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ACCESS CAVITY
PREPARATION
Dr. Ahmed Negm
Access is the first and most important phase of root canal
treatment. A well-designed access preparation is essential for a
good endodontic result.
Pulp space morphology
Pulp horn
Coronal pulp
Pulp chamber
Orifice
Lateral canal
Radicular pulp
Root canal
Apical foramen
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.
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.
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.
b. Shape of pulp chamber:
Anteriors
Premolars
Molars
Triangular.
Oval or ovoid.
Triangular.
c. Number and direction of root canals.
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.
2.
3.
4.
Unobstructed access to the orifices.
Direct access to the apical foramina.
Complete authority over the instrument.
Expansion to accommodate filling techniques.
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.
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.
Instruments
Low speed contra
High speed contra
DG 16 endodontic explorer
Round bur size
2,3,4
Safe-end tapered stone
Transmetal bur
Endo Z bur
Tapered stone with
round end
Pulpout bur
Endo access bur
Ultrasonics
Surgical operating microscope
Loupes
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
Steps
1
Entrance is gained through the middle of the middle
third of the palatal surface.
2
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.
3
The bur is positioned in a 45 degree to the long axis of the
tooth then advanced to penetrate the pulp chamber.
4
Removal of the pulp chamber (deroofing)
5
Removal of lingual shoulder.
In canine the outline is oval
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.
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.
4- Missed canal due to insufficient convenience extension.
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.
Premolars
Upper oval
Lower ovoid
Maxillary premolars
Buccal canal is located under
the buccal cusp tip.
Palatal canal is located at the
base of the palatal cusp.
1
Initial penetration is made parallel to the long axis of the tooth in
the exact center of the central groove
2
A round bur is used to open into the pulp chamber. The bur will be
felt to “drop” when the pulp chamber is reached.
3
An endodontic explorer is used to locate orifices.
4
A round bur is used to deroof the pulp chamber.
5
Finishing and flaring of the cavity walls.
Upper
Lower
Errors
Under extended
access cavity
Over extended
access cavity
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).
Molars
Lower
Upper
B
B
M M
D
D
L
P
Trapezoid
Upper
MB1
MB2
DB
Palatal
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.
Lower
Point of entry
MB
Distal
ML
•
•
•
•
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.
Errors
Under extended
access cavity
Over extended
access cavity
Perforation in the furcation area
Failure to locate all the canals
Crown perforation
Root perforation
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.
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.
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.
Laws of the pulp chamber anatomy
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.
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
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.
D
5-Law of color change: The pulp chamber floor is always darker in color than the walls.
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.
8-Third law of orifice location: The orifices of the root canals are always located at
the terminus of the roots’ developmental fusion lines.
Thank you
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