Cleaning the Root Canal

Objective

  1. To clean the root canal system (debridement):
    1. within the mechanical limits of the instruments available
    2. within the limits of the natural configuration of the canal space
  2. To maintain the natural apical architecture in the cleaning process and avoid procedural accidents. [Retention form + resistance form].
  3. To shape the root canal system above the apical region of the root so that a proper filling material can be placed and, thereby, seal the root canal system.
  4. To maintain a balance that will allow thorough cleaning and shaping but avoids procedural errors caused by overly zealous debridement of the canal system. Therefore, good judgement must accompany good clinical skills.

Endodontic inraradicular Preparation Begins With

Good coronal access opening

  1. Outline form
  2. *Convenience form
  3. Removal of caries
  4. Toilet of the coronal access cavity
  5. Intraradicular cleaning and shaping:

    1. Resistance form: retaining or improving the apical foramen to resist extrusion of filling material and, thereby, preventing periapical irritation.

    2. Retention form: retaining the master point in the fully enlarged root canal cavity from which all debris and necrotic dentin have been removed. Good retentive form at the apex can be evaluated by tugback of the master gutta percha cone at the apex.

    3. Toilet of the root canal cavity: the extension of the resistance form throughout the root canal system to allow removal of all debris and affected dentin.

An understanding of some general principles is necessary before starting Intraradicular cleaning and shaping of the root canal system:

  1. The root canal is not straight or regular in form.

  2. The root canal is a system of:
    a) cul de sacs
    b) lateral canals
    c) apical ramifications
    d) concavities

  3. Although these irregularities can occur anywhere along the root canal system, they predominate in the apical third of the canal.

  4. Many roots have some curvature within the root canal system.

  5. Good and thorough cleaning of the root canal system requires:
    a. a proper access cavity
    b. contact between the instrument being used and the walls of the root canal system.

  6. The ideal goal of cleaning and shaping of the root canal system would be to remove all debris and clean the canal system completely. Since this is not possible, mechanical instrumentation is augmented by:
    a. copious irrigation
    b. chemical sterilization
    c. sealing of the "cleaned" root and space

  7. Even with the above mentioned limitations, cleaning and shaping is the most important step in the successful treatment of the root canal system.

  8. *What is removed from the root canal system is more important than what is placed into it.

Mechanical instrumentation to clean and shape root canaql system requires:

  1. Rubber dam isolation for maintenance of a sterile field. (There is no valid reason for not using rubber dam isolation).
  2. A good x-ray of the tooth being treated is necessary to determine the length of the canal.
  3. Instruments for cleaning and shaping:

    Hand-held Used with slow-speed handpiece
    1. K-type file
    2. reamer
    3. Hedstrom type file
    4. Broach
    1. gates glidden reamer
    2. peezo reamer
    3. gyromatic (reciprocating handpiece) files
    4. ultrasonic files

  4. Irrigant of the root canal system
  5. Chelating agent
  6. Intervisit medicaments - antibactierial

Steps leading to thorough cleaning and shaping of the root canal system.

  1. Make proper straight line access
  2. Explore pulp chamber for canals
    1. pulp stones
    2. calcifications
  3. Locate canals with ENDODONTIC EXPLORER
  4. Irrigate pulp chamber for visibility
  5. Review starting x-ray taken with parallel cone technique for more accuracy.
  6. Estimate diagnostic length of the root(s) in question from the start x-ray.
  7. Place the largest file that will fit snugly, but will not bind, into the canal within 1 mm of your estimated length. (Do not force a file apically. If necessary, use a file of a smaller size).
  8. Files should only be inserted into an irrigated (wet) canal.
  9. Defining the location of the apical region of the tooth:
    1. The anatomic apical region of the root canal can be variable.
    2. Anatomical studies show that the apical region of a root canal can vary an average length of .5 mm to 1 mm from the radiographic apex noted on the x-ray.
    3. If cleaning and shaping are performed to the radiographic apex of a tooth, the apical construction may be eliminated and the retention form of the canal lost.
    4. The diagnostic measurement of the canal system will be extrapolated from the x-ray with the file in place.
  10. Since many canals have curves along their lengths, the files at the working length should be gently precurved to avoid procedural problems. 08, 10, 15 and 20 K files are flexible. 25K files and larger are not flexible.
  11. The canal should be irrigated thoroughly between the use of each instrument.
  12. After the canal has been cleaned at the working length, the shaping of the coronal part of the canal can proceed.
  13. Larger size files after the last file to the working length will be used to clean and shape the coronal part of the canal.
  14. These files start 1 mm less than the working length and continue with a second larger file, 2 mm less than the working length, etc., until the coronal part of the canal is completely cleaned and shaped.

Always remember to:

  1. irrigate and
  2. use the initial file to the anatomic length (radiographic apex) to prevent blockage with debris.

Problems that occur during cleaning and shaping of the root canal system

Problems ... Usual Causes ...
1. ledge formation:

a. incorrect measurement
b. using files out of sequence

2. perforation a. apical zipping of canal (over enlargement of apex)
b. not following curved canal
3. blocking out - apical region a. not enough irrigation
b. using files out of sequence
c. not going back to apex wiith anatomic length file
4. separated instruments: a. using instruments improperly, i.e. rotating hedstrom file
b. using instruments out of sequence
not observing Physical state of files, i.e. using unwound or bent files
5. stripping root a. over-zealous instrumentation
b. not paying attention in root anatomy
6. poor condensation inadequate cleaning and shaping of the root canal system will lead to poor condensation

Summary:

1. Good access is critical to good cleaning and shaping of the root canal system.

2. Convenience form dictates enlarging access enough to allow straight line unstrained motion for all cleaning instruments as they are used to debride the canals.

3. Pre-curve all files to the working length.

4. 08, 10, 15, 20 K and stainless steel files have flexibility enough to conform to curved canals.

5. 25 K files and above are not flexible enough to conform to curved canals and can cause perforations and ledges if not used carefully.

6. Never use a file out of sequence. Always make sure that the smaller file is loose in the canal before using a larger file.

7. Use easily observable landmarks on the occlusal, (incisal), surfaces of teeth to measure the canals.

8. Reduce undermined tooth structure around cusp landmarks before taking a diagnostic measurement x-ray.

9. Make sure rubber stoppers do not move during instrumentation.

10. Use clinical judgment when applying the guidelines of cleaning and shaping of the canal system.

Be flexible according to the specific case at hand.

Important Notes

Cleaning is the removal of all contents of the root canal system before and during shaping. Cleaning entails both the mechanical removal of canal contents and the chemical dissolution, detoxification, and flushing away of inflammatory and potentially inflammatory substances.

Pathways of The Pulp p.203

Determine the following locations and measurements:

  1. the apex ?
  2. anatomic length ?
  3. working lenth ?

Use:

  1. parallel cone technique for the starting x-ray (without the rubber dam in place)?
  2. vatiation of x-ray technique with the rubber dam in place?
  3. foreshortening of x-ray vs. elongation?

You may encounter difficulty in reading the x-ray due to:

  1. anatomical obstruction and overlap
  2. multiple rooted teeth
  3. buccal object rule

Chelating agents

Actions:

  1. chelation (demineralization/self limiting
  2. antibacterial effect
  3. lubricating effect

Types:

  1. EDTA (ethylene diamine tetraacetic acid)
  2. RC-preparation: 1) EDTA 2) yrea peroxide (glyoxide), 3) carbowax base
  3. Citric acid

Intervisit medicaments (antibacterial):

  1. Eugenol
    1. pain obtundant
    2. tissue dessicant
  2. CMCP (camphorated paramonochlorphenol)
  3. Calcium hydroxide
    1. bacteriocidal effect (high Ph)?
    2. space filler
  4. Sterile cotton pellet without medicament.

All above are contact medicaments, i.e. need to be in contact with bacteria to be effective. Again, because of the irregularity of the canal system, effectiveness of above medicaments is limited. Therefore, emphasis should be on cleaning and shaping rather than chemical sterilization.