Quiz 2- Principles of Endodontic Access + Working Length and Apical Stop

What are the 4 goals of access?

1. Locate all canals

2. Straight-line access to canals

3. Removal of chamber roof and coronal pulp tissue

4. Conservation of tooth structure

What is “straight line” access?

Unimpeded access of the instruments in the canals to the apical one third of the canal or the first curve

What effect does opening the orifice in a straight line access have on the file?

Less stress on file

What dictates the shape of access?

Pulp chamber anatomy

Your access should be as small as possible, but

As large as necessary

What are the consequences of having an access that is too small?

1. Difficulty locating canals

2. Missed canals

3. Difficulty achieving straight-line access

What are the consequences of having an access that is too big?

Unnecessary removal of tooth structure

Why is it necessary to remove pulp material from the pulp horns/ crowns?

To prevent coronal discoloration

What is outline form?

The recommended shape of the access: it should be a projection of internal tooth anatomy onto external root structure

What may change over time with calcification of the chamber?

Outline form

What is convenience form?

Modification of ideal outline form to facilitate instrument placement and manipulation

Why it is pertinent to remove caries prior to access?

1. Prevent contamination of root canal system

2. Access restorability

3. Provide sound tooth structure for temporization / restoration

The toilet of the cavity should be kept clean. How can you prevent debris from blocking the canal?

By frequently irrigating

The first step to opening the access is to study the

Pre-operative radiographs and determine the depth of access from it

When opening the access, you may/may not remove restorations, but it is important to

Remove all caries

What bur is used for access opening?

701 in high-speed handpiece (may use slow speed when closer to chamber)

What should you use to detect the chamber / canal oriface?

DG- 16 endo explorer

Tactile sensation can help during access because you can

Re-evaluate as needed

In calcified cases, for access opening, it may be helpful to

Exposure the radiograph if needed

Which tooth has 1 canal?

Maxillary anterior teeth

Which tooth has a 30% chance of having 2 canals?

Mandibular canine

30% of mandibular canines may have 2 canals, of the 30%, what percent have 2 canals that join?

20%

30% of mandibular canines may have 2 canals, of the 30%, what percent have 2 canals that separate?

10%

What is the root shape of central incisors?

Usually straight

What is the root shape of lateral incisors?

Usually apical curvature to distal or palatal

What is the root shape of canines?

Long root, usually apical curvature

Why might it be difficult to radiographically interpret canine apices?

Due to a small root tip

What is the canal shape of a maxillary central incisor?

Usually round

What is the canal shape of a maxillary lateral incisor?

Usually oval / round

What is the anatomical variation in this lateral incisor?

Lingual developmental or palato-radicular groove

What is the anatomical variation in this lateral incisor?

Dens invaginatus

What is the anatomical variation in this lateral incisor?

Talon cusp

When creating your access in maxillary central incisors, what should you observe in your radiograph?

Anatomy, shape, and location of canal

The access outline is determined by the “incisal limit.” What does this mean?

The use of the incisal edge as the coronal reference point for measuring working length and initiating access cavities, particularly for mandibular incisors

Your access outline should be triangular in shape and 3mm×2mm in size. Why do you need to make an outline?

To have a strategically designed cavity prep designed to provide straight-line access to root canals

Which burs are slow speed latch? What do they do?

GG #4, #3, #2: help with smoothing the opening

This bur is used to cut the cavo-surface outline

#701

This bur is used to extend the access prep into the pulp chamber down the long axis of the tooth

Sx #2

After extending the access prep into the pulp chamber. Use this instrument to explore the pulp chamber and check for pulp horns

G2 explorer

If you need to remove a lingual shoulder, you can use this instrument to smooth out the access opening

GG 2,3,4 and Hedstrom File

Biomechanical instrumentation refers to

Instrumentation and access + canal enlargement

Chemomechanical instrumentation refers to

Disinfection of canal and access

What you take out of the tooth is more important than

What you put in

What are the goals of biomechanical and chemomechanical preparation?

1. Reduce # of viable bacteria

2. Remove all tissues and debris

3. Avoid irritation of PA tissues

4. Keep instruments and irrigants inside tooth

Correct working length is critical to meet the goals of biomechanical and chemomechanic preparation. What is working length?

From the coronal to the apical extent of the root canal system

This material is used to disinfect the canal system (kill microbes)

Sodium hypochlorite (NaOCl) - bleach

This material is used to remove the smear layer of dential debris that accumulate on the canal walls

17% EDTA (ethylenediaminetetraacetic acid)

For the purposes of our lab course, what will you be using instead of bleach?

Water in 10mL with side vented needles

What is a precaution to take with bleach when using it in clinic?

It stains

Apical patency is technique where

The apical portion of the canal is maintained free of debris by recapitulation (using smaller endo files to remove debris) with a small file through the apical foramen

Working length is the distance from

A coronal reference point tot he point at which canal preparation and obturation should terminate

This is the largest file used to the full working length of the completely preparaed root canal

Master apical file (MAF)

When should the the apex terminate?

0.5-1mm from radiographic apex

For the working length, if there is difficulty viewing the file, you can use

A 15K file or larger

_______ thickens with age. This is why apical constriction occurs within this area

Dentin; dentinal area

To determine working length, this helps clinically along with radiographic WL

Combination of apex locator measurements + radiographic WL

As you reach apical constriction, use your tactile sensation for working length determination

“Feel” an increase in resistance

What is an advantage of using tactile sensation for working length determination?

1. Saves time

2. No radiation exposure

What is a disadvantage of using tactile sensation for working length determination?

Not always accurate- this is very important!

How can you use a paper point to determine working length?

Moisture or blood present on apical part of paper point tells you where the canal ends

What is an advantage of using paper points for working length determination?

Useful in teeth with open apices or as an adjunct to other methods

What is a disadvantage of using paper points for working length determination?

Not always accurate

Working length is important. These can affect treatment outcome

Apical termination of instrumentation and obturation

Obturation within 0-2mm of apical termination has a ____ % success rate

94%!

Obturation within >2 mm of apical termination has a ____ % success rate

68%

Obturation past the apex has a ____ % success rate

76%

For every 1mm loss in working length, there is ______ % decrease in success

14%

Root canals are ____ % more successful when you fill up to (but not past!) the apex

29%

Your apical stop size is

The size of the smallest K-file that cannot be pushed (without force) beyond working length

This is the apical stop size BEFORE instrumentation

Initial apical stop size

This is the apical stop size AFTER instrumentation

Final apical stop size

What are some reasons why the initial and final apical stop size might differ?

1. Overinstrumentation

2. Debris packed apically

3. Inaccurate assessment

The initial and final apical stop size must be physically checked using tactile sensation. What happens if you fail to check?

Common cause of overfilling

First to bind is

The smallest file that feels resistance when twisting at working length

Often the first to bind is the same size as

The initial apical stop size

The first file to bind will determine the “ideal” final apical size used to

Enlarge the apex of canal to adequately debride the canal walls

The final apical size will be 3 sizes larger than the first file to bind when handfiling.

If your first file to bind is #30K file, 3 sizes larger would be size #35 (#25, #30, #35)

What are the steps for maintaining the apical stop?

1. Initial stop (1st to bind)

2. Instrumented MAF

3. Stop maintained

What is a consideration if you have a calcified canal?

You may need to start with a smaller K file (size 15)

How can you create a repeatable reference?

Make sure the reference point is touching the stopper (incisal edge or cusp)