Principle of Endodontic Shaping Flashcards
(100 cards)
1
Q
Why instrument root canals?
A
- Remove infected soft and hard dentine.
- Provide access for disinfecting irrigants.
- Access to the apical canal space.
- Create space for the delivery of medicaments and subsequent obturation.
- Retain the integrity of radicular structures.
2
Q
What do we use to obturate (fill) root canals?
A
Gutta percha.
3
Q
What are the 5 mechanical objectives of canal shaping?
A
- Continuously tapering funnel from the apex to access cavity.
- Cross sectional diameter should be narrower at every point apically.
- Root canal prep should flow with the shape of the original canal.
- Apical foramen should remain in its original position.
- Apical opening should be kept as small as practical.
4
Q
What are the 4 biologic objectives of canal shaping?
A
- Confinement of the instrumentation to the roots themselves.
- No forcing of necrotic debris beyond foramen.
- Removal of all necrotic or inflamed tissue from the root canal space.
- Creation of sufficient space for intra-canal medicaments.
5
Q
What are the goals of shaping?
A
- Provide access to the pulp cavity and the radicular space.
- Remove infected vital or necrotic tissues from the main and lateral extensions of the root canal system.
- Creation of adequate space for effective disinfection and medication.
- Preserve original anatomy avoiding iatrogenic alterations.
- Respect to the PA tissues.
- Create a shape that allows the obturation with current filling methods.
- Preserve tooth structure by removing the least possible amount of dentine necessary to achieve effective disinfection.
6
Q
What is estimated working length?
A
Length from coronal reference point to radiographic apex minus 1mm.
7
Q
What is correct working length?
A
Length at which instrumentation and subsequent obturation should be limited.
8
Q
How to obtain the correct working length?
A
Electronic apex locator and/or working length radiograph with a file or GP cone in the tooth.
9
Q
What is the master apical file?
A
Largest diameter file taken to working length, indicating size of apical preparation. Needs to be 2-3 ISO sizes greater than the first file used in apical portion.
10
Q
What is the master apical cone?
A
Must have exact fit to apical prep to enable apical control during obturation and avoid extrusion of material beyond the apex.
11
Q
What instruments can be used to debride and shape the root canal?
A
- Barbed broach.
- Gates Glidden.
- Stainless steel instruments.
- Hand instruments/files.
12
Q
What are barbed broaches used for?
A
Extirpating, not enlarging. Should select the largest size broach which will fit freely in canal.
13
Q
What are Gates Glidden?
A
Traditional instruments used to shape orifice canal, used in slow speed handpiece.
14
Q
How to use a Gates Glidden?
A
Use passively on withdrawal from canal using brush-like circumferential movement.
15
Q
What size maximum Gates Glidden should be used?
A
3.
16
Q
What speed should Gates Glidden not exceed?
A
800 rpm.
17
Q
What does ISO stand for?
A
International Standards Organization.
18
Q
What size working end do stainless steel instruments have?
A
16mm.
19
Q
What determines the diameter of the file?
A
Diameter at the tip.
20
Q
Why is the taper 2% for hand instruments?
A
Taper is 0.32 over 16mm.
21
Q
What are some different hand instruments?
A
- K-reamers.
- K-files.
- H-files.
22
Q
What are H-files?
A
Hedstrom files.
23
Q
What are H-files used for?
A
Removing GP or fractured instruments in cases of re-treatment. Should not be used for canal preparation anymore.
24
Q
How do Hedstrom files work?
A
With a filing motion, they cut on withdrawal.
25
What are hand files used for (except H-files)?
1. Exploration.
2. Canal patency.
3. Establishing glide path.
4. Cleaning.
5. Shaping.
6. Apical gauging. Must never be used with filling motion due to increased risk of iatrogenic damage.
26
What motion should never be used with hand files (except Hedstrom) and why?
Filing motion - can cause iatrogenic damage.
27
What is a glide path?
A smooth radicular tunnel from canal orifice to apical constriction.
28
What shape indicates a k-reamer?
Triangle.
29
What shape indicates a k-file?
Square.
30
What shape indicates a H-file?
Circle.
31
Where is the cutting edge of k reamers?
Nearly parallel to long axis.
32
How to use a k reamer to be effective?
Must be in contact with the walls of the canal.
33
Where is the cutting edge of the k file?
Almost perpendicular to long axis.
34
How to use a k file?
Use with balancing force technique. Do not use larger instruments too quickly or it may ledge within canal.
35
What are k flexofiles?
Greater flexibility than standard k files and older file types.
36
What shape are k flexofiles in cross section?
Sizes 6, 8 and 10 are square; larger sizes are triangular.
37
When are k flexofiles indicated?
Curved and narrow root canals.
38
Benefits of k flexofiles over other file types?
More flexible. Non cutting bat tip -> less likely to result in iatrogenic damage.
39
Why are smaller k files square in cross section?
To give them strength.
40
What are c+ files?
Have additional carbon added to the alloy to make the files harder.
41
What shape are c+ files in cross section?
Square.
42
When are c+ files useful?
Canal location and instrumentation where there is calcification.
43
What shape identifies a flexofile?
Empty square.
44
What sizes are c+ files available in?
8 to 15 only.
45
What size file is pink?
6.
46
What size file is grey?
8.
47
What size file is purple?
10.
48
Which technique is used for canal instrumentation using hand files?
Balanced force technique.
49
How to do the balanced force technique?
Insert file into canal, rotate a quarter turn (90°) clockwise into dentine with gentle downward pressure. With continued gentle pressure, rotate counter clockwise (180°) to strip dentine away. Repeat 1-3x, then remove from canal, remove debris and check file for plastic deformation. Remove, clean, irrigate, reintroduce, work way towards working length.
50
What are some complications of hand instrumentation?
1. Mishaps e.g. ledges, blockages, perforation, transportation of apical foramen.
2. Debris extrusion especially when used with filing motion.
3. Time consuming.
4. Less predictable shapes in curved canals.
5. Instrument fracture (more common with smaller file sizes).
51
What is a blockage?
Dentine debris gets packed in apical portion of canal. When packed tightly it can be as hard as surrounding dentine. Attempts to remove blockage can result in a false canal being cut and possible perforation.
52
What are ledges?
Internal transportation of canal. Occurs when short of working length. Can be bypassed but this is difficult.
53
How to bypass a ledge?
Placing a curve at the tip of a small file.
54
How do perforations occur?
Extension of incorrect working length.
55
How can perforations be diagnosed?
1. Persistent bleeding into canal.
2. Multiple radiographs.
3. Electronic apex locator reading within canal rather than at apex.
4. Microscope.
56
What materials can be used to treat a perforation?
Hydraulic calcium silicate cements.
57
What affects the prognosis of a perforation?
Location, time elapsed, size, periodontal irritation, material used for repair.
58
What causes zipping/apical transportation?
Occurs as a result of the tendency of the instrument to straighten inside a curved canal.
59
What can zipping/apical transportation result in?
Over enlargement along outer side of curvature, under preparation of inner aspect at apical endpoint, teardrop/hourglass shape in canal cross section.
60
What material do we use for treatment of perforations?
Hydraulic calcium silicate cements.
61
How to minimise/avoid zipping/apical transportation?
Pre curving with small hand files, ensuring you do not skip any files in the sequence.
62
What is NiTi?
Nickel titanium alloy.
63
Benefits of nickel titanium files?
Superelasticity -> can undergo greater strain before permanent deformation, better corrosion resistance and biocompatibility, shape memory after heat treatment, greater tapers and variable tapers possible.
64
Advantages of NiTi over SS instruments?
Increased flexibility in larger sizes and tapers, increased cutting efficiency, safer if used appropriately, user friendly - less instruments and simple sequences, less ledging, zipping, apical transportation.
65
Disadvantages of NiTi over SS instruments?
Fracture if used incorrectly, more expensive, access in posterior teeth may be difficult, use with extreme caution where complex canal anatomy.
66
What are the 2 modes of file fracture?
Cyclic fatigue and torsional fatigue.
67
What is cyclic fatigue?
When an instrument is rotated in a curved canal due to repeated compressive and tensile stresses.
68
What is torsional fatigue?
Occurs when the tip of the file binds in the canal and the motor continues to rotate.
69
How to minimise the risk of file fracture?
Ensure straight line access, avoid overuse of files, ensure speed and torque settings are correct, inspect files for unwinding during use, continually move files within canal in no more than 3 strokes, continual irrigation and flushing of debris, advance files gradually by 2mm at a time.
70
Which size instruments are more likely to succumb to cyclic fatigue?
Larger instruments.
71
What are the different phases of NiTi?
Martensite, austenite, R phase.
72
What is the martensite phase of NiTi?
Hexagonal close packed structure, stable at lower temps, great flexibility, easily deformed.
73
What is the austenite phase of NiTi?
High temp phase, centered cubic structure, super elastic properties, low plastic deformation.
74
What is the R phase of NiTi?
Hybrid between austenitic and martensitic phases.
75
What is M wire treatment?
Treatment applied to NiTi wire which gives it both the martensitic phase and the pre martensitic R phase. Maintains the main properties of traditional NiTi alloys in the austenitic phase at room temp (super elasticity, high flexibility etc).
76
How can NiTi shift from the austenitic phase to the martensitic phase?
Temperature stresses, mechanical stresses, both.
77
What are the components of rotary endodontic instruments?
1. Taper.
2. Flute.
3. Cutting edge.
4. Land.
5. Relief.
6. Helix angle.
78
What is the taper of rotary endo instruments?
The change in diameter along the working surfaces.
79
What is the flute of rotary endo instruments?
The groove to collect dentine and soft tissues.
80
What is the cutting edge of rotary endo instruments?
Forms and deflects dentine chips line.
81
What is the land of the rotary endo instruments?
The surface extending beyond the flutes.
82
What is the relief of rotary endo instruments?
The reduction in surface of the land.
83
What is the helix angle of rotary endo instruments?
The angle the cutting surface forms with the long axis of the file.
84
Benefits of shaping with Protaper Ultimate?
1. Produces safer mechanical apical preparations.
2. Optimises fluid exchange to promote 3D disinfection.
3. Controls apical obturation and appropriate sealing.
85
How to shape with Protaper Ultimate files?
Use slider file first, use shaper files next, finish with finisher files.
86
What are the two types of taper you can have with Protaper Ultimate files?
Progressive and regressive.
87
Where do shaper files work?
Coronal 2/3.
88
Where do finishers work?
Apical 2/3.
89
What affects the colour of the wire?
Thickness of titanium oxide.
90
Which Protaper Ultimate file can be used instead of a hand file?
Slider.
91
When would you use FX and FXL Protaper Ultimate files?
Wide root canals.
92
Which heat treatment is most flexible?
Gold.
93
Benefit of good heat treated Protaper files?
Increased resistance to cyclic fatigue.
94
What is blue heat treatment?
Martensitic at room temp, transitions to austenitic during use, increased resistance to cyclic fatigue than M wire.
95
What are the two different shapes of tip on Protaper Ultimate files?
2 blade design and 3 blade design. There is a move towards a 2 blade design (2 cutting edges).
96
Which Protaper Ultimate file to use for shaping the coronal two thirds?
One shaper.
97
Which Protaper Ultimate file to use for sliding the glide path?
Slider purple gold file.
98
What sequence to follow when using the Protaper Ultimate rotary files?
Hand files, white Protaper, yellow Protaper, red finisher F2, purple finisher F3.
99
When to use auxiliary files?
If need to, allows you to treat more cases.
100
What are the 4 interrelated traits of an ideal file?
1. Flexibility.
2. Cyclic fatigue resistance.
3. Cutting efficiency.
4. Torque strength.
