2. Cleaning & Shaping Flashcards
What are the 5 objectives of cleaning and shaping?
- Remove pulp and infected dentine from the root canal
- Avoid irritation and infection of apical tissues
- Shape the root canal by incorporating the original root canal system into the prepared shape
- Facilitate the entry of irrigants and medicaments
- Facilitate obturation
What are the usual irrigants and medicaments used for C&S?
Irrigant: Sodium hypochlorite
Medicament: Calcium hydroxide
Based on the ISO standards, what are the order of colours for file sizing?
W Y R B G B
White (15), Yellow (20), Red (25), Blue (30), Green (35), Black (40)
- 15, 45 and 90 are the starting points for the colours
- Gradations increase from 5 to 10 from size (60) and above
- Grey used for size (8), purple used for size (10)
What are the different file actions and their uses?
Reaming, Watchwinding, Circumferential filing, Anticurvature filing
- Reaming: Bind canal wall then rotate file 1/4-1/2 turn with apical pressure, withdraw to cut. Done to enlarge canal around the file tip
- Watchwinding: 1/2 turn clockwise then 1/2 turn anticlockwise with apical pressure. Done to enlarge canals and advance file further into the canal
- Circumferential filing: Lean file against dentine thencut with withdrawal strokes. Done to enlarge middle and cervical third of canals, ONLY FOR STRAIGHT CANALS
- Anticurvature filing: Lean on greater curvature of canal and withdraw. Used for curved canals, dentine is usually thinner on the lesser curve compared to the greater curve
What is the Working Length and how is it measured?
The working length is the distance from a consistent coronal reference point to the apical terminal point where C&S ends.
The coronal reference point is usually a cusp tip or incisal edge
The apical reference point should be at the apical constriction (AKA cemento-dentinal junction) as it is the narrowest part of the canal
Note: Apical foramen =/= Apical Constriction =/= Apex
What are the intial and master apical files?
- IAF is the file that binds to the canal at the desired working length before any instrumentation is done. The IAF has to be at least size 15
- MAF is the file that binds to the canal at the desired working length after instrumentation is done. The MAF has to be at least size 35
Sequential apical enlargement is done to a point where the MAF is at least 3 sizes up from the IAF
What is cervical flaring and why is it done?
Cervical flaring is the instrumentation of the canals to enlarge the cervical third of the canal into a funnel shape. It is done to remove the shoulder that interferes with WL determination.
The funnel shape allows the irrigants to stream into the canal
How do we determine the working length for a tooth?
- We measure the length of the tooth from the coronal reference point to the apex (this is called the diagnostic WL)
- Minus the DWL by 1mm then transfer the length to the IAF (at least size 15) and mark the rubber bung. Expose a radiograph to check if the WL is appropriate
We minus 1mm since the average distance between the radiographic apex and apical constriction is 1mm
Note: If length is more than 1mm from desired WL, we may need to expose another radiograph to confirm WL
What are the steps carried out for hand instrumentation of canals?
- Access cavity to remove lingual/palatal shoulders
- Cervical flare with GG drills or SS files
- Determine working length
- Sequential enlargement of the apical third of canal with SS files
- Step-back technique
What is the purpose of the Step Back Technique?
It is to create a tapered canal by reaming and filing the canals with a file that is 1 size larger, at 1mm from the previous length. We repeat this process 6 times in total. This will create a 5% taper due to the 0.05mm increment for each 1mm stepped back
Eg: MAF is 35 at WL of 20mm. We take a size 40 file and place it at a length of 19mm, then ream and circumferential file. Irrigate and recapitulate then repeat process with size 45 file at 18mm. Step back is done after using size 60 at 14mm.
What are the criteria to determine good C&S?
- Original root anatomy unchanged
- Working length maintained
- Root canal free of debris
- Definite apical stop
- No ledges and gouges
- Instrument separation and root perforation avoided
- Adequate flare (Place MAF in canal then place MF finger spreader in canal 2mm short of the WL)
What are some common consequences of careless C&S (both SS and rotary instrumentation). How do we avoid them?
- Transportation: Canal deviated from original curve. Can occur when rotary files are left rotating in the canal for more than a few seconds
- Ledges: Step in the canal due to a lack of a smooth glide path
- Lateral perforations
- Apical perforations due to lack of WL discipline
- Apical compaction of dentinal debris when the flutes are not cleaned constantly, also due to lack of recapitulation and irrigation
- Torsional strain of files due to overuse and inadequate intracanal lubrication. We should always ensure the canals are wet with EDTA or at least water
- Locking of the file in the canal when there is no rotation
Can avoid these by using NITI instruments with constant irrigation and recapitulation. We can also pre-bend SS files according to the curve of the canal.
What is the alternative to the Step Back technique?
Crown Down technique.
After determining IAF and WL, we determine the MAF (at least 3 sizes up from first binding file). We then instrument the canal from the cervical portion in an apical direction, starting with larger file sizes and progressively use smaller file sizes to finally reach MAF at WL.
This principle is used for rotary instrumentation…
How does rotary instrumentation incorporate the Crown Down technique?
- The files are manufactured with varying tapers (unlike k-files fixed at 2% tapers) and there are different degrees of taper at the parts of each file. Each file is worked to the full working length
- The order of file usage is as follows: S1, S2, F1, F2, F3, F4, F5
- S1 is broad at the cervical third, narrow at mid and apical thirds.
- S2 is broad at mid third, narrow at cervical and apical thirds
- F1-F5 are broad at the apical third, narrow at the cervical and mid thirds
What are the apical sizes and colours of the different files used for rotary instrumentation?
S1 - 0.17mm (Purple) SX - 0.19mm (Unlabelled) S2 - #20 (White) F1 - #20 (Yellow) F2 - #25 (Red) F3 - #30 (Blue) F4 - #40 (Black) F5 - #50 (Yellow)
Note: The files must be rotating before entering the canals and brushing along the walls of the canals is needed with each stroke. CLEAN FLUTES upon withdrawal and recapitulate to WL!!
