Introduction

• Access is the first and the most important phase of root canal

treatment. A well designed access preparation is essential for

good endodontic success.

• A proper coronal access forms the

foundation of pyramid of endodontic

treatment. Any improperly prepared

access cavity can impair the

instrumentation, disinfection and

therefore obturation resulting in poor

prognosis of the treatment.

Instruments for access cavity preparation

• The basic principles of access opening was established by G.V. Black, as

following:

1. Outline form: The outline form of the endodontic cavity must be

correctly shaped and positioned to establish complete access for

instrumentation, from cavity margin to apical foramen. To achieve

optimal preparation, three factors of internal anatomy must be

considered:

Principles of access opening

A. Pulp chamber size: In young patients, these preparations must be more

extensive than in older patients, in whom the pulp has receded and the

pulp chamber is smaller in all three dimensions.

B. Pulp chamber shape: The finished outline form

should accurately reflect the shape of the pulp

chamber. For example, the floor of the pulp chamber in

a molar tooth is usually triangular in shape, owing to

the triangular position of the orifices of the canals.

C. Number, Position, and Curvature of root canals: To prepare each canal

efficiently without interference, the cavity walls often have to be extended

to allow an unstrained instrument approach to the apical foramen.

Variations from the normal number of canals:-

1. Maxillary Molars: A second separate canal in the mesiobuccal root.

2. Mandibular molars: A second canal often is found in the distal root.

2. Convenience form: In endodontic therapy, convenience form

makes the preparation and filling of the root canals more convenient

and accurate. The benefits of it are:

A. Unobstructed access to the canal orifice:

• Enough tooth structure must be removed to allow

instruments to be placed easily into the orifice of

each canal without interference from overhanging

walls.

• The clinician must be able to see each orifice and

easily reach it with the instrument points.

• Failure to observe this principle not only endangers

the successful outcome of the case but also adds

materially to the duration of treatment.

B. Extension to accommodate filling techniques:

• It's often necessary to expand the outline form to make certain filling

techniques more convenient or practical. If a softened gutta-percha technique is

used for filling, where in rather rigid pluggers are used in a vertical thrust, then

the outline form may have to be widely extended to accommodate these heavier

instruments.

C. Direct access to the apical foramen:

• Enough tooth structure must be removed to allow the endodontic instruments

freedom within the coronal cavity so they can extend down the canal in an

unstrained position. This is especially true when the canal is severely curved or

leaves the chamber at an obtuse angle.

4. Debridement of the cavity:

• All of the caries, debris, and necrotic material must be removed from the

chamber before the radicular preparation is begun. If the calcified or

metallic debris is left in the chamber and carried into the canal, it may act

as an obstruction during canal enlargement.

• Soft debris carried from the chamber might increase the bacterial

population in the canal. Coronal debris may also stain the crown,

particularly in anterior teeth.

• Round burs are most helpful in cavity debridement. The long-blade

endodontic spoon excavator is ideal for debris removal. Irrigation with

sodium hypochlorite is also an excellent measure for cleaning the chamber

and canals of persistent debris.

3. Removal of the remaining carious dentin and defective restorations: The

advantages of its removal are:

A. To eliminate mechanically as many bacteria as possible from the interior

of the tooth.

B. To eliminate the discolored tooth structure, that may ultimately lead to

staining of the crown.

Guidelines for access opening

Laws for determination number and location of orifices

1. Centrality: Floor of pulp

chamber is always located in

the center of tooth at the level

of CEJ junction.

2. Concentricity: Walls of pulp chamber are

always concentric to external surface of

tooth at the level of CEJ, that is, the

external root surface anatomy reflects the

internal pulp chamber anatomy.

• The authors proposed six guidelines (laws) of pulp chamber anatomy to

help clinicians to determine the number and location of orifices on the

chamber floor. More than 95% of examined teeth by the investigators

were conformed to these laws.

3. 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 the CEJ, making the CEJ is the most consistent repeatable

landmark for locating the position of the pulp chamber.

4. Color change: The pulp chamber floor is always darker in color than the walls.

5. Symmetry: Except for maxillary molars.

• Canal orifices are equidistant from a line drawn in a mesiodistal direction

through the center of pulp chamber floor.

• Orifices lie on a line perpendicular to a line drawn in a mesiodistal direction

across the center of the pulp chamber floor.

6. Orifice location:

• Canal orifices are located at the junction of floor and walls.

• Orifices are always located at the terminus of the roots developmental fusion

lines.

Maxillary First Molar

• The shape of pulp chamber is rhomboid

with acute mesiobuccal angle, obtuse

distobuccal angle and palatal right angles.

• Palatal canal orifice is located palatally.

Mesiobuccal canal orifice is located under

the mesiobuccal cusp. Distobuccal canal

orifice is located slightly distal and palatal to

the mesiobuccal orifice. A line drawn to

connect all three orifices (MB, DB, P) forms

a triangle, termed as molar triangle.

• Generally 3 roots with 3 canals , additional canal is located in MB root.

• Large pulp chamber triangular in shape with the base toward the buccal and

the apex toward the palatal surface.

• Almost always a second mesiobuccal

canal, i.e. MB2 is present in first

maxillary molars, which is located

palatal and mesial to the MB1.

Though its position can vary

sometimes it can lie a line between

MB1 and palatal orifices.

• Because of presence of MB2, the

access cavity acquires a rhomboid

shape with corners corresponding to

all the canal orifices, i.e. MB1, MB2,

DB and P.

• Average length: MB= 20mm, DB=19.5mm, P=20.5mm.

• MB canal opening is closer to buccal wall than DB orifice.

• DB canal is closer to the middle of the tooth than to the distal wall , and it is

shorter and finest of the 3 canals.

• Studies of apical canal configurations for the MB root

• Studies of apical canal configurations for the DB root

• Studies of apical canal configurations for the P root

Maxillary Second Molar

• MB2 is less likely to be

present in second molar.

• The three canals form a

rounded triangle with

base to buccal.

• Mesiobuccal orifice is

located more towards

mesial and buccal than

in first molar.

• Access opening of maxillary second molar is similar to that of first molar except

few differences:

• Studies of apical canal configurations for the MB root

• Studies of apical canal configurations for the DB root

• Studies of apical canal configurations for the P root

• Mesiobuccal orifice is under the mesiobuccal cusp. Mesiolingual orifice is

located in a depression formed by mesial and the lingual walls. The distal

orifice is oval in shape with largest diameter buccolingually, located distal to

the buccal groove. Orifices of all the canals are usually located in the mesial

two-thirds of the crown.

• Distal root has also shown to have more than one orifice, i.e. distobuccal,

distolingual and middle distal. These orifices are usually joined by the

developmental grooves.

• The shape of access cavity is usually trapezoidal or rhomboid.

• Average length: 21 mm.

• Triangular outline form reflect the anatomy of pulp chamber with the base

toward the mesial and the apex toward the distal wall.

Mandibular First Molar

• Studies of apical canal configurations for the M root

• Studies of apical canal configurations for the D root

• Access opening of mandibular second molar is similar to that of first

molar except few differences:

Pulp chamber is smaller in size.

One, two or more canals may be present.

Mesiobuccal and mesiolingual canal orifices are usually located

closer together.

When three canals are present, shape of access cavity is almost

similar to mandibular first molar, but it is more triangular and less

of rhomboid shape.

When two canal orifices are present, access cavity is rectangular,

wide mesiodistally and narrow buccolingually.

Mandibular Second Molar

• Average length= 20mm.

• Mesial root have 2 canals, while distal root have one canal.

• Studies of apical canal configurations of mandibular second molar

• Mandibular molars usually have two roots. However, occasionally three

roots are present with two or three canals in the mesial and one, two, or

three canals in the distal root.

Radix Entomolaris

• De Moor et al reported that mandibular

first molars occasionally have an

additional distolingual root (radix

entomolaris, RE). The occurrence of

these three-rooted mandibular first

molars is less than (3-5%).

• For optimal treatment of teeth with this

state; radiograph and knowledge of

clinical anatomy.

C-shaped Canals

• The main cause for C-shaped roots and canals is the failure of Hertwig’s

epithelial root sheath to fuse on either the buccal or lingual root surface.

• The most C-shaped canals occur in the mandibular second molar, they

have also been reported in the mandibular first molar, the maxillary

first and second molars and the mandibular first premolar.

• These can be classified into:

1. Category I (C1): The shape is an uninterrupted “C” with no separation

or division.

2. Category II (C2): The canal shape resembles a semicolon resulting

from a discontinuation of the “C” outline.

• Extirpation of pulp may be difficult leading to more bleeding which can

be mistaken for perforation. Removal of pulp tissue at coronal isthmus

is difficult. To overcome these difficulties, the dental operating

microscope, sonic and ultrasonic instrumentation and thermoplastic

obturation techniques should be used.

3. Category III (C3): Two or three separate canals.

4. Category IV (C4): Only one round or oval canal is in the cross-section.

5. Category V (C5): No canal lumen can be observed (is usually seen near

the apex only).

Extensive restorations • If possible, complete removal of extensive restoration allows the most

favorable access to the root canals.

• If the restorations show no defect, leaky margins, fractures or caries, access

can be made through them. For cutting porcelain restorations diamond

burs are effective and for cutting through metal crowns, a fine cross-cut

tungsten carbide bur is very effective.

• When restoration is not removed, and access cavity

is made through it, following can occur:

Coronal leakage because of loosening of fillings

due to vibrations while access preparation.

Poor visibility and accessibility.

Blockage of canal, because broken filling pieces

may struck into the canal system.

Misdirection of bur penetration (because in

some cases restorations are placed to change

the crown to root angulations so as to correct

occlusal discrepancies).

• If tooth is severely tilted, access cavity should be prepared with great

care to avoid perforations. Preoperative radiographs are of great help in

evaluating the relationship of crown to the root. Sometimes it becomes

necessary to open up the pulp chamber without applying the rubber

dam so that bur can be placed at the correct angulation.

Tilted and angulated crowns

• If not taken care, the access cavity

preparation in tilted crowns can result

in:

Failure to locate canals.

Gouging of the tooth structure.

Procedural accidents such as:

instrument separation,

perforation.

Improper debridement of pulp

space.

• Calcifications in the pulp space are of common occurrence. Pulp space

can be partially or completely obliterated by the pulp stones. Teeth with

calcifications result in difficulty in locating and further treatment of the

calcified canals.

• Special tips for ultrasonic handpieces are best suited for treating such

cases. They allow the precised removal of dentin from the pulp floor

while locating calcified canals. But magnification and illumination are

the main requirements before negotiating a calcified canal.

Calcified canals

• If special tips are not available then a

pointed ultrasonic scaler tip can be used for

removal of calcifications from the pulp

space. One should avoid over cutting of the

dentin in order to locate the canals, this will

further result in loss of landmarks and the

tooth weakening.

• Sometimes sclerosed canals are found in teeth which make the

endodontic treatment a challenge. For visualization, magnification and

illumination are the main requirements.

Sclerosed canals

• Dyes can be used to locate the sclerotic canals. While negotiating, the

precised amount of dentin should be removed with the help of

ultrasonic tips to avoid over cutting.

• Long shanked low speed No. 2 round burs can also be used. Use of

chelating agents in these cases is not of much help because it softens the

dentin indiscriminately, resulting in procedural errors such as

perforations.

Teeth with no or minimal crown• Some precautions are needed while dealing with such cases:

Evaluate the preoperative radiograph to assess the root angulation.

Start the cavity preparation without applying rubber dam.

Evaluate the depth of penetration from preoperative radiograph.

Apply rubber dam as soon as the canals have been located.

• If precautions are not taken in case of missing crown, there are chances of

occurrence of iatrogenic errors like perforations due to misdirection of the bur.

In such cases, sometimes it becomes imperative to rebuild the tooth previous to

endodontic treatment. In teeth with weakened walls, it is necessary to reinforce

the walls before initiating endodontic treatment. In other words, it is necessary

to restore the natural form of a crown of the tooth to achieve following goals:

Return the tooth to its normal form and

function.

Prevent coronal leakage during treatment.

Allow use of rubber dam clamps.

Prevent fracture of walls which can complicate

the endodontic procedure.

Advanced endodontics 1st ed. 2009.

Endodontics (Principles & Practice) Torabinejad 4th ed. 2009.

Endodontics- Castellucci 12th ed. 2009.

Endodontics- Ingle 6th ed. 2008.

Pathways of the pulp 10th ed. 2011.

PDQ endodontics 1st ed. 2009.

Textbook of endodontics- Nisha Garg 3rd ed. 2014.

References