Endodontics 3 Instrumentation Of The Root Canal System Flashcards
What is the purpose of root canal instrumentation? (4)
- Remove infected soft and hard tissue (get all the stuff out)
- Give disinfecting irrigants access to apical canal space (widen canal for bleach)
- Create space for the delivery of medicaments and subsequent obturation (make it easier to fill)
- Retain integrity of radicular structures (keep the same shape as before)
What are the design objectives of RC instrumentation? (3)
- Create a continuously tapering funnel shape
- Maintain apical foramen in original position
- Keep apical opening as small as possible
What is the purpose of chemo mechanical preparation in a tooth? (2)
- Chemo
- irrigate to kill microorganisms and remove smear layer - Mechanical
- prepare shape
- flush out debris
What are the main challenges of root canal preparation? (2)
- Root canal system is very complex
2. Number, length, curvature and diameter of canals can vary considerably
State the definition of estimated working length (1)
- Estimated length at which instrumentation should be limited
How is estimated working length obtained? (1)
Measuring pre-operative radiograph to determine the distance between coronal reference point and radiographic apex then subtracting 1mm
State the definition of correct(ed) working length (1)
Length at which instrumentation and subsequent obturation should be limited.
How is correct(ed) working length achieved?
Use of an electronic apex locator and/or working length radiograph
What is the master apical file?
The largest diameter of file taken to working length
What does the master apical file represent? (1)
Represents the final prepared size of the apical portion of the canal at the working length
What are the 5 types of motion in RC instrumentation? (5)
- Filing
- Reaming
- Watch-winding
- Balanced forced motion
- Envelope of motion
Describe how to perform the watch winding technique and what it is useful for (3)
- Back and forward oscillation of 30-60 degrees
- Light apical pressure
- Useful for passing small files through canals
State the stages of irrigation protocol performed after RC instrumentation (4)
- EDTA 17% for 1 min
- Sodium hypochlorite 3%, 30 ml for 10 min
- Slow injection (don’t use thumb)
- Revise restorative synopsis and chemo mechanical disinfection section
What are drawbacks of the barbed roach instrument? (2)
- Extremely fragile - will break easily if misused
2. Must not engage canal walls - difficult
What length are the flutes in ISO-sized stainless steel instruments? (1)
16mm
What are drawbacks of hedström files? (1)
Can cause iatrogenic damage
What are hedström files mainly used for currently?
Removing gutta-percha or fractured instruments in cases of retreatment
Name and explain the main advantage of NiTi files? (3)
Superelasticity -
- Can be strained more than other alloys before permanent deformation
- allows NiTi files to be placed in curved canals with less lateral forces exerted
- less transportation, zipping and ledging
- more centrally places preparation in harmony with the original canal shape
List and describe the components of an endodontic rotary instrument12)
- Taper - diameter change along working surface
- Flute - groove to collect dentine and soft tissue
- Leading/cutting edge - forms and deflects dentine chips
- Land - surface extending between flutes
- Relief - reduction in surface of land
- Helix angle - angle cutting axis forms with long axis of file
List advantages of NiTi over stainless steel (4)
- Increased flexibility in larger sizes and tapers
- Increased cutting efficiency
- If used appropriately, good safety in use
- Can be more user friendly with less instruments and simple sequences
List disadvantages of NiTi instruments (4)
- Instrument fracture
- Expense
- Posterior teeth access difficult
- Unsuitable for complex canal anatomy
Describe true reciprocation + it’s advantages and disadvantages (5)
- Mimics manual movement
Advantages:
2. Reduces risks associated with continuously rotating file through canal curvatures
Disadvantages:
3. Decreased cutting efficiency
- Requires increased inwards pressure
- Limited capacity to auger debris out of a canal
What are the guidelines for rotary instrumentation? (5)
- Straight line access
- Cross-sectional diameter
- Root canal system anatomy
- Speed and sequencing
- Lubrication and “light touch”
Describe the steps involved in creating a glide path (6)
- Confirm straight line access
- Explore anatomy
- Always introduce files 10-25 to resistance only (coronal only)
- Coronal flare
- Size 10 with watch winding to establish apex
- Irrigate and repeat using sizes 15 (WW) and 20 (BF)
What are the angles of reciprocation in a computer controlled rotary instrument? (2)
150 degrees CC
30 degrees CW
What are the main causes of instrument separation? (2)
- Torsional stress
2. Flexural stress
How does torsional stress cause instrument separation? (2)
- extensive instrument surface encounters excessive friction on canal walls
- if instrument tip is larger than canal section to be shaped:
(Tip may lock, torque exceeds critical level)
How can flexural stress cause instrument separation? (1)
- repeated cyclic metal fatigue
• cannot be influenced by clinician
