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					         Lecture three-------   ------------------------------------------------------------


                         Access Cavity Preparation

     Endodontic Coronal Cavity Preparation

     I. Outline Form

     II. Convenience Form

     III. Removal of the remaining carious dentin (and defective restorations)

     IV. Toilet of the cavity



     Endodontic Radicular Cavity Preparation

     I and II. Outline Form and Convenience Form (continued)

     IV. Toilet of the cavity (continued)

     V. Retention Form

     VI. Resistance Form



     Access opening rely, is the key of endodontics.

     Rules for proper access preparation: to ensure that the most efficient
     access cavity is prepared, the following rules should be observed:

1.     give direct access to the apical foramen, not only to the canal orifice.
2.     access cavity preparations are different from typical operative occlusal
   preparations, in that they are not depend on the topography of occlusal
   grooves, pits, fissures and on the avoidance of underlying pulp. But the need
   to uncovering the roof of the pulp chamber and divergent walls.
3.     the likely interior anatomy of the tooth under treatment must be
   determined.


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4.     endodontic entries are prepared through the occlusal or lingual surface-
   never through the proximal or gingival surface.
5.     as part of the access preparation, the unsupported cusps of posterior
   teeth must be reduced.



     Principle I. 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. Moreover, external outline form evolves from the
     internal anatomy of the tooth established by the pulp. Because of this internal-
     external relationship, endodontic preparations must of necessity be done in a
     reverse manner, from the inside of the tooth to the outside. That is to say,
     external outline form is established by mechanically projecting the internal
     anatomy of the pulp onto the external surface. This may be accomplished only
     by drilling into the open space of the pulp chamber and then working with the
     bur from the inside of the tooth to the outside, cutting away the dentin of the
     pulpal roof and walls overhanging the floor of the chamber. This intracoronal
     preparation is contrasted to the extracoronal preparation of operative
     dentistry, in which outline form is always related to the external anatomy of the
     tooth. The tendency to establish endodontic outline form in the conventional
     operative manner and shape must be resisted. To achieve optimal
     preparation, three factors of internal anatomy must be considered:

            (1) the size of the pulp chamber,

            (2) the shape of the pulp chamber, and

            (3) the number of individual root canals, their curvature, and their
                   position.

             Size of Pulp Chamber. The outline form of endodontic access cavities
     is materially affected by the size of the pulp chamber. 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. This
     becomes quite apparent in preparing the anterior teeth of youngsters, whose
     larger root canals require larger instruments and filling materials—materials
     that, in turn, will not pass through a small orifice in the crown. Shape of Pulp


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Chamber. 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. This triangular shape is extended up the walls of the cavity and out
onto the occlusal surface; hence, the final occlusal cavity outline form is
generally triangular. As another example, the coronal pulp of a maxillary
premolar is flat mesiodistally but is elongated buccolingually. The outline form
is, therefore, an elongated oval that extends buccolingually rather than
mesiodistally, as does Black’s operative cavity preparation. Number, Position,
and Curvature of Root Canals. The third factor regulating outline form is the
number, position, and curvature or direction of the 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.
When cavity walls are extended to improve instrumentation, the outline form is
materially affected. This change is for convenience in preparation; hence,
convenience form partly regulates the ultimate outline form.



Principle II: Convenience Form
        Convenience form was conceived by Black as a modification of the
cavity outline form to establish greater convenience in the placement of
intracoronal restorations. In endodontic therapy, however, convenience form
makes more convenient (and accurate) the 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.



1- Unobstructed Access to the Canal Orifice.

       In endodontic cavity preparations of all teeth, 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


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to observe this principle not only endangers the successful outcome of the
case but also adds materially to the duration of treatment.

        In certain teeth, extra precautions must be taken to search for
additional canals. The lower incisors are a case in point. Even more important
is the high incidence of a second separate canal in the mesiobuccal root of
maxillary molars. A second canal often is found in the distal root of mandibular
molars as well. The premolars, both maxillary and mandibular, can also be
counted on to have extra canals. During preparation, the operator, mindful of
these variations from the norm, searches conscientiously for additional canals.
In many cases, the outline form has to be modified to facilitate this search and
the ultimate cleaning, shaping, and filling of the extra canals.

2- Direct Access to the Apical Foramen.

       To provide 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. Infrequently, total decuspation is necessary.


3- Extension to Accommodate Filling Techniques.

       It is 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, wherein rather rigid pluggers are used in a vertical thrust,
then the outline form may have to be widely extended to accommodate these
heavier instruments.


4- Complete Authority over the Enlarging Instrument.

        It is imperative that the clinician maintain complete control over the root
canal instrument. If the instrument is impinged at the canal orifice by tooth
structure that should have been removed, the dentist will have lost control of
the direction of the tip of the instrument, and the intervening tooth structure will
dictate the control of the instrument. If, on the other hand, the tooth structure
is removed around the orifice so that the instrument stands free in this area of
the canal, the instrument will then be controlled by only two factors: the


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         Lecture three-------   ------------------------------------------------------------


     clinician’s fingers on the handle of the instrument and the walls of the canal at
     the tip of the instrument. Nothing is to intervene between these two points.

             Failure to properly modify the access cavity outline by extending the
     convenience form will ultimately lead to failure by either root perforation,
     “ledge” or “shelf” formation within the canal, instrument breakage, or the
     incorrect shape of the completed canal preparation, often termed “zipping” or
     apical transportation.



     Principle III: Removal of the Remaining Carious Dentin and
     Defective Restorations
             Caries and defective restorations remaining in an endodontic cavity
     preparation must be removed for three reasons: (1) to eliminate mechanically
     as many bacteria as possible from the interior of the tooth, (2) to eliminate the
     discolored tooth structure, that may ultimately lead to staining of the crown,
     and (3) to eliminate the possibility of any bacteria-laden saliva leaking into the
     prepared cavity. The last point is especially true of proximal or buccal caries
     that extend into the prepared cavity.

            After the caries are removed, if a carious perforation of the wall is
     allowing salivary leakage, the area must be repaired with cement, preferably
     from inside the cavity.



     Methods of determining anatomical details:

1.          A      radiograph many clues to anatomic “aberrations” lateral
     radiolucencies indicating the presence of lateral or accessory canals, an
     abrupt ending of a large canal significantly a bifurcation, where it is assumed
     that it has bifurcation (or trifurcation) in to much finer diameters. To confirm
     this division a second radiograph is exposed from mesial angulations of 10 to
     30 degrees. The resulting film shows either more roots or multiple vertical
     lines indicating the peripheries of additional root surfaces. A knoblike image
     indicating an apex that curves toward or away from beam of the x-ray .
     multiple vertical lines indicating the possibility of a thin root, which may be
     hourglass shaped in cross section and susceptible to perforation.


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2.          the endodontic pathfinder inserted into the orifice openings reveals the
     direction that the canals take in leaving the main chamber.
3.          digital perception with a hand instrument can identify curvatures,
     obstruction, root division and additional canal orifices.
4.          fiber-optic illumination can reveal calcifications, orifice location, and
     fractures.
5.          further knowledge of root formation can save the clinician difficulties with
     instrumentation. For example what appears radiographically to be normal
     palatal root of maxillary first molar, but is actually a root with a sharp apical
     curvature toward the buccal.
6.        ethnic characteristics and other physical differences can be occurs, for
     example the occurrence of 4 canals in mandibular first molars.



     Endodontic Access Preparation of maxillary Anterior Teeth
             The access cavity preparation is begun by using a round-point
     tapering fissure bur in the exact center of the lingual surface. In past, they
     were advocated that initial entry made at right angle to the long axis of the
     tooth, the after entrance into pulp chamber maintain point of bur in central
     cavity and rotate handpiece toward incisal so burs parallels long axis of tooth.
     Now a day new endodontic schools suggested that if the access is begun at a
     right angle to the long axis, there is a possibility for penetration too far labially,
     or for completely missing the pulp canal on a tooth with considerable dentinal
     sclerosis, So instead of that, the initial penetration with long axis of the root in
     the center of the tooth must eventually reach the canal. As maxillary anterior
     teeth have distal inclination, the handpiece must be distally inclined.

             Large, triangular, funnel-shaped coronal preparation is necessary to
     adequate debrided the pulp chamber. Note beveled extension towered incisal
     that will carry the preparation labially and thus nearer central axis. After initial
     entry of the pulp the preparation completed usually by round burs by working
     from inside the chamber to outside to remove the lingual and labial walls of
     the chamber and ensure unroofing of the pulp chamber. The resulting cavity is
     smooth, continuous, and flowing from cavity margin to the canal orifice. After
     outline form is completed, surgical length bur or Gates-Glidden bur were used
     carefully to remove lingual “shoulder” and to give continuous, smooth-flowing
     preparation.


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     Maxillary central incisor
             Maxillary central incisor always has one root and type I canal
     configuration. The root is bulky with slight distal inclination. Multiple canals are
     rare, but accessory and lateral canals are common of more than 60% and the
     apical foramen frequently exits short of the apex in 45%. The root apex
     directed to the labial or distal direction. The extend of the pulp horn to the
     crown depend on the age and pathological factor. A labiolingual section of the
     tooth shows that the pulp cavity comes to a point near the incisal edge,
     becomes wider , as it approaches the cervical lines, then narrows to the apex.
     A mesiodistal section discloses that the pulp cavity is wider toward the incisal
     area and then tapers to the apex. Cross section area at three levels revealed:

1.     cervical level: pulp wider in mesiodistal dimension.
2.     mid-root level: canal continues ovoid and required multiple cone
   Obturation.
3.     apical third level: generally round in shape in the older and tend to be
   more oval in young age.



     Maxillary lateral incisor
             Maxillary lateral incisor always has one root and type I canal
     configuration. The root more slender than in the maxillary central incisor and
     has frequently distal and\or lingual curvature or dilacerations. There are a
     number of rare morphology oddities that occur in the maxillary lateral incisor.
     Occasionally the crown is “pegged” and assumed the shape of a blunt-ended
     pencil. Some others have a groove on the lingual, starting at the cingulum,
     that on rare occasions extends deep into the root structure, creating an
     untreatable periodontal defect. On rare occasions, access is complicated by a
     dense in dente (an invagination of part of the lingual surface of the tooth into
     crown). These teeth are predisposed to decay because of this anatomic
     malformation, and pulp may die before the root apex is completely developed.

             The apical foramen is generally closer to the anatomic apex than in the
     central incisor but may found on the lateral aspect within 1-2 mm of the apex.
     Cross section area at three levels revealed:

     1. cervical level: pulp wider in labiolingual dimension.


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2. mid-root level: canal continues ovoid and required multiple cone Obturation.

3. apical third level: generally round in shape in the older and tend to be more
oval in young age and gradually curved.



Maxillary canine
        Maxillary canine always has one root and type I canal configuration.
The root is slender from labial view. But bulky as viewed proximally, with an
irregular out line. It is the longest tooth in the dental arch, thickly enameled
crown sustains heavy incisal wear but often displays deep cervical erosion
with the age. The apex often curves, in any direction (distally more) in the last
2-3mm. the thin buccal bone over the eminence often disintegrates, and
fenestration is a common finding. The apical foramen is usually close to the
anatomic apex but may be laterally positioned, especially when apical
curvature is present.

      The region of the maxillary incisors corresponds to an area of
embryological risk, presenting a variety of malformations: Cleft lips,
supernumerary teeth, peg shaped teeth, shovel shaped teeth, dens invaginatus.



Endodontic Access Preparation of mandibular Anterior Teeth
        The access cavity preparation is begun by using a round-point
tapering fissure bur in the exact center of the lingual surface. The direction of
entries same as upper maxillary anterior teeth. The preliminary cavity outline
is funneled or ovoid and fanned incisally and the enamel short bevel toward
incisal. And the same steps followed after initial drop inside the pulp chamber
as maxillary anterior teeth.



Mandibular central & lateral incisor
       Both are similar in shape, configuration, and dimension that on
description will hold true for both. They have only one root, which narrow
mesiodistally but relatively wide labiolingually, and may have a distal and \or


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lingual curvature. The canal may be of type I, II, III in that order of frequency.
When two canals were present, the labial canal the straighter. The point of
division for divided canals was in the cervical third of the root. mesiodistal
section shows that pulp canal is quite narrow( so, the access must be precise
poisoned to avoid perforation) and is particular constricted in the root portion
of the tooth, with both the root and the canal taking a gradual distal curve.
These teeth come right behind the molars and multicanaled mandibular
bicaspids in degree of difficulty. The major reason for this is the narrow
mesiodistal dimension compared with buccolingual width, which makes it
almost impossible to enlarge the canal or canals evenly in every direction
(Gates-Glidden or pesos if used, here with great precaution). also, the 40%
of teeth with tow canals reported , which is almost never reached by
practitioners during clinical situations. To added the problems, because of
their proximity, it is virtually impossible to radiograph these teeth from a
sufficient angle to know in advance that two canals are present.

      The reason why these teeth do not cause us as many problems as
they might is that a high percentage of the two-canal cases rejoin near the
apex.



Mandibular canine
       The have one root but in rare cases may have two separated roots.
Teeth with one root may have type I, II, III configuration. These teeth usually
the longest of the mandibular teeth but, have greater length variation than do
maxillary cuspids. the root canal is thin mesiodistally but wide labiolingually.
The cervical cross section is oval, as is the suggested entry. This tooth usually
has a slight labial axial inclination of the crow. Therefore, the access is
directed toward the lingual surface. However, if two canals are present, only
the extra bucciolingual width of the access will permit proper location,
preparation, and filling.



Maxillary first bicuspid
      It have a number of variations in root and canal configuration.
Approximately 80% have two roots, one buccal and one lingual each with


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single canal. The roots may be completely separate or merely twin projections
rising from middle third of the root to the apex. The roots are usually equal in
length from cusp to the apex. In approximately 18% of maxillary first
premolar, only one root is present., usually with two separate canals (type III).
Type II canal is present less frequently. Type I is very rare. The access cavity
is a thin oval. The buccal canal lies beneath the buccal cusp, whereas the
palatal canal lies beneath the palatal cusp. The root is considerably shorter
than in the canine, and distal curvature is not uncommon. The apical foramen
is usually close to the anatomic apex. After endodontic treatment, full occlusal
coverage is mandatory to ensure against cuspal or crown root fracture.



Maxillary second bicuspid
         Most common with one root (85%) and type I, but type II, III or IV may
be present, with degreasing frequency. The approximately 15% of the time,
two separate roots are present, each with a single canal. At the cervical line if,
one canal is present, the canal shape is slightly oval and at the center of the
root. If two canals are present, the canal shape resembles a ribbon or figure
eight. When more than one canals are present they tend to be anastomose or
webbing. But most of these canals 75% are merge just at the apex with one
foramen. Most studies reported that when two canals joint into one, palatal
canal frequently exhibits a straight-line access to the apex. We should notes
that when periapecal film shows a sudden narrowing or even disappears, it
means that at this point the canal divides into two parts. Like first premolar,
After endodontic treatment, full occlusal coverage is mandatory to ensure
against cuspal or crown root fracture.



Mandibular first bicuspid
        For many years this tooth was considered to have only one root with a
single canal. However, there is no question that a single root that divides
apically or a type IV canal system is present in a very significant cases. The
coronal anatomy consist of one well develop buccal cusp with and a small or
almost nonexistent lingual outgrowth of enamel. Access is made slightly
buccal to the central groove and is directed in the long axis of the root toward



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the central cervical area. The cross section of the cervical pulp chamber is
almost round in a single canal tooth and is ovoid in two canal teeth.

       75% of this teeth had one canal and foramen at the apex, and one
study reported two canal and foramen at the apex, while one reported three
canals in 0.5%. C-shape root canal also reported in 14% .



Mandibular second bicuspid
        Very similar to first mandibular premolar with less radicular problems.
Its crown has well developed buccal and lingual cusp. Access are made ovoid
in the central groove. One root and well centered canal, rarely type II, III or IV
canal configuration are present. An important consideration that must not be
overlooked is the anatomic position of the mental foramen and the
neurovascular structures that pass through it. This proximity can result in
temporary paresthesia from the fulminating inflammatrory process when acute
exacerbation of mandibular premolars occurs. Exacerbation in this region
seem to be intense and more resistant to nonsurgical therapy than in the other
parts of the mouth.



Maxillary first molar
        The tooth largest in volume and most complex in the root and root
canal anatomy. This posterior teeth with highest endodontic failure and
unquestionably one of the most important teeth. Three roots: palatal root,
which is the largest and longest and MB and DB roots which about the same
length. A rhomboid-shaped or quadrilateral , with four unequal sides access
preparation helps to located these mesial canal although previously describe
access cavity preparation for both maxillary and mandibular molars as a
triangular in outline. The corners of the access must be rounded, the shorter
side the palatal, parallel to the central groove. The next shorter side is the
buccal and has a slop toward the distopalatal aspect because the position of
the distobuccal orifice id father toward the palatal than the mesiobuccal orifice.
The longest side is the mesial, with opposite side toward the distal slightly
shorter. Since all the orifices of this tooth lie on the mesial three fifth of the



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crown, there is no need to violate the oblique ridge in preparing the access
cavity.

        the palatal root is often curved buccally in the apical third and its easy
to located, its orifice lies well toward the palatal surface and root is sharply
angulated from the midline. Both P and DB root canal always have one canal
each, but MB may have type I, II, III which make it the most difficult one to be
treated. 2 foramen were present in 14% of MB and 42% manifest 2 canals
indicated the second ML canal present in the MB root. One study reported that
95.5% of the MB root examined contain this additional canal although not all
canals reach the apex, this study revealed that 71.5% had 2 patent canals at
the apex. The extra orifice lies somewhere between the mesiobuccal and
lingual canals. It may at times lie quite mesial to a line between these 2
canals, appearing to be almost under margin ridge. The orifice of the MB
canal is located beneath the MB cusp, but the orifice to the DB canal has no
direct relation to its cusp, but they usually located by means of its relation to
MB orifice which approximately 2-3mm to distal and slightly to the palatal
aspect of the MB orifice. The distance between the 2 buccal orifices will
greater when a considerable dentinal sclerosis has occurred.

        If any preoperative symptoms (chronic draining, sensitivity to
temperatures or apical soreness over that root persist), further efforts to locate
the additional canal should be made. The routine periapical view of this tooth
gives no additional information concering the possibility of an additional MB
canal. However, angled from mesial to distal side radiograph are helpful in
anticipating the fourth canal before starting treatment.



Maxillary second molar
       It is usually has similar canal configuration combinations to the first
molar: 2 buccal root and one palatal. The access cavity is prepared in the
same manner and shape as for first molar, except that the buccal side of
quadrilateral is not as long since the buccal canals are usually found closer
together. In second molars with sclerotic canals or those that have crowns
compressed mesiodistally, the distobuccal orifice may be located toward the
center of the access rather than the mesiobuccal orifice.. a differing type of
root configuration may also be presenting the maxillary second molar that
contains only two roots, one buccal and other palatal in 10%.


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Mandibular first molar
       Mandibular first molar is the earliest permanent posterior tooth to erupt,
it seems to be the most frequently in need of endodontic treatment. It usually
has two roots (namely mesial and distal), but occasionally three, with a
supernumerary distolingual root, the frequency of this trait range from 6-44%.
The mesial root has two canals (mesiobuccal and mesiolingual) and one or
two canals in the distal root . some studies reported that approximately one
third of mandibular first molar studies had four root canals.
       The mesial roots are usually curved, with the greatest curvature in the
mesiobuccal canal . It has always two distinct canals leaving the floor of the
pulp chamber, which exists as separate apical foramina in approximately 85%
of cases but merge to form one apical foramina in the reminder.
       As the mesial root leaves the crown, it curves to the mesial but then it
makes a gradual turn to the distal and generally has a distal curve in the
apical third. From a buccal view, this root has a crescent shape.
        The two mesial canals have the same directional curvatures when
viewed from the buccal; first to the mesial and then to the distal. From the
proximal view the mesio-buccal canal curves first to the buccal and then to the
lingual. The coronal portion of the mesiolingual canal is straighter and then in
the middle third begins a more gradual buccal curve. Therefore, from this
view, the canals diverge coronally but then converge apically.
       The degree of curvature and configuration of root canals creates some
technical difficulties to the clinician during biomechanical preparation. The
presence of dumbbell-shaped mesial root in mandibular molars with severe
distal concavities creates difficulties in properly instrumenting in three
dimensions.
       The distal root is slightly narrower buccolingually than the mesial root,
but they are equal in mesiodistal width. The distal root often has a mesial
curvature. Usually, only one distal canal is present with a large kidney-shaped
orifice. The presence of two separate distal roots is rare but does occur. The
distolingual root is smaller than the distobuccal root and usually very curved
(radix endomolaris). The canals of the distal root are larger than those of the
mesial root. Occasionally, the orifice is wider from buccal to lingual.
       A mesiodistal section through the tooth reveals that the orifice of both
the mesial and the distal canals lie in the mesial two thirds of the crown and
that the canals are well centered in their roots. A buccolingual section shows
that the pulp chamber is in the center of the crown and that the distal canal is
wide and ribbon shaped, whereas the mesial canals are thin.



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         If the distal root has two root canals, the canals may remain divided
throughout their length, terminating in two separate apical foramina, may unite
terminating in a common apical foramina or may communicate with each other
partially or completely by means of traverse anastomose.

         Access preparations for both first and second mandibular molars are
essentially identical. The general outline is trapezoidal with rounded corners.
The shortest side is to the distal aspect, and the mesial side is slightly longer.
The buccal and lingual sides are of approximately the same length and taper
toward each other distally. The ML canal lies beneath the ML cusp. The MB
canal is most difficult to locate, but it is usually found on a straight line to the
buccal from the ML orifice and is tucked deeply beneath the MB cusp. When
difficulty is encountered in locating the MB canal, the operator should have no
qualms about cutting down the mesiobuccal portion of the tooth, otherwise if
the canal cannot be located and would be failed so, conservation of the tooth
structure would be useless.

        Previously many authers have suggested the triangular shaped entry
for this tooth, however, the distal canal is kidney shaped in most cases, with
the greatest width BL. Also, 2 canals exiting the floor of the chamber are
founded in the distal root approximately 30% of the time, one on the buccal
aspect and the other toward the distal and lingual aspects.



Mandibular second molar
        This tooth has more variants than any of the molar teeth, even though
the most common configuration is the same as that of the mandibular first
molar. Although only mesial canal is never occur in the second molar, it does
occur in the second molar. Usually when only one canal is present, it is
located in the middle of mesial half of the chamber. This tooth may have only
a single root with several variants: one single, large canal; 2 canals that merge
or remain separate or so called C-shaped tooth, in which orifices of the canals
are not individually distinct but that there is a C-shape taught on the floor of
the chamber.




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                       Assessment of access opening:
        In anterior teeth, access opening is evaluated with a file when placed
deep in the canal, the file should not be deflected from the incisal enamel.
Ideally, the file should site passively in the canal. Pulp horn removal evaluated
with the small hooked end of an explorer. They should be no incisal catch.

        In the posterior teeth, the access opening is evaluated with files, which
should not be deflected from enamel. In a single canal premolars, the file
should pass straight into the canal. In the multicanaled tooth, the file handles
ideally are parallel when are placed in there respective canal simultaneously,
or at least the files shaft should be nearly parallel. Pulp horn should not be
necessary to be opened excessively to removed the horn as anterior teeth
WHY?...........

        Misorientation of the burs and access opening lead gouging of the
dentin in the anterior and premolars in any direction, while in the mandibular
molars there are 2 regions tend to be abused, the mesial aspect under the
marginal ridge and the lingual surface beneath the lingual cusps. The teeth
crown and the crowns tend to tip mesially and lingually. A bur directed straight
inferior will gouge these areas. In the maxillary molars as in the mandibular
molars, the is a tendency to remove dentin beneath the mesial margin ridge.

       Also Misorientation and lake of dental anatomy knowledge lead to
mistaken of canals and perforation of crown\ or roots.



Principle IV: Toilet of the access opening
        All of the caries, debris, denticles, pulp tissues and necrotic materials
must be removed from the chamber before the radicular preparation begun,
otherwise, these elements my be 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 of anterior teeth..

         Round burs and longer blade spoon excavator are ideal for this task.
Irrigation with sodium hypochlorite or hydrogen peroxide is also an excellent
measure.


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         Lecture three-------      ------------------------------------------------------------


                                Exploration of the Canal Orifice
            Before the canals can be entered their orifices must be found. In the
     older patient, finding a canal orifice may be the most difficult and time
     consuming operation.

1.        Quite obviously, knowledge of pulp anatomy- knowing where to look and
     expected to find the orifices- is the first importance.
2.        The radiograph is invaluable in determining just where and in which
     direction canals enter into pulp chamber. A bite-wing radiograph is particularly
     helpful in providing an understood view of the pulp chamber.
3.        Color is another invaluable aid in finding a canal orifice. The floor of the
     pulp chamber and the continuous anatomic lines that connects the orifices is
     dark- dark gray or some times brown in contrast to the white or light yellow of
     the walls of the chambers.
4.        The endodontic explorer is the greatest aid in finding a minute canal
     entrance.
5.        Canal Blue Localizes root canals easily It has never been so easy to find
     root canals: Coat the floor of the pulp chamber with Canal Blue,after10
     seconds rinse and dry. The remaining blue dots indicate the canal locations.
     (new method ).



                                      Radicular Access
            Radicular access creates spaces in the coronal regions of the canal,
     which facilitates placing and manipulating subsequent files and increases the
     depth and effectiveness of irrigation. Generous enlargement of the coronal
     half of the canal developed with radicular access provides important
     advantages in irrigation efficacy, apical control zone, cone fit, and compaction
     procedures, regardless of the Obturation technique used. Apical preparation is
     easier and more consistent, apical blockage, ledging, ripping, and perforation
     are less likely. Radicular access may be accomplished with :

1.       engine-driven : which is the preferred method of developing a radicular
     access by Gates-Glidden drills.      The access is flooded with sodium
     hypochlorite and the radicular access is initiated by passing rotating No. 2
     Gates-Glidden drill into the canal. This drill pulls inwardly as a result of


                                                        16
        Lecture three-------   ------------------------------------------------------------


   rotation. The drill should be backed out of the canal after penetrating 1-2mm
   and cleared of debris before moving closer to the apex. The drill is then
   returned to the previous depth. Clean and ready to continue shaping. In and
   out movements are repeated until the No. 2 drill reaches its intended depth or
   until the clinician determines that curvature is preventing further penetration.
   After that a progression of drill diameters and shorter working depths is
   continued until the coronal portions of the canal are well cleaned and shaped.
   While preparing a radicular access, you must guided your work with the shape
   of each canals and the cutting stroke must be away from the concavity of the
   root.
2.      manual radicular access: with circumferential filing action. This process
   works best when there is no curvature is present. If the curvature is present,
   the portion of the file that passes beyond the curve consistently presses
   against the same wall regardless of the direction of the clinician moves his or
   her hand. This task was accomplished with either K-type file or more rapidly
   with H -type file.



                                    Pulp extirpation
   Extirpation with a broach does not represent “pulpectomy” which is total
   removal of the pulp tissues. Rather, portions of pulp are dislodged and pulled
   out, leaving shredded remnants. Complete removal is not accomplished until
   working length is established and considerable canal preparation has been
   done. The preferred time for pulp extirpation is early during access.
   Completion of access preparation is difficult without good visibility, which is
   not possible with continues hemorrhage into the chamber from a torn pulp
   stump. The best time when the chamber is unroofed and canals are
   discovered.




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