شرح اندو , اندو



4- IRRIGATION (record) l Endodontics series


 

Biomechanical preparation
And Irrigation techniques

HEADLINES :

  1. objectives of cleaning and shaping.
  2. Challenges and how to overcome.
  3. Preparation of root canal system.
  4. Endodontic microbiology and infections.
  5. Irrigation hydrodynamics and Activation of irrigation.
  6. Biomechanical preparation.
  7. Mishaps.

Objectives of Biomechanical preparation :

  • Cleaning : removal of organic debris and microbial content.
  • Shaping : to achieve fluid tight seal.
  • Mechanical objectives :

  1. Continuously tapering funnel from the apex to the access cavity.
  2. Preserve the natural curve, cross section and taper of the canal.
  3. The apical constriction should be kept as small as practical.
  4. The apical foramen should remain in its original position.

Biological objectives :

  • Procedures should be confined to root canal system; avoid pushing the debris beyond the apex.
  • Removal of all tissue from the root canal space (vital or necrotic).
  • Creation of sufficient space for intra canal medication and irrigation.

Challenges in achieving biomechanical preparation :  

  • Microbial challenge : 

                                      Bacteria plays a major rule in the failure of RCT.
                                      Planktonic bacteria : normal flora.
                                      biofilm : bacteria surrounded by external polymeric  
                                                      matrix which is more resistant.

  • Complex morphology : 

                                         Accessory canals and canal anastomosis
                                         curved canals
                                         lateral exit
                                         furcal canal in lower molars
                                         multiple portal exit

                   files are straight so they are 70-75% in contact  with canal walls.

How to overcome the challenges :

  • Knowledge of the pathogenesis of pulp and periapical pathosis.
  • Knowledge of complex anatomy of the root canal systemand all the possible variations.
  • Proper knowledge of current instruments, materials, and devices to upgrade treatment outcome.

Steps of biomechanical preparation :

Straight line access : 

  • to avoid unnecessary tension on the file that may lead to ledge, apical transportation or perforation.

Working length determination: 

  • by apex locator and radiographs, resting on a sound reference point.
  • In multi-rooted  use shift technique and SLOB rule (same lingul opposite buccal) to prevent superimposition of the roots.

 

 

 

Instruments :

According to use :

  • Hand driven : K-files , H-files & reamers
  • Engine driven : gates glidden drills & rotary files.

According to material :

  • carbon steel : good cutting efficiency , doesn’t resist tarnish and corrosion
  • stainless steel : less cutting efficiency than carbon steel , but more tarnish and corrosion resistant
  • Nickel-Titanium alloy: 55% Ni , 45% Ti; shape memory and super elasticity

Standardization of instruments :

Length :  

              cutting part =16mm
               overall (handle-tip) =21mm “short” , 25mm  “standard” , 31mm  “long”
               taper = 2%

Taper :

              Manual files = 2% .. 0.02mm gain for each mm of cutting length
              Rotary files = 4 ,6 or 8%

Tip angle : 

  • 75 +or – 15

Color coding : 

  •     white , yellow, red, blue, green and black (#15-40, 45-80, 9
  •     #6 pink, #8 grey & #10 purple

Size of the file : 

  • diameter at the tip eg. File #25 … tip = 0.25 mm

 
Motion of the files :

Filing motion :

                           circumferential push and pull motion
                           used in the coronal 2/3 of the canal
                           can be done using H & K-files but better with H-file

Rotational motions :

  • used in the apical 1/3 of the canal
  • Done by K-file not H-file
  • Reaming motion = clockwise rotation
  • turn and pull motion = ¼ circle clockwise
  • watch winding motion = ¼ circle clockwise and ¼ anti-clockwise
  • Balancing motion = watch winding + apical pressure
  • pressure to keep the file centered and to avoidzipping  and WW to retrieve the debris.

 

Techniques of root canal enlargement :

Basic “Apical stop” tech. :

  • use all files to the full working length
  •  disadvantage  : ledging , transportation & stresses on large files

 

Step-back tech. :

  •  from apical part to coronal part
  •  Initial file selection : the smallest file achieve resistance at the apical 1/3
  • Master apical file :  at least 3 files after the initial file to create the apical stop
  • Apical stop : apply slight pressure on MAF , it should be some resistance
  • after MAF selection, start preparation of coronal 2/3 … use the next larger file 2mm shorter than the working length, then the larger file 1mm shorter and etc.
  • between 2 enlarging file “recapitulation” by the MAF and irrigation to avoid step formation and canal blockage.

 

Modified step-back :

  •  same as step-back except in the flaring phase, leave 3-5mm between the files

 

Crown-down tech. :

  •  start the preparation from the orifices coronally and prepare down the apex.

 

Hybrid tech. :

  • Mix  between crown-down and step-back techniques.