Cleaning and Shaping of the Root Canal System

Edit by Hou Tiezhou 02988088507

Objectives of Canal Preparation Start with the end in mind

Objectives of root canal preparation The root canal system must be:  Cleaned of its organic remnants  Shaped to receive a three dimensional filling of the entire root canal space

Objectives of root canal preparation The canal is   Cleansed primarily by irrigation Shaped primarily by instrumentation

Cleansing of the root canal Objectives  Removal of organic debris  Elimination of bacteria

Irrigation An ideal irrigant:  Is nontoxic    Dissolves vital and necrotic tissue Is bactericidal Lubricates the canal  Removes the smear layer

Sodium hypochlorite    Dissolves vital and necrotic tissue Is bactericidal Lubricates the canal

Sodium Hypochlorite Cannot be considered non-toxic!!!

Prolube EDTA and carbamide peroxide in a water soluble base

Prolube    Facilitates placement of file Entraps debris Aids in removal of the smear layer

EDTA   Chelating agent Effectively removes smear layer

Shaping of the root canal   Canal shape – produced by instrumentation Objective is a smooth tapered preparation

Shaping of the root canal

Instruments Instruments differ according to:       Metal Taper Tip design Cross sectional geometry Length of cutting blades Sizing

Nickel titanium

Metals

Stainless steel

Excellen flexibility Conforms to canal curvature Less flexible Straightens and transports canal Plastic deformation Permanent deformation

Metals Stainless steel files demonstrate permanent deformation

Metals Nickel titanium files demonstrate plastic deformation

Taper Definition Increase in diameter per unit length

What is Taper?

D16 D1 0.32 mm diameter increase D16 D1 0.96 mm diameter increase

What is taper?

Taper Taper of instruments in U of M file kit     Stainless steel files – 0.02 taper OS – variable tapers ranging from 0.05 to 0.08

Series 29 rotary Profiles – 0.06 taper NiTi hand files – 0.04 taper

Tip Design    Non-cutting tip Bullet nose (60 degree) tip Smooth transition angle where tip meets flat radial lands

Tip Design   Designed to follow a pilot hole Guides instrument through canal during preparation

Tip Design

Cross-sectional geometry     Three radial lands Each contains bidirectional cutting edges Keep instrument centered in the canal Cutting edges scrape dentin

Cross sectional geometry

Cross sectional geometry • • • •

Self Threading

Cross sectional geometry    Radial lands separated by three u shaped flutes Provide space for accumulation of debris Moves debris out of canal

Length of cutting blade   Traditionally 16 mm Orifice shapers – 10 mm

Sizing of instruments ISO sizes  Number refers to tip diameter in tenths of mm  The tip diameter increases by 0.05 mm from sizes 10 to 60, then by 0.10 mm

Sizing of instruments   % increase in diameter from #10 to #15 file is 50% Difference between #55 and #60 is only 9%

Sizing of instruments Series 29  Progressive 29% increase in tip diameter   Instruments are better spaced More instruments in smaller sizes and fewer large instruments

Crown Down Technique   The coronal portion is prepared before the apical portion Follows medical principle of cleansing before probing a wound

Crown Down Technique

Crown Down Technique    Eliminates constrictions in the coronal region Reduces effect of canal curvature Improves tactile awareness during apical preparation

Crown Down Technique    Allows more effective irrigation Removes majority of tissue and microbes before apical third is approached Reduces change in working length during apical preparation

Crown Down Technique    Coronal third Middle third Apical third Orifice shapers 0.06 taper rotary Profiles 0.04 taper hand Profiles

Clinical Procedure    Estimate working length Parallel radiograph Estimated working length is the distance from the reference point to the radiographic apex

Parallel Radiograph

Clinical Procedure  Establish straight line access to apical third

Clinical Procedure Explore canal patency    Ensure that canal is negotiable to radiographic apex Small file – #10 K-file May need to precurve these SS files

Clinical Procedure   Files used in a push/pull or quarter turn pull motion

Never rotate these files through 360 degrees

Clinical Procedure

Clinical Procedure

Clinical Procedure Estimate canal size    Radiographic appearance Crown/root morphology Standardized tables

Estimation of canal size

Estimation of canal size See Table in manual

Clinical Procedure Actual WL determination Preparation should terminate at  Apical constriction  1 mm short of radiographic apex

Clinical Technique   Actual WL determination Radiograph Apex locator

Clinical Procedure Actual Working Length Determination

Clinical Procedure

Clinical Procedure Apex Locator

Clinical Procedure Crown down cleaning and shaping of canals

Clinical Procedure This technique applies only to teeth ranging from 18 – 23 mm in length   Coronal third measurement is WL minus 8 mm Middle third measurement is WL minus 4 mm  Apical third measurement is WL

Preparation of the coronal third   Coronal third measurement is working length minus 8 mm Prepared using Profile orifice shapers

Preparation of the coronal third   Profile orifice shapers In sequence larger to smaller

Preparation of coronal third   Measure WL minus 8 mm on largest OS Lubricate the canal with Prolube

Preparation of coronal third  Rotate OS at 300 rpm

Note: Orifice shaper should be rotating at 300 rpm before it is placed in the canal

 Advance the OS in 1 mm increments   When resistance is encountered retract OS while still rotating Never force any instrument apically

Preparation of the coronal third   This OS will not extend to WL minus 8 mm Irrigate copiously

Irrigation

Preparation of coronal third     Move to next smallest OS

This will extend further than previous instrument

Repeat the steps described for largest OS Move to next smallest OS Continue this sequence until working length minus 8 mm is reached

Preparation of coronal third    Return to largest OS This will now extend further into the canal than it did previously Repeat this sequence until this (the largest) OS reaches WL minus 8 mm

Preparation of the coronal third    Never force any instrument apically Irrigate after every instrument Use copious amounts of Prolube

Preparation of coronal third

Preparation of middle third   Middle third measurement is WL minus 4 mm Prepared using 0.06 taper Series 29 rotary Profiles in sequence larger to smaller

Preparation of middle third Prepared with 0.06 Series 29 NiTi rotary Profiles

Preparation of middle third    Measure working length minus 4 mm on the largest 0.06 taper series 29 rotary file Set green rubber stop at that length Lubricate the canal with Prolube

Preparation of middle third     Rotate at 300 rpm

File must be rotating at 300 rpm before it is placed in canal

Advance file in 1 mm increments When resistance is encountered retract file while still rotating Copious irrigation with NaOCl

Preparation of middle third

Preparation of the apical third   Prepare to actual working length Use 0.04 taper NiTi hand files in sequence smaller to larger

Preparation of apical third

Preparation of apical third    Measure working length on #15 file Set rubber stop at that length Lubricate the canal with Prolube

Preparation of apical third    Advance size 15 file to working length Rotate file through 360 degrees Irrigate copiously with NaOCl after each file

Preparation of the apical third   Advance size 20 file to working length Continue through sequence, seating each file to working length

Preparation of apical third    The largest file that extends to working length is the Master Apical file (MAF) For large canals – minimum MAF #40 - 50 For small canals – minimum MAF #35 - 40

Master Apical File  Take a radiograph with MAF in place. This confirms: • Length • Placement

Mission accomplished Smooth tapered preparation