Exploration for the canal orifice:-

Anatomic consideration and terminology:-

Working length: -the distance from a coronal reference point to the point of which canal preparation and obturation shouldterminate, the ideal apical reference point in the canal, the "apical stop",

Anatomic apex: - is the tip or the end of the root determined morphologically,

radiographic apex is the tip or end of the root determined radiographically.

Anatomic consideration and terminology:-

Apical foramen: - is the main apical opening of the root canal.

Dentino-cemental junction (DCJ).It is the junction between the cementum and dentin in the apical constriction of the tooth. It is the most apical point

of the working length. The root canal preparation should be limited to this junction and form a constriction to

prevent over instrumentation and over obturation.

Objective of the working lengthObjective of the working length

To establish the length of the tooth at which the canal preparation andsubsequent obturation are to be completed.To establish the length of the tooth at which the canal preparation andsubsequent obturation are to be completed.

The apical end of the root canal is the CDJ, which is usually 0.5-1mm short of theradiographic apex.The apical end of the root canal is the CDJ, which is usually 0.5-1mm short of theradiographic apex.

Sometimes the apical foramen is laterally positioned so it would be more than 1 mm from the radiographicapex.Sometimes the apical foramen is laterally positioned so it would be more than 1 mm from the radiographicapex.

Reference point: It is the site on the incisal edge or occlusal surface from which

measurements are made. Usually it’s the highest point on the incisal edge in anterior teeth & the

tip of the cusp in posterior teeth.

It should be:

1) stable,

2) easily visualized during preparation

3) will not change during or between appointment.

Ideal method:-o To achieve the highest degree of accuracy in working lengthdetermination, combination of several methods should be used.

o The most common methods are radiographic methods,digital tactile sense, and electronic methods.

Methods of determining working length:-

1) Good, undistorted, preoperative radiographs showing the totallength and all roots of the involved tooth.

2) Adequate coronal access to all canals.

3) An endodontic millimeter ruler.

4) Working knowledge of the average length of all teeth.

5) A definite, repeatable plane of reference to an anatomic landmarkon the tooth, a fact that should be noted on the patient's record.

Procedure of Working Length Determination

1 mm

• In this case,estimatedworking lengthis equal to thefinal workinglength.

• EWL = FWL

-1 mm +1 mm

If the radiograph shows that the discrepancy is more than 2mm, thena new radiograph should be taken after computing for the workinglength

Buccal Object Rule (Cone Shift)

Digital Tactile Sense:-

An experienced clinician may detect an increase in resistance as the fileapproaches the apical 2 to 3mm. This detection is by tactile sense. In thisregion, the canal frequently constricts before exiting the root.

An experienced clinician may detect an increase in resistance as the fileapproaches the apical 2 to 3mm. This detection is by tactile sense. In thisregion, the canal frequently constricts before exiting the root.

Determination of Working Length by Electronics:-Determination of Working Length by Electronics:-

"Apex Locator" is commonly used andhas become accepted terminology,"Apex Locator" is commonly used andhas become accepted terminology,

These devices all attempt to locate the apical

constriction, the cementodentinal junction or the apical

foramen.

These devices all attempt to locate the apical

constriction, the cementodentinal junction or the apical

foramen.

All apex locators function by using the human body to complete an electrical circuit.All apex locators function by using the human body to complete an electrical circuit.