1. Field of the Invention
The present invention relates to an improved rotary handpiece and an endodontic file for use therewith whereby the endodontic file can be advanced, retracted and rotated at controlled rates.
2. Description of the Prior Art
Endodontics is the branch of dentistry which involves the treatment of pulp through root canal therapy. Such therapy generally includes the cleaning of the root canal to remove damaged tissue therefrom and to enlarge the root canal so that it can be filled with an inert sealing material, e.g., gutta-percha. Typically, a dentist will drill into the upper part of the tooth to locate the root canal and thereafter clean and enlarge the root canal using small endodontic instruments, generally referred to in the art as "files."
The cleaning and enlarging of a root canal is complicated by the fact that the root canal is not only very small, but often follows a curved path. Accordingly, the file must be very thin and flexible in order to enter the root canal and follow its path. Also, the file must have sufficient strength so that it is not easily broken off within the root canal. A particularly suitable endodontic file which readily follows the paths of root canals is the K-type file disclosed in my U.S. Pat. No. 4,443,193 issued on Apr. 17, 1984. As described in detail in the patent, the inventive K-type file includes a tapered working portion defined on a flexible shaft. The working portion includes three spiral rotationally bi-directional cutting edges formed thereon. A tapered tip is formed on the flexible shaft which intersects the ends of the cutting edges on the working portion of the file. The tapered tip is shaped such that sharp cutting points at the intersections between the ends of the cutting edges and the tip are eliminated so that lateral transportation of the instrument when cutting a curved root canal is also eliminated. The file can be formed of various materials including, but not limited to, stainless steel or a nickel titanium alloy.
Heretofore, the most common procedure followed by dentists in performing root canals has been to utilize hand manipulated K-type files of progressively increasing size. When a K-type file is manipulated by hand to clean and enlarge a root canal, a number of types of cutting strokes can be utilized which generally fall into the categories of filing or reaming. A filing stroke utilizes axial reciprocation of the cutting instrument along the length of the root canal without rotating the instrument. Thus, the edges of a K-type instrument cut the interior walls of the root canal when a filing stroke is used therewith. A reaming stroke refers to the use of rotational motion established by rotating the instrument about its longitudinal axis. While there are various kinds of instruments, some of which cut in a single rotational direction, K-type files have spiral edges which are rotationally bi-directional in that they cut when rotated either clockwise or counterclockwise. The spiral cutting edges are generally right-handed whereby when a K-type file is rotated clockwise it tends to thread itself into the root canal like a wood screw. Thus, the dentist must be careful not to penetrate too deeply into the root canal as a result of self-threading which can damage the tooth and subject the file to excessive loading.
A variety of dental instrument drive devices, known in the art as "handpieces," have been developed for rotating dental instruments. While the use of rotary handpiece driven endodontic files has achieved some degree of success, a continuing problem involves the self-threading of the endodontic file into the canal whereby the file penetrates the canal too rapidly and becomes excessively loaded. Such excessive stress on the instrument driven by a handpiece can result in sticking or breaking of the instrument in the canal, a condition which is difficult to correct.
An improved rotary handpiece and methods of cleaning and enlarging a root canal of a tooth utilizing the handpiece and a rotary endodontic file are described in my U.S. Pat. No. 5,586,886 issued on Dec. 24, 1996. As described in the patent, the improved handpiece basically comprises a rotary drive which rotates a chuck for holding and rotating the endodontic file. A retractable support rod is attached to and extends from the handpiece positioned adjacent and substantially parallel to the endodontic file. The support rod is adapted to rest on a tooth whereby the retraction of the support rod controls the advance of the endodontic file into the root canal. Means are attached to the handpiece and to the support rod for retracting the support rod and advancing the endodontic file at a controlled rate into the root canal whereby the endodontic file does not become excessively loaded while the root canal is being cleaned and enlarged. While this patented handpiece constitutes a distinct improvement over prior art endodontic file handpieces which do not control the rate of advance of the endodontic file into a root canal, it has the disadvantage that it is more difficult for a dentist using the handpiece to see the file as it is being fed into or out of a root canal and to feel the progress or non-progress of the file in cleaning and enlarging the root canal. Further, the patented handpiece design depends upon the presence of sound tooth structure beneath the support rod and thus, it can limit the freedom of position needed to accomplish root canal treatments and reduce the full positioning ability sometimes required in clinical situations.
Thus, there is a continuing need for an improved rotary handpiece for cleaning and enlarging a root canal of a tooth with a rotary endodontic file which prevents the file from becoming excessively loaded whereby it sticks or breaks off in the canal.