Endodontics

Question 1

What do studies show about root fillings which extend beyond the apex?

Answer 1

If they extend beyond the apex or are 2mm short of the apex they are associated with a higher chance of failure.

Question 2

What are the different names for where the root canal filling can end?

Answer 2

• Anatomical apex
• Radiographic apex
• Major apical constriction/foramen
• Minor apical foramen/constriction
• Cemento-dentinal junction

Question 3

What is the anatomical apex?

Answer 3

Anatomical apex is the end of the root as determined from a macro perspective. It is not particularly useful as it doesn’t take into account the microanatomy

Question 4

What is the radiographic apex?

Answer 4

It is similar to the anatomical apex but as determined by radiography. It is inaccurate as the foramen is often located to one side of the radiographic apex. This often varies from 0.3-0.6mm but can be up to 3mm. Deposition of cementum at the apex can cause further discrepancies. Pathology such as external resorption can also change the position of the foramen.

Question 5

What is the major apical constriction?

Answer 5

It is the widest point of the foramen where it exists in the root. It is considered to be entirely within cementum. It is not an ideal point to finish a root filling as it does not produce a natural stop for the filling material.

Question 6

What is the minor apical foramen?

Answer 6

It is the narrowest point of the foramen also known as the apical constriction. The cementum narrows up from the major apical foramen to the minor apical foramen. The location is variable and in some canals it may not even be present. It is usually 0.5-1mm short of the radiographic apex. It is at or close to the point where the cementum fuses with the dentine (CDJ)

Question 7

What is the cemento-dentinal junction?

Answer 7

It is the point where the cementum fuses with the radicular dentine. It is considered to be the point where the root canal system finished and the periodontium begins. It is considered to be the ideal limit of a root canal treatment. However it can only be detected histologically and can be irregular as one side may go up to 3mm higher than the other. Therefore it is not considered a practical landmark to use in endodontics.

Question 8

What landmark should we use to finish the root filling at?

Answer 8

We should use the minor apical constriction which is the narrowest point of the root canal system and forms a good natural barrier. It is a consistent anatomical reference point. It is the most practical landmark. Be aware it can vary in its anatomy.

Question 9

What are the methods for determining working length?

Answer 9

• Tactile feedback from instruments
• The paper point technique
• Radiographic determination of working length
• Electronic apex locator

Question 10

How can tactile feedback be used to determine working length?

Answer 10

It is an essential aspect of endodontic treatment, however even experienced endodontists could only detect the apical constriction in 60% of cases by tactile sensation alone. It is made even more complicated by sclerosis, resorption and anatomical differences. It is not a recommended technique for determining working length.

Question 11

What is the paper point technique?

Answer 11

It is based on the premise that the root canal system of an uninfected tooth is dry whilst the periodontium is wet (hydrated tissue). The wet/dry interface is therefore used as a reference point. Paper points are placed at incrementally shorter lengths until no moisture is detected. It can be useful for teeth with open apices or abnormal apical anatomy. However it is complicated by apical exudate in infected cases and when patency is not achieved. There is no good evidence to support the use of this technique.

Question 12

What is radiographic determination of working length?

Answer 12

It is probably the most commonly used technique for determining working length. It must be undertaken with paralleling technique. It uses the premise that the apical constriction is on average 0.5-1mm short of the radiographic apex. This is inherently flawed however as the apical constriction can be significantly further away resulting in over instrumentation of the apex. It can be difficult to determine due to overlying structures or superimposition of canals. It exposes the patient to ionising radiation.

Question 13

How can electronic apex locators be used to determine working length?

Answer 13

They have become a commonly used method for working length determination. Modern apex locators are very reliable. They can be used in conjunction with other methods of working length determination or if the reading is reliable it can be used as the sole method of working length determination. It uses resistance/impedance of the root canal and PDL.

Question 14

How do electronic apex locators work?

Answer 14

An electrical circuit is formed starting at the apex locator, running through a clip on the file, through the root canal, through the apical constriction, out the PDL and finally through the mucosa and to the clip on the patients lip and back to the apex locator, completing the circuit. The tooth can be thought of as a capacitor. Dentine and cementum are insulators of the current. The PDL, apical constriction and file in the canal are all conductors of electricity. The advancing file in the canal and the PDL will act as conductors in the capacitor. The dentine, cementum (and any associated fluid) will act as the insulator. You deduct 0.5mm from the red line on apex locator.

Question 15

How did first generation apex locators work?

Answer 15

They are resistance based apex locators. The resistance between an endodontic instrument at the apical foramen and an electrode on the oral mucosa is approximately 6.5kw. The apex locators were set up to detect this value. They are accurate when dry but significantly affected by exudate, pulp tissue, haemorrhage or electrolytes. They sometimes resulted in a small electric shock to the patient.

Question 16

How did second generation apex locators work?

Answer 16

They are impedence based apex locators. Theoretically they are more accurate than the solely resistive devices. However, they are still affected by the presence of electrolytes and tended to be highly variable between teeth. They are not accurate enough for reliable clinical use.

Question 17

How did third generation apex locators work?

Answer 17

They use multiple frequencies to determine the distance between an endodontic instrument and the end of a canal. They are usually calibrated to detect the apical constriction but if the apical constriction is abnormal this can result in misreadings. They are often improved in accuracy by the presence of electrolytes e.g. naocl and accuracy is decreased if the canal is dry. They have an accuracy of 83-100%. They can be attached to rotary instruments to give instant readings but this may decrease accuracy.

Question 18

What are fourth generation apex locators?

Answer 18

They use two frequencies to detect the apical constriction but only uses one at a time. This apparently reduces ‘noise’ from using multiple frequencies and therefore negates the need for a filter. The manufacturers claim fourth generation apex locators are therefore more accurate. However studies have failed to show improved accuracy with third and fourth generation apex locators both proving to be equally as reliable.

Question 19

What are the problems with apex locators?

Answer 19

• Metallic restorations will short circuit the apex locator resulting in a mis-reading. Ideally replace metallic restorations prior to treatment. If this is not possible ensure the file does not touch the restoration and that the pulp chamber is not flooded with irrigating solution
• Perforations will trigger an apex response when the file touches the perforation. This prevents an accurate apex locator reading from a perforated canal until the perforation has been repaired. This effect can be advantageous e.g. if you are unsure if a perforation has occurred an apex locator will help confirm this.
• Large lateral canals may cause a mis-reading. This should be relatively easy to detect as the apex locator will give an apex reading too soon.

Question 20

Should the canal be wet or dry to use an electronic apex locator?

Answer 20

There should be no fluid in the pulp chamber so use gentle drying with a 3 in 1 syringe. Modern apex locators work best with a moist canal so use paper points but not until the canal is completely dry.

Question 21

Does it matter what irrigating solution is used when using electronic apex locators?

Answer 21

The different irrigating solutions do not impact significantly on the performance of modern apex locators.

Question 22

What file should be used with an electronic apex locator?

Answer 22

A file should be chosen which will contact the walls of the root canal. A file which is too narrow will be less accurate. The metal which the file is made of e.g. stainless steel and nickel-titanium does not affect the accuracy.

Question 23

How should the apex locator be used to give a reading?

Answer 23

Advance the file until the visual display reads ‘apex’ or ‘0’. The apex locator is most accurate when it is giving an apex or 0 reading and contacting the PDL. Earlier readings such as 0.5 and 1 do not indicate the distance in mm from the apex. Therefore the best approach is to advance the file until it gives an apex or 0 reading then manually subtract 0,5mm from the length. This will ensure the file is within the root canal but still close to the PDL. Commercial apex locators are only calibrated to the apex. The working length is calculated by subtracting 0.5mm from the apex locator measurement.
Ensure the batteries are charges as low voltages cause electronic errors.

Question 24

Why should you recheck the working length?

Answer 24

You should do this with the apex locator after the coronal 2/3 has been shaped. The working length will decrease from the initial reading due to a decrease in the curvature of the canal. This must be checked prior to shaping the apical terminus.

Question 25

What are the signs of unstable readings and what should you do?

Answer 25

Apex readings should only be accepted when the scale bar is stable and moves in sympathy with movements of the file. If the visual scale bar does the following things, the apex reading should not be accepted:
- Flashes intermittently
- Moves erratically
- Displays no bars
Unstable readings can be due to a number of reasons including a faulty machine, obliterated anatomy, excessive exudate etc. If this occurs either use other methods of determining working length or dress the canal and re-check on subsequent visits.