Method of endodontic preparation of a root canal and a file set for use in ...

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METHOD OF ENDODONTIC PREPARATION
OF A ROOT CANAL AND A FILE SET FOR
USE IN THE METHOD

This application is a continuation of application Ser. No. 5 08/788,479, filed Jan. 28, 1997, now abandoned, which is a continuation of application Ser. No. 08/373,626, filed Jan. 17, 1995, now abandoned.

PRIOR ART 10

Cleaning and shaping root canals with files, and particularly with tapered files having at least one spiral groove thereon, is well known. For reference to background material relating to the use of metal tapered files having spiral grooves formed thereon reference may be had to U.S. Pat. 15 No. 4,934,934 that issued Jun. 19, 1990 entitled "Dental File/Reamer Instrument" and U.S. Pat. No. 5,106,298 that issued Apr. 21,1992 and entitled "Endodontic Dental Instrument". Both of these patents, and the references cited in them, are incorporated herein by reference. 20

U.S. Pat. No. 5,106,298 is particularly relevant to the method of this invention. This patent discloses a tapered file having a proximal portion and an apex end and having at least one spiral groove formed thereon extending from the proximal portion to the apex end. The file described in this 25 patent is important in that it teaches a groove or grooves forming scraping shoulders that intersect the peripheral surface of the drill at an angle of about 90° to a tangent to the drill surface at the point of intersection. This angular relationship between the shoulder of the groove and the 30 peripheral surface of the drill is commonly referred to as a neutral rake angle. This neutral rake angle is important in the practice of the method of the present invention in that a tapered drill with one or more spiral grooves forming scraping shoulders having neutral rake angles function to 35 clean and shape a root canal as the file is rotated in the root canal without tending to grab or engage the root canal in a screw like action. That is, rotation of a tapered drill having grooves forming a neutral rake angle tends to remove the pulp and clean the interior of the tooth and shape it without 40 the file tending to self-thread itself aggressively towards the apex of the root canal.

BRIEF SUMMARY OF THE INVENTION

This invention relates to an improved method of preparing 45 a root canal in a tooth to receive endodontic filler material. A root canal and tooth has a proximal portion and an apex portion. The method includes the steps of manipulating tapered files in the root canal, the files being a part of a set in which each file has a taper greater than 0.02 millimeters 50 increase in diameter for each millimeter of length and in which the files of the set have tip diameters that are separated from each other by a selected size progression, and in which the files have scraping surfaces each having a neutral rake angle. By the method of this invention, files are 55 selected for manipulation in a root canal so that the root canal is cleaned and shaped essentially from the coronal area of the tooth in the direction towards the tooth apex. The method of this invention is contrasted with the typical and long practiced endodontic procedure wherein root canals 60 have historically been treated by the use of files constructed and dimensioned to clean a root canal starting essentially with root apex followed by the use of increasingly larger sizes of files so that the cleaning and shaping action takes place from the apex towards the coronal area. 65

More specifically, the invention is related to a method of cleaning and shaping a root canal in a tooth in preparation

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for filling the root canal with a filler material, such as gutta percha, as a part of an endodontic procedure. A root canal of a tooth has a proximal portion adjacent the tooth crown or enamel bearing coronal area. The root canal progresses towards the root apex from which the nerves extending from channels in the jawbone enter into the tooth.

More particularly, the method of this invention is practiced by the practitioner first drilling a hole in the tooth crown and into the pulp chamber to provide access to the root canal proximal portion. A first file is inserted into the root canal proximal portion, the first file being selected from a set of files so that the diameter of the file is such that initial contact is made between the spirally formed scraping edge and the proximal portion of the root canal to first clean and shape the proximal portion.

Thereafter, a second file is selected of a tip diameter that, when inserted into the root canal, contacts the portion of the root canal adjacent to the first mentioned proximal portion. The selection of files having different apex diameters from the set and manipulation thereof in the tooth is continued until a file apex end reaches the apex of the tooth.

The cleaning and shaping of the root canal thus proceeding from the coronal area of the tooth in the direction towards the tooth apex.

A set of files as used in practicing the method of this procedure preferably has tip diameters that progress in a series from the smallest to the largest, each step representing an increase in tip diameter of a selected arithmetic or geometric size progression. The typical file set may have nine files, the tip diameters ranging from approximately 0.129 mm to 1.0 mm. In the typical endodontic procedure of this invention only four or five files of this set are employed. The size ranges of the files used for an endodontic procedure is determined by the root canal characteristics. A size progression of, by example, 29% has functioned well in experimental applications.

While the procedure of cleaning and shaping a root canal as a part of an endodontic process of this invention can be carried out by manually manipulating files when positioned in a root canal, the preferred procedure is to support the proximal end portion of each file in a power driven hand piece that is manipulated by the practitioner (endodontist or dentists) in which the practitioner, after placing a file in a hand piece, positions the file in a root canal and energizes the hand piece to rotate the file. The practitioner applies only gentle pressure on the file as it is rotated in a root canal, it being a characteristic of the files of the set that as a file shapes and cleans a portion of a root canal it will advance in the canal until the file has formed a substantially circular root canal shape at the file apex. Where further advancements does not easily take place or when easy advancement of the rotating file ceases, the practitioner knows that a different size file needs to be selected to shape and clean a different portion of the length of the root canal. The rotating file brings the tooth pulp tissue and dentinal debrish coronally where they can be easily removed.

DESCRIPTION OF THE DRAWINGS

FIGS. 1 through 4 show representatives of portions of dental files that are used in practicing the method of this invention. The four files illustrated in FIGS. 1 through 4 are a part of a set of dental files for use in practicing the method, the typical set consisting of approximately nine files that are preferably substantially identical to each other in degree of taper and cleaning shoulder structure but differing from each other in that the diameter of the tips are progressively larger in a geometrical progression.

FIGS. 5 and 6 show files as used in practicing the method of this invention wherein the file contour is shown diagrammatically. FIG. 5 and 6 show the external appearance to files as employed in the invention, the files having head portions that are constructed and dimensioned to be received in a 5 hand piece (not shown) as typically used by dentists and endodontists. FIGS. 5 and 6 show two different size files.

FIGS. 7 through 14 show the sequence of steps employed in practicing the method of this invention. Specifically, FIGS. 7 through 14 each show a file positioned in the root 1° canal of a typical tooth and illustrate the sequence of steps whereby a typical root canal in a tooth is cleaned and shaped in the direction from the root coronal area to the root apex.

FIG. 15 shows a final step of flaring the upper portion in the area of the pulp chamber and the opening through the 15 tooth crown to facilitate placement of a filler material, such as gutta percha, in the fully cleaned and shaped root canal.

FIG. 16 shows the tooth with the root canal cleaned and shaped, and the coronal area flared, the tooth being ready to 2Q receive filler material.

FIG. 17 shows the tooth as illustrated in FIGS. 7 through

16 as the tooth typically appears in cross-section prior to the initiation of an endodontic procedure.

FIG. 18 is a highly enlarged cross-sectional view of a file 25 as typically employed in practicing the method of this invention, taken along the line 18—18 of FIG. 4. This figure shows how the flutes are formed in a way to provide scraping shoulders having neutral rake angles. The number of spiraled flutes can vary from two to four or five or more, 30 with radial lands existing between the flutes.

DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENT

Referring first to FIG. 17 a typical tooth is illustrated in 35 cross-section as an example of a tooth as it appears prior to the initiation of an endodontic procedure. Endodontic procedures are typically carried out when a tooth becomes abscessed, that is, when the pulp material formed in the tooth root canal becomes infected. The tooth as illustrated in FIG. 40

17 includes a dentin portion 10 that forms the body of the tooth. Formed on the upper exterior of the tooth is the enamel 12 that is the hard outer portion of the crown area of the tooth which is visually exposed. Inside dentin 10 there

is a root canal 14 that is enlarged in the upper portion within 45 the crown, the enlarged portion being termed the pulp chamber 16. The transition from the pulp chamber 16 to the root canal proper is termed the orifice area 18. The root canal ends at the tooth apex 20 at a root canal apex opening 22 through which the apical foramen (not shown) passes to 50 connect the pulp material that constitutes the tooth nerve with the plexus of nerves in the jaw bone structure (not shown). The root canal 14, including the pulp chamber 16, in a healthy tooth is filled with pulp material that is essential during the tooth growth. When a tooth has reached maxi- 55 mum size the function of this pulp material diminishes and it can become infected—typically termed an abscess— which can be exceedingly painful. In the past, when the pulp material in a tooth root canal or pulp chamber become infected there was no recourse other than to extract the tooth. 60 In present day dentistry tooth extraction is required much less frequently. Due to the advancement of the science of endodontics an abscessed tooth can usually be preserved to the great benefit of the patient. To preserve the tooth, the pulp material in the pulp cavity 16 and root canal 14 must 65 be carefully removed and the root canal cleaned. The canal cannot be left open but must be filled with a filler material

to prevent body fluids from entering the root canal after the pulp material has been removed. The technique of removing the pulp material from root canal 14, including pulp center 16, and replacing it with a hygienic filler material, such as gutta percha, to enable the tooth to remain in the body and free of pain to the patient, is the basic practice of endodontics. This invention is concerned with an improved method of cleaning and shaping the root canal 14.

Herebefore, a common practice of endodontics is to clean the root canal in a process generally termed the "step back" method. In this method the practitioner first selects a file from a set in which the files have a 0.02 taper, the first file being selected to have a tip diameter so that tip will substantially reach to the root canal apex opening 22 to first clean the apex area. Subsequently, the practitioner selects files of increased cross-section, that is, files of essentially the same 0.02 taper but of greater diameter, to progress upwardly towards the coronal area to enlarge and shape the root canal, each file cleaning the root canal primarily by engagement with the root canal by the portion of the file adjacent the file tip. Since the technique is carried out essentially from the bottom of the tooth, that is, from the apex area of the tooth towards the coronal area, the method is called "step back". In contrast, the method of this invention is the opposite, that is, the procedure that will be described herein is a "crown down" approach.

For the purpose of carrying out the method of this invention a set of dental files is required that is different than the set of dental files utilized in the "step back" method. FIGS. 1 through 4 illustrate four files taken from a set employed in the present invention. The four files of FIGS. 1 through 4 are taken from a set of files which typically includes nine sizes, usually identified as sizes number 2 through number 10.

Each of the files 24A through 24D of FIGS. 1 through 4 consist of a main body portion having spiral grooves 26 formed thereon, the grooves forming spiral lands 28. The body portion of each of the files extends from an apex 30 to a file proximal portion 32. The proximal portion has an enlarged diameter portion that forms a shank 34, only a portion of which is seen in FIGS. 1 through 4. Shank 34 is shaped and dimensioned to be received in a typical hand piece that is commonly employed by dentists and endodontists. A typical hand piece (not shown) has provision for selectively imparting rotation to a file retained in it. The dentist or endodontist employs the hand piece for inserting a file into a root canal and for rotating the file in a method that will be described in detail subsequently.

FIG. 18 is a cross-sectional view taken of file of FIG. 4 that represents the cross-sectional arrangement of all of the files making up a set of files used to practice the method of this invention. The file 24D as shown in FIG. 18 has a body portion 36 that is formed of strong yet flexible metal. Into this tapered body is machined at least one spiral groove. In the embodiment illustrated in FIG. 4 and FIG. 18, the file is formed with two intertwining spiral grooves 38A and 38B. Between the grooves 38A and 38B are the circumferential lands 40A and 40B that form the exterior of the file before grooves 38A and 38B are machined. Where groove 38B intersects land 40A a scraping shoulder 42A is formed. In like manner, where groove 38A intersects land 40B a scraping shoulder 42B is formed. Each of these scraping shoulders 42A and 42B is formed so that a tangent of the arc of groove 48B intersects a tangent of circumferential land 40A at right angles as indicated by the dotted lines 44 and 46. This forms what is called a "neutral rake angle". By "neutral rake angle" is meant that the scraping surface 42A scrapes 5

a portion of a root canal that it contacts without a tendency to cut into the root canal surface as would be caused by a positive rake angle, such as is employed in drill bits. A negative rake angle which would tend to slide over the surface of a root canal without scraping or shaping it. Thus, 5 the employment of a neutral rake angle in the file set used in the method of this invention is critical, however, obviously the actual angle can depart very slightly from exactly 90° as represented by the dotted lines 44 and 46, but for optimum results the rake angle as indicated by the dotted 10 lines 44 and 46 should be approximately a right angle.

Shoulders 42C and 42D are formed as shown in FIG. 18, however, if the file is rotated only in one direction while in a root canal, such as clockwise in the cross-sectional view of FIG. 8, the shoulders 42C and 42D do not perform any ^ function, that is, they do not scrape nor do they take any part in the shaping of the root canal. In the typical application of this invention it is not necessary to reverse the rotation of a file while in a root canal, however, if a file should inadvertently become stuck in a root canal it can augment the 2o extraction of the file in some instances by rotating it in the opposite direction. Thus, the surfaces 42C and 42D would function primarily, if used at all, to assist in extracting the file from a root canal but do not play any part in the cleaning and shaping of a root canal. 25

The files making up a set are essentially identical to each other, as previously indicated, except for a change in the apex diameter. The apex diameter of the file of FIG. 1 as indicated by the numeral 48A; the apex diameter for the file of FIG. 2 by 48B; the apex diameter of file of FIG. 3 by 48C; 30 and the apex diameter of the file of FIG. 4 by 48D. The apex diameters vary from each other by a fixed arithmetic or geometrical progression. In a preferred embodiment of this invention the set of files have apex diameters that vary geometrically by a ratio of about 29%. That is, the apex 35 diameter 48B is 29% greater than the apex diameter 48A of file 24A. In like manner, the apex diameter 48C of file 24C is approximately 29% greater than the apex diameter of 48B of file 24B, and so forth. Obviously, some other percentage of size change could be selected or the tip diameters 48A 40 through 48D can vary by a fixed amount, such as 0.05 millimeters. In order for a dentist or endodontist to easily identify file sizes the shank portions 34 are typically color coated. The typical apex diameters of files making up a set of files as employed in the preferred practice of the method 45 of this invention are as follows:

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that are slidably positionable on the files. These washers 50 are utilized to gauge the spacing between the washers and the file apexes 30 so the dentist or endodontist can know the depth of the file in a root canal.

FIGS. 7 through 14 illustrate the sequence of steps employed to endodontically prepare a typical tooth, such as an incisor or canine. The first step is illustrated in FIG. 7. In this first step the practitioner (endodontist or dentist) drills a hole 52 through the crown enamel 12 into the pulp chamber 16 to expose the root canal 14. The root canal and pulp chamber then must be cleaned and shaped so that the interior of the tooth can be filled with a filler material such as gutta percha. After hole 52 is drilled a file 24 is inserted into the root canal. The file 24 is selected to be of a size that the portion thereof four or five millimeters up the file shaft from the tip 30 engages the sidewall of the orifice area 18 of the root canal. That is, in the method of this invention, contrary to an endodontic procedure in common present use, the practitioner selects a relatively larger file size such as a number 4 or whatever intermediate sizes is required to engage the upper portion of the root canal 14. In contrast, a common procedure that has long been practiced calls for the practitioner to select a small diameter file that penetrates substantially to the tooth apex 20 to first clean the area of the root canal adjacent the apex opening 22. Following the currently used procedure the practitioner would then gradually increase file diameter size to enlarge and shape the root canal starting from the tooth apex 20 and working upwardly in what is known as "step back" procedure. The present procedure is the opposite, that is, file 24C is of a relatively larger size, that is one that is normally much larger than would be feasible to extend all the way to or adjacent the apex opening 22 as the first step in the procedure. The larger file shown in FIG. 7 is employed to clean and shape the upper portion of the root canal 14, that is, the portion at the orifice area 18 that communicates the root canal with the pulp chamber 16.

In step 2 as shown in FIG. 8, file 24C has been advanced in the root canal typically using the same size file as in step 1, such as a No. 4. Using the type of file as previously discussed with reference to FIG. 18, the practitioner will find that when the file has advanced to the point where the canal has been cleaned and shaped in proportion to the size of the file selected so that the portion of the file engaging the root canal shapes the root canal to substantially circular crosssections, and the circular cross-sections extend to the file apex 30, the file will not easily further advance. The practitioner can tactically determine after a short amount of practice when a file has performed its function and a different size file is required to further downwardly advance the cleaning and shaping action in the root canal.

Step 3, FIG. 9, shows the use of a larger size file such as a No. 5, indicated by 24D. The larger size file further cleans and shapes the upper portion of the root canal. In step 4, FIG. 10, the practitioner employs a smaller size file, such as a size 3, to extend the shaping and cleaning action farther into the root canal. In step 5, FIG. 11, a number 2 size file 24A has been selected by the practitioner, the size being such as to extend the cleaning and shaping action all the way to apex 20. Thus, it can be seen that in steps 1 through 5 the technique has employed larger size files followed (but not necessarily in strict sequence size order) by smaller size files to shape the root from the top down, that is, from the orifice area adjacent the pulp chamber 16 to root apex 20 as contrasted with a currently used procedures of shaping the root canal from the apex upward.

After size 2 file, as an example, has been used in step 5, FIG. 11, a size 3 file 24B is then employed to further shape