Canal preparation II Flashcards
It is essential that canal preparation does ___________ within the root structure.
NOT transport canal
Effects of canal curvature
- Increased frictional resistance
- Increased compressive forces
- Increased torsional stress
Ability of K-file to follow canal curvature is determined by:
- Flexibility
- Tip design
- Instrumentation technique
List file properties for canal preparation
- Rotating flexible files under compression cause them to bend in direction of least resistance (i.e. natural canal curvature)
- Rotating a file that’s too stiff will cause it to fracture in root canal
Describe balanced force technique
- Rotation of flexible, straight files to prepare curved root canals: can only use K-files, not Hedstrom files
What is wet-field instrumentation
Everything must be wet with irrigant
Describe irrigation role
- Tissues solvent
- Suspends debris particles (prevents formation of debris sludge)
- Anti-bacterial activity
- Elimination of smear layer
- Facilitates shaping of canal: chelating effect, lubricant effect
Effectiveness of irrigation depends on:
- Volume of irigant
- Duration of contact (there are different irrigant for different purposes: e.g. disinfected and chelating agents, don’t alternate between agents)
- Number of solution exchanges: dentine releases a buffer; irrigant only active for couple of minutes in canal
List four common irrigants
- Sodium hypochlorite (NaOCl)
- chlorohexidine (CHX)
- Ethylene diamine tetra-acetic acid (EDTA)
- RC Prep
Describe sodium hypochlorite
Primary irrigant
- Dissolves vital and necrotic tissue
- alkaline irrigant - pH 11-12
- Anti-bacterial activity - releases chlorine gas to produce hypochlorous acid: superior anti-bacterial activity to other intra-canal irrigant
- As low as 1.0% NaOCl was effective at removing pulpal remnants and predentine from walls. Higher concentrations (5.25%) showed better anti-bacterial properties (i.e. penetrated deeper into dentine tubules)
- e.g. Miltons solution
Describe chlorohexidine (CHX)
- Cannot dissolve necrotic tissue
- Anti-fungal
- Can NOT use with NaOCl (forms toxic precipitate)
- Rarely used today
Describe EDTA (ethylene diamine tetra-acetic acid)
- Chelating agent -> removes calcium ions to demineralized dentine
- Removes smear layer
- Usually combined with ammonium compound (e.g. centrimide)
- Centrimide provides a lubricating effect by reducing surface tension
Describe RC Prep
- Viscous chelating agent
- Holds debris in suspension
- Use for lubrication
- Contains EDTA, peroxide and lubricant
Describe irrigation sequence
- EDTA if canal calcified
- NaOCl to remove pulp tissue and disinfect canal
- EDTA periodically to remove accumulated smear layer (do NOT alternate NaOCl and EDTA)
What is effective irrigant use?
- Employ crown-down technique
- Saturate canal with NaOCl
- EDTA used to only to access and remove smear layer
- Final irrigant with NaOCl or CHX (after final rinse with EDTA)
- NEVER irrigate with irrigating needle tip under pressure
Anti-curvature filing
Focus the filing on towards the area with more tooth bulk (away from furcation area)
Master Apical File size is determined by
- Degree of canal curvature
- Initial size and patency of the canal
- Path of instrument insertion
- Bulk of dentine which forms apical rest
Choosing master apical file size
In straight canals, use file size three sizes larger than first file size that binds, assuming the dentine bulk at the root apex is NOT compromised
Checking canal preparation
- Check smoothness/patency with file size one below master apical file
- Check matrix resistance form (i.e. apical seat) with file size one larger than master apical file
- check flaring -> must be able to place spreader within 3 mm of working length
Apical matrix (apical seat) establishes
resistance form that can hold dense apical filing
Apical matrix (apical seat) reduces
Reduces potential to extrude canal filling material beyond apical foramen.
Check flaring with?
Master Gutta-Percha point in the finger spreader should reach within 3mm of working length.
This is needed to ensure proper obturation of apical region.
Most significant procedural problem
Transporting root canal in curved roots
