Quartz 4

Instrumentation and Preparation of Root

9 min read

Preparation Appointment1

Lecture Focus

This lecture focuses on the practical aspects of the root canal preparation appointment, building upon the previous discussion of required instruments. The two primary stages covered are:

  1. Establishing the working length.
  2. Preparing or instrumenting the root canal.

A thorough understanding of root canal anatomy, particularly the apical region, is critical for successfully completing these stages.

  • Local Anaesthesia
  • Rubber Dam
  • Access
  • Establish “working length”
  • Prepare / instrument the canal
    • With anti-bacterial irrigation
  • Medicate the canal
  • Temporary restoration

Apical Anatomy23

Note

The anatomy of the apical third of the tooth root is extremely important for establishing the correct working length.

  • ==Physiological Foramen (Apical Constriction): The root canal narrows to a point known as the physiological foramen, or apical constriction. This is generally located at the level of the cementodentinal junction (CDJ).==
    • The pulp tissue exists within the dentin portion of the canal.
    • The periodontal ligament exists where there is cementum on the root surface.
    • The apical constriction marks the end of the pulp space and is the narrowest part of the canal, making it the ideal termination point for preparation and filling. This helps confine filling materials to the canal system and prevent extrusion into periapical tissues.
  • ==Cutler’s Research and Average Anatomy: Research by Cutler on thousands of teeth provides average measurements for apical anatomy.==
    • ==The apical foramen (where the canal exits the root) is very rarely at the actual radiographic apex of the tooth. It typically exits short of the apex and to one side (mesial, distal, buccal, or lingual).==
    • ==Average Distances:==
      • ==From the radiographic apex to the apical foramen: 0.5 to 0.7 mm.==
      • ==From the apical foramen to the apical constriction: an additional 0.5 to 0.7 mm.==
    • ==Total Distance: This means the apical constriction is, on average, located 1.0 to 1.5 mm short of the radiographic apex.==
  • ==Anatomical Variations: The
File No.Size (mm)Length
252020 mm
201520 mm
151020 mm
1020 mm
402517 mm
352518 mm
302519 mm
2520 mm

Gates Glidden #2 (60)

  • 16 files/burs + irrigation = 32 steps
  • 25 at WL
File SizeLength (mm)
2520mm
2020mm
1520mm
1020mm
File SizeLength (mm)
4017mm
3518mm
3019mm
2520mm

Gates Glidden #2 (60)

Establishing the Working Length4

Note

This is the process of determining the precise length to which the canal will be filed and shaped.

Preoperative Estimation

  1. ==Measure the Preoperative Radiograph: An estimated working length is determined before starting.==
    • ==Film-Based Radiographs: Using a modified parallel technique, the image is close to a 1:1 representation. A ruler can be used to measure from a reference point (e.g., incisal edge) to the radiographic apex.==
    • ==Digital Radiographs: Software measuring tools can be used, but their accuracy depends on the quality and angulation of the image. The modified parallel technique with a film holder yields the most accurate image.==
  2. ==Calculate the Estimate: Subtract 1.0 to 1.5 mm from the total radiographic tooth length.==
    • ==Example: A tooth measuring 26.5 mm on the radiograph would have an estimated working length of 25.0 to 25.5 mm.==
    • ==Crucially, this is only an estimate to guide the initial file placement.==

The Role of Tactile Sensation

Tip

Tactile sensation is a learned skill that comes with experience. It is the ability to

Root Canal Preparation Techniques5

Info

The chosen preparation technique must be compatible with the instruments being used (e.g., file design), the planned root filling technique, and the operator’s skill.

The Typical “Abbott” Technique

Basis of Technique

  • Hedström files
    • → 25 mm length
    • → Stainless steel
    • → Hand files
    • → 0.02 taper
  • Min. rotation of files
    • → 1/8 turn max.
  • “Push - Pull” action
  • Circumferential filing
    • → Flare with ALL files
  • Only 5 instruments

Info

The entire preparation can be completed with as few as five instruments, with irrigation between each step.

Sequence for a Narrow Canal6

Example: Mesiobuccal canal of a molar

  1. ==Initial Negotiation (First Appointment):==

    • ==Use a size 10 file to negotiate partway down the canal. The goal is not to reach the apex, but to open up the canal and create coronal flare.==
    • ==Follow with a size 15 file to further flare the coronal portion.==
    • Place medicament and a temporary restoration.

  2. ==Preparation (Second Appointment):==

    • ==Negotiate to the estimated working length with a size 10 file, then a size 15 file.==
    • ==Take the working length radiograph with the size 15 file in place and confirm the final working length.==
    • ==Continue working the size 15 file at the full working length with push-pull/circumferential filing until it is very loose. Irrigate.==
    • ==Introduce the size 20 file. It should go to within 1-1.5 mm of the working length. Use a slight rotation to advance it the final distance, then use push-pull/circumferential filing until it is loose. Irrigate.==
    • ==Introduce the size 25 file in the same manner. Work it at the full working length until loose. Irrigate.==
    • ==Use a Gates Glidden #2 bur in the coronal and middle third of the canal to create the final flare, being careful not to create a ledge.==

Filing Motion and Progression7

Slight Rotation + Push-Pull + Circumferential filing

Filing Motion Steps

  1. Negotiation: Gently place the file into the canal until resistance is felt. This resistance is usually along the body of the file, not the tip.
  2. Engage: Perform a slight rotation (1/8th of a turn) to engage the file’s flutes into the dentin.
  3. Withdrawal Stroke: Pull the instrument out a few millimeters while pressing it against one wall of the canal. This is the cutting stroke.
  4. Circumferential Filing: Repeat the push-pull motion at this same depth, working around the entire circumference of the canal wall until the file feels loose.
  5. Advance: The file can now usually be advanced another 1-2 mm deeper into the canal.
  6. Repeat: Repeat this process of engaging, circumferential filing, and advancing until the working length is reached.
  7. Shaping at Working Length: Once the file is at the full working length, no more rotation is used. Shaping is accomplished purely with the push-pull and circumferential filing motion.

The image below illustrates the technique using different file sizes and shows a radiograph example.

ImageFile Size and Motion
# 10
# 15
Radiograph Example
# 15

Slight Rotation + Push-Pull + Circumferential filing

# 20# 25GG # 2

Canal after preparation

Shape of Some Prepared Canals8910

Goal of Instrumentation

The goal of instrumentation is to create a continuously tapered, conical preparation, similar in shape to the Washington Monument.

  • The original shape of the canal is generally maintained but is enlarged in all dimensions.
  • The narrowest point of the preparation is at the apical constriction (the working length).
  • The widest point is at the canal orifice.
  • This tapered shape facilitates effective irrigation and allows for a dense, well-adapted root canal filling.

Endodontic Treatment Details11

Recording Treatment Details

It is essential to meticulously record all treatment details. In a clinical setting, this is done in the patient’s electronic record. The following information must be recorded:

  • ==Date of the procedure.==
  • ==Tooth Number.==
  • ==Canal Identification (e.g., Mesiobuccal, Palatal).==
  • ==Reference Point for all measurements (e.g., Mesiobuccal cusp tip). It is simplest to use the same reference point for all canals in a tooth.==
  • ==Length on Radiograph: The actual measured length of the file on the working length radiograph. If adjustments and a second radiograph are needed, that length is also recorded.==
  • ==Final Working Length (FWL): The definitive length to which the canal was prepared. This may be slightly adjusted from the radiographic length based on clinical judgment.==
  • ==Master Apical File (MAF): The size of the largest file used at the full working length (e.g., size 25). This determines the size of the master gutta-percha point for obturation.==
  • ==Notes: Any relevant observations, such as canal curvature.==
  • ==Date of Completion: The date the root canal filling is completed.==
DateToothCanalLengths on PARef. Pt.Final LengthPrepⁿ SizeNotesRCF Date
5/3/0626MB18.5 / 19.25MB cusp19.2525DP curve15/5/06
DB19.0 / 20.020.030
Pal21.5 / 22.021.545Bu curve
MPal- / 17.517.525Joins MB
9/6/0614Bu19.0 / 19.5Bu of temp.20.25305/8/06
Pal19.5 / 20.521.035

Intra-canal Medicaments12131415161718

Note

After the canal preparation is complete, the final steps at the appointment are:

  1. ==Final Irrigation Sequence:==
    • ==Irrigate with EDTAC to remove the smear layer.==
    • ==Irrigate with Sodium Hypochlorite (NaOCl) to disinfect.==
    • ==Perform a final rinse with EDTAC.==
  2. ==Drying: Dry the canal thoroughly using absorbent paper points.==
  3. ==Medicament Placement: Place an intracanal medicament into the dried canal.==

Tip

The choice of medicament depends on the original diagnosis of the tooth.

Main functions:

  • ✓ Anti-bacterial
  • ✓ Anti-inflammatory
  • ✓ Hard tissue repair

Dental Restoration Procedure Example19

Temporary Restoration

After placing the medicament, a multi-layer temporary restoration is placed in the access cavity to provide a seal between appointments.

  1. A small cotton wool pellet is placed over the canal orifices.
  2. A layer of Cavit (a temporary filling material) is placed over the cotton wool.
  3. The remainder of the access cavity is filled with IRM (Intermediate Restorative Material).

The image displays a sequence of dental procedures, showing the treatment of a tooth.

The main image shows a close-up of a tooth restoration, possibly a crown or large filling,

Footnotes

  1. Original PDF page 1: Instrumentation and Preparation of Root Canals, p.1 ↩

  2. Original PDF page 2: Instrumentation and Preparation of Root Canals, p.2 ↩

  3. Original PDF page 3: Instrumentation and Preparation of Root Canals, p.3 ↩

  4. Original PDF page 13: Instrumentation and Preparation of Root Canals, p.13 ↩

  5. Original PDF page 14: Instrumentation and Preparation of Root Canals, p.14 ↩

  6. Original PDF page 15: Instrumentation and Preparation of Root Canals, p.15 ↩

  7. Original PDF page 16: Instrumentation and Preparation of Root Canals, p.16 ↩

  8. Original PDF page 17: Instrumentation and Preparation of Root Canals, p.17 ↩

  9. Original PDF page 18: Instrumentation and Preparation of Root Canals, p.18 ↩

  10. Original PDF page 19: Instrumentation and Preparation of Root Canals, p.19 ↩

  11. Original PDF page 20: Instrumentation and Preparation of Root Canals, p.20 ↩

  12. Original PDF page 21: Instrumentation and Preparation of Root Canals, p.21 ↩

  13. Original PDF page 22: Instrumentation and Preparation of Root Canals, p.22 ↩

  14. Original PDF page 23: Instrumentation and Preparation of Root Canals, p.23 ↩

  15. Original PDF page 24: Instrumentation and Preparation of Root Canals, p.24 ↩

  16. Original PDF page 25: Instrumentation and Preparation of Root Canals, p.25 ↩

  17. Original PDF page 26: Instrumentation and Preparation of Root Canals, p.26 ↩

  18. Original PDF page 27: Instrumentation and Preparation of Root Canals, p.27 ↩

  19. Original PDF page 28: Instrumentation and Preparation of Root Canals, p.28 ↩

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