Dentistry – Apparatus – Having gauge or guide
Reexamination Certificate
1999-10-22
2001-04-10
Manahan, Todd E. (Department: 3732)
Dentistry
Apparatus
Having gauge or guide
C433S102000, C433S165000
Reexamination Certificate
active
06213771
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates generally to dental instruments. More particularly, the present invention relates to an endodontic instrument for use in an endodontic procedure that has an adjustable working length.
2. The Relevant Technology
In order to preserve a tooth that has diseased pulp material therein, it is necessary to prevent bacterial proliferation within the pulp canal of the tooth by removing the diseased or necrotic pulp material from the pulp cavity or root canal. After the pulp material has been removed or extirpated from a tooth, the pulp cavity or root canal is typically filled or obturated with an inert material before being sealed off with an inert sealer of an aseptic material in order to prevent future infection of the tooth root. This procedure is referred to as root canal therapy.
During root canal therapy, it is essential that the entire root canal, including the root tip, be cleaned and filled to eliminate all organic matter contained within the root canal. The typical method followed for root canal therapy is to open the tooth to the pulp chamber and then work down to the root end. Root canal cleaning or preparation is generally achieved by hand or mechanical instrumentation with files or bits that are configured to bore and/or cut. In order to gain access to the pulp chamber in a tooth, a hole is drilled through the tooth to the pulp chamber and subsequently widened. A variety of endodontic instruments are then used to enlarge and clean out the root canal to remove all the pulp tissue.
Conventional dental instruments used during root canal therapy such as various file instruments generally include a thin, flexible, metal shaft or file with an abrasive surface or sharp edges, which enables efficient cleaning of the root canal. A handle or hub end is securely affixed at one end of the file instrument and is adapted for gripping by an operator or attachment to a mechanical device such as a dental drill.
It is often necessary to repeatedly insert and remove various file instruments into the root canal of a tooth during root canal therapy. Extreme care must be taken to prevent penetration of such file instruments beyond the root canal apex in order to avoid injury and possible infection of the adjacent periodontal tissue and bone structure. The file must be inserted no more than a specific maximum distance inside the root of the tooth. The occurrence of errors in depth penetration of the file into the root canal, either too deep or too shallow, are the major cause of failure in endodontic procedures. Thus, it is important in the preparation of the root canal to control the working length of the file utilized. Since it is physically impossible for a practitioner to see inside the tooth to the root apex, a determination must be made as to how far the file can enter the root.
Before a file instrument is inserted to remove the pulp material, the length of the root canal is determined to identify a suitable working length for the file instrument. Generally, the working length is the distance from a fixed reference position on the crown of a tooth to or near the apical constriction opening of the root canal. Typically, a practitioner initially ascertains the depth through which the various sized root canal instruments should penetrate into the root canal by utilizing an x-ray of the tooth. A full scale x-ray of the tooth is taken and the insertion distance is measured on the developed x-ray photograph by measuring the length of the tooth involved, as well as the length of the root canal therein.
A significant problem that can result from root canal cleaning is apical perforation from insertion of a file or shaft of a file instrument to the apex of the root canal. Perforating the apex can result from an error in estimating or measuring the length of a root canal. Similarly, the apex can be perforated by extrusion of infected pulp material through the apex due to the force exerted by the file on the pulp material as the file is pushed downward to reach the apex. In addition to exposing the tissue surrounding the tooth to the infected pulp material, apical perforations also substantially complicate subsequent filling of the root canal with a filling or obturating material.
Various techniques and devices have been developed for limiting the depth of penetration of dental instruments to the root canal tip. For example, once the length of the root canal has been determined, it is possible to use a dental instrument having a file extending beyond the handle by the predetermined maximum allowable length.
More commonly, an adjustable stopper has been typically placed over each dental instrument along the shaft or file so that the distance between the tip of the instrument and the stopper equals the distance between the top or the occlusal surface of the tooth and the apex of the root canal. Thus, the stopper sets the root canal instrument to the proper length or penetration depth for the root canal. The stopper located at the proper point along each root canal instrument intended to be used ensures that the instrument is inserted the proper depth into the root canal.
Examples of instruments utilizing stoppers are shown in FIG.
1
and
FIG. 2
respectively at
10
and
20
. Instrument
10
has a peanut-shaped handle
12
which is particularly adapted to be gripped by a practitioner during a root canal procedure. Handle
12
is accordingly typically used for manual filing. Instrument
20
has a latch handle
22
for attachment to an endodontic handpiece for rapid rotation as shown in
FIG. 3
at
60
. A stopper
40
is shown positioned on file
14
of instrument
10
and on file
24
of instrument
20
. Such stoppers are typically formed of a simple block of rubber or plastic material, or constructed of a housing and a compression spring. In addition to a single stopper as shown in FIG.
1
and
FIG. 2
, several movable stoppers may be utilized and positioned on the shaft such that one stopper abuts the handle. An additional example of an endodontic device utilizing stoppers is disclosed in U.S. Pat. No. 5,154,611 to Chen.
The position of the stopper on the file determines the working length of the instrument, which is the length of the file to be inserted into the tooth during treatment. As shown in
FIG. 4
, stopper
40
prevents further penetration of file
24
into the root canal of the tooth when the bottom surface of stopper
40
abuts the occlusal surface of the tooth
90
being treated, such as the incisal edge or cusp tip. In this manner, when the dental instrument enters the root canal, the dentist can limit insertion by observing the contact of the stopper at the edge of the tooth.
Since a variety of file instruments are used throughout the root canal procedure, conventional practice has been to individually measure and position the stoppers on the various implements used. It is frequently necessary for the dentist to fit a stopper on the dental instrument while the patient's mouth is held open. Thus, it is desirable that the operation be carried out as fast as possible. At the same time it is essential that stoppers be placed with perfect accuracy, as otherwise the possibility of poking the instrument beyond the tooth is presented.
The problems with the conventional stopper procedure are numerous. The individual measurement and placement of the stoppers on the dental instruments is very time
1
consuming and at times somewhat inaccurate. Each individual instrument and its stopper must be separately gauged against a separate scale or ruler and then individually set to the length indicated in an x-ray photograph. This procedure can involve inherent inaccuracies and a great deal of time and inconvenience to the dentist. In addition, there is also the potential for introduction of contaminants on the instrument during placement of a stopper thereon.
Further, the stoppers can be easily displaced or can slip from their intended position on the file instrument during use within the limited area of a pa
Manahan Todd #E.
Ultradent Products Inc.
Workman & Nydegger & Seeley
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