliminate drawbacks and problems associated with conventional endodontic instruments including, but not limited to, “screwing in” issues and the inability to cut in more than one direction encountered during the use of conventional endodontic instruments.

SUMMARY

The above and other needs are met by an endodontic instrument adapted to be axially reciprocated within a root canal to remove material from walls of the root canal having an elongate rod having a proximate end and an opposite distal tip end defining a working portion disposed between the proximate end and the distal tip end, the working portion including an upper region and a lower region; a plurality of flutes extending helically around the working portion, each flute including a curved concave flute surface, a pair of flute shoulders at the peripheral edges of the concave flute surface, a flute width defined by a distance between the pair of flute shoulders, and a flute depth defined by a point of maximum depth between the pair of flute shoulders; and a plurality of lands extending helically around the working portion, each land positioned between a pair of axially adjacent flutes and including a curved concave land surface, a pair of land shoulders at the peripheral edges of the concave land surface, a land width defined by a distance between the pair of land shoulders, and a land depth defined by a point of maximum depth between the pair of land shoulders. The land width is less than the flute width and the land depth is less than the flute depth in the upper region of the working portion.

According to certain embodiments, the land width is substantially the same as the flute width and the land depth is substantially the same as the flute depth in the lower region of the working portion. In certain embodiments, the land width is approximately ½ to ¾ of the flute width in the upper region of the working portion and/or the land depth is approximately ¼ to ½ of the flute depth in the upper region of the working portion.

According to certain embodiments, the plurality of flutes consists of three flutes and the plurality of lands consists of three lands.

According to certain embodiments, the flute and land shoulders form six distinct cutting edges, each of the six distinct cutting edges including a positive cutting angle of about 75° to about 110° and a negative cutting angle of about 5° to about 30° depending on whether the instrument is rotated in a clockwise or counterclockwise direction.

DETAILED DESCRIPTION

FIGS. 1-3illustrate features of an endodontic instrument10according to one embodiment of the present disclosure. The elongate instrument is preferably formed from an elongate rod12of stainless steel or nickel-titanium alloy having a diameter of from about 0.3 millimeters to about 1.6 millimeters, although the rod12may have a larger or smaller diameter and/or a varying diameter along its length as needed. In suitable embodiments, rods12made from other suitable metals and/or alloys may be used. In one embodiment, the instrument10is formed from a controlled memory material allowing the instrument to be pre-formed before inserting the instrument into a root canal.

The elongate rod12extends from a proximal end14to a distal tip end16of the instrument10. The proximal end14is typically secured to a fitting portion (not shown) for mating with a dental drill or hand-piece. In other embodiments, the proximal end14may be secured to a handle to facilitate hand manipulation of the instrument10. The rod12includes a working portion18extending from adjacent the distal tip end16of the instrument10along the length of the rod12to adjacent the proximal end14. The working portion18preferably has a length of from about 10 millimeters to about 20 millimeters. The diameter of the working portion18of the instrument10preferably tapers at a rate of from about 0.02 mm/mm to about 0.12 mm/mm, however it is also understood that the diameter of the working portion18may be substantially constant along a length of the working portion18and/or vary along a length of the working portion18.

The working portion18of the instrument10includes two or more helical flutes20formed along a peripheral surface of the working portion18. As best shown inFIG. 2, each of the flutes20define a curved concave flute surface when viewed in transverse cross section. Each flute20includes a pair of helical flute shoulders24aand24cat the peripheral edges of the concave flute surface. Each of the flutes20further include a flute base24bdefined by the point of maximum depth from the flute shoulders24aand24c. The peripheral surface of the working portion18of the instrument10further includes two or more helical lands22each positioned between axially adjacent flutes20. Similar to flutes20, each helical land22includes a curved concave land surface with helical land shoulders26aand26cat the peripheral edges of the concave land surface. As shown, each land shoulder26acoincides with one of the flute shoulders24aand each land shoulder26ccoincides with one of the flute shoulders24c. Each of the lands22include a land base26bdefined by the point of maximum depth between land shoulders26aand26c. According to preferred embodiments, the instrument10preferably includes three helical flutes20formed along the working portion18of the instrument10and three helical lands22disposed between axially adjacent flutes20. In alternate embodiments, the flutes and lands are straight as opposed to helical.

Referring toFIG. 2, which depicts the cross section of the working portion18of instrument10taken along line A-A ofFIG. 1, the dimensions of the flutes20are preferably greater than the dimensions of the lands22in at least the upper region of the working portion18adjacent the proximal end14. In particular, the width of the helical lands22are preferably smaller than the width of the flutes20and the land depth26bis less than the flute depth24b. According to preferred embodiments, the width of the lands22are approximately one-half to approximately three-quarters of the width of the flutes20in the upper region, and most preferably approximately two-thirds of the width of the flutes20. According to preferred embodiments, the land depth26bis approximately one-quarter to approximately one-half the flute depth24b, and most preferably about one-third the flute depth24b. For purposes of the present disclosure, the upper region of working portion18generally refers to the top portion adjacent the proximal end while the lower region generally refers to the lower portion adjacent the distal tip16. In preferred embodiments, the upper region includes roughly the top two-thirds of the working portion18adjacent the proximal end14while the lower region of the working portion18includes roughly the lower third of the working portion18adjacent the distal tip16.

Referring toFIG. 3, which depicts the cross section of the working portion18of instrument10taken along line B-B ofFIG. 1, the dimensions of lands22are generally the same as the dimensions of the flutes22in the lower region of the working portion18. As a result, according to preferred embodiments where the dimensions of the lands22are smaller than the dimensions of the flutes20in the upper region of the working portion18and generally the same in the lower region of the working portion18, the flutes20and lands22of the lower region are configured to do more cutting of a canal cavity while the flutes and lands of the upper region are configured to transport debris out of the canal cavity. In preferred embodiments, the dimensions of lands22gradually conform to the dimensions of the flutes22as one moves from the upper region to the lower region of the working portion.

Referring toFIGS. 4A-4F, a process for grinding the flutes20and lands22of a three-fluted and three-land instrument10as shown inFIGS. 1-3is depicted according to one embodiment of the disclosure. Referring toFIG. 4A, a rotating rod12is moved past a grinding wheel to form a first flute20ain the rod12. The rod12is then indexed and again moved past the grinding wheel a second time to form second flute20bas shown inFIG. 4B, and indexed and moved past the grinding wheel a third time to form third flute20cas shown inFIG. 4C. Referring toFIG. 4C, the cutting depths and widths of the flutes20a,20b,20care controlled to leave three convex outer surfaces30a,30b,30cof the original rod12intact between axially adjacent flutes.

After forming the three flutes20a,20b, and20c, rod12is indexed such that the rod's fourth pass past the grinding wheel begins between axially adjacent flutes20a,20bto form helical land22ain convex outer surface30aas shown inFIG. 4D. Rod12is again indexed and moved past the grinding wheel a fifth time to form helical land22bin convex outer surface30bas shown inFIG. 4Eand a sixth time to form helical land22cin convex outer surface30cas shown inFIG. 4F.

As compared to traditional processes, the flutes20are cut into instrument10at a relatively shallow depth20busing a smaller radius wheel to leave convex outer surfaces30a,30b,30cwith a sufficient width for forming lands22. In preferred embodiments, the grinding wheel has a radius of about 0.01 inches to about 0.02 inches, and most preferably about 0.015 inches, resulting in a depth20bof flutes in the upper region of working portion18of about 0.01 inches to about 0.02 inches, and most preferably about 0.015 inches. This compares to more traditional processes using a grinding wheel with a radius of about 0.01 inches to about 0.03 inches.

Referring toFIG. 5, the six passes of rod12past the grinding wheel as described above forms an instrument with three concave flute surfaces20and three concave land surfaces22disposed between axially adjacent flutes20. This results in the peripheral edges of the flutes20and lands22in the upper region of the working portion18forming six distinct cutting edges40awhen the instrument10is rotated in the clockwise direction and six distinct cutting edges40bwhen the instrument10is rotated in the counterclockwise direction. More specifically, referring to cutting edge40depicted inFIG. 6, each cutting edge40in the upper region of the working portion includes either a positive cutting angle α of about 75° to about 110°, and most preferably about 95° about or a negative cutting angle β of about 5° to about 35°, and most preferably about 25° depending on which direction the instrument10is rotated due to the flutes20having a greater width and depth as compared to lands22. In this regard, cutting edge40includes a positive cutting angle when the instrument10is rotated such that the cutting edge40trails flute20while cutting edge40includes a negative cutting angle when the instrument is rotated such that cutting edge40trails land22. Accordingly, cutting edges40aas shown inFIG. 5includes three positive cutting edges and three negative cutting edges when rotated in the clockwise direction, and cutting edges40binclude three positive cutting edges and three negative cutting edges when rotated in the counterclockwise direction.

In use, the cutting edges with larger cutting angles make an aggressive and sharp cutting edge, which does the majority of cutting in the root canal. On the other hand, the negative cutting angles are less aggressive and will mostly clean and finish the cuts performed by the larger cutting angles. The negative cutting angles also provide a path for the micro cuts of debris to flow out of the root canal. Multi-directional cutting is also enhanced due to the positions of the positive and negative cutting angles in the instrument10.

As noted above, the lower region of the working portion18preferably includes lands22with substantially the same width and depth as flutes20. More specifically, referring back toFIG. 2, the lower region preferably includes six cutting edges40each having mostly negative cutting angles of about the same size whether the instrument is rotated in the clockwise or counterclockwise direction. Thus, the lower region of the working portion18preferably includes all sharp cutting edges.

The foregoing description of preferred embodiments of the present disclosure has been presented for purposes of illustration and description. The described preferred embodiments are not intended to be exhaustive or to limit the scope of the disclosure to the precise form(s) disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the disclosure and its practical application, and to thereby enable one of ordinary skill in the art to utilize the concepts revealed in the disclosure in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the disclosure as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.