The document discusses guidelines for preparing an access cavity for endodontic treatment. It describes the importance of the access cavity in allowing visualization and access to all root canals. Key steps in access preparation include complete removal of the pulp chamber roof, removal of dentinal shoulders, and preparation of cavity walls to allow straight-line access to the canals without obstruction. Examples of access cavity designs are provided for different types of teeth, focusing on locating canal orifices and achieving optimal access. The document emphasizes that a properly designed access cavity is essential for successful root canal treatment.

1. ENDODONTIC
ACCESS
CAVITY
Dr. Ridwana Kawsar
BDS (CMC), BCS (Health)
MS (Conservative Dentistry &Endodontics - BSMMU)
Lecturer, Dept. of Conservative Dentistry & Endodontics
Shaheed Suhrawardy Medical College( ShSMC)
Sher-E-Bangla Nagar, Dhaka

2. INTRODUCTION
• Access cavity preparation is the endodontic coronal
preparation which enables unobstructed access to the canal
orifices, a straight line access to apical foramen, complete
control over instrumentation and accommodate obturation
technique.
• It is the most important phase of the technical aspects of root
canal treatment.

3. Preparation of the root canal system starts with preparation of a properly designed access cavity. The
access cavity should:
• Allow full control of the pulp chamber.
• Allow removal of all tissue from the pulp chamber and proper disinfection. This will result in elimination
of a significant load of microorganisms.
• Allow a proper intracoronal diagnosis (cracks, dentin colors, pulp stones, calcifications).
• Allow location of all root canal systems and relevant anatomical structures (isthmi, lateral extensions).
• Allow fast and straight-line introduction of endodontic instruments without coronal interferences. Ideally,
the straight-line access should be extended to the beginning of the curvature.

4. Incomplete removal of the roof of the pulp
chamber resulting in insufficient root
canal preparation. At least one root canal
has not been detected.

5. A. Improper primary and secondary access did not allow detection and preparation of all root canal systems.
B. Three root canals could be located but improper secondary access still prevents complete instrumentation.
C. Following extension of the access all three root canals could be accessed, prepared and obturated.

6. Coronal
pulp
Radicular
pulp
Pulp chamber
Pulp horn
Orifice
Root
canal
Lateral
canal
Apical
foramen
Roof
CEJ
The pulp space is the central cavity within a tooth and is entirely
enclosed by dentin except at the apical foramen.
The pulp space may be divided into the following:
• A coronal portion → Pulp chamber
• A radicular portion → Root canal
• Roof of the pulp chamber consists of dentin covering the pulp
chamber occlusally or incisally.
• Pulp horn is an accentuation of the roof of the pulp chamber directly
under a cusp or developmental lobe. The term refers more commonly
to the prolongation of the pulp itself directly under a cusp.
• Floor of the pulp chamber runs parallel to the roof and consists of
dentin bounding the pulp chamber near the cervical area of the tooth,
particularly dentin forming the furcation area
• The canal orifices are openings in the floor of the pulp chamber
leading into the root canals. The canal orifices are not separate
structures, but are continuous with both the pulp chamber and the
root canals.

7. Various views of the root canal system: (a) Labial view of a central incisor. (b) Apical third of a
root. (c) Buccal view of a maxillary first molar. (d) Buccal view of a mandibular first molar.

8. ROOT CANALS
The root canal is the portion of the pulp space from the canal orifice to the apical foramen. For
convenience, it may be divided into three sections, namely: coronal, middle, and apical thirds.
• Accessory canals, or lateral canals, are lateral branching of the main root canal generally occurring in the
apical third or furcation area of a root.
• Lateral canal is an accessory canal that branches to the lateral surface of the root and may be visible on a
radiograph.
• Apical foramen is an 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.
• Accessory foramina are the openings of the accessory and lateral canals in the root surface.

9. It is of paramount importance as
this the vital stage that governs
the success or ease of the
subsequent treatment stages.
It is the foundation of pyramid of
successful endodontic treatment.
Straight line access cavity
WLD
BMP
Obt.

10. OBJECTIVES
1) Removal of all carious lesion and coronal pulp tissue
2) Complete deroofing of pulp chamber and locating all the canal
orifices
3) Achieve straight-line access to the apical foramen or to the initial
curvature of the canal.
4) Conserve sound tooth structure as much as possible

11. PRINCIPLES OF ENDODONTIC CORONAL
PREPARATION
Outline Form
Convenience Form
Removal of the remaining carious dentin (and defective restorations)
Toilet of the cavity

12. Outline form:
The outline form of the endodontic cavity must be correctly shaped
and positioned to establish complete access for instrumentation, from
cavosurface margin to apical foramen.
Factors regulating the outline form:
(1) the size of the pulp chamber,
(2) the shape of the pulp chamber, and
(3) number and directions of root canals.

13. It is important that it is the anatomy of the
pulp chamber that is being treated, and not
a preconceived idea held by the operator,
which dictates the outline of the access
cavity.
It is unlikely, that access cavities will exactly
match an ideal diagram or picture as the
vast majority are in fact created in teeth
where a significant amount of dentine and
enamel has been replaced by restorative
materials.

14.  Convenience form:
In endodontic therapy, this provides more convenient and accurate
preparation and filling of the root canal.
Four important benefits are gained through convenience form
modifications:
(1) Unobstructed access to the canal orifice
(2) Direct access to the apical foramen
(3) Cavity expansion to accommodate filling techniques, and
(4) Complete authority over the enlarging instrument.

16. Removal of the remaining carious dentin
and defective restorations:
This should be done for the purpose of
(1) Elimination of bacteria,
(2) Elimination of the discolored tooth structure,
(3) Elimination of the possibility of coronal leakage.

17. Toilet of the cavity:
• All caries, calcified debris and necrotic materials should be removed
by irrigation from the pulp chamber before radicular preparation is
begun to avoid obstructions of the root canal.
• Sodium hypochlorite (NaOCl) should also be used during the access
preparation for its added benefits of disinfection, removal of
hemorrhagic or purulent fluids, and flushing action of debris and
dentin chips.
• This should be done without the use of an air syringe due to the
possibility of an air embolism.

18. The significance of the access cavity is too frequently overlooked
where the technical stages are often thought to be limited to 'clean,
shape and fill'.
A poorly executed access cavity will compromise the subsequent
steps
Without adequate access, instruments and materials become
difficult to handle properly in the highly complex and variable
root canal system.
Significance of an ideal Endodontic Access

19. A root canal treatment may fail,
for example, due to an
untreated canal; however,
rather than this being a failure
of adequate preparation, it
could is ascribed to inadequate
access leading to inability to
locate untreated root canal.

20. Insufficient cavity preparation could also lead to instrument
fracture, aberration of the original root canal anatomy and
other iatrogenic problems.
In such cases, the infection perseveres and the treatment
fails.

21. Under extension Over extention

22. Mouse hole effect
Orifice on the pulp floor
• Mouse hole effect: If the lateral wall of the
cavity has not been sufficiently extended and
the pulpal horn portion of the orifice still
remains in the wall, the orifice will have the
appearance of a tiny “mouse hole.” This
feature occurs due to the extension of the
canal orifice into the axial wall. By extending
the lateral wall of the cavity, thus removing all
intervening dentin from the orifice, the
“mouse hole” in the wall will be eliminated
and the orifice will appear completely on the
floor.

25. Guidelines for Preparation of the Primary Access Cavity
o Determination of the point of penetration: Usually, entry is in the center of the occlusal table but in certain teeth
(e.g., maxillary molars) it is deceiving, as the center of the occlusal table does not reflect the center of the pulp
chamber
o Assessment of occlusal and external root form: Once the point of entry has been determined, the bur’s
angulation in three dimensions has to be mentally envisioned. This is determined by taking into account the
angulation of the teeth in the jaws and assessing the external root surface at the level of the CEJ.
o Radiographic measurement of the depth of the pulp chamber roof from the occlusal table: The initial bur in the
high-speed handpiece is placed against a radiograph or a measurement determined from a calibrated digital
image.
o Assessment of complicating factors: Rotations/tipping of teeth, calcifications (pulp stones, mid-root calcification),
deep restorations, buccal/lingual restorations, root length, width, and curvature affect the angle of entry and the
degree of extension of the access cavity in the horizontal and vertical dimensions.
o Radiographic assessment: Angled views should be taken in an attempt to visualize the breadth of the roots and
the position of the canal within it. One also has to assess the angle at which the canal leaves the pulp chamber.

26. KEY STEPS TO CONSIDER IN ACCESS
PREPARATION:
I. Visualization of the likely internal anatomy and evaluation of the
cementoenamel junction
II. Complete deroofing along with removal of dentinal shoulders
III. Preparation of access cavity walls that do not restrict straight passage
of instruments
IV. Tapering of cavity walls and evaluation of space adequacy for a
coronal seal

27. Maxillary Central Incisors
The roots are usually straight and
have the least incidence of
dilacerations.
Initial penetration should be
approximately in the middle of the
lingual surface of the tooth, just above
the cingulum, almost perpendicular to
the lingual surface. After locating the
canal, long tapered diamonds can be
used to extend the access into a
roughly triangular outline

28. Note the extension of the mesial and distal incisal areas to
open up the pulp horns.

29. Maxillary Lateral Incisors
The root typically curves to the distal although some can be
straight or curving to the mesial. There is often a deep
developmental groove running along the cingulum on the
lingual surface. Usually the tooth shows one single root canal.
The access opening for the maxillary lateral incisor is similar to
that for the maxillary central incisor, but it is smaller and
usually more ovoid. The technique for entry is the same as that
for the maxillary central incisor, except that a No. 2 round bur
may be used instead of a No. 4.

30. Mandibular Central and Lateral Incisors
The mandibular central incisor is usually the smallest
tooth in the mouth. Bilateral symmetry is common.
There are slight differences between central and
lateral incisors, but the most important with regard to
access is that the crowns of lateral incisors are not as
symmetrical as central incisors from the incisal view
as they curve distally to accommodate the curvature
of the arch and correspondingly the cingulum is
displaced slightly to the distal. Lateral incisors are
also slightly larger than the centrals.

31. Outline form of central and lateral incisors are triangular with the base of the
triangle towards the incisal edge and the apex towards the cingulum.
Incisal edge
Cervical line
Base
Apex

32. Potential design of access into a maxillary incisor with schematic drawings based on an original radiograph A. The preoperative relation of the
canal within the root can be estimated B. Note how the true straight-line access (SLA) is labial to the incisal edge C. The initial access entry site
and angulation D. tan-colored highlights show the restrictive dentin impeding SLA. E. The completed lingual access preparation with SLA can
be compared to a completed access preparation done from a labial approach F. Note how far more tooth structure may be conserved with a
labial access but at the cost of disrupting the labial esthetic surface.

33. Entrance is gained through the
middle of the middle third of the
palatal surface.
1
Initial entrance Is prepared with a
round bur at a high speed operated at
a right angle to the long axis of the
tooth. Only enamel is penetrated.
2

34. The bur is positioned in a 45 degree to the long axis of the
tooth then advanced to penetrate the pulp chamber.
3

35. Removal of the pulp chamber (deroofing)
4

36. Removal of lingual shoulder.
5

38. Maxillary Canines
The position of the cusp tip relative to the
long axis of the root is in line with the center
of the root tip in the labial view but lies
labial in the proximal view.
It is usually the longest tooth and the largest
root in the mouth and often curves apically.
As with the central and lateral incisors, the
lingual triangle must be removed. The main
difficulty with these teeth is that they can be
long, often over 30 mm.
Mandibular Canines
These teeth are very similar to their
maxillary counterparts but are usually
narrower (approximately 1 mm) and shorter
in root length by 1 to 2 mm. The mesial edge
is almost straight and therefore the access
cavity can be prepared more mesially to the
center point of the lingual surface. The
shape of the preparation ranges from an
oval to a rounded slot, depending on the
size of the pulp chamber inside.

39. Maxillary canine Mandibular canine

40. • Posterior teeth requiring root canal procedures typically have been
heavily restored or the carious process was extensive.
• Such conditions, along with the complex pulp anatomy and
position of posterior teeth in the oral cavity, can make the access
process challenging.

41. Premolars
Upper oval Lower ovoid

42. Maxillary premolars
Buccal canal is located under
the buccal cusp tip.
Palatal canal is located at the
base of the palatal cusp.

43. Initial penetration is made parallel to the long axis of the tooth in
the exact center of the central groove
1
1

44. A round bur is used to open into the pulp chamber. The bur will be
felt to “drop” when the pulp chamber is reached.
2

45. An endodontic explorer is used to locate orifices.
3

46. A round bur is used to deroof the pulp chamber.
4

47. Finishing and flaring of the cavity walls.
5

48. Upper Lower

49. Access cavity for molars

50. Upper Lower
Trapezoid
B
P
L
M
D
M
B
D

51. MB1
MB2
Palatal
Upper
DB
Point of
entry
• MB1 is located under the buccal cusp tip.
• MB2 is located mesial and palatal to MB1 (at the end of a comma tail).
• DB is located under the central fossa.
• Palatal is located at the junction of mesiopalatal cusp and oblique ridge.
• Point of entry is the center of the occlusal table.

52. MB
ML
Distal
Point of entry
Lower
• MB is located under the mesiobuccal cusp tip.
• ML is located at the same line lingual to the central fissure.
• Distal is located distal to the central fossa.
• Point of entry is the central fossa.

53. Angle of penetration toward the largest canal
(palatal) in a maxillary molar.
Safety-tip carbide bur is used to shape the axial wall in one
plane
from the orifice to the cavosurface margin

54. A, Pulp roof/pulp horn removal. The round bur hooks under the lip of the pulp
horn. B, The bur is rotated and withdrawn in an occlusal direction to remove the
lip. C, Removal of a cervical dentin bulge. A Gates-Glidden bur is placed just apical
to the orifice and withdrawn in a distoocclusal direction. D, A safety-tip tapered
diamond bur is used to blend and funnel the axial wall from the cavosurface
margin to the orifice.
A
B
C
D

55. Axioms of pulp anatomy
1- The two orifices of the maxillary first
premolars are further to the buccal.
2- The orifices of the mesio-buccal canals in
molars are well up under the mesio-buccal cusps
and the outline form should be widely extended
into the cusp.

56. 3- The orifices of the palatal canal in maxillary
molars is not too far to the lingual, but is
actually in the center of the mesial half of the
tooth
4- The orifices of the disto-buccal canal in
maxillary molars is not too far to the disto
buccal, but it is almost buccal to the palatal
orifice.

57. 5- The orifice of the distal canal in
mandibular molars is not too far to the
distal, but is actually in the exact center of
the tooth
6- The orifice of the mesio-lingual canal in
mandibular molars is not too far to the
mesio-lingual, but is almost mesial to the
distal orifice.

58. 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 the CEJ. The CEJ is the most consistent, repeatable landmark for
locating the position of the pulp chamber.
• 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.

59. 1-Law of centrality: The floor of the pulp chamber is always located in the center of
the tooth at the level of the CEJ.
2-Location of 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.

60. 3-First law of symmetry: Except for the maxillary molars, canal orifices are equidistant
from a line drawn in a mesiodistal direction through the center of the pulp chamber
floor.
M
D
4-Second law of symmetry: Except for the maxillary
molars, canal orifices lie on a line perpendicular to a line
drawn in a mesiodistal direction across the center of the
pulp chamber floor.

62. 5-Law of color change: The pulp chamber floor is always darker in color than the walls.
Law of Color Change
• Enamel → White
• Dentin → Yellow
• Floor of the pulp chamber → Gray
• Root canal orifice → Dark gray or black
• Pulp stone → Pearly white/dark yellow

63. 6-First law of orifice location: The orifices of the root canals are always located at the
junction of the walls and the floor.
7-Second law of orifice location: The orifices of the root canals are always located at
the angles in the floor–wall junction.

64. 8-Third law of orifice location: The orifices of the root canals are always located at
the terminus of the roots’ developmental fusion lines.

65. Modification of Access Preparation
□ Canals are often buried under a bridge of dentin.
□ Presence of additional canals
□ The location of additional root canals may vary greatly.
The anatomy of the canals dictates modifications of the cavity
preparation. If, for example, a fourth canal is found or suspected in a
molar tooth, the preparation outline will have to be expanded to
allow for easy access into the accessory canal.

66. The access cavity should be prepared in such a way that the location
of the second canal can be attempted.
Upper first molar showing
MB2 canal located with a #10 file
Completed access
cavity showing four
canal orifices

67. Six canals in upper first
maxillary molar
Obturation of an upper first
molar with three mesial
canals

68. Modified access cavity showing two palatal orifices

69. 41.4% of lower incisors have two canal orifices. The access cavity is commonly
prepared in such a way so that the lingual canal can be missed, it should extend
from the cingulum to the incisal edge to ensure that this does not occur.
a) initial identification of the lingual canal underneath cingulum; b) initial negotiation of
the canal and c) successful obturation of both canals
(a) (b) (c)

70. Clues in locating extra root canals: (a) Prominent cingulum of a mandibular incisor; an extra canal may be found lingually. (b)
Prominent lingual cusp of a mandibular bicuspid; extra canal may be found lingually. (c) Prominent buccal cusp and wide crown
mesiodistally; a mesiobuccal canal or root may be found in the maxillary first premolar. (d) Prominent buccal cusp and wide
crown buccolingually on the mesial half in the maxillary molar; a second mesiobuccal canal may frequently be found. (e) Where
unusually small canals are seen, an extra canal may be found, as in the distal root of a mandibular molar.

71. Clinical Note
• On entering the roof of the pulp chamber, the operator has to
change to a lateral cutting motion instead of proceeding in an
apical cutting direction.
• The following dentinal shoulders should be taken into
consideration to achieve straight line access:
–– Mandibular anteriors → Lingual shoulder
–– Maxillary anteriors → Palatal shoulder
–– Premolars → Mesial and distal shoulders
–– Mandibular molars → Mesial and distal shoulders
–– Maxillary molars → Mesial and buccal shoulders
Complete deroofing and removal of mesial shoulder
in a mandibular molar would facilitate straight line
access during the
shaping procedure.

72. Endodontics has seen an unparalleled advancement in
technology and materials in the past couple of decades.
This period has witnessed remarkable development in
endodontic technologies which has brought about various
modifications in all phases of endodontic treatment
including access opening.
Access preparation in the Era of Modern Endodontics

73. • Handpieces
• Burs
• Endodontic explorers
• Endodontic spoon
• Ultrasonic unit and tips
• Magnification and illumination

74. Figure: Dental operating microscope Figure: Dental loupes
Magnification & illumination:

75. Ultrasonic unit & tips:
• In general, these are used to create trough along the grooves to
expose hidden orifices, remove pulp stones, negotiate calcified
canals and finish access preparation.

76. Access Opening Burs:
• Carbide Round Burs
i. Use: caries removal and defining
the external outline shape.
• Diamond Round Burs
i. To gain entry into tooth
structure and restorative materials
ii. Used for axial wall extensions.

77. • Transmetal Burs
i. This is used for cutting any type of
metal.
ii. This bur is especially helpful for
entering in hot tooth.
• Tapered Diamond Burs
To flatten, flare and finish the
axial walls of the pulp chamber
in absence of Endo Z bur.

78. • Endo Z Burs
i. It is safe-ended tapered
carbide bur.
ii. Lateral cutting edges of Endo Z bur
are used to flare, flatten and refine
the internal axial walls.
iii. Its noncutting tip can be
safely placed on the pulpal
floor without the risk of
perforation.

79.  Endodontic explorer & spoon:
An endodontic explorer is used to search for canal
orifices
Endodontic explorer (A: DG-16 & B: JW-17)
Endodontic spoon

80. In 2011 the American Association of
Endodontists and the American Academy of
Oral and Maxillofacial Radiology issued a joint
position statement on the use of CBCT in
endodontics.
In terms of access cavity preparation, it
suggested that CBCT is indicated to identify
potential accessory canals in teeth with
suspected complex morphology based on
conventional imaging, and identification of
root canal system anomalies and root
curvature.
CBCT

81. Trouble shooting and some clinical pointers
Failure to analyze the pre-operative radiograph
adequately
This can result in removal of dentine away from
the pulp camber and and destroy the dentinal
map, weakening the tooth and risking
perforation.
Before starting the access cavity preparation, the
depth of preparation can be checked by aligning
the bur and handpiece against the radiograph.

82. Tooth with significant loss of structure
If, during access cavity preparation, there is a
concern that the remaining tooth is at risk of
fracture, an orthodontic band or a copper
band can be place. This helps to rebuild the
missing tooth structure and allowed creation
of four-walled access cavity.
The band may be left in place until the tooth is
prepared for cuspal protection.
Furthermore this will aid in placement of the
clamp of the rubber dam for proper isolation.

83. Sclerosed canals
In cases of sclerosis in multi rooted teeth it is best
to go 'for the pulp horns' or the part of the pulp
chamber that has the greatest volume on the
pre-operative radiograph.
Another strategy is to commence canal location
in the area of the largest canal, that is, the palatal
canal of maxillary molars and the distal canal in
mandibular molars.
Laws of orifice location and dentinal map aids in
location of orifices

84. Indirect restorations
If the anatomy of a tooth has been radically altered
by an indirect restoration, consider aligning an
endodontic or periodontal probe with the mesial
surface of the mesial root and preparation with the
bur in same alignment.
In such cases, one can avoid placing rubber dam
until correct location has been confirmed to ensure
that the long axis of the tooth can be clearly seen in
relation to the crown/root trunk angulation.

85. Hyperaemic pulps
In cases of acute pulpitis where initial access results
in profuse bleeding, exploration of the pulp chamber
floor is not recommended until the bleeding is
controlled.
If a fast handpiece is used, a safe-ended bur is
recommended. Employing this technique will result
in little chance of pulp floor perforation.
Copious irrigation with sodium hypochorite and/or
local anaesthetic that contains a vasoconstrictor will
aid haemostasis in such cases.

86. Take away points:
• Understanding access as the most important phase of nonsurgical
root canal treatment.
• Comprehend principles of cavity preparation and proposed
guidelines to accurately prepare the endodontic access.
• Understanding the differences in chamber and access shape for
each tooth type and protocol to follow when performing on each.

87. REFERENCES:
Evans, M., 2020. Ingle's Endodontics 7.
Berman, L.H. and Hargreaves, K.M., 2015. Cohen's pathways of the pulp expert consult. Elsevier Health Sciences.
Chandra, S., 2014. Grossman’s endodontic practice. Wolters Kluwer India Pvt Ltd.
Garg, N. and Garg, A., 2010. Textbook of endodontics. Boydell & Brewer Ltd.
Rozo, L. and Fullmer, J., Guidelines for Access Cavity Preparation in Endodontics.
Kuriakose, A., Joy, B., Mathew, J., Hari, K., Joy, J. and Kuriakose, F., Modern Concepts in Endodontic Access
Preparation: A Review.
Kokane, V.B., Patil, S.N., Gunwal, M.K., Kubde, R. and Atre, S., 2014. Treatment of two canals in all mandibular
incisor teeth in the same patient. Case reports in dentistry, 2014.
Pawar, A.M. and Kokate, S.R., 2014. Contemporary endodontic management of four rooted maxillary second
molar using waveOne. Contemporary clinical dentistry, 5(1), p.130.
Adams, N. and Tomson, P.L., 2014. Access cavity preparation. British dental journal, 216(6), pp.333-339.