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Endodontic instruments with pilot tips and parabolic cutting flutesRelated Patent Categories: Dentistry, Apparatus, BroachEndodontic instruments with pilot tips and parabolic cutting flutes description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060228667, Endodontic instruments with pilot tips and parabolic cutting flutes. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is a United States filing from PCT application Ser. No. PCT/US 03/33359 which claims priority from U.S. Provisional Application No.: 60/419,662, filed Oct. 18, 2002. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates generally to endodontic instruments and, more particularly, to cutting burs which are used in the creation of ideal access preparations into root canal systems of human teeth and to shaping files which are used to enlarge and shape the root canals present therein so that they may be prepared for filling. [0004] 2. Description of the Related Art [0005] A relatively common but difficult dental procedure is the entry into and the cleaning, shaping, and filling of root canals in human teeth that have become pathologic. In the performance of a root canal procedure, a hole is first cut in the crown or exposed portion of the tooth, typically either in the biting surface of the tooth, for posterior teeth, or in the side of the tooth on the interior of the jaw for incisor teeth. [0006] The creation of ideal access form has been difficult with available cutting tools, specifically preparing an ideal entry path for handpiece-driven files to effortlessly enter root canals. Cutting the correct entry path is critical because without a relatively straight approach for these rotary files, they are prone to breakage due to cyclic fatigue. Another difficult aspect of endodontic therapy has been the creation of a smooth transition between each of the access line-angles and the canal orifices apical to them. Leaving an irregularity at this transition level makes every introduction of a file, paper point, or gutta percha point into the root canal a challenge. When the line angle of the access preparation drops smoothly into the canal the rest of the procedure is easier and more controlled. [0007] Several solutions have been offered by manufacturers, such as Peezo burs which come in different configurations and access burs with no cutting flutes or diamond grit on the tip of the instrument, [0008] Peezo burs come in different configurations, two with different degrees of parabolic flute silhouettes, and another with a pilot tip, a quarter-round flute-tip radius with parallel shank flutes. All of these burs have cutting flute lengths of around 6-8 mm. The advantages of these burs when used in access procedures are the funnel shapes they make into canals, and the pilot tip which prevents ledge formation. Unfortunately, the flute length of these burs is only half the height of most access preparations, several of the Peezo designs are able to ledge canals, and those that have pilot tips are limited in their use because these passive guides are not of the ideal dimension. [0009] Access burs with pilot tips but without flutes or diamond grit at their ends are an improvement over those burs that can cut ledges in access and canal walls. These burs are quite limited in their use as they only cut sideways. What is needed is an access bur that has flutes the full length of the access cavity, that cuts aggressively in apical and lateral directions, that will not ledge, and will always follow the canal path. After the access preparation is completed and each of the root canals present in the tooth is located and negotiated, small endodontic instruments known generally as root canal files are then used to clean out the material present in the root canal, and to impart a specific shape to the root canal so that filling material may be inserted into the root canal to seal it. However, many problems can occur during this process. [0010] Most common is the uncontrolled transportation of the original canal path. This occurs with traditional root canal files having aggressive tip geometry, as described by Roane patent 4,536,159, as well as with other file designs such as those by McSpadden in patents 4,299,571 and 4,332,561, and in Maillefer et al. patent 5,658,145. Files with passive radiussed tip geometries, such as those described by Buchanan in previous patents, such as 4,836,780, 5,752,825, 5,836,764, 5,842,861, 5,897,316, and 5,921,775 faithfully follow the original canal path as they cut, but these safe file tips give up a certain amount of cutting efficiency to more aggressive designs. While clinicians initially react positively to the added cutting efficiency of these files, they find in a short time that apical lacerations can easily occur if length has been mis-determined or if the files are held at length for more than one second (Manufacturer's cautions in DFU). [0011] Furthermore, there has been some concern that the relatively narrow apical shapes created by the files described by Buchanan might not clean the ends of root canals as well as a technique which enlarged the end of root canals more. The apical stop preparation apparently accomplished this but, as Weine showed--"The Effect of Preparation Procedures on Original Canal Shape and on Apical Foramen Shape", Journal of Endodontics, vol. 1, No. 8, August 1985, pp. 225-262--it is difficult to create these larger apical shapes in root canals without damaging the root. [0012] McSpadden, as disclosed in his patent 4,299,571, designed a pilot tip for root canal files which attempted to resolve this problem. Unfortunately, the pilot tips of this design were 3 mm long and the cutting flutes behind them had a small 0.02 mm/mm taper. The function of this file concept was limited because the pilot tip often bound in the canal before the flutes contacted the canal wall, so larger shapes were impossible with these files. SUMMARY OF THE INVENTION [0013] The objective of the present invention is to allow faster and safer cutting tools to enter and shape root canals. This is realized primarily through a design logic incorporating sophisticated pilot tip geometry, parabolic cutting flutes in the region behind the pilot tip (referred to herein as the "alpha" or .alpha. region), and flutes of a consistent length and lesser taper comprising the region (referred to herein as the "beta" or .beta. region) between the alpha region and the shank. This design concept is applied to access preparation burs, to initial enlargement files, and to finishing files. [0014] Files disclosed in my prior application, Ser. No. 10/630,028, are provided with two distinct degrees of taper for the two portions of each file. I contemplate as part of the present invention additional groups of multi-taper files where the taper at the tip is one value, the taper of the flute portion adjacent the shank is another value, and there is a gradual but continuous change from one value to the other with distance from the tip. In other words, files of these groups, are not limited to two fixed tapers for corresponding sections of the flute but rather the change of taper from tip to shank portion occurs over a radius. I refer to these types of files in which the change of taper occurs over a radiussed section as parabolic files. These are incorporated in my parabolic system of endodontic implements. [0015] Files of the type described herein are improved significantly if they are provided with a radiussed pilot tip. Parabolic shaping files with radiussed pilot tips are far safer by virtue of the radiussed tip and are virtually guaranteed to eliminate the danger of ledging in a root canal. [0016] In one preferred arrangement of my invention, the radiussed pilot tips of different parabolic shaping files in a set are 1 mm in length and have eight different diameters, taken at the 1 mm point, for eight different parabolic shaping files. The alpha taper section behind the non-cutting pilot tip is 3 mm in length and has a 0.10 mm/mm slope for all files of this parabolic file system. The beta taper which extends to the shank is 12 mm in length and has a 0.05 mm/mm angle or slope for all files. With a 1 mm pilot tip length, an alpha length of 3 mm, and a shank length of 12 mm, all instruments have the traditional 16 mm limit to the shank-end fluted portion. These are provided in hand and handpiece-driven versions, with the hand files made in both left-hand and right-hand flute directions. [0017] Various critical dimensions for these parabolic shaping files are set out in the following Table I. The dimensions are given in millimeters. TABLE-US-00001 TABLE I (In millimeters) D1 D4 D16 .1 .4 1.05 .2 .5 1.15 .3 .6 1.25 .4 .7 1.35 .6 .9 1.55 .8 1.1 1.75 1.0 1.3 1.95 1.3 1.6 2.25 [0018] D1 is the diameter at 1 mm from the end of the file. D4 is the diameter at 4 mm from the end (3 mm from the tip). D16 is the diameter at 16 mm from the end (15 mm from the tip). [0019] For negotiating instruments, the parabolic negotiating files are simpler and fewer in number than the parabolic shaping files described above. These are provided in tip diameters of 0.06 mm, 0.08 mm, 0.10 mm, and 0.15 mm and all have 16 mm of 0.02 mm/mm tapered flute length. A second series incorporates variable tapers between files and some different tip diameters; specifically a 075-0.02, a 10-0.03, a 15-0.04, and a 20-0.05. Both series have the unique radiussed pilot tips and can be provided as either hand or rotary files. [0020] The pilot tips on this family of instruments are distinguished by their fully-radiussed geometry which absolutely prevents the ledging of canals and their use-specific designs which allow unique functionality. While all of the instruments in this set of tools have pilot tips, alpha parabolas, and beta tapers, each of the three sets of instruments has a different function and therefore requires a different concept and sizing of pilot tips. In the access burs, the pilot tips vary by increments relating to coronal canal diameters in small, medium, and large roots; 0.2, 0.3, and 0.4 mm. These pilot tips become proportionally longer as the diameter increases between sizes. This helps prevent dangerous over-extension into curved canals. [0021] In the initial enlargement files, the pilot tips are all 0.2 mm in diameter by 1 mm in length because they are designed to track the guidepath cut by the #15 negotiating file taken to length as prerequisite to rotary shaping. Because of the tracking function of these pilot tips, aggressive cutting flutes and relatively high speeds can be used in these files without forsaking safety. 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