Dentistry – Apparatus – Having motor or means to transmit motion from motor to tool
Reexamination Certificate
2000-07-12
2001-09-25
O'Connor, Cary E. (Department: 3732)
Dentistry
Apparatus
Having motor or means to transmit motion from motor to tool
C433S102000
Reexamination Certificate
active
06293795
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a handpiece for rotating endodontic files to clean and enlarge root canals of teeth. More particularly, the invention focuses upon a handpiece and its control system and method of use that improves debris removal while reducing risk of file breakage.
2. Description of the Prior Art
A key procedure in endodontic therapy of treating an infected tooth is cleaning and enlarging tooth root canals of the tooth prior to filling with an inert obturating material such as gutta percha. Such a procedure wherein infected tissues are successfully removed from the tooth greatly improves the likelihood that a patient will retain the tooth rather than need to have it extracted. The procedure for debridment and cleaning of infected material from the canal and to properly shape the canal to receive the obturating material is time consuming, generally employing a series of endodontic files that are rotated and advanced into the canal to clean canal surfaces and eject the debridment material from the canal for removal.
In the past, endodontic files were employed by the dentist manually, a very tedious process requiring substantial skill. It soon became evident that employing a handpiece to mechanically duplicate hand techniques, including rotating a file, would be a beneficial improvement in efficiency. However, a difficulty with motorized rotation or engine-driving of files is that the dentist sacrifices his “feel” and control of the procedure. The files are typically provided with helical cutting edges, presenting a danger of threading or screwing into the canal surfaces. Under such conditions a file, in negotiating tight curves or other root canal irregularities, might “lock up” and be subjected to excessive torque that could cause the file to fail by breaking. Additionally, rotation of instruments around a curve produces internal stresses resulting in metal fatigue that may cause a file to fail by breaking. Metal fatigue is induced more rapidly as the degree of curvature increases and/or the radius of the curve decreases. Such damaging results may require an extremely difficult effort at extraction of the broken file or other remedial action, including even extraction of the tooth. The dangers of lateral perforation, straightening, zipping and ledging are also all enhanced by engine-driven instrumentation.
Various rotary handpiece designs and techniques for using them have developed, some focused upon varying the motion of the files from simple rotation to reciprocating eliptical patterns, in the effort to duplicate hand operating procedures. Other handpiece improvements have focused upon controlling engine parameters, particularly by reducing speeds of rotation, setting limitations on torque applied to the file and the like to avoid file breakage.
An earlier limitation of the overall endodontic preparation process was lack of flexibility of files, which tended to discourage engine-driven procedures altogether, particularly with respect to aggressive K-files. New file designs, including for example radial landed cutting edges, that avoid screwing-in and which are made of highly flexible nickel-titanium alloys present new opportunities for engine-driven procedures. These files will better follow root canal curves, but even so may be at risk of metal fatigue as they rotate in curved canals. Of course, new files and procedures must insure that adequate removal of debris is achieved.
It is an objective of the present invention to provide a handpiece and control systems and method of use that operate at appropriate speed and torque, positively act to avoid imparting excessive torque to a file to cause a breakage, reduce the buildup of internal stress in the metal, improve tactile feedback and insure improved removal of debris while properly shaping the canal to receive obturating material.
SUMMARY OF THE INVENTION
The invention includes a rotary handpiece, related control systems, and a method of use for rotating an endodontic instrument or file in a manner that significantly reduces the possibility of lock-up or imparting excessive torque and internal stress to a file, yet continues removal of debris from the canal. A key feature of the invention is inclusion of a control system for an electric motor driving the handpiece file that rotates the file through a cutting or planing first arc of rotation, preferably clockwise, and sequentially rotates said file through a second arc of rotation, preferably counterclockwise, wherein the first arc of rotation exceeds that of the second arc of rotation such that material debrided from canal surfaces is ejected from the cleaned surfaces as the file is advanced in the canal.
In a preferred rotary handpiece of the invention, the first arc of rotation is about 90-180° (120°) and the counter, second arc of rotation is about 45-120° (90°).
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Bieber James B.
Dentsply Research & Development Corp.
O'Connor Cary E.
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