Patent Application
20060068362
The invention relates generally to dental instruments and, more particularly, relates to endodontic instruments for extirpating pulp tissue and dentin from a root canal before obturating the root canal.
Successful root canal therapy effectively alleviates the pain and trauma originating from the decayed, damaged or dead circulatory and neural pulp tissue so that the tooth need not be extracted. After the pulp chamber, and subsequently the coronal root canal orifice(s), have been accessed during a root canal procedure, pulp tissue is extirpated from the root canal(s) of the tooth. Some surrounding dentin is also removed in the shaping of the root canal(s). After the root canal(s) have been sufficiently shaped and cleaned, sealant and obturation materials are used to fill and seal the root canal(s). To conclude the procedure, the access cavity in the coronal portion of the tooth is sealed using a restorative procedure to prevent future infection and decay.
Various endodontic instruments are employed to remove the pulp tissue and dentin from the root canal and to enlarge and shape the root canal in preparation for obturation. Conventional endodontic instruments, such as reamers or files, employed for extirpation during root canal therapy generally include a thin, flexible, metal shaft with an abrasive surface or sharp edges, which promotes efficient cleaning of the root canal. A shank at one end of the endodontic instrument is adapted for gripping by a dentist or attachment to a mechanical device such as a dental drill. Obturation material may be packed into the prepared root canal using similar endodontic instruments. Endodontic instruments are normally rotated and moved into and out of the root canal along the instrument's longitudinal axis.
During root canal therapy, the pulp material is removed from the full length of the root canal to the canal's apex. A problem that may be encountered during root canal therapy is apical perforation, i.e., excessive perforation of the apex of the root canal. Apical perforations typically result from pushing the tip of the endodontic instrument well beyond the apex of the canal, which not only exposes the periapical tissue to the infected debris, but also results in an enlarged and poorly shaped apex. The exposure to the infected debris may result in sensitivity and lengthen the healing process, while the enlarged and poorly shaped apex may result in a bad seal, leading to apical leakage and ultimately the need for retreatment or tooth extraction. Another problem relates to not introducing the file deep enough into the canal and failing to remove infected material from the vicinity of the apex, thereby leaving infected tissue within the root canal. The position of the tip of the endodontic instrument should be gauged relative to the apex of the canal so as to avoid significantly penetrating the apex while removing substantially all the pulp tissue from the root canal and sufficiently shaping the root canal.
Practitioners typically have at their disposal several techniques to determine the location of the apex. For example, many practitioners rely on an electronic apex locator to identify the location of the apex during a root canal procedure. Electronic apex locators, however, are costly and unreliable under some circumstances. Consequently, practitioners often resort to alternative techniques to determine the apex location or to confirm the readings made with the electronic apex locators.
A method of locating the apex without the use of an electronic apex locator may be accomplished, for example, in the following manner. The practitioner estimates the distance from a visible reference location, such as an occlusal landmark, to the apex utilizing a pre-operative radiograph of the tooth, and his/her education and experience. The practitioner then chooses an appropriate size endondontic instrument and places a moveable rubber stop on the shaft of the instrument at the estimated distance from the tip in order to indicate depth against the visible reference location, or datum. The practitioner works the instrument into the canal until the rubber stop reaches the datum and then takes a radiograph with the instrument remaining inside the tooth. Based on the information provided on the radiograph the practitioner may then, if required, adjust his/her estimate of the distance from the datum to the apex and alter the location of the rubber stop as necessary. The process is repeated as often as required until the practitioner can see on the radiograph that he/she has reached the desired depth with the appropriate size instrument. The practitioner can then determine the distance from the datum to the apex by removing the instrument from the patient's mouth and measuring the distance from the rubber stop to the tip of the instrument. The practitioner may then calculate and place, as appropriate, a moveable rubber stop on each successive instrument to be used in the procedure, and utilizing the rubber stops and the datum, he/she will shape the canal with the subsequent instruments as necessary.
A common problem with using moveable rubber stops to locate the apex is that after the radiograph is taken the rubber stop may be inadvertently moved by the patient while the instrument is still in the mouth, or by the practitioner while in the process of removing the instrument from the mouth, thereby rendering a false measurement. Another issue with using rubber stops is that they are generally too large to fit into the access cavity of the tooth and may be difficult to see on the radiographs. This precludes the practitioner from using the pulp chamber floor, which may be 10 to 15 millimeters closer to the apex than the occlusal landmark and be a significantly more planar surface, as the datum for measuring to the apex.
In the absence of a moveable rubber stop the practitioner may utilize, when present, a plurality of fixed visual markings on the shaft of the instrument, which are located at known distances from the tip of the instrument. These visual depth marks are typically circumferential rings inscribed into the shaft of the instrument using a laser marking process, or cut into the instrument with a cutting tool such as a grinding wheel. The advantage of using the visual markings that have been cut into the shaft is that, when sufficiently deep, the distinct reduction from the mean shaft diameter may be seen on a radiograph. The practitioner may therefore use the pulp chamber floor as the datum, taking advantage of its relatively flat surface and the fact that it is much closer to the apex than any occlusal features. The drawback to these cut-in depth marks is that to be readily identified on a radiograph their diameters must be significantly less than the mean shaft diameter, thereby weakening the overall structural integrity of the instrument. The likelihood of fracture at the groove locations therefore increases, subsequently resulting in a higher failure rate for these instruments.
In an effort to reduce the propensity for fracture, a manufacturer may create grooves just deep enough to be seen visually, but not radiographically. Likewise, the depth mark rings inscribed using a marking process such as laser marking do not significantly reduce the diameter of the instrument shaft thereby retaining its resistance to fracture, but also preclude the markings from being radiographically visible.
Visual depth markers that can not be seen on a radiograph have a number of additional drawbacks when used to identify the tip of the instrument relative to the apex of the root canal. First, in many situations the visual markers are difficult to see. This may be caused by the inability of the patient to open his/her mouth wide enough or may be due to the practitioner being poorly positioned to observe the markers. For instance, the inability to visualize the markers may occur when performing root canal therapy from the lingual side of a canine or incisor. Another drawback when using visual markers is that it is often difficult to find and maintain a reproducible reference datum for gauging the penetration depth. For instance, the jaggedness or irregularity of the crowns of molars make it difficult to specify a unique and repeatable datum. Additionally, a visual comparison between a marker and a reference datum often changes depending on the angle at which the comparison is made.
Thus, there would be a need for an endodontic instrument that overcomes these and other deficiencies of conventional approaches for apex location and provides for improved endodontic depth marking.
The invention overcomes the foregoing and other shortcomings and drawbacks of conventional depth markers on endodontic instruments and conventional methods of determining apex location, as described above. According to the principles of the invention, an endodontic instrument includes a shank adapted for interfacing or gripping the instrument with a chuck or collet of a motorized rotary dental handpiece, or alternatively, for manually manipulating the instrument with a hand grip of some form, and an elongated shaft defining a longitudinal axis and coupled to the shank having a working length capable of being inserted into the root canal of a tooth. The elongated shaft also includes a shaft portion between the shank and working length, and a tip positioned at the distal end of the instrument, which would therefore be inside the root canal when the working length of the instrument is so inserted. The working length may include one or more edges adapted to extirpate tissue from the root canal when the shank is manipulated. The instrument further includes a plurality of markers on the shaft portion for indicating the depth of the tip in the root canal. Each marker is perceivable in a radiograph taken of the tooth when the distal portion of the instrument is inserted into the root canal.
In one embodiment of the invention, the markers project radially outward from the shaft portion by an amount sufficient to distinguish each marker from the shaft portion. For instance, the shaft portion may have a first diameter and the markers may have a second diameter greater than the first diameter. The shaft portion and markers are configured such that the plurality of markers define a first total length along the longitudinal axis, the shaft portion between the plurality of markers define a second total length along the longitudinal axis, where the second total length is greater than the first total length. The markers may be integrally formed with the elongated shaft or may be separate pieces, such as rings or bands, that may be coupled to the elongated shaft at selected positions. Due to cost, manufacturability and other considerations, the markers may be made from the same material as the elongated shaft or may be made from a different material.
In another embodiment, the radiopacity of each marker may differ from the radiopacity of the elongated shaft by an amount sufficient to distinguish the markers from the elongated shaft. This could be done, for example, by making the elongated shaft and markers out of materials having different radiopacities. Another way to do this, however, may be to selectively coat the elongated shaft with materials such as paints, dyes, inks or combinations of these substances, having a greater radiopacity. The markers may take the form of circumferential rings around the elongated shaft or may include other indicia, such as numerals, letters, geometric shapes or combinations of these indicia.
The plurality of markers of the invention may be used in conjunction with a selected datum to determine the depth of the instrument relative to the apex of the root canal. When the tip of the instrument nears the apex of the root canal, a practitioner will often take additional radiographs of the tooth while the endodontic instrument is disposed within the root canal. In the invention, as described herein, each marker on the instrument is clearly perceivable in the radiograph. Since there are multiple markers, each marker may be separated from an adjacent marker by a known amount. The plurality of markers will therefore provide a reference or scale for estimating the distance from the tip of the instrument to the apex of the root canal, as determined from the radiograph. In this way then, a practitioner can reasonably estimate how much further the instrument should penetrate into the root canal in order to reach the apex.
The above and other objects and advantages of the invention shall be made apparent from the accompanying drawings and the description thereof.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the invention.
Referring first to
Manipulation of the instrument 10 for extirpating pulp tissue and dentin under conventional circumstances includes rotating the instrument 10 in the direction of arrows “A” and reciprocating the instrument 10 in the direction of arrows “B” by the practitioner to clean out and enlarge root canal 16.
As shown in the enlarged view of the elongated shaft 20 in
Depth markers 28 are advantageously adapted to be perceivable on a radiograph of the elongated shaft 20 and tooth 12 when tip 24 and portion 26 is inserted into root canal 16. In accordance with the invention, and as shown in
Instrument 10 is not limited to a constant diameter shaft portion 25 and may have a diameter that varies between the shank 19 and the working length 27. In this case, for each specific marker 28, the marker diameter 34 must be greater than the shaft diameter 32 adjacent that specific marker 28 such that each marker 28 may be distinguished from shaft portion 25 in the radiograph. In either case, each marker diameter 34 is preferably between approximately 10% and approximately 100% larger than the shaft diameter 32 adjacent each marker 28. In this way, when a radiograph is taken with tip 24 and portion 26 inserted within root canal 16 of tooth 12, depth markers 28 are perceivable and identifiable on the radiograph. The bump configuration of the depth markers 28 in the invention is advantageous in that the marker diameter 34 has been increased over the shaft diameter 32, not decreased as in the grooved markers of prior instruments. As a result, the structural integrity of instrument 10 is not compromised by including depth markers 28.
As shown in
The depth markers 28 may be incorporated into elongated shaft 20 in a variety of ways. For instance, as shown in
In use and with reference to
To do this, a practitioner will insert the instrument 10 into the root canal 16 of a patient's tooth 12 and take a radiograph while the instrument is disposed within the root canal. From the radiograph, the practitioner may readily identify the depth markers 28 along shaft portion 25 of elongated shaft 20 of the instrument 10. For example, because the markers 28 have a diameter 34 larger than the diameter 32 of the elongated shaft 20, such as that shown in
With reference to
The depth markers 40 may also be incorporated into elongated shaft 20 in a variety of ways. For instance, an elongated shaft 20 may be made from a first chemical composition having a first radiopacity while depth markers 40 may be made from a second chemical composition having a second radiopacity that differs from the first radiopacity. The markers 40 and elongated shaft 20 may be coupled during the manufacturing process of the instrument 38. When using radiopaque properties to identify markers 40, the diameter 32 of the elongated shaft 20 and the diameter 34 of depth markers 40 may be equal, such as that shown in
Another method used to incorporate markers 40 into elongated shaft 20 is by coating elongated shaft 20 with a material having a radiopacity greater than the radiopacity of elongated shaft 20. This coating may include, for example, various paints, dyes or inks with known radiopaque properties. Thus, the markers 40, such as that shown in
Alternate embodiments of endodontic instruments having depth markers comprising coating materials having a radiopacity greater than the radiopacity of elongated shaft 20 are shown in
As appreciated by those of ordinary skill in the art, the embodiments shown in
While the invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For instance, the present invention may be incorporated into a wide range of endodontic instruments including not only reamers and files but also spreaders, pluggers, and others. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicants' general inventive concept.
