Y3 L7 NiTi instrumentation and instrument failure Flashcards
Compare NiTi rotary files to stainless steel hand files.
- Hand files have good tactile feedback
- Hand files are more time consuming to use and not as flexible as NiTi, more difficult to fit into the shape of distorted canals
- Engine driven files are faster, easier, more effective, more reproducible and predictable
Describe the main characteristics of NiTi instruments.
- Nickel titanium alloy, approx. 50:50 ratio
- Variety of trade names e.g. M-Wire, CM-Wire, Rphase
- At approx. body temperature, the files become quite elastic and can be deformed multiple times
- Super-elasticity, stress induces instrument to change phase from austenite to martensite, in martensite phase the material is softer and easier to deform
- Shape memory
- Expensive and difficult to manufacture
What types of endodontic NiTi files are there?
- Rotary e.g. ProTaper gold
- Reciprocating e.g. Waveone, Reciproc
- Self-adjusting files, new file type, lattice shape
Describe the ProTaper gold file design.
- Helical flutes around the instrument
- Areas between the flutes are where the cut dentine ends up
- Distance between flutes and angles changes between sizes
- Active blade
- Non-cutting tip
- Taper varies from tip to end of file (whereas hand files have constant taper)
Why is the diameter of the core of the file important?
- The smaller the core = more flexible
What are the advantages of NiTi instruments?
- Uncomplicated system, simple sequence to follow, few instruments required to complete the preparation
- Efficient, rapid removal of dentine, small number of instrument changes required
- Simple technique that is easy to teach and learn, inexperienced operators can produce decent canal shapes
- Fewer problems with instrument manipulation
- Better working time, fewer file changes
- Less likely to block canals
What are the disadvantages of NiTi instruments?
- Requires a glide path, so still requires hand files to begin with to create a loose and open pathway down the canal
- Risk of fracture if hand files not used prior to rotary instruments
- Large instrumers may pose a risk of straightening curved canals and damaging the tip
- More expensive than hand files
- Unable to pre-bend
How do you ensure patency when using files?
Regular irrigation and recapitulation.
Want to mnimise amounts of extruded debris.
What procedural erros might occur with NiTi instruments?
- Blockage
- Ledge
- Strip perforation
- Zip/apical transportation
What is a blockage?
- If we don’t thoroughly irrigate, recapitulate and check patency it can lead to a blockage at the end of the canal
- Dentine packs at the bottom, end up with gradually shortening working length
- If this occurs, use small files ISO06 and 08 under copious irrigation, and gradually work through the blockage
What is a ledge?
- Occurs with larger file sizes which don’t like to bend, results from excessive apical force or repeated insertion of the same file to a fixed level in a canal
- Creates a false path where the instrument can’t progress further
- To manage this, you have to bypass the ledge with small instruments, pre-curve the hand files and pass it back down the true canal path in an up and down motion, progressively increase file size
What is a strip perforation?
- Excessive canal preparation resulting in overpreparation, often on the inner wall of a curved canal
- Most common in the mesial root of a lower molar on the distal wall
- Prevent this by having excellent straight-line access, limit the enlargement of particular canal walls (know the anatomy of the tooth), use magnification
How is a strip perforation managed?
What is zipping/apical transportation?
Removal of canal wall structure on the outside curve in the apical half of the canal due to the tendency of files to restore themselves to their original linear shape during canal preparation.
This may lead to ledge formation and possible perforation.
- Result of using large diameter files constantly in the same position, resulting in the apical constriction being transported to the outer aspect of the curve
- Destruction of apical constriction and the creation of a large canal exit
- When dealing with a curved canal, gradually work your way up from small flexible files to larger ones, avoid size 30 and up- higher risk of ledge formation
- Happens with large instruments with sharp cutting tips
How should you manage a canal with sharp curvature?
- May need to use hand files instead of NiTi as they can be pre-curved and follow the curvature better
- Use pre-curved stainless steel hand files
- NiTi hand files instead of motor driven NiTi files, more tactile feedback
- Use files with less taper as they are more flexible
- Correct access cavity and glide path management are essential, best possible straight-line access
Describe flexural (cyclic) fatigue.
- Fatigue is the process of permanent structural change occuring in a material subject to fluctuating stresses and strains at certain points
- Repeated compression on one side, tension on the other
- If a file is constantly bent back and forth it will fracture
- The smaller the radius of a curve and the greater the angle = higher risk of fracture
Describe torsional failure.
- Aka shear fracture
- Normally occurs in the end section of the file, part of the file gets caught, if the motor continues to spin the file reaches it elastic limit and the tip fractures
- Instrument in contact with canal wall
How can file fracture be prevented?
- Can be prevented/reduced by making sure you have a good glide path prepared using hand instruments
- Glide path allows clinician to understand and appreciate the anatomy of the canal and develop an image in their head of the canal system
- Allows better access and view
- Files ae single use only
- Limit contact area of instruments against canal wall
- Crown down technique
- Use light pressure with instruments
- Keep instruments moving
- Clean instruments regularly in sponge
What are the management option for a fracture instrument?
Tell supervisor.
- Attempt removal of file piece, can use small forceps to retrieve, or specialist small ultrasonic tip to create channel around the file
- Bypass with small file and incorporate into the root filling
- Prepare and fill the root canal coronally to the level of the fractured instrument and then monitor the tooth (most common option)
