Dentistry – Apparatus – Having gauge or guide
Reexamination Certificate
2000-08-18
2002-05-21
O'Connor, Cary E. (Department: 3732)
Dentistry
Apparatus
Having gauge or guide
C433S102000
Reexamination Certificate
active
06390814
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to the field of dental instruments. More particularly, the invention pertains to appliances which keep files and/or reamers from progressing too far into a root canal during treatment.
2. Description of Related Art
When a tooth experiences trauma including infection or a nerve in the root being adversely affected by proximity to a deeply set filling, the body (dental pulp) takes defensive measures to constrict the root canal to isolate it, or its defenses may be overcome by the irritant. If the diagnostic tests of the tooth reveal irreversible damage, a root canal or endodontic procedure is needed. A root canal treatment entails the removal of the central soft portion (nerves, blood vessels, tissues etc.) of the tooth. The empty space or canal is then filled with an inert material. The canal is sometimes too narrow and/or infected to effectively place the inert material inside it. Instruments, usually files and/or reamers, herein collectively termed “files”, are used to clean and/or widen this canal. Their mode of action while being used is either a push-pull or twisting motion.
In cleaning out the canal, it is important that the clinician not change the general shape of the canal, for example, by creating a ledge in it or by changing its curvature since if either of these events occur, there is an increased probability that one of the successively larger and stiffer files used to clean the canal will perforate the root wall. This in most cases requires surgical correction or extraction of the tooth. This complicates and prolongs the treatment, causing discomfort to patients.
In the preparation of root canals, it is the present practice to enter the chamber of the tooth with a file to enlarge the root canal. A plurality of endodontic files of increasing diameter are employed to enlarge the root canal to create a channel of size that can practically be filled with a medicament and then sealed. It is important in the preparation of the root canal to control the length of the file in order to limit the depth of penetration to avoid injury. The desired depth is called the working length.
The length of the tooth involved, as well as the length of the root canal, is determined by means of X-rays, and various techniques and devices have been devised in the past for limiting the depth of penetration of the root canal files to the root tip. Thus, many dentists employ a stop member which is penetrated by the root canal file for the desired distance, with the stop member being positioned to engage the top of the tooth to limit penetration.
However, these stop members, which are generally rubber stoppers, are easily displaced, particularly in working within the limited area of a patient's mouth and considering the relatively small size of the instruments involved. There is nothing to stop the files from going too far into the canal.
It is difficult for the endodontist to precisely judge when the file has reached the end of the tooth. Additionally, the rubber stopper is both flexible and movable and can therefore allow the file to proceed deeper into the root canal then may be actually desired. In other instances, the inadequacies of the equipment result in incomplete penetration. Either too great or too shallow depth penetration could cause failure of the entire procedure. An additional problem is presented in that each individual file and its rubber stopper must be separately gauged against a separate scale or ruler and then individually set to the depth indicated in the x-ray. This procedure can involve inherent inaccuracies and a great deal of time and inconvenience to the dentist. Inaccuracies can also occur because of the number of manual operations involved. Further, problems relating to contamination of the file during this measurement or gauging procedure are likely to occur.
During an endodontic procedure, accuracy is compromised in both the determination of the working length, and maintaining this working length. In determining the working length, measuring any length requires two points. The first point that a dental practitioner uses is the tooth apex. The second is however an arbitrary point on the tooth that is lined up with a rubber stopper. Most times there is no clear reference point on the tooth that can be used repeatedly to get the same correct length. Either a different point is used or it is viewed at a different angle to get another measurement. It is very difficult to remember the reference points for each canal in multi-canal procedures. Some in the field say that practice and experience allows them to work around this problem. However, in reality, accuracy is not in the eye of the beholder.
When attempting to maintain the working length, assuming the accuracy of this length based on only one fixed point, the files are not effectively stopped from going too far into the canal. The point(s) chosen is not a platform that can support anything. The rubber stoppers do not provide any support if pressure is applied. During filing, the rubber stops give in a millimeter or two. Since in root canal treatment dentists generally go into the half-mm range, this reduces the accuracy of the whole procedure. A common defense to this problem is that the apical constriction stops the file. However, if this were the case, then there would be no reason to determine the length in the first place. Why not simply go ahead and file without finding the working length? In essence, this is currently what is being done since a working length is being determined and then can not be maintained.
It is almost impossible to move an unsupported object manually in one plane and keep it fixed in another plane. This principle is what root canal treatment has been based or more accurately not based upon for decades. Radiographs along with sophisticated and expensive instruments are used to determine the working length of the tooth. This length is indicated on the file. There is, however, no way to stop the file from overextending in the canal while it is being used.
Several prior art patents have tried to solve these problems.
U.S. Pat. No. 3,781,996, “ROOT CANAL REVERSIBLE STOP,” Saffro (1974), shows an endodontic file with an intermediate part between a cutting portion and a handle which contains a series of reversible stop members. The fact that the stop is found on the instrument means that the point of measurement or reference changes with the movement or shifting of the instrument, hence it is impossible to get the same measurement twice. Since the essence of root canal treatment is to transfer measurement all the time, this system is not very accurate.
U.S. Pat. No. 3,838,517, “COMBINATION DEPTH STOP AND GAUGE ASSEMBLY FOR A DENTAL DRILL”, Michnick (1974), is an assembly which attaches to a dental drill. The assembly includes a surface which controls the depth of the cut by the drill. The drill bit runs through this surface, and acts as a depth stop for the drill. The surface controls the depth of a cut, but the invention is not interested in working length, nor is it used for files. This mechanical and electrical device has stops that project between the device and the tooth limiting the extent to which the drill or instrument goes into the tooth. These stops work only with mechanical or electrical devices. They cannot currently be used for manual manipulation of the root canal since the stops are an integral part of the assembly of the device.
U.S. Pat. No. 3,961,422, “STOP DEVICE FOR ENDODONTIC INSTRUMENTS,” Riitano et al. (1976), shows a stop for limiting the depth of penetration of an elongated dental instrument usable in an endodontic procedure. The stop is in the form of a disc divided into two halves. Manually assembling the two halves requires that they are big enough to handle with the fingers. If they were this big, then the assembled disc would be bulky and too large to work with in the confines of the mouth.
U.S. Pat. No. 4,028,810, “ROOT CANAL FILE,” Vice (1977), is an endodontic instrument f
Brown & Michaels PC
O'Connor Cary E.
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