1. PHASE 1- PATENCY FILING
   1. The concept of creating a path up to the working length without blocking or altering the original root canal anatomy is known as patency filing.
   2. This is usually performed with a size 10 or smaller K file instrument that is negotiated passively just through the apical foramen.
   3. This helps in maintaining a continuous and clear path to the apical foramen by removing debris, especially when combined with irrigation.
2. PHASE 2- CORONAL PRE-ENLARGEMENT
   1. concept of enlarging the coronal third of the root canal prior to the estimation of the working length.
   2. The working length of the tooth should be determined only after coronal pre-enlargement of the canal is completed.
   3. Advantages
      1. Prevents premature binding of the shaping instrument to the canal walls
      2. Removes the coronal third debris before the shaping instruments negotiate the apical third.
      3. This reduces the potential for extrusion of debris beyond the working length
3. PHASE 3- WORKING LENGTH DETERMINATION
   1. METHODS
      1. Radiographic methods
         1. Ingle's technique (Recommended)
         2. Best's method
         3. Bregman's method
         4. Bramante's technique
         5. Grossman's method Weine's method
         6. X-ray grid method
         7. Xeroradiography
         8. Direct digital radiography
      2. Electronic apex locators
      3. Nonradiographic methods (not recommended)
         1. Tactile sense
         2. Apical periodontal sensitivity
         3. Paper point method
   2. Ingle's Radiographic Technique
      1. exact working length for each canal is determined by adjusting the length of inser- tion, so the tip of the instrument ends 0.5-1.0 mm from the radiographic root apex.
      2. The working length should be arbitrarily established 0.5-1.0 mm shorter than the radio- graphic canal length because the actual length
      3. WEINE'S MODIFICATIONS
         1. If periapical bone resorption is evident in a radiograph, the working length should be reduced 1.5 mm short of the radiographic apex as the apical constriction would have been destroyed by the resorption.
         2. • If apical root resorption is seen, the working length is reduced to 2 mm short of the radiographic apex. In such an event, an apical stop is created short of the radiographic apex to prevent overinstrumentation and subsequent overfilling of the root canal.
      4. Two length-determination radiographs may be necessary at times, one at the normal angulation and the other at a 20° mesial or distal horizontal angulation
   3. Electronic Apex Locators
      1. CLASSIFICATION
         1. RESISTANCE based
            1. first generation of apex locators which were developed based on the resistance principle.
            2. They worked best in dry canals.
            3. the presence of pus, pulpal tissue, blood, and irrigants leads to inaccurate readings
            4. eg. the root canal meter
         2. Low-frequency apex locator
            1. This device would indicate the apex when two impedance values approach each other.
            2. This apex locator had to be calibrated with the periodontal sulcus prior to each use.
            3. This procedure was technique sensitive and error prone.
         3. High-frequency apex locator
            1. These locators were based on the principle that a high- frequency (400 kHz) wave, as a measuring current, produces a more stable electrode.
            2. This device is able to perform even in the presence of electrolytes due to the presence of a special coating on the file.
            3. eg Endocater
         4. Voltage gradient apex locator
         5. Dual-frequency apex locator
            1. These apex locators determine the canal terminus as the difference between two impedance values at two different frequencies.
            2. eg. Endex apex locator
         6. Multiple-frequency apex locator
            1. uses two wavelengths: one high (8 kHz) and one low (400 Hz) frequency.
            2. It assesses the apical terminus by the simultaneous measurements of the impedance of two different frequencies that are used to calculate the quotient of the impedances.
            3. Root ZX by J. Morita,
4. PHASE 4- SHAPING TECHNIQUES
   1. STEP-BACK
      1. Given by Clem, Weine
      2. Involves preparation of the apical third initially followed by middle and coronal third of the canal using larger instrument sizes
      3. Phase 1: Apical-third instrumentation Phase II: Middle third Phase III: Coronal third Hand instruments
      4. Coronal instrumentation with reaming motion and apical instrumentation with circumferential filing
      5. • Popular technique employed with 2% standard SS files
      6. Ability to prepare a proper apical stop prior to preparation of the middle third and coronal third
      7. Extrusion of debris into the periapex Tendency to straighten in the canal
      8. Loss of working length
   2. STEP-DOWN
      1. Given by Goerig
      2. Involves preparation of the coronal two-thirds of the canal first followed by middle and apical third of the canal
      3. Phase 1: Coronal-third instrumentation phase
      4. Phase II: Middle third Phase III: Apical third Hand and rotary instruments
      5. Reaming motion
      6. Shaping is easier
      7. Elimination of the bulk of the tissue, debris, and microorganisms from coronal and middle third before apical shaping
      8. Minimizes debris extrusion
      9. Better access and control over apical enlarging instruments
      10. Better penetration of irrigants
      11. Gauging of the apical third is done as the last phase of the procedure
      12. MODIFICATIONS
          1. Crown-Down Pressureless Technique This
             1. technique was suggested by Marshall and Pappin. Early coronal flaring with Gates-Glidden drills is followed by an incremental removal of den- tin from coronal to apical direction, and hence called "crown-down" technique. Straight K-files are then used in a large to small sequence with a reaming motion and no apical pressure-hence called "pressureless" technique (Table 13.9).
          2. Double-Flare Technique
             1. This technique was proposed by Fava. Coronal to apical shaping with K files up to the working length Step back with K-files of ascending sizes
          3. Balanced Force Technique
             1. Roane and Sabala are credited with developing the balanced force technique which employs a new K-type file design known as Flex-R file (Moyco Union broach) or Flexofile (Dentsply Maillefer) or any flexible
      13. ADVANTAGES
          1. Shaping of the canal is subjectively easier
          2. removal of coronal obstructions allows removal of the bulk of tissue, debris, and microorganisms before apical shaping
          3. This technique minimizes the extrusion of debris through the apical foramen, thereby preventing postoperative discomfort.
          4. It allows better access and control over the apical enlarging instrument, thus decreasing the incidence of zipping.
          5. It allows better penetration of the irrigants.
   3. HYBRID
      1. use with stainless instruments
      2. Involves a combination of we crown-down and step-back e techniques.
      3. Phase I: Coronal-third instrumentation
      4. Phase II: Apical third Phase III: Middle third
      5. Hand and rotary instruments
      6. coronal instrumentation with reaming motion and apical instrumentation with circumferential filing
      7. Ability to shape the canal
      8. predictably with hand instrumentation using stain- less steel instruments Optimizes the advantages of crown-down and step-back techniques
      9. Middle third preparation has to be done carefully in order to prepare a continuous tapered canal preparation
      10. ADVANTAGES
          1. Ability to shape the canal predictably with a combination of hand and rotary stainless steel instruments
          2. Optimizes the advantages of crown-down and step-back techniques
   4. RECAPITULATION
      1. Returning to a smaller instrument from time to time before advancing to a larger size helps to prevent the packing of dentin filings and ensures patency of the root canal through the apical foramen.
5. SCHILDER'S OBJECTIVES
   1. MECHANICAL
      1. Should have a continuous, tapering, conical shape, with the narrowest cross-sectional diameter apically and the widest diameter coronally
      2. The walls should taper evenly toward the apex and should be confluent with the access cavity
         1. i.e., a shape that permits plasticized gutta-percha to flow against the walls without impedance
      3. Should keep the apical foramen as small as practical
      4. Should shape and clean the canal without transporting the apical foramen
   2. BIOLOGICAL
      1. Confinement themselves of instrumentation to the roots Ensuring that the necrotic debris are not forced beyond the foramen
      2. Removal of all tissues from the root canal space
      3. Creation of sufficient space for optimal obturation of the radicular space