3- cleaning and shaping (clinical handouts) l Endodontics series

3- cleaning and shaping (clinical handouts) l Endodontics series

 

CLEANING AND SHAPING

 

HEADLINES:

1.         Root mapping.
2.       Canal location.
3.       Scouting & patency.
4.       Working length.
5.       Glide path.
6.       Shaping.
7.       Precautions for rotary files.
8.       Selection of last file & irrigation.

 

 

1)   Glide path:

• No manual file = no rotary file.
• With manual files: smoothen canal walls, create glide path then introduce your rotary file.
• The goal is to obtain smooth wall and maintain this smooth wall.
• Importance of glide path:

1. Decrease fracture of files.
2. Saves anatomy.
3. Gives you a 3D idea about the internal anatomy of the canal through the shape of the file. When you introduce the file into the canal till the w.l then remove it in up & down motion without rotation, it directs you to the curves inside, as if you’re taking an impression to the canal.

• Glide path is done with file 10 and maximum 15.
• Apical transportation is a fatal mistake that may happen due to sudden size transmission (from 10 to 15), so, in severe cases use an intermediate file (12.5) after 10. This is called micro glide path.
• Macro glide path is done using flexible Ni-Ti instruments 15 & 20.
• You’ve to maintain patency between files.

 

 

2)   Shaping:

• The previous steps were just preparation for shaping.
• During shaping, we have fear of files separation.
• We’ve 2 mechanisms of fracture:

1. Cyclic fatigue (with large instruments and repeated use).
2. Torsional overloading (in narrow canals when the file become locked).

• To overcome cyclic fatigue: change motion or change metallurgy.

Motions:

1. Continuous rotation.
2. Reciprocation: it’s not recent in endodontics, but recent in rotary systems. It increases fatigue resistance.
3. Alternate reciprocation (same as watch-winding).
4. Rotating reciprocation: 90 degrees CW and 30 degrees CCW (wave one gold and reciproc). There’s no single file system for canal preparation, single file can be only for canal shaping or enlargement part, but you’ll need manual files for glide path and patency.
5. Combined motion: in TF adaptive file, when it meets resistance, it turns from continuous rotation to reciprocating rotation.
6. OTR / OGP (optimum torque reduction / optimum glide path): Alternate reciprocation, it rotates CW and CCW at the same degrees, when it meets resistance, it turns into rotating reciprocation.

Metallurgy:

• Before 2008, all Ni-Ti were nitinol which had unpredictable fracture.
• They were then heat treated to transform them from austenitic phase to martensitic phase which can withstand bending and has high cyclic fatigue resistance. That’s the M-wire (protaper next files).
• R-phase files (such as TF or K3XF) are thermo-processed to reach a phase between austenitic and martensitic, it also withstands extreme bending.
• Controlled memory files (CM files): shape memory of Ni-Ti files put a lot of pressure on the file inside the canal, it may lead to transportation, because it cuts through the outer side of the curve more than the inner side. That was overcome with CM files such as hy-flex. Proceed it inside the canal (inactive – static) until it meets resistance then activate it, the file takes the same curve as the canal and never makes transportation.
• Protaper gold: it’s not controlled memory but decreased shape memory files.
• To overcome torsional overloading: there shouldn’t be total frictional fit between file and canal. To avoid:

1. Coronal apical technique.
2. Less vertical force & torque.
3. Less stress on files.         

 

 

3)   Precautions for rotary files:

• Pre-operative radiographs: gives an idea about the curve, its radius and abruptness.
• TTT planning before shaping.
• Before using new files in a case, you’ve to try it 1^st on extracted teeth.
• When the file is loaded with debris its cutting efficiency is decreased, then it should be removed, cleaned and re-introduced into the canal.
• The rotary file should be inspected before, during and after use. Any bent, shiny spot or permanent deformity within the file indicates that it needs to be discarded.
• You’ve to make brushing action after finishing shaping because the canal is always oval not round.
• Whenever you reach the reference point, retract your hand-piece, because if the file kept rotating it will break the apical stop.
• The time a file should spend inside a canal is 5-10 seconds maximum.

 

 

4)   Selection of last file & irrigation:

Objectives of shaping:

• Mechanical cleaning: visual gauging: inspect by your eyes that you touched all canal walls, you should see clear white dentin chips at least in the apical 3 mm of the file.

Irrigation:

• I need my irrigant to reach 2 mm before working length to be effective.
• Type of irrigant: NaOCl is the best to be used + chelating agent and the delivery system.
• NaOCl half concentration is preferred over full concentration because of less toxicity and side effects.
• Passive irrigation: luer lok plastic syringe is used. Needles must be side-vented because end-vented ones cause NaOCl accident.
• Active irrigation: by ultrasonic.
• Final irrigation protocol: 3-5 minutes’ irrigation for each canal. Drop of NaOCl for 30 seconds, I give time for chlorine ions to work on dissolving pulp tissue, then flushing by saline to put EDTA. If I put EDTA immediately on NaOCl, it decreases its effect and action.

Obturation:

• Bioceramic material is hydrophilic and follows wetness of canals and fills them, given you’ve made good and efficient irrigation.
• Biominimalism concept: once you feel that you can obturate and your canals are cleaned don’t overcut and enlarge more.
• Final finishing file depends on your ability to clean and obturate.