Root Canal Biomechanical Preparation

• Biomechanical preparation is an operative procedure accessing the cementodentin-canal union for pulp removal, canal cleaning, and shaping for disinfection and obturation.

Biomechanical Preparation Objectives

• Limit instrumentation within the canal.
• Prevent necrotic material displacement beyond the apical foramen.
• Eliminate irritants from root canals.
• Create sufficient amplitude in the coronal half.

Mechanical Objectives

• 3D canal shaping.
• Prepare a solid apical dentin matrix at the dentin-cementum junction.
• Prepare the canal to taper apically to the narrowest diameter.
• Limit cleaning and shaping to maintain foramen apical integrity.
• Eliminate debris that may obstruct the apical foramen.

Anatomical Considerations

• The narrowest part of the dentinal canal, the apical constriction, is approximately 0.5 mm from the root's external surface, increasing with cementum formation.
• The dentin-cementum junction marks the apical end of the dentinal canal, beyond which is the cemental canal.
• The apical foramen may not be at the exact root apex, often with lateral exits.
• Instrumentation should start only after knowing canal length.
• Canal interiors are irregular with depressions and inter-canal communications varying by root morphology, curvature, age, and tooth condition.
• Irritants can cause more dentin formation at the base of tubules near the pulp, narrowing the canal.

Biomechanical Preparation Rules

• There must be straight-line access to the root canal.
• Instruments should be used sequentially by size, without skipping numbers.
• Conductometry must be known beforehand.
• Pre-curve the first 3-5 mm of instruments.
• Measure instruments and set rubber stops to the correct length.
• Use each instrument with three movements: impulsion, rotation, and traction.
• Instrumentation should be done with a humidified canal.
• Instruments should not be forced if they jam, use light digital pressure and maneuver gently.

Steps for Biomechanical Preparation

• Conductometry: determining the precise length between the apical constriction and the incisal edge/occlusal surface, considering 0.5-2 mm from the radiographic apex as optimal length.
• Reference Point: An anatomical site where measurements are taken.
• Establishing Conductometry:
  • Take an initial radiograph with the tooth centered.
  • Measure the tooth length from the incisal edge/occlusal cusp to the most apical portion.
  • Subtract 1 mm for the periodontal ligament-apical constriction distance.
  • Slide a fine file's rubber stop to this length.
  • Insert the file into the canal.
  • Take a radiograph to check file placement relative to the radiographic apex.
  • Remove the file, measure the distance between the stop and tip, and record as the working length.
• To determine conductometry in teeth with overlapping roots/canals, use horizontal angulation variations:
  • Mesiorradial: 15-30° mesial modification.
  • Distorradial: 15-30° distal modification
• Telescopic Preparation:
  • File the entire canal with the file used for conductometry.
  • Use circumferential instrumentation, moving counterclockwise.
  • Use the next file sequentially.
  • Enlarge the canal with slight widening motions.
  • After instrumenting to the apical constriction, subtract 1 mm from the next file for telescopic preparation.
  • Recapitulate with the master or memory file for two reasons:
    • Remove dentin remnants.
    • Smooth canal walls.
  • Turning the memory file ¼ turn prevents it from acting as an embolus.

Telescopic Preparation Advantages

• Less chance of perforations or steps.
• Uniform widening in irregular canals.
• Better cleaning.
• Net time savings.
• Better guttapercha obturation due to conicity.
• Reduces overextension.

Biomechanical Preparation Completion

• The memory instrument reaches working length easily.
• A stop is felt at the apical constriction.
• Canal walls are smooth without irregularities.
• The canal has a tapered shape from the constriction to the cervical third.
• There is no bleeding or biological leakage, the periodontal space, towards the buccal.
• Criteria to determine the diameter of an apical preparation include factors and conditions:
  • Radiographic image, canal condition.
  • Experience.
  • Tactile development.
• File two or three more instruments more adjusted instruments to the side walls of the canal.

Corono-Apical Technique

• It's a technique starting cleaning from the coronal regions.
• It progressively works toward the apical region.
• It facilitates the tapered preparation of root canals.
• It minimizes the extrusion of bacteria and debris towards the area.

Combined Corono-Apical- Telescopic Technique

• The technique can be adjusted for canal sizes and shapes.
• There are two phases:
  • Preparation of the coronal and middle third of the canal.
  • Preparation of the apical third of the canal.

Phase A: Coronal and Middle Third Preparation

Step 1

• Determination of the working length
• They are located, then canals are permeabilized with files 8 or 10.
• Proceed to do the conductometry

Step 2

• PreGates instrumentation
• Start the enlargement of the canal with files 8, 10, 15, and 20.

Step 3

• Use gates to remove the cervical dentin protuberance on the coronal third.
• Abundant irrigation should be present.

Step 4

• Instrument in a manual way the coronal and middle third with the files 55, 50, 45, and 40 until it is 16 to 17 mm.
• The apical thirds (3 and 4 mm) remain for the second phase of the preparation.
• Irrigation and recapitulation is made between each instrument.

Phase B: Apical Third Preparation

Step 1

• Preparation of the apical stop.
• It depends on the caliber, the degree of curvature and volume radicular.

Step 2

• Starting from the memory file go 3 or 4 instruments of bigger caliber, Recapitulattion with the memory file.
• Irrigation is done between each instrument and at the end of the preparation.