RCT Instrumentation Techniques
Too many instrumentation techniques are prevalent today which can confuse even an astute clinician. Whatever the technique it should eventually help us to achieve our GOAL. The current concept is that you have to get coronal flare before starting apical prep. We can achieve this by crown down ( for crown and midroot) technique by use of tapered rotary instruments, Gates-Gliddens or Peeso reamers. Using crown down for apical third with rotary tapered instruments results in inadequate apical enlargement (some companies recommend finishing at 20 or 25). Prepare apical region to larger sizes and finish by step back technique.
Here is a primer of all the techniques for your easy reference.
When any two techniques are combined it is called hybrid technique.
Here is the description of various techniques:
Step back technique Access coronal portion and middle third with a gates glidden drill
Establish working length using small flexible file and locate the apex
Step back from the apex, while increasing file size
Once we get to the middle portion of the canal, you may switch back to Gates Gliddens
Your goal is to achieve a funnel shape
Description: The "Step Back" method indicates that the dentist works from the bottom of the canal back towards the crown. Following the bulk removal of the pulp in the extirpation phase, small hand files are used nearest the apex. The dentist progresses to larger sizes of files working his or her way back up the canal. Each file cuts and removes a little bit more dentin. Usually these advance about one millimeter with each new instrument. Towards the mid-root area, the dentist will switch to Peeso reamers or Hedstrom files. Gates Glidden instruments are generally reserved for shaping the coronal third of the canal.
Passive Step back technique
Use k type files passively with light pressure, rotate 1/8 to 1/4 turn. Use progressively larger K files to establish a minimal flare before using Gates Gidden number 2 and 3. Confirm WL. Apical prep is done by sequentially larger files passively in the canal rotating 1/8 to 1/4. Finally step back the apical prep to blend with coronal flare.
Crown down technique
Begin at the coronal portion with Gates-Gliddens
Continue down the canal, reducing the size of each file as you get closer to the apex
Your goal is to achieve a funnel shape
Description: In the crown down technique the dentist essentially works from the crown of the tooth, shaping the canal as he or she moves towards the apex. The instruments are used in a large to small sequence. The first instruments are the Gates-Gliddens which do the coronal flaring. The Peeso reamers or Hedstrom files follow in the mid-root region. Finally, progressively smaller files take the dentist towards the apex.
Instrumentation of all walls equally during the root canal preparation
Hedstrom files are very effective for this.
Anticurvature filing - (selective filing in the coronal portion of curved canals to prevent strip perforations into the furcation. The walls on the opposite side from the curve are instrumented more than the inner walls resulting in a decrease of the overall degree of canal curvature)
Lim SS, Stock CJR. The risk of perforation in the curved canal: anticurvature filing compared with the stepback technique. Int Endod J 1987;20:33-9.
Bottom Line: Anti-curvature approach can preserve dentinal thickness near furcation. It also gives a more straight line access deeper into the canal.
Balanced force technique
Uses Flex-R files in sequential order in a clockwise-counterclockwise-clockwise manner. Technique was developed to address problems with conventional techniques:
a. K-type file design invites transportation of the canal
Transportation occurs at the outer curvature of the canal due to unbalanced
forces and cutting edges at the tips of the files
Uses a file with a modified tip design (Flex-R). It should not be used with Hedstrom instruments or even K- files without a modified tip.
Use of Gates-Glidden drills (sizes #2 and above) for coronal flaring is recommended early in the technique.
The first file to bind short of the WL is inserted into the canal and rotated to the right (clockwise) a quarter of a turn. This causes the flutes to engage a small amount of dentin. The file is then rotated to the left (counterclockwise) at least one-third of a revolution. The counterclockwise rotation tends to unthread the instrument, so slight pressure in an apical direction is required. It is the counterclockwise rotation with APICAL pressure that actually provides the cutting action by shearing off the small amount of dentin engaged during the clockwise rotation.
The counterclockwise rotation can be one or two rotations if there is little curvature or if the instrument does not bind. It should not be forced to the left as the instrument can fracture.
The files should gradually feed into the canal to the working length. At the working length, the file is rotated passively to the right for a 1/2 turn or more while preventing further apical movement. This loads the file with debris and fractured dentin which is removed when the file is withdrawn from the canal. The files are not precurved, even in more severely curved canals. . Sequentially larger files are used until a master apical file is determined. The use of a patency file is required between each sequentially larger file.
The apical preparation is completed with the step-back technique. The use of frequent irrigation is necessary as with any technique.
Careful inspection of files is required because they may fracture more easily with rotational cutting techniques.
Crown down Pressureless
Insert #35 file until it just binds and measure depth - this is the “radicular access length”
Flare coronal portion of canal using #2 and #3 Gates to radicular access length
Starting with #30 file, insert beyond radicular access length until resistance first encountered
Rotate #30 clockwise two full rotations using NO pressure
Step down using sequentially smaller files rotated as in #4 above to a point 3mm from the radiographic apex. This is the “provisional working length”. Take a radiograph with the file at the provisional WL and estimate your “true” WL.
Continue stepping down with smaller files to the true WL
Place a #35 file until resistance is just met (should be at or beyond your radicular access length)
Rotate passively two full turns and then proceed with smaller files in step-down to the true WL
Do additional sequences of step-downs starting with #40, then #45, then #50, etc until apical matrix is developed and apical flare blends with the coronal flare created with Gates-Gliddens in #2 above.
RCT Instrumentation Techniques instrumentation techniques