4_18746_797l.doc

Lecture three------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

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. 2.

give direct access to the apical foramen, not only to the canal orifice. 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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Lecture three------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

4.

endodontic entries are prepared through the occlusal or lingual surfacenever 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 internalexternal 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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Lecture three------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

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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Lecture three------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

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 4

Lecture three------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

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. 5

Lecture three------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

2. 3. 4. 5.

6.

the endodontic pathfinder inserted into the orifice openings reveals the direction that the canals take in leaving the main chamber. digital perception with a hand instrument can identify curvatures, obstruction, root division and additional canal orifices. fiber-optic illumination can reveal calcifications, orifice location, and fractures. 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. 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. 6

Lecture three------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

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. 2.

cervical level: pulp wider in mesiodistal dimension. 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. 7

Lecture three------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

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 8

Lecture three------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

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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Lecture three------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

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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Lecture three------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

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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Lecture three------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

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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Lecture three------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

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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Lecture three------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

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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Lecture three------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

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------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

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------------------------------------------------------------------------ ‫ احمد غانم‬.‫د‬

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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