Endodontics 3 Instrumentation Of The Root Canal System

Question 1

What is the purpose of root canal instrumentation? (4)

Answer 1

1. Remove infected soft and hard tissue (get all the stuff out)
2. Give disinfecting irrigants access to apical canal space (widen canal for bleach)
3. Create space for the delivery of medicaments and subsequent obturation (make it easier to fill)
4. Retain integrity of radicular structures (keep the same shape as before)

Question 2

What are the design objectives of RC instrumentation? (3)

Answer 2

1. Create a continuously tapering funnel shape
2. Maintain apical foramen in original position
3. Keep apical opening as small as possible

Question 3

What is the purpose of chemo mechanical preparation in a tooth? (2)

Answer 3

1. Chemo
   - irrigate to kill microorganisms and remove smear layer
2. Mechanical
   - prepare shape
   - flush out debris

Question 4

What are the main challenges of root canal preparation? (2)

Answer 4

1. Root canal system is very complex

2. Number, length, curvature and diameter of canals can vary considerably

Question 5

State the definition of estimated working length (1)

Answer 5

1. Estimated length at which instrumentation should be limited

Question 6

How is estimated working length obtained? (1)

Answer 6

Measuring pre-operative radiograph to determine the distance between coronal reference point and radiographic apex then subtracting 1mm

Question 7

State the definition of correct(ed) working length (1)

Answer 7

Length at which instrumentation and subsequent obturation should be limited.

Question 8

How is correct(ed) working length achieved?

Answer 8

Use of an electronic apex locator and/or working length radiograph

Question 9

What is the master apical file?

Answer 9

The largest diameter of file taken to working length

Question 10

What does the master apical file represent? (1)

Answer 10

Represents the final prepared size of the apical portion of the canal at the working length

Question 11

What are the 5 types of motion in RC instrumentation? (5)

Answer 11

1. Filing
2. Reaming
3. Watch-winding
4. Balanced forced motion
5. Envelope of motion

Question 12

Describe how to perform the watch winding technique and what it is useful for (3)

Answer 12

1. Back and forward oscillation of 30-60 degrees
2. Light apical pressure
3. Useful for passing small files through canals

Question 13

State the stages of irrigation protocol performed after RC instrumentation (4)

Answer 13

1. EDTA 17% for 1 min
2. Sodium hypochlorite 3%, 30 ml for 10 min
3. Slow injection (don’t use thumb)
4. Revise restorative synopsis and chemo mechanical disinfection section

Question 14

What are drawbacks of the barbed roach instrument? (2)

Answer 14

1. Extremely fragile - will break easily if misused

2. Must not engage canal walls - difficult

Question 15

What length are the flutes in ISO-sized stainless steel instruments? (1)

Answer 15

16mm

Question 16

What are drawbacks of hedström files? (1)

Answer 16

Can cause iatrogenic damage

Question 17

What are hedström files mainly used for currently?

Answer 17

Removing gutta-percha or fractured instruments in cases of retreatment

Question 18

Name and explain the main advantage of NiTi files? (3)

Answer 18

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

Question 19

List and describe the components of an endodontic rotary instrument12)

Answer 19

1. Taper - diameter change along working surface
2. Flute - groove to collect dentine and soft tissue
3. Leading/cutting edge - forms and deflects dentine chips
4. Land - surface extending between flutes
5. Relief - reduction in surface of land
6. Helix angle - angle cutting axis forms with long axis of file

Question 20

List advantages of NiTi over stainless steel (4)

Answer 20

1. Increased flexibility in larger sizes and tapers
2. Increased cutting efficiency
3. If used appropriately, good safety in use
4. Can be more user friendly with less instruments and simple sequences

Question 21

List disadvantages of NiTi instruments (4)

Answer 21

1. Instrument fracture
2. Expense
3. Posterior teeth access difficult
4. Unsuitable for complex canal anatomy

Question 22

Describe true reciprocation + it’s advantages and disadvantages (5)

Answer 22

1. Mimics manual movement

Advantages:
2. Reduces risks associated with continuously rotating file through canal curvatures

Disadvantages:
3. Decreased cutting efficiency

4. Requires increased inwards pressure
5. Limited capacity to auger debris out of a canal

Question 23

What are the guidelines for rotary instrumentation? (5)

Answer 23

1. Straight line access
2. Cross-sectional diameter
3. Root canal system anatomy
4. Speed and sequencing
5. Lubrication and “light touch”

Question 24

Describe the steps involved in creating a glide path (6)

Answer 24

1. Confirm straight line access
2. Explore anatomy
3. Always introduce files 10-25 to resistance only (coronal only)
4. Coronal flare
5. Size 10 with watch winding to establish apex
6. Irrigate and repeat using sizes 15 (WW) and 20 (BF)

Question 25

What are the angles of reciprocation in a computer controlled rotary instrument? (2)

Answer 25

150 degrees CC

30 degrees CW

Question 26

What are the main causes of instrument separation? (2)

Answer 26

1. Torsional stress

2. Flexural stress

Question 27

How does torsional stress cause instrument separation? (2)

Answer 27

• 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)

Question 28

How can flexural stress cause instrument separation? (1)

Answer 28

• repeated cyclic metal fatigue

• cannot be influenced by clinician