Dentistry – Method or material for testing – treating – restoring – or... – Endodontic
Reexamination Certificate
2001-05-03
2003-05-06
Shaver, Kevin (Department: 3732)
Dentistry
Method or material for testing, treating, restoring, or...
Endodontic
C433S102000
Reexamination Certificate
active
06558163
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention is related to the field of endodontistry. More particularly, the invention is related to systems and operating methods for the preparation of root canals for obturation. The systems and methods involve the use of at least instruments which are dedicated for specific purposes in the inventive methods and systems and are designed for minimal intrusion into the apical portion.
2. The Relevant Technology
To preserve a tooth with a pulp that is diseased or is potentially diseased, it is generally necessary to remove as much of the pulp material as is possible from the pulp canal of the tooth, to shape the root canal(s) without excessively weakening the root canal walls, to prevent or minimize the presence of bacteria through the use of irrigants and dressings, and lastly, to clean the walls of the root canal(s) by removing the smear layer created during instrumentation of the root canal(s). These steps are all done to prepare the root cavity for sealing or obturation which involves filling the root canal with biocompatible materials, such as gutta percha, before the pulp cavity is sealed, thereby promoting the healing and functional recovery of the tooth. This procedure is referred to as root canal therapy.
As indicated hereinabove, root canal preparation involves pulp removal, cleaning of the root canal walls and shaping of the canal walls. This is typically achieved through a guided procedure with the use of instruments which are moved either manually, mechanically or by combinations thereof These instruments are files or bits that are configured to bore and/or cut. Mechanical instrumentation can be achieved through the use of endodontic handpieces coupled to instruments such as files. The endodontic handpieces can impart rotational motion to a file, reciprocal motion by alternately rotating a file clockwise and counterclockwise, sonic movements or ultrasonic movements.
With regard to operating procedures, there are two basic methods from which all of the canal-preparation techniques can be derived. These methods have been interpreted by various authors in an operational context and also in terms of the instrumentation. The primary conventional systems and methods for removing pulp material from the root canal of a tooth are the apico-coronal (step-back) technique and the corono-apical (crown-down) technique. Although these conventional cleaning techniques both rely generally on sequential increases in the diameter of instruments inserted into the root canal. The step-back technique involves the sequential use of instruments by first inserting an instrument all the way down to the apex of the root canal and then using progressively larger files to clean the root canal. So the step-back technique involves cleaning the root canal from the apex toward the crown. The crown-down technique uses a set of files that are inserted sequentially further and further into the root canal until reaching the apex and then instrumenting along the entire length of the root canal after the apex has been reached. Each technique has its own unique benefits and disadvantages.
In the step-back technique, each file that is sequentially used in the root canal has a larger tip diameter and a larger diameter at the top of the file. First, a series of instruments are inserted all the way to the apex that are increasingly larger until the apical portion is cleaned Then the remainder of the canal above the apical portion is cleaned and tapered by using a series of instruments that are successively larger and shorter. With each increase in diameter, the rigidity increases and the flexibility of the files decreases. As a result, it is not possible for the files to be moved in a manner that enables them to adjust to or to follow the contours of the perimeter surfaces of the root canal. This reduced flexibility also increases the likelihood that the files will fail to contact some portions while removing too much of the surrounding dentin in some areas through excessive abrasion and resulting in overthinning of the walls.
Not only is the completeness effected by the use of a set of files wherein each file is larger and more rigid than the preceding file but the ability to safely move the file within the canal is also limited. More particularly, the increasing rigidity results in decreased ability to negotiate the curves in the canal. Significant problems that can result from inserting increasingly rigid files and also from initially inserting a file all the way down to the apex includes laceration and transportation of the apical foramen, as well as misdirection and perforation of the wall.
The apex can be perforated by extrusion of the infected material through the apex due to the force exerted by the file on the material as the file is pushed downward to reach the apex. As a result, the periapical region can be invaded and contaminated. The potential for extruding infected material through the apical foramen of a necrotic tooth during the initial insertion of a file instrument all the way down to the apex is a particular disadvantage of the step-back technique. Another disadvantage is that the procedure has identical steps for working in either necrotic or vital root canals. In addition to exposing the tissue surrounding the tooth to the infected material, apical perforations may allow irrigants, filling or obturating material to flow out of the apex. Such apical perforations, as well as wall perforations, may delay tooth healing and may compromise the outcome of the therapy.
Perforations can also occur due to a failure to maintain a proper working length of the instrument during the procedure. As the canal is widened, curvatures are straightened thereby decreasing the required working length needed for the instrument to work. To properly determine the appropriate working length, many radiographs must be taken throughout the operation as the canal is continuously being modified, which alters the length. The time required to obtain the x-ray photographs or images and to adjust the working length of the instruments by repositioning the stops can result in a lengthy process. The step-back technique is also time intensive because a large number of instruments are required to complete the root canal therapy.
Another problem is the formation of ledges which can occur when a practitioner attempts to insert a file as far as the apex and the file is too inflexible to properly curve with the root canal or move around a protrusion. When a file is too inflexible to curve or flex as needed and is halted prematurely, the downward pressure exerted on the file, in conjunction with the tendency of the file to straighten itself, causes the tip of the file to dig into the side of the root canal and form a ledge. Such ledges are difficult to bypass; and if the ledge occurs very close to the apex, the ledge may give the practitioner the mistaken impression that the apex has been reached.
The crown-down technique was developed for several reasons. It was desired to shape the canal “conically” so as to keep the diameter of the foramen as straight as possible. The crown-down technique was also developed to prevent the discharge of septic material or obturation material from the apex after the initial canal-preparation step and to prevent subsequent vertical condensation due to the vertical pressure used to obturate the canals with heated gutta-percha. Additionally, the crown-down technique was intended to reduce the number of instruments utilized compared with the step-back technique. However, as discussed hereinbelow, significant potential problems may inherently result from use of the crown-down technique.
The crown-down technique generally involves the use of a set of file instruments that are incrementally inserted further and further into the root canal until reaching the apical portion. A file is first used that is sufficiently large that it binds near the top of the root canal. Then an incrementally smaller file is used so that it binds further down
Bumgarner Melba
Shaver Kevin
Ultradent Products Inc.
Workman & Nydegger & Seeley
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