5. Objectives of access cavity preparation:
1- Straight line access to apical
foramen or to the initial
curvature of the canal.
2- To locate all root canal
orifices.
3- To conserve sound tooth
structure.
6. Principles of access cavity preparation
1. Outline form.
2. Convenience form.
3. Removal of remaining carious dentin and defective
restorations.
4. Toilet of the cavity.
7. 1.Outline form:
Established by mechanically projecting the internal anatomy
to the external surface.
Three factors regulating the outline form:
a. Size of pulp chamber:
Young patients extensive.
Old patient limited.
8. b. Shape of pulp chamber:
Anteriors Triangular.
Premolars Oval or ovoid.
Molars Triangular.
c. Number and direction of root canals.
9. 2. Convenience form:
It is the form given to the access cavity to improve visibility, instrumentation and
obturation of the root canal by providing a straight line access from occlusal surface
to the apical foramen.
Benefits:
1. Unobstructed access to the orifices.
2. Direct access to the apical foramina.
3. Complete authority over the instrument.
4. Expansion to accommodate filling techniques.
10. 3- Removal of remaining carious dentin and
defective restorations:
Reasons of removing caries and defective restorations:
1. Elimination of bacteria.
2. Elimination of discolored tooth structure.
3. Elimination of the possibility of coronal leakage.
11. 4- Toilet of the cavity:
All caries, calcified debris and necrotic material should be removed by irrigation
from the pulp chamber before radicular preparation is begun to avoid obstruction
of the root canals.
16. Access cavity preparation in anterior teeth
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
18. Entrance is gained through the middle of the middle
third of the palatal surface.
1
19. 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
20. The bur is positioned in a 45 degree to the long axis of the
tooth then advanced to penetrate the pulp chamber.
3
25. Errors
1- GOUGING of the labial wall caused by failure to
recognize the 29-degree lingual-axial angulation of the
tooth.
2- GOUGING of the distal wall caused by failure to
recognize the 16-degree mesial-axial inclination of
the tooth.
26. 4- Missed canal due to insufficient convenience extension.
3- PERFORATION at the labiocervical caused by failure to
complete convenience extension toward the incisal, prior
to the entrance of the shaft of the bur.
27. 5- DISCOLORATION of the crown caused by failure to remove
pulp debris. The access cavity is too far to the gingival with no
incisal extension.
6- LEDGE formation at the apical-distal curve caused by using
an uncurved instrument too large for the canal. The cavity is
adequate.
37. PERFORATION at the cervical area
caused by failure to recognize that
the premolar has tilted to the distal.
FAILURE to locate the third canal of
the maxillary first premolar (6% of
the time).
41. MB1
MB2
Palatal
DB
Point of
entry
Upper
⢠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.
42. 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.
47. 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.
48. 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.
49. 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.
50. 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.
Laws of the pulp chamber anatomy
51. 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.
52. 5-Law of color change: The pulp chamber floor is always darker in color than the walls.
53. 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 floorâwall junction.
54. 8-Third law of orifice location: The orifices of the root canals are always located at
the terminus of the rootsâ developmental fusion lines.
