This document discusses guidelines and principles for locating canals and preparing access cavities for endodontic treatment. It covers: - The three main factors for endodontic success: cleaning and shaping, disinfection, and obturation. - Preparing the access cavity is an important first step to identify all root canals so they can be treated. - General principles for access cavity preparation include doing no harm, confirming diagnosis, and allowing straight-line access. - Techniques for locating canals using anatomical landmarks like the cementoenamel junction and developmental root lines are described. - Armamentarium and steps for access cavity preparation in different tooth types are outlined.

1. Locating canals……
Dr Prasanth Balan
Associate Professor
Dept of Conservative Dentistry and Endodontics
Govt Dental College Calicut
drprasanthb@gmail.com

2. The success of endodontic therapy depends on
three main factors
Cleaning and Shaping
Disinfection
Three-Dimensional Obturation

3. One step that precedes these factors is the preparation of
access cavity and canal location

4. The success of endodontic treatment depends on the
identification of all root canals so that they can be
cleaned, shaped, and obturated.

5. Endodontic Pyramid

6. General Principles
“Do no harm”
Confirmation of etiology of pulpal pathosis
Asessment of restorability
Straight line access
Three dimensional positin of teeth in jaw
External root surface as a guide
Knowledge of numbers of canals with in a root
Mind set

7. Straight line access
improved instrument control
improved obturation
decreased incidence of iatrogenic errors

8. Designing the access cavity to allow straight line access (SLA)
is a dynamic process.
It involves
¤Create initial access cavity
¤Penetrate canal
¤Flare canal
¤Adjust access cavity
¤Penetrate deeper
¤Flare canal
... and so on

9. Armamentarium
Basic armamentarium includes
 Mouth mirror
 DG16 endodontic explorer
 High and slow speed hand pieces
 Access opening burs - #2 and #4 round diamond burs
 Access refining burs - Safe ended tapered Diamonds
and TC burs
 Other burs - Endo access, Endo Z burs
Munce burs,
Mueller burs etc

10. Endo Z Bur Endo Access Bur

11. Munce discovery bur

12. DG 16 endodontic explorer

13. Preoperative Clinical Guide Lines
 Determination of point of penetration
 Must carefully examine teeth for rotation,tipping & angle in
arch
 Assessment of occlusal and external root form
 Radiographic assessment
 Radiographic measurement of depth of pulp chamber
 Assessment of complicating factors

14. Access cavity preparation
Minimum size of access cavity must be the maximum size of
the pulp chamber
Objectives of access cavity preparation
• Penetrate through the occlusal surface
• “Unroof” the dentin that covers the chamber
• Find the pulp chamber
• Obtain the uniform contact of the file with
the access cavity wall
• To obtain SLA

15. Mandibular First Molar
Anatomy And Morphology
Buccal cusp tips are located more to the
mid line on the occlusal table
Lingual cusp tips are almost directly over
the outer surface at the neck

16. Anatomy And Morphology Cont…
CEJ
Bifurcation (3mm Below the CEJ)
Concavity

17. • Local anaesthesia
buccal infiltration - maxillary arch
buccal infiltration - mandibular incisors and canine
inferior alveolar nerve block –mandibular premolars and
molars
Pain after 1st
LA give 2nd
one
Still pain intraligamentary injection
Still pain if pulp chamber is not open----cotton dipped with LA
should be placed
Still pain with sharp round bur with out pressure
if pulp chamber is open try intra pulpal
Clinical Procedures

18. Clinical Procedures cont….
• Remove all unsupported tooth structure to prevent
tooth fracture during treatment.
• Remove all carious portion or any restoration
• Determine the shape and size of pulp chamber
• Lingual and mesial inclination of tooth should be
determined & bur should mimic this angulation

19. • Orifices of all the canals all usually located in the mesial
2/3rd
of the crown
• Shape of access cavity is usually trapezoidal or
rhomboidal
• Check the depth of preparation by aligning the bur and
hand piece against the radiograph

20. Schematic representation of out line of access cavity preparation

21. Initial entry using round bur

22.  Once drop into chamber is obtained bur is moved
from inside to outside

23. Now the bur is replaced by tapered fissure bur

24. Clinical photographs of access cavityClinical photographs of access cavity
preparationpreparation

25. Access refining using burs with non cutting tips

26. Final access cavity preparation

27. Out line of prepared access cavity of mandibular molar

28. In summary
• Check the depth of preparation by aligning the bur and
hand piece against the tooth
• Place a safe ended bur in hand piece to complete the
access cavity preparation
• When locating the canal orifices is difficult, one should
not apply the rubber dam
• Remove all unsupported tooth structure

29. Remove the pulp chamber roof completely as this will
allow the
• removal of all the pulp tissues
• Calcification
• Caries
• Any residual filling
If the pulp chamber is not completely deroofed it can result in
• Contamination of pulp space
• Discoloration of endodontically treated teeth

30. • Walls of pulp chamber are flared and tapered to form a gentle
funnel shaped with larger diameter towards the occlusal surface
• Access cavity is prepared through the occlusal surface and
lingual surface and never through the the proximal or gingival
surface
• Inspect the chamber for determining the location of
canals,curvatures,calcification using well magnification and
illumination

31. How many canals are there??
How to locate these canals??

32. • Explore the canal orifice with sharp endodontic
explorer
• All canal orifices are located in the pulp chamber so
relationship of the pulp chamber and clinical crown
should be understood
• Locating canals or in search of canals

33. Relationship of the Pulp Chamber to the Clinical Crown

34. Law of the CEJ:
The CEJ is the most consistent,
repeatable landmark for locating the position of the
pulp chamber.

35. Probing of CEJ

36. Law of centrality:
The walls of the pulp chamber is always located in the
center of the tooth at the level of CEJ

37. Relationship of the Pulp Chamber to the Clinical Crown
The pulp chamber is always in the center of the tooth at the level
of the CEJ.

38. The distance from the external surface of the clinical crown to the wall
of the pulp chamber was the same throughout the circumference of the
tooth at the level of the CEJ
a

39. Law of concentricity :
The walls of the pulp chamber are always
concentric to the external surface of the tooth at the level of
CEJ, that is the external root surface anatomy reflects the
internal pulp chamber anatomy.

40. The walls of the pulp chamber are always concentric to the
external surface of the crown at the level of the CEJ

41. Cut specimen showing CEJ bulge (CB) with concentric chamber wall.

42. Law of color change:
The color of pulp chamber floor is always
darker than the walls

43. The floor of the pulp chamber is always darker than the
surrounding dentinal walls

44. Floor of the Pulp Chamber

45. Color difference creates a distinct junction where the walls
and the floor of the pulp chamber meet ..

46. Laws of orifice location 1:
The orifices of the root canals are always
located at the junction of the walls and floor

47. The orifices of root canals are always located at the junction of the
walls and floor

48. Law of orifice location 2:
The orifice of the root canals are located at the
angles in the floor – wall junction

49. Diagram of mandibular molar showing orifice location (OL )at the
angles of the chamber floor and floor-wall junction.

51. Law of orifice location 3: The orifices of the root canals are
located at the terminus of the root developmental fusion lines if
present

52. The developmental root fusion lines are darker
than the floor color .
Reparative dentin or calcifications are lighter
than the pulp chamber floor and often obscure it and the
orifices.

53. The orifices lie at the terminus of developmental root fusion
lines, if present.

54. Law of symmetry 1: Except for maxillary molars,
the orifices of the canals are equidistant from a line
drawn in a mesial distal direction across the center of
pulp-chamber floor

55. Cut specimen of mandibular molar showing
equidistance of orifices from mesiodistal line

56. Law of symmetry 2: Except for maxillary molars, the
orifices of the canals lie on a line perpendicular to a line
drawn in a mesial-distal direction across the center of
the pulp floor

57. Cut specimen of mandibular molar showing
orifices perpendicular to mesiodistal line.

58. Cut specimen showing the laws of symmetry 1 and
2 and orifice locations 1, 2, and 3.

59. Mandibular second molar
Access opening similar to 1st
molar except for few differences
they are
 Pulp chamber are smaller in size
 Mesiobuccal & mesiolingual canal orifice are located closer
together
 it is necessary to reduce a larger portion of the mesiobuccal
cusp to gain convenience form for mesiobuccal canal

60. Mandibular third molar
Have significant variations and anomalies,
usually less developed ,with oversized crowns
and undersized roots
Bifurcated or fused roots
Clinical procedures similar to first molars

61. Mandibular Molar Teeth
Errors in Cavity Preparation
Overextended preparation undermining enamel walls. The
crown is badly gouged owing to failure to observe pulp recession
in the radiograph.
Perforation into furcation caused by using a longer bur and
failing to realize that the narrow pulp chamber had been passed.
The bur should be measured against the radiograph and the depth
to the pulpal floor marked on the shaft

62. .
Failure to find a second distal canal owing to lack
of exploration for a fourth canal.
Ledge formation caused by faulty exploration and
using too large of an instrument.

63. Maxillary First Molar
Anatomy And Morphology
Buccal view of first molar
• Large pulp chamber
• Mesiobuccal root with two separate
canals,distobuccal,and palatal
roots, each with one canal
• Slightly curved buccal roots
• Slightly curved palatal root
Care must be taken to explore for an additional mesiobuccal canal

64. Mesial view
• Apical-buccal curvature of the palatal root
(55% of the time)
• Buccal inclination of buccal roots
• Vertical axial alignment of the tooth
Sharp buccal curvature of the palatal canal
requires great care in exploration and
instrumentation.

65. Occlusal surface
• Two major fossae & two minor fossae
central fossa-mesial to the oblique ridge
distal fossa -distal to the oblique ridge

66. Preoperative Clinical Guidelines
• Determination of point of penetration
• Assessment of occusal and external root form
• Radiographic assessment
• Radiographic measurment of depth of pulp
chamber
• Assessment of complicating factors

67. Access Cavity Preparation for Maxillary First Molar
Remove all carious portion or any restoration
Determine the shape and size of pulp chamber
Bulk of the pulp chambers are located mesial to the oblique
ridge
Determine the starting point of bur into the enamel
Determined by mesial and distal boundary
Mesial boundary …..line joining the mesial cusps
Distal boundary ……oblique ridge

68. Outline of access cavity

69. • Penetrate the enamel using round bur in the central groove
directed palatally and prepare an external outline form.
• Penetrate deep into dentin until you feel drop into the
chamber.
• Completely remove the roof of pulp chamber using round
bur, safety tip diamond bur or carbide bur working from
inside to out side

70. A Penetration with no 2 or no 4 round bur
B Exposure of pulp chamber with tapered fissure bur
C Refinement of pulp chamber & removal of roof using
round bur from inside to out side
D Complete refinement of pulp chamber space
A
D

71. The cavity is entirely within the mesial half of the
tooth and should be extensive enough to allow positioning of
instruments and filling materials .

72. Laws for canal location in maxillary molars
• Law of centrality
• Law of concentricity
• Law of CEJ
• Law of color change
• Law of orifice location 1
• Law of orifice location 2
• Law of orifice location 3

73. • 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
• Mesiopalatal canal orifice (MB2) is located palatal and
mesial to the mesiobuccal canal orifice (MB1)

74. Cut specimen showing position of a mesiopalatal orifice
(MPC) after the laws of orifice location.

75. Maxillary Second Molar
• Basic technique is similar to that of 1st
molar
with following differences
• Three roots are found closer
• MB2 (mesiopalatal canal is less common)
• Three canals form a rounded triangle with base
towards buccal

76. Maxillary Third Molar
• These teeth tend to have a underdeveloped crown
• Roots are often fused to forming one large root
• Modification must be made in accessing these teeth
compared 1st
and 2nd
molar

77. Clinical management of difficult cases
• Management of case with extensive restoration
• Tilted and angulated crowns
• Calcified canals
• Teeth with No or Minimal crown

78. Clinical tips……
• I can …..
• Positive approach
• Postponing the appointment
• Take your time
• Perforation
• Two instruments in same canal
• Always try to put blame on patient
• Inform or not to inform
• Never skip any step
• Comment about success percentage
• Use of broken instrument

79. Conclusion
The cause of most endodontic failures is inadequate
biomechanical instrumentation of the root-canal system. This can
result from inadequate knowledge of root-canal anatomy.
Only a systematic knowledge of pulp– chamber-floor anatomy
can provide greater certainty about the total number of root canals in
a particular tooth.

80. This presentation showed that consistent patterns of anatomy
of both the chamber and the pulp-chamber floor exist.
These laws can be used to help practitioners identify the total
number of canals in any tooth and their specific orifice location
on the pulp-chamber floor.
With the proposal of a systematic anatomic approach to pulp
chamber and root canal orifice location, the practice of
endodontics can now be based on fundamental surgical anatomic
principles.