Written by : Dr. Urusa I Inamdar

Diagnostic radiograph of tooth used to estimate the working length by measuring the tooth from a stable occlusal reference point till radiographic apex

Subtract atleast 1 mm from this length as minor constriction is present short of the anatomic apex and compensation for radiographic image distortion.

This measurement is transferred to a diagnostic instrument with a silicon stop then placed in the root canal and working length radiograph is taken.

Now measure the difference between the end of the instrument and radiographic apex of the root , on the radiograph.

Tip of the instrument ends 0.5 mm – 1 mm from the radiographic root apex – working length established .

• Short of the radiographic apex by more than 1.0 mm – then add this value to the earlier estimated length and adjust the stopper on diagnostic instrument accordingly.
• Beyond the radiographic apex – reduce this value from the earlier estimated length and adjust the stopper on diagnostic instrument.

Retake the working length radiograph .

Weine’s modification:

• If periapical bone resorption is evident in a radiograph , the working length should be reduced 1.5 mm short of the radiographic apex as the apical constriction would have been destroyed by the resorption .
• If apical root resorption is seen , the working length is reduced to 2 mm short of the radiographic apex , in such an event , an apical stop is created short of the radiographic apex to prevent overinstrumentation and subsequent overfilling of the root canal .

https://youtu.be/fcKelPcZzds

Reference:

• Grossman’s Endodontic Practice (13th edition)
• Dental notes
• Youtube.com

Written by : Dr. Urusa I Inamdar

Krasner and Rankow’s Laws of Access Opening

• Law of centrality : The floor of the pulp chamber is always located in the center of the tooth at the level of the CEJ .
• Law of concentricity : The walls of the pulp chamber are always concentric to the external surface of the tooth at the level of the CEJ .
• Law of the CEJ : The distance from the external surface of the clinical crown to the wall of the pulp chamber is the same throughout the circumference of the tooth at the level of CEJ .
• Law of symmetry 1 : Except for maxillary molars , the orifices of the canals are equidistant from a line drawn in a mesiodistal direction through the pulp chamber floor .
• Law of symmetry 2 : Except for maxillary molars , the orifices of the canals lie on a line perpendicular to a line drawn in a mesiodistal direction across the center of the floor of the pulp chamber .
• Law of color change : The color of the pulp chamber floor is always darker than the walls .
• Law of orifices location 1 : The orifices of the root canals are always located at the junction of the walls and the floor .
• Law of orifices location 2 : The orifices of the root canals are located at angles in the floor – wall junction .
• Law of orifices location 3 : The orifices of the root canals are located at the terminus of the root developmental fusion lines .

References:

• Dental notes
• Grossman’s Endodontic Practice (13th edition)
• Google search

Written by : Dr. Urusa I Inamdar

ISTHMUS:

Ribbon shaped or thin connecting structure between two root canals.

Kim et al. have classified the isthmus into following categories:

• Type I : Faint communication between two canals.
• Type II : Complete isthmus with a definite connection between two canals.
• Type III : A complete but very short isthmus between two canals.
• Type IV : Complete or incomplete isthmus between three or more canals.
• Type V : Two or three canal openings without visible connections.

Apical Foramen:

In young , incompletely developed teeth , the apical foramen is funnel shaped , with the wider portion extending outward . The mouth of the funnel is filled with periodontal tissue , which is later replaced by dentin and cementum.

As the root develops , the apical foramen becomes narrower .

It is not necessary to shape , clean , or fill root canals to their anatomic apices , but rather to the cementodentinal junction , which usually lies within the canal just short of the apex .

The apical foramen is not always the most constricted portion of the root canal. Constrictions can and do occur before the extremity of the root ks reached. Apical constrictions are found 0.5-1.0 mm away from the root apex.

The apical foramen is not always located in the centre of the root apex . It may exit on the mesial , distal , labial or lingual surface of the root , usually slightly eccentrically.

In few cases , the apical foramen has been found as much as 2-3 mm away from the anatomic apex.

The root canal obturation should end approximately 0.5-1.0 mm short of the anatomic root apex .

Lateral canals and Accessory foramina:

The periodontal vessels curve around the root apex of a developing tooth and often become entrapped in Hertwig’s epithelial root sheath , resulting in the formation of lateral canals and accesory foramina during calcification .This phenomenon frequently occurs in the apical third of the root .

Lateral canals may also occur in the area of bifurcation or trifurcation of multirooted teeth.

With increasing age , the accesory foramina diminish in number because of calcification of their contained soft tissue.

Reference:

• Dental notes
• Grossman’s Endodontic Practice

Written by : Dr. Urusa I Inamdar

It is the portion of the pulp cavity from the canal orifice to the apical foramen.

It is divided into 3 sections :

• Coronal
• Middle
• Apical

1. Accessory canals or lateral canals : lateral branching of the main root canal generally occurring in the apical third or furcation area of a root.
2. Lateral canal : accessory canal that branches to the lateral surface of the root and may be visible on a radiograph.
3. Apical foramen : aperture at or near the apex of a root through which the blood vessels and nerves of the pulp enter or leave the pulp cavity.
4. Accessory foramina : openings of the accessory and lateral canals in the root surface.

A straight root canal extending the entire length of the root is uncommon. Either a constriction is present before the apex is reached or , as is often the case , a curvature is present.

The curvature may be :

• A straight canal extending with minimal apical curvature.
• A gradual curvature of the canal with a straight apical ending.
• A gradual curvature of the entire canal.
• A sharp curvature of the canal near the apex.

A curvature of about 20° in a narrow root canal may be difficult or even impossible to negotiate with endodontic instruments, whereas a curvature of even 30° may be negotiated if the root canal is wide.

Success in negotiating a narrow , curved canal depends on following :

• Degree of curvature.
• Size and constriction of the root canal.
• Size and flexibility of the endodontic instrument blade.
• Skill of the operator.

The various classification proposed are as follows :

• Vertucci’s Classification:

1. Type I : Single canal extends from the pulp chamber to the apex (1)
2. Type II : Two separate canals leave the pulp chamber and join short of the apex to form one canal (2-1)
3. Type III : One canal leaves the pulp chamber and divides into two in the root , the two then merge to exit as one canal (1-2-1)
4. Type IV : Two separate distinct canals extend from the pulp chamber to the apex (2)
5. Type V : One canal leaves the pulp chamber and divides short of the apex into two separate distinct canals with separate apical foramina (1-2)
6. Type VI : Two separate canals leaves the pulp chamber , merge in the body of the root , and redivide short of the apex to exit as two distinct canals (2-1-2)
7. Type VII : One canal leaves the pulp chamber, divides and then rejoins in the body of the root , and finally redivides into two distinct canals short of the apex (1-2-1-2)
8. Type VIII : Three separate distinct canals extend from the pulp chamber to the apex (3)

• Weine’s classification :

1. Type I : Single canal from pulp chamber to apex
2. Type II : Two canals leaving from the chamber and merging to form a single canal short of the apex
3. Type III : Two separate and distinct canals from chamber to apex
4. Type IV : One canal leaving the chamber and dividing into two separate and distinct canals

• Classification based on canal cross – section:

1. Round (circular)
2. Oval
3. Long oval
4. Flattened (flat/ribbon)
5. Irregular

References:

• Dental notes
• Grossman’s Endodontic Practice (13th edition)