INSTRUMENTS, MATERIALS, AND DEVICES l Preclinical Endodontics MCQs

 INSTRUMENTS, MATERIALS, AND DEVICES l Preclinical Endodontics MCQs (multiple choice question) for dental student

 

Endodontic instruments

FDI classification

Group I

• Hand use only: K files, H files, reamers, broaches

Group II

• Latch type engine driven [ like group I but attached to a hand piece]

Group III

• Latch type engine driven drills and reamers [ peso reamer, Gates Glidden]

Group IV

• RC points [ Gutta percha, silver points, paper points]

 

Hand instruments: [ numbered from 10- 100]

• The number represents the diameter of the instrument in [1/100 of a mm ] at the tip
• Working blade in any size is always 16 mm extending from D1 [ the tip ] to D2 [ 16 mm away from D1]
• Hand instruments have a constant increase in taper of 0.02 mm per mm of length [ every 1 mm away from the tip has a taper greater by 0.02mm → Diameter of D2 is greater than diameter of D1 by 0.32 mm
• Tip angle = 75 ± 15°
• Available lengths = 21,25,28,31 mm
• Hand instruments are color coded
• [Number represents the diameter of the tip in 1/100 of a mm

Instruments for cleaning and shaping the canals

 

Reamers

Used by:

•    Insert – twist to ¼ or ½ turn then withdraw
•    Less flutes than a file – but same cutting efficiency [ because more spaces between the flutes → better debris removal ]
•    Remain self centered in the canal → less chance of canal transportation

 

K file

Used by:

•     Insert – apply pressure against canal wall – withdraw the file while maintaining pressure
•     Stainless steel wire that is triangular or square in C.S that is twisted to form the file

 

H file

Used by:

•    Insert – apply pressure against canal wall – withdraw the file while maintaining pressure
•    Flutes that look like successive triangles on top of each other [ Christmas tree] – cut only when the file is withdrawn [ because the edge faces the handle of the instrument] Aggressive cutter but lack flexibility and break easily

 

Lentilospiral:

• latch type attachment – used to carry the sealer into the canals

 

Peeso Reamer :

• Very stiff - Does not follow canal curvature and may cause canal perforation
• Used for : Preparing space for a post

 

Gates Glidden :

•   Flame shaped cutting point – latch type attachment to a slow speed hand piece – set of 6
•   Used for :

1.        Coronal flaring of the canal
2.        Removal of GP
3.        Preparing space for a post

Nickel titanium instruments: NiTi

1. Very good elasticity and resilience
2. Shape memory
3. Corrosion resistance

• Visual examination is not a reliable method to evaluate NiTi files because they can break without any signs of permanent deformation or unwinding – to reduce this risk Bend the file at least 80 ° to see if the instrument breaks every time before you re- insert the file
• spreaders: used to pack GP [ sizes from 15-45]
• pluggers : diameter wider then spreaders – blunt end

Rotary endodontics

Gates Glidden burs: [GG]

• 6 sizes [ you know the size from the number of stripes on the shank of the bur]
• When using GG stripping perforation mostly occurs in the distal wall of the mesial root of lower molars – this can be prevented by using the GG in a brushing motion against all walls.

Advantages

1. Easy to use
2. Inexpensive
3. Easy to retrieve if it breaks

Disadvantages

1. Can cause ledges / stripping
2. Cannot be used in curved canals
3. Aggressive + remove a lot of tooth structure
4. Difficult to seal the coronal 3rd of the canal if you are using lateral condensation 

NiTi rotary instruments:

Similarities

• All made from same alloy [ Niti]

1.          New advancement: heat treated alloys → better flexibility and resistance to cyclic fatigue

• All need a specific engine motor [ slow speed and controlled torque ]
• All are used in crown down technique
•  Have non cutting tips

Differences

1. Sizes
2. Taper [ increase in diameter of the file for every 1 mm increase in length ]
3. Cross section & tip design
4. Length of the cutting blade and number of spirals

N.B :

1. Rake angle = angle formed between the radius of the file and the cutting edge.
2. Cutting edge is exactly on the radius → zero rake angle
3. Cutting edge infront of the radius → +ve rake angle [ cutting action]
4. Cutting edge behind the radius → -ve rake angle [ scraping action] 

Tapers in endo instruments explanation:

• Taper = how much the diameter of the file/ instrument increases with every 1 mm increase in length
• D0 = the tip of the file
• D1= 1 mm away from the tip
• D2 = 2 mm away

N.B :

• Hand files have 3 lengths [ 21 mm, 25 mm , 31 mm ] but regardless of the length of the file the length of the active part is ALWAYS 16 mm only [ located at D16]
• In rotary the length of the active part is variable but the maximum is 14 mm [ located at D14]

benefits of multiple tapers:

Increase file elasticity

Increase cutting ability

No need for recapitulation during prep

Decrease torsion and number of files in the system

 

• we try to decrease the number of contact points between the file and the canal walls to avoid taper lock which can break the file or the dentine walls.

 

Thread tendency :

• The cutting edges in the rotary files are continuous helices → this leads to thread tendency [ the feeling of the file sinking inside the canal when you want to remove it , at this point if you don’t stop the rotation the file will break ] – Thread tendency is mostly experienced when you are doing beck motion and the file rotation is full rotation

1.          If the helicals are placed parallel to each other [ constant helical angle]→ higher thread tendency
2.          If the helicals are not parallel [ variable helical angle] → lower thread tendency
3.          Advantage of thread tendency: allows the file to reach the apical part easily
4.          Disadvantage of thread tendency: the file can break 

Q: why is it better to use rotary files?

1. Faster preparation
2. Provides the desired shape of the canal [continuous tapered conical form]
3. Lesser chance of perforations, apical transportation and zipping
4. Centered preparation

Q: what are the disadvantages of rotary files?

1. Higher risk of fracture compared to k files
2. Might create micro cracks in the dentine
3. Can’t be used in curved narrow canals
4. Don’t clean oval / wide canals very well. [ fixed by doing brushing motion]

 

why do rotary files have less complications?

• Because they have non active tip + they are made from nickel titanium alloy [ flexible ] 

N.B :

• heated treated niti alloy systems are more flexible and can be used in curved canals.
• Rotary files can be used in all RCT cases EXCEPT: narrow canals, C or S shaped canals, oval and wide canals.
• C or S shaped canals : use manual filing and focus on irrigation