Preclinic Hw Questions Flashcards
When do we use NaOCl?
During the canal shaping and cleaning process (in between instruments)
Why do we use NaOCl?
- bactericidal agent (0.5-6%) –> kills bacteria and yeasts
- dissolves organic material (collagen, pulp tissue, biofilm)
- flushing action (removes debris)
- lubricant (reduces friction of instruments)
- facilitates dentine removal (lubricant)
What factors should be considered when determining the master apical file (i.e., How do you know if your instrumentation has adequately cleaned the canal?)
- Tactile (tug-back)
- Debris (on last 3mm of flute)
- apical gauging (use hand file or rotary instrument one size larger than master apical instrument. If this instrument does not stop at least 3mm from the apex it means the canal is larger than the instrument chosen in the apical 3mm and that the canal has not been shaped to that instrument. You must go up in size.
Why do we melt the root-filling to a suborifice level?
- Minimize risk of visible discolouration (grey discoloration can occur to gutta percha over time) → particularly important for anteriors (aesthetics)
- Provide a greater depth of seal
Explain what an ”overextended and underfilled” root-filling is, and how it occurs.
When the filling is long, extruding past the apical foramen, but the preparation width is inadequate. This may occur for several reasons.
- Incorrect working length determination
- Over-instrumentation or inadequate instrumentation
- Poor lateral compaction
- Incorrect selection of master GP cone and not enough accessory GPs used
- Voids present
- Excessive sealer
What is AH26 and its advantages/disadvantages?
An epoxy resin-based sealer.
Advantages:
- has antibacterial effect due to formaldehyde release in the first 24 hrs
- Favourable healing outcome
- Biocompatible once set
- Gold standard in terms of sealing (great record)
Disadvantages:
- Formaldehyde release may irritate periapical tissues (but minimally)
- Long setting time
- Primarily shrink upon setting → expansion would be preferred as fill in irregularities
What is AH26 Plus and its advantages/disadvantages?
A modified epoxy resin-based sealerwith no formaldehyde production.
Advantages:
- Faster setting time
- Greater biocompatitbility
- Easier to mix and manipulate
Disadvantages:
- More $
What is the purpose of cuspal coverage following endodontic treatment?
- Restore function (ie. mastication) and occlusal stability
- Help prevent fracture as endodontically treated teeth have less natural tooth structure and are weaker → increases longevity of restoration
- Optimal seal of root canal → preventing reinfection
- Aesthetics
NaOCl is a very effective antibacterial agent - why do we need to instrument the root canal system?
- Instrumentation aids in mechanically removing debris and microorganisms from the root canal system
- Shaping: Necessary for shaping the walls of the root canal to facilitate the cleaning and obturation of the canals
- Patency: to create a clear pathway from orifice of the canal at coronal part to apical part
- Patency produces better healing of chronic lesions and improves deliver of irrigants into the apical third
Gp does not seal - sealer provides the seal. Why do we use GP?
- Functions as the material that provides the bulk of the filling to create a dense fill and is able to adapt well to the canal to ensure proper entombment of any bacteria/microorganisms
- Elastic
- Biocompatible
- Retrievable
- Can be thermally or chemically softened to fill irregularities
What is torsional stress?
“bind and break” - the tip of the instrument binds tightly inside the canal but the coronal portion continues to turn. When force > metal strength = fracture
Cyclic (flexural) fracture
“bend and break” - occurs due to repetitive flexing at one point. Instruments can break suddenly without distortion.
What factors can influence the likelihood of a torsional fracture?
- Smaller diameter instruments at greater risk (due to small cross-sectional diameter) → hand files
- Increased risk when there is excessive apical pressure placed on the instrument
How can you minimize the risk of torsional fracture?
- Using gentle apical pressure
- Using a torque control motor
- Avoid excessive engagement along a long length of instrument (crown-down approach is best)
- Irrigate canal (reduce friction).
- Remove instrument after 3 cutting cycles to clean debris off flutes
- Always check if the instrument appears “unwinding” before each insertion. If it does, it is going to break so stop using it
What factors can influence the likelihood of a cyclic (flexural) fracture?
- Larger taper instruments are at higher risk → more bending at the edges of the instrument (greater compressive and tensile forces) → rotary instruments
- If root exhibits more curvature or sharper curve, at greater risk of cyclic fracture
