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Masters in General Dental Practice

A.S. McRobert

The Ideal Access Cavity Requirements

Pre-operative Assessment

Straight Line Access

My Approach – Hands On Session 1

Alternative Approach

Anatomical Variation

Pre-existing Restorations

Hand Files, Negotiation and Glide Path Creation

Hand Instrumentation – Hands On Session 2

“ The objective of an access preparation is to create a smooth, straight-line path to the canal system and, ultimately the apex”

Pathways of the Pulp

Cohen & Burns

Must have Convenience form BUT must be done without weakening tooth structure needlessly.

Must walk a fine line.

Always an opportunity for disaster!

Prognosis can plummet within seconds!

Perforations occurring during access are typically difficult to repair.

Inability to locate canals leads to short term failure of treatment – embarrassing!

Enter the pulp chamber with care and suspicion

Good quality PA’s with Holder

Perpendicular and mesially angled views

Assess opening

Check ACJ with Perio probe

Palpate attached gingivae to discover root location and direction

Discuss procedure with patient – eg. Dam

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Canal disappears as it extends apically

Appearance of two periodontal ligaments along one side of root

“Straight-line access allowed the greatest proportion of the root canal wall to be instrumented…”

Mannan et al. IEJ 2001;34:176-83

“…opening the coronal end and straightening the curvature….generates a lesser restoring force (for instruments).. Roane et al. JOE 1985;11:203-11

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Armamentarium

Principles

Execution

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Follow natural depressions of pulpal floor

Canals calcify from crown down

Punch through calcification

Pick at white spots Canal is in centre

of single canalled roots

CT 4

UT 4

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0.5 0.7 0.9 1.1 1.3 1.5

Width (mm)

Allows you to see where the bur is cutting.

Turbine head does not obscure view as much.

Ideal for refining access cavity to match anatomy.

Allows you to see where the bur is cutting.

Turbine head does not obscure view as much.

Ideal for refining access cavity to match anatomy.

Allows you to see where the bur is cutting.

Turbine head does not obscure view as much.

Ideal for refining access cavity to match anatomy.

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Helps eliminate ‘Taper Lock’

Ensures you don’t ‘lose the canal’

Gives room for GG’s to work

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Use on up-stroke

Apply slight lateral pressure

Size 4 then 3 then 2. (2,3,4 if sclerosed)

Slower speeds

Use to blend coronal third of canal into wall of access cavity – create a GLIDE PATH.

Anticurvature instrumentation

Inappropriate use of Gates Gliddens

Coke bottle prep

Only use nos.(1), 2, 3

in the root canal

Done using hand held stainless steel K-Files

Watch wind-pull action

Sizes (10) 15, 20 (25)

Followed by Gates Glidden drills as required

Confirm Straight Line Access and Working Length before canal preparation

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Extracted teeth or Plastic Blocks

Complete access

Locate all canals, scout coronal third

Pre-shape with k-files

GG drills

Refine access and check straight line access

Scout canal with size 08 or 10 stalinless steel K-file. (use EDTA)

Pre-shape to start Glide Path creation 10,15,20.

(GG work and SLA achieved before next stage.)

Determine patency to EWL if possible.

Confirm actual WL with EAL after SLA achieved.

-Beware curves and branches.

-If you hit a stop, precurve file and attempt to proceed, rotate slightly and try again.

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Armamentarium

Principles

Execution

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Equivalent to GG 1 to 4

Use at 500 to 800 rpm.

Text book access cavity designs should be used as a guide only.

Access cavity should be shaped according to the individual internal anatomy of the tooth.

Must be aware of variations in anatomy for individual teeth.

“..classic access drawings are far too mesial.”

Wilcox et al JOE 1989;15:315-318

Ovoid or rounded triangle access palatally.

Needs to approach incisal edge for straight line access.

Danger of perforation labially.

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Narrow Mesio-Distally at ACJ level

May have Ovoid or Hourglass X-section

Easy to perforate

2 canals in 41% or more

Projection of central axis of canal exits at incisal edge or even labially

4’s usually 2 rooted, 5’s usually 1.

May be 3 roots in either.

Width of root at ACJ only 2/3 width of crown.

Mesial concavity on 4’s, easily perf’d.

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P. Lumley

P. Lumley P. Lumley

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Rounded X-section

Usually 1 canal in middle of root.

Straight line access usually to buccal cusp tip.

Occlusal table rarely perpendicular to long axis of root.

Can easilly perf buccally if drilling perpendicular to occlusal plane.

Traditionally triangular but more likely trapezoid.

MB2 canal or fin present in 90%+.

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Variation in distal root

Always treat distal as if two canals

Triangular or Trapezoid access

Crown lingually inclined

MB canal opening may be under cusp tip

Watch for mesial incline if teeth have been extracted

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Radiographic assessment

To replace or not to replace

Full coverage restorations

Pick the correct tools for the job

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S.S. K-Files.

Insert into canal to light resistance.

Apply only light apical pressure.

Watch-wind in fingers 2-3 times.

Sharp pull.

Used for Pre-shaping with size 10,15,20 in coronal and middle thirds of canal as soon as canals are located before GG’s.

After SLA with GG’s

Size 10 K-file (8 if necessary)

EDTA gel

Watch wind down to estimated WL

Confirm with EAL

Watch for taper lock

Curvatures and impediments are the challenge

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Lubricants Initial irrigant Keep debris in suspension Emulsify pulp stump

in vital cases Faster cutting Cleaner canal Less file separation

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Performed after straight line access is achieved and working length established.

Using watch-wind and pull motion.

Try to get 10, 15 and 20 K-files to WL.

Can then use any canal preparation method with ease and safety.

File Manipulation (K-Files)

Watch-wind

Push-Pull

Balanced forces

Reversed balanced force

Canal Preparation technique

Step back

Crown down

As file passes into canal, gently rotate slightly back and forth until resistance met.

Apply slight apical pressure.

Rotate file slightly in one direction and then immediately in the other direction.

Repeat this twice more.

Pull file swiftly out of the canal in anti-curvature direction.

Use with care!!

Small in-out motion, only 1-2mm

Used to open very narrow areas of the canal which were difficult to locate

Move to Watch-Wind as soon as possible

Can ledge canal if not used appropriately

Placement;

Apply inward pressure and rotate clockwise 60°

Cutting;

Apply inward pressure (to match file size) and rotate counterclockwise 120°

Removal;

Withdraw gradually while rotating clockwise

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GT Files – Reverse Balanced Forces

Insertion

Watchwinding until snug Engage 45-90o anti clockwise

Cutting (Apical pressure & clockwise)

Flute loading (Coronal pull & anti clockwise)

Check where debris is when pull intsrument out

Preparation Techniques

Crown Down

Double Flare

Step back

File Manipulation Techniques

Watch Wind

Push-pull

Balanced Forces

Reverse Balanced Forces

After WL is established complete final Glide Path creation

Size 20 k-file to WL

Complete step back preparation with k-files using Watch-Wind

Hand GT or Protaper can be used instead

Objective of glide path creation with straight line access allowing a size 20 K-file to glide smoothly from the occlusal surface down to the working length.

This allows the operator to safely use any of the recognised canal preparation systems to shape the root canal.

Failure to achieve glide path creation in this way will increase the incidence of problems and failure.