5- cleaning and shaping canals

What is the main goal and 2 objectives of clinical endodontics?

Prevent and treat microbial contamination of pulp and root canal

To cure periradicular periodontitis

Preserve natural teeth for long term function and aesthetics

What is the success rates of orthography root canal treatment

95% in irreversible pulpitis

85% in infected, necrotic pulp

What are causes of pulpal pathosis?

Microorganisms breaching the dental hard tissue barrier, common in caries

What are the 4 objectives in cleaning and shaping?

Remove infected soft and hard tissue

Disinfecting irritants access apical canal space

Can deliver medicaments and subsequent obturation

Retain integrity of radicular structures

What is the mechanical objective of root canal treatment?

ensure that all root canal surfaces are properly cleaned and shaped

Irrigants help clean areas that mechanical instruments cannot reach

What are 3 potential challenges in mechanical preparation and what do they do?

Deviations- instruments stray from natural canal path

Zipping- over enlargement of canal near apex

Perforations- accidental creation of hole in the root

These leave parts of canal inaccessible for disinfection

Why do we preserve radicular dentin and what do we need to ensure it?

Prevents weakening of root structures and fractures

Need to keep 0.3mm of dentin thickness to avoid perforations

Need proper access cavity prep and coronal third enlargement

What is the Schiller’s tapering principle?

Advocates a uniform continuous taper to facilitate obturation- should maintain og shape and guided by curvature of root canal

The canal shape after prep also influences antimicrobial efficacy

How do you achieve effective irrigation?

Dispense fluid with syringe and needle- passive irrigation reaches 1mm beyond needle tip

Larger apical canals and flexible needles- deeper penetration and better debridement

Always irrigate between files

Intermittent agitation of canal content to prevent debris forming

Better- open ended needles

What are characteristics of k type instruments?(made of, use, type, motion)

Stainless steel

Use to penetrate and enlarge root canals

2 types- k- endo, h- reendo (re treatment)

Has reaming motion- continuous rotations- less canal transportation or filing motion- inserted and withdrawn- higher risk of transportation

Can be precurved

How is the precurving technique achieved?

Overbending k files

Be careful to avoid xs strain

Can cause permanent deformation- flutes may be too tightly wound or open so can’t be used as it may fracture

What are 4 uses of k files?

Conductometry- determining working length

Create glide path

Manual shaping techniques- step back or crown down

Patency

How is coronal third enlargement conducted?

Initially small gg drills then bigger rotary instrument so form bigger coronal canal so file can fit in easier

What and how is the reference point found in conductometry?

Use either 10, 15 or 20 k file

reference point- repeatable landmark on tooth from which the working length is measured

What is a glide path, achieved by and minimises?

smooth and clear route from the coronal orifice (top opening) to apex

Achieved with manual and rotary instruments

Apical pre enlargement minimises biomechanical prep failures like canal transportation and ledge formation at diff levels, reduces pecking motions for working length

What does the size of the master apical file refer to, matches and depends on?

Largest file size used at apical extent

Theoretically matches final gutta percha used to fill the canal

Depends on anatomy of root, calcification of canal, vital or necrotic

What is the importance of MAF?

Effective cleaning and shaping

Prevent perforation and fractures- large size helps with clean and shape but higher risk of fractures

Optimal filling- ensures root canal is filled with gutta percha so good seal to prevent bacteria re entering

How do we determine the size of the master apical file?

Tactile feedback- initial binding/resistance gives idea of size of canal at apex, then increase 2-3 file sizes

Root canal averages- usually 20, 30, 40, posterior and smaller anterior teeth

Use larger files for necrotic teeth- tissue causes walls to be irregular and harder to clean, increase size by 1 or 2 than vital

What is patency?

Canal prep technique where you keep apical portion clear, can pass small file (6-10 k file) through foramen to ensure canal is negotiable

Small k file passively moved through apical constriction 0.5-1mm beyond minor diameter

What is the step back technique?

Gradually widen canal from apex to crown

The smallest file reaches the working length first, and each subsequent file is stopped 1 mm shorter than the previous one

Why is the step back technique used?

Create continuously tapered tunnel and smooth walls

Maintain og canal shape and position of apical foramen

Keep apical opening as small as possible to stop infection

Why do you need a tapered shape in the step back technique?

Remove infected dentin

Irrigation

Obturation (condensation)

How is the step back technique conducted?

Determine working length

Prep apical portion of canal- shape and widen, use files 10, 15, 20, 25 for the glide path

Choose MAF at WL

Enlarge canal by 3 more sizes, each step you remove 1mm of dentin to get taper shape

Movements for prep- watch winding- both ways, reaming- clockwise cutting

What is recapitulation?

MAF is inserted to working length to clear out any debris collecting in apical part

What is different with the crown down technique?

From crown to apex

Don’t use MAF

Use files from largest to smallest- start with 80 till resistance then 70, 60

Don’t apply pressure

What are the 5 objectives of irrigation in endo?

Flush out debris

Lubricate canal

Dissolve tissue

Prevent or dissolve formation of a smear layer during instrumentation

Detach biofilms

What are the criteria for irrigants?

High efficacy and broad antimicrobial activity against anaerobic and facultative microorganisms

Inactive endotoxin

Non toxic when in contact with vital tissues

No anaphylactic reaction

What does the effectiveness of irrigation rely on? (4)

Penetration depth of the needle

Diameter of the root canal

Irrigation pressure, viscosity of the irrigant

Type and orientation of the needle

Advantages vs disadvantages of Sodium Hypochlorite (NaClO)

Cheap, lubricant, whitens, broad spec, inactivates endotoxins

Bad taste and smell, corrosive, very toxic, unstable, reduce adhesion to dentin

How do you increase the effect of NaOCl?

Heat solution before

Increase conc of hypochlorite

More time in canal, more disinfection

Vibration of hypochlorite

Advantages vs disadvantages of Chlorhexidine?

No bad smell or taste, stable, high antimicrobial activity, low toxicity, increase adhesion with dentin

Can’t remove pulp tissue, doesn’t neutralise endotoxins, reacts with other irrigants

What is the advantage of EDTA?

Can remove smear layer with another component