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Access to the Root Canal System: Coronal

Cavity PreparationAccess to the Root Canal System: Coronal Cavity Preparation

Careful cavicy preparation and obturation are the keystonesto successful root canaltreatment. As in restorative dentistry, the final restoration is no better than the initial cavitypreparation. Endodontic cavity preparation begins the instant the tooth is approached with acutting instrument (Figure 1 ). Hence, it is important that adequate access be developed toproperly clean and shape the canal system and obturate the space. When first approachingthe tooth, one must have in mind the three-dimensional anatomy of the pulp chamber aboutto be entered, not the two-dimensional image revealed by the radiograph {Figure 2). It is thischamber outline that is to be "projected" out onto the occlusal or lingual surface of the crown(. (Figure 3

Figure 1:A-C, Entrance is always gained through the occlusal surface of posterior teeth andthe lingual surface of anterior teethB. Specialized end-cutting, fissure burs are used for theinitial entre through enamel or goldA,and a special end-cutting, amalgam bur is used toperforate amalgam fillingsC. The same burs and stones may be used to extend the wallsto gain full access. bearing in mind, that they are end cutting and can and can damage the

.chamber floor

Figure 2 :Astandard radiograph (left) in buccolingual projection provides only a two-dimensional view of what is actually a three-dimensional problem. The maxillary second.premolar is actually an ovoid ribbon, rather than a round thread

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Figure 3 To gain adequate access to both canals, it is this broad ovoid outline that is.projected out onto the occlusal surface, rather than a round hole in the central pit

Figure 4 : Blacks principles of cavity preparationoutline, convenience, retention, andresistance formsapply to endodontic preparations as they do for coronal preparations: tothe former to gain unlimited access to the canal orifices, to the latter as extension for. prevention

Endodontic cavity preparation is separated into two anatomic entities: coronal preparationand radicular preparation. Coronal preparation is discussed in this chapter. In doing soone may fall back on Blacks principles of cavity preparationoutline, convenience,retention, and resistance formsadmittedly developed by Blackfor extracoronal preparation but just as applicable to intracoronal preparation (Figure 4).One may add removal of remaining cariousdentin (and defective restorations)as well astoilet of the cavity(both of which are necessary) to make Blacks principles complete.Outline form is often thought of as only the coronal cavity. But actually the entire preparation,from enamel surface to the apical terminus, is one long outline form (Figure 5). Onoccasion outline may have to be modified for the sake of convenience to accommodate theunstressed use of root canal instruments and filling materials (Figure 6). In other words, toreach the apical terminus without interference from overhanging tooth structure or ultra-.curved canals, one must extend the cavity outline

Also, on occasion the canal may be prepared for retentionof the primary filling point (seeFigure 5). However, more important is resistance form, to prepare an apical stop at thecanal terminus against which filling materials may be compressed without overextendingthe filling (see Figure 5). Proper preparation of the apical one-third of the canal is crucial to

.success

Figure 5 : Concept of total endodontic cavity preparation, coronal and radicular,Bas a continuum, based on Blacks principles.A,Radiographic apex.Resistance form at the apical stop.C,Retention form to retain the primary,filling material. D,Convenience form subject to revision to accommodate largerless flexible instruments. E,Outline form with basic preparation throughout its.len th, crown to a ical sto

Mosby's Review for the

NBDE I

B-TECH Dent-O-Soft

2.3.0.41991 with crack

Problem Solving in

Orthodontics

LEGAL NOTICE

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Figure 6A,Obstructed access to a mesial canal. The overhanging roof misdirectsthe instrument mesially, with a resulting ledge formation.B,Completelyremoving the roof brings canal orifices into view and allows immediate access.to each canal

Power-driven rotary instruments are used to penetrate the crown. Round carbide burs

commensurate in size with the chamber, as seen on a radiograph, or round-tip, end-cutting-tapered burs (TransmetalCaulk/Maillefer) or diamond stones (EndoAccess-Caulk/Maillefer, Tulsa, OK) are best forperforating enamel and entering the chamber (Figure 7). Enamel and precious metals areeasily removed with carbide burs, but extra-coarse, round-tip diamonds are best forpenetrating porcelain- fused-to-metal and all-porcelain restorations. Once the chamber isentered, the remaining tooth structure covering the chamber is removed with round ortapered burs or stones (Figure 8). Initially, high-speed rotary instruments are used. But oncethe chamber is entered,the neophyte is advised to use slower-speed instruments so thattactile sensation may, in part, guide the removal of the remaining structure. To overcut the.crown only weakens it more

Figure 7 :According to the size of the chamber, a no.4 or no.6 round bur may.be used to remove the roof of the pulp chamber

Figure 8 :A,Final finish of the convenience form. In the case of a lower molar, the entirecavity slopes to the mesial aspect allowing easier access to the mesial canal orifices.B,.Pulp-Shaper bur with noncutting tip (Dentsply/Tulsa) used to extend the access

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As soon as the canal orifices have been exposed, they may be entered with endodontic filesto determine whether the instruments are either under stress or free of interfering toothstructure (Figure 9). If binding, convenience form dictates that the coronal outline form beextended to free up the shaft of the file. There should be unobstructed access to the canalorifices and direct access to the apical foramen. This is done with high-speed tapered bursor stones, preferably with noncutting tips (see Figure 8). Warning: fissure burs often.chatter, distressing to the patient

Figure 9 : Unobstructed access to the canal orifices and down the canals to the apical.stop area

MAXILLARY ANTERIOR TEETHMaxillary anterior teeth are entered from the lingual aspect. The enamel is perforated with around carbide bur, an end-cutting, tapered bur, or a diamond stone held parallel to the longaxis of the tooth (Figure 10). As soon as the pulp chamber is entered, the tapered bur isused to remove tooth structure incisally (Figure 11). This convenience removal allowsadequate room for the shaft of burs that will enter deeper into the pulp chamber to removeits roof (Figure 12). Once the preparation is completed on the incisolabial surface, a(. tapered stone is used to remove the lingual shoulder (Figure 13

Figure 10 : Maxillary anterior teeth. Entrance is always gained through the lingual surface.Initial penetration is made at the exact center of the lingual surface. The bur should be heldapproximately parallel to the long axis of the tooth. This initial cut may be made with high-speed instruments, but the neophyte is warned to use slower speeds in proceeding toward.the canal

Figure 11 : Maxillary anterior teeth. The preliminary cavity outline is funneled and fannedfrom theincisal edge to allow room for the shaft of the bur to follow and penetrate.the chamber

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Figure 12Maxillary anterior teeth. Use of a slower-speed round bur is suggested to enterthe pulp chamber, keeping in mind the verticality of the tooth. The roof of the pulp chamber is.removed toward the incisal surface in a convenience extension

Figure 13 Maxillary anterior teeth. Afissure-style bur or diamond is used to remove thelingual shoulder and prepare the incisal extension to allow unobstructed access to the.entire canalThe final outline form on the lingual surface should reflect the size and shape of the pulpchamber, usually dictated by age (Figure 14). The entire outline form, from incisal to apex,must be free of any encumbrances that would interfere with cleaning, shaping, and(. obturation (Figure 15

Figure 14 Maxillary anterior teeth. The lingual outline form reflects the size of the pulpchambera larger, fan-shaped outline in youngsters and a long, ovoid outline in olderpatients. Be sure to remove any pulpal remnants to the mesial or distal aspects to prevent.future staining

Figure 15 Maxillary anterior teeth. Final preparation with the instrument in place. The

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instrument shaft clears the incisal cavity margin and the reduced lingual shoulder, allowingan unstrained approach, under the complete control of the clinician, to the apical third of the.canal

Virtually the same procedures and precautions apply to maxillary lateral incisors and.canines as to anterior teethOperative ErrorsThe common error of perforating or badly gouging the gingivolabial aspect (Figure 16) isusually due to two factors: not allowing adequate access toward the incisal aspect of thepreparation (see Figure 11) or not properly aligning the bur vertically with the long axis of the

tooth. Another common failure is not providing adequate access or removal of the lingualshoulder (see Figures 11 and 13). Loss of control of the instrument results in a pear-shaped and inadequate preparation of the apical third (Figure 17). Asimilar failure, theresult of inadequate access, diverts instruments from the canal lumen, as il lustrated here ina canine with a labial root curvature, undetectable in a standard labial-lingual radiograph(. (Figure 18

Figure 16 Operative errormaxillary anterior teeth. Perforation of the labiocervical aspectcaused by failure to complete the convenience extension toward the incisal prior to entranceof the shaft of the bur. This also can be caused by a failure to align the bur parallel to the.long axis of the tooth

Figure 17 Operative error maxillary anterior teeth. Pear-shaped apical preparation causedby a failure to complete the convenience extensions. The shaft of the instrument rides onthe cavity margin and the lingual shoulder that direct the control of the instrument..Inadequate debridement and obturation ensure failure

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Figure 18 Operative errormaxillary anterior teeth. Ledge formation at the apicolabial curve(not discernible in a radiograph) caused again by a failure to complete the convenience.extension at the incisal surface and the lingual shoulder

MANDIBULAR ANTERIOR TEETHMandibular anterior teeth also are entered from the lingual surface. The enamel isperforated with a round carbide bur, an end-cutting tapered bur, or a diamond stone, heldparallel to the long axis of the tooth (Figure 19). As soon as the pulp chamber is entered, thebur/stone is used to remove tooth structure toward the incisal aspect (Figure20). This

convenience removal allows adequate room for the shaft of burs that will enter deeper into(. the pulp chamber to remove its roof (Figure 21

Figure 19 Mandibular anterior teeth. Entrance is always gained through the l ingual surface.Initial penetration is made in the exact center of the lingual surface. An endcutting, fissure.bur is turned to cut at right angles to the lingual surface

Figure 20 Mandibular anterior teeth. As soon as the enamel is penetrated, the bur is turnedvertically, beginning the convenience cut toward the incisal. Once enough overhangingstructure has beenremoved, the pulp chamber may be entered vertically with a no. 4 round bur in a slow.handpiece

Figure 21 Mandibular anterio teeth. The orifice is widened with a fissure bur or a diamond.toward the incisal and the shoulder toward the lingual to give a smooth-flowing preparation

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The final outline form on the lingual surface should reflect thesize and shape of the pulpchamber, usually dictated by age (Figure 22). The entire outline form, from incisal to apex,must be free of any encumbrances that would interfere with cleaning, shaping, or obturation(. (Figure 23

Figure 22 Mandibular anterior teeth. Again, the shape of the lingual outline form reflects the.size of the pulp chamber, which in turn reflects the age of the patient

Figure 23 Mandibular anterior teeth. Final preparation with the instrument in place. Theinstrument shaft clears the incisal cavity margin and the reduced lingual shoulder, andpenetrates unimpeded to the apex, under complete control of the clinician. Always searchfor a secondcanal to the labial or the lingualin lower incisors. Virtually the same

procedures and precautions apply to mandibular lateral incisors and canines as to anterior.teeth

Operative ErrorsThe common error of gouging or perforating at the incisogingival aspect (Figure 24) isusually due to two factors: not allowing adequate access toward the incisal of thepreparation (see Figures 20 and 21) or not aligning the bur vertically with the long axis of thetooth (see Figure 19). Inadequate access leads to the inability to explore, dbride, and(. obturate the second canal, often not seen in a standard labiolingual radiograph (Figure 25Never enter the pulp chamber from a proximal surface (Figure 26). As inviting as it mightappear in some situations, total loss of control of enlarging instruments is the result.!Failure looms

Figure 24 Operative errors mandibular anterior teeth. Inadequate lingual access controls.the shaft of the bur and misdirects it to the labial. Cervical perforation can result

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Figure 25 Operative errors mandibular anterior teeth. Again, inadequate access preventsthe exploration for a second canal toward the labial. Straight-on radiographs do not reveal.this common error

Figure 26 Operative errors mandibular anterior teeth.Neverattempt to enter the canalfrom the proximal surface. Atotal loss of instrument control leads to ledging and/or.perforation

MAXILLARY PREMOLAR TEETHEntrance is always gained through the occlusal surface of all posterior teeth. The enamel or

restoration is perforated in the exact center of the central groove with a round carbide bur, anend-cutting, tapered bur, or a diamond stone held parallel to the long axis of the tooth(. (Figure 27Once the chamber is entered, an explorer or endodontic file is used to explore the orifices ofthe labial and lingual canals of the first premolar or the central canal (or possibly additionalcanals) in the second premolar (Figure 28). From this exploration one learns the necessaryextension of the buccolingual outline form. Always probe for the possibility of additional.canals in either premolar

Figure 27 Maxillary premolar teeth. Access to all posterior teeth is through the occlusalsurface. Initial penetration is made parallel to the long axis of the tooth in the exact center ofthe central groove. Ano. 4 round bur may be used to penetrate into the pulp chamber. Thebur will be felt to drop when the pulp chamber is reached. If the pulp is well calcified, thedrop will not be felt, so the bur penetrates until the nose of the handpiece touches theocclusal surface9.0 mm. The orifice is then widened to allow exploration for the canal.orifices

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Figure 28 Maxillary premolar teeth. An endodontic explorer is used to locate the orifices ofthe buccal and lingual canals of the first premolar or the central canal of the secondpremolar. Always search for extra canalsthe third canal in the first premolar or a second.canal in the second premolar

Buccolingual cavity extension is best done with tapering fissure burs or stones (Figure 29).Adequate buccolingual endodontic cavity outline form is in contrast to the mesiodistalrestorative outline form (Figure 30). The final preparation should provide adequate,unimpeded access to all canal orifices (Figure 31). Cavity walls should not impede.complete authority over the enlarging instruments

Figure 29 Maxillary premolar teeth. The cavity outline is then extended buccolingually with a

tapered, fissure bur or diamond

Figure 30 Maxillary premolar teeth. The buccolingual preparation reflects the internal

anatomy of the pulp chamber and the entrance to the canal orifices

Figure 31 Maxillary premolar teeth. Final preparation should

provide unobstructed.access to the canal orifices

Operative ErrorsAn error that occurs in maxillary premolar teeth is overextendedpreparation in a fruitlesssearch for a receded pulp (Figure 32).The white color of the roof of the chamber is a cluethat the pulp hasnot been reached. The floor of the chamber is a dark color.Failure toobserve the mesiodistal inclination of a drifted toothleads to a gingival perforation owing to

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(. the misaligned bur. The recededpulp is missed completely (Figure 33

Figure 32 Operative errorsmaxillary premolars. Overextended preparation from a fruitlesssearch for areceded pulp. The enamel walls have been completely undermined and the toothhopelessly weakened. Gouging relates to a failure to refer to the radiograph, which clearly.shows the depth of pulp recession

Figure 33 Operative errorsmaxillary premolars. Perforation at the mesiocervicalindentation caused by failure to observe the distoaxial inclination of the tooth. The recededpulp is also completely bypassed. The maxillary first premolar is one of the most frequently

.perforated teeth

An instrument can be broken or twisted off in a crossover canal (34). Failure may beobviated by extending the internal preparation to straighten the canals. Inadequate occlusal(. access leads to the failure to explore, instrument, and obturate a third canal (Figure 35

Figure 34 Operative errorsmaxillary premolars. Abroken instrument fractured in acrossover canal. This frequent occurrence may be obviated by extending the internal(. preparation to straighten the canals access (dotted lines

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Figure 35 Operative errorsmaxillary premolars. Inadequate occlusalaccess leads to thefailure to explore dbride, and obturate the third canalsecond premolar (24% of the time).(6% of the time), and to find and instrument thesecond canal in the

MANDIBULAR PREMOLAR TEETHEntrance is gained through the occlusal surface of all posterior teeth. The enamel orrestoration is perforated in the exact center of the central ridge with a round carbide bur, anend-cutting, tapered bur, or a diamond stone held parallel to the long axis of the tooth(Figure 36). Once the chamber is entered, an explorer or endodontic file is used to explore

the canal and to search for a second canal (Figure 37). From this exploration one learns theneeded extent of the outline form. Additional canals in lower premolars are more prevalentin black patients. Removal of the roof of the pulp chamber and expansion of the occlusal(. outline form is best done with tapering fissure burs or stones (Figure 38

Figure 36 Mandibular premolar teeth. Initial penetration is made with a no.4 round bur in thecentral groove of mandibular premolars. When the chamber is entered, the bur is felt todrop into the space. If the pulp has receded, the bur should cut vertically until the nose ofthe contra-angle touches the occlusal surface9.0 mm. In removing the bur, the orifice is.widened buccolingually

Figure 37 Mandibular premolar teeth. An endodontic explorer is used to locate the directionand the extent of the chamber and the central canal. One should also be cautious to searchfor additional canals, particularly in black patients, in whom 32.8% of first mandibular

premolars have two canals and 7.8% of mandibularsecond premolars have two canals

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Figure 38 Mandibular premolar teeth. Buccolingual extension is completed with a tapered.fissure bur or a diamond

The ovoid outline form reflects the shape of the pulp chamber and must be extensiveenough to accommodateinstruments and filling materials (Figure 39). Search for a secondcanal, especially in the first premolar. The final preparation should provide access from theocclusal surface to the apex (Figure 40). Cavity walls should not impede complete authority.over the enlarging instruments

Figure 39 Mandibular premolar teeth. Buccolingual ovoid outline form reflects the internalanatomy of the pulp chamber and orifice to the canal

Figure 40 Mandibular premolar teeth. Final preparation is a tapered funnel from the occlusalsurface to the canal, providing unobstructed access to the apical third of the canal

Operative ErrorsAn error that occurs in mandibular premolar teeth is perforation at the gingiva owing to thefailure to recognize the distal tilting of the tooth that often follows extraction of the lower first.molar (Figure 41). The pulp is missed m entirely

Never enter the pulp from the buccal aspect (Figure 42). Total loss of instrument control andimminent separation of the file follows. Bifurcation of the canal is missed owing to the

failure to thoroughly explore the canal in all directions (Figure 43). Perforation at the apicalcurvature owing to the failure to recognize by exploration the curvature to the buccal aspect(Figure 44). Astandard buccolingual radiograph does not reveal buccal or l ingual curvatures

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Figure 41 Operative errorsmandibular premolars. Perforation at the distogingival aspectcaused by a failure to recognize that the premolar has tilted distally. The same error canoccur with a mesial til t

Figure 42 Operative errors mandibular premolars.Neverenter from the buccal aspect!The instrument is immediately under stress, will cause ledging, develop a pearshapedpreparation, or fracture

Figure43 Operative errors mandibular premolars. Bifurcation of the canal is completely.missed owing to a failure to adequately explore the canal with a curved instrument

Figure 44 Operative errors mandibular premolars. Perforation at the apical curvature iscaused by a failure to recognize, by exploration, buccal curvature. Astandard buccolingualradiograph does not show buccal or l ingual curvature. One should also be wary ofperforating the apical foramen in perfectly straight canals, a common cause of acute apicalperiodontitis

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MAXILLARY MOLAR TEETHMolar teeth are always entered through the occlusal surface. Enamel or restorations arebest perforated with a round carbide (no. 4) bur, an end-cutting, tapering fissure bur, or adiamond stone. The point of entrance should be the central pit, and the bur should beaimed at the orifice of the palatal canal, the largest canal (Figure 45). The same instrumentcan be used to remove the remaining roof of the pulp chamber

Figure 45 Maxillary molar teeth. Molar teeth should all be opened through the occlusalsurface. The initial cut is made in the exact center of the central pit. After perforating theenamel or restoration, the bur should be directed toward the palatal canal orifice, the largest

canal. Using a round or tapered fissure bur, the occlusal opening should be enlarged sothat an endodontic explorer can be used

.Once the opening is large enough, the orifices of the canals should be explored withexplorers or files (Figure 46). In this manner, convenience extension is established. Finalconvenience extension is best done with a non-end-cutting,tapering fissure bur or stone(. so as not to nick the floor of the chamber (Figure 47

Figure 46 Maxillary molar teeth. Using the explorer the floor of the chamber is carefully

explored to locate the canal orifices and the direction of the canals so that one knows in.which direction to enlarge the outline form

Figure 47 Maxillary molar teeth. Atapered fissure bur or diamond is used to remove all theoverhan in roof of the chamber and extend the outline form so that enlar in instruments

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.can be used unimpeded

The final occlusal outline form reflects not only the size and shape of the pulp chamber butthe convenience extensions necessary to free the shafts of the enlarging instruments(Figure 48). Do not assume there are only three canals. One must always probe for extracanals!Keep in mind, however, that some maxillary second molars may have only two.canals,Outline form, from occlusal to apex, must be free of any encumbrance(. allowing unimpeded use of the enlarging instrument (Figure 49

Figure 48 Maxillary molar teeth. The outline form can usually be confined to the mesial halfof the occlusal aspect and should reflect the internal anatomy of the chamber and thedirection of the canals. The preparation is sloped to the buccal aspect to give easieraccess. One must also search carefully for the possibility of a fourth canal, which is.present in half of cases. On the other hand, a few second molars may have only two canals

Figure 4-49 Maxillary molar teeth. Since all instrumentation is introduced from the buccalaspect, the cavity is sloped buccally for easier access. Each endodontic instrument, wheninserted down the canal, must be unimpeded, free from any interfering wall

Operative ErrorsOne of the most common errors that occurs in maxillary molar teeth is perforation into thefurcation, using a surgical-length bur and unknowingly passing through the narrow pulpchamber (Figure 50). The depth to the chamber should be measured on the radiograph andmarked with Dycal on the shaft of the bur. In an underextended preparation, only the pulphorns are nicked. White-colored dentin is a clue to the underextension (Figure 51). The truefloor of the chamber is marked by dark-colored dentin. An imperfect vertical preparation canoccur in a molar tipped to the buccal aspect (Figure 52). The preparation should be parallel.to the true long axis of the tooth

Figure 50 Operative errorsmaxillary molars. One of the most common errors isperforation of the furcation while searching for a receded pulp with a surgical-length bur.Wider access helps prevent these accidents, as does measuring the depth on theradiograph. These perforations maybe repaired with placement of mineral trioxide(. aggregate (MTA, Dentsply/Tulsa

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Figure 51 Operative errorsmaxillary molars.A,Underextended preparation. The roof of thepulp chamber has not been removed. The white color of the dentin in contrast to the darkcolor of the dentin on the floor of the chamber should be the clue. The pulp horns havebarely been nicked, and the clinician has assumed that the canal orifices have beenlocated. Total control of the instruments will be lost if instrumentation proceeds through tinyorifices.B,Example of the failure to remove the roof of the pulp chamber. One can easilyvisualize how the interfering tooth structure will control the path of the instrument

Figure 52 Operative errorsmaxillary molars. Inadequate vertical preparation related to afailure to recognize the severe buccal inclination of an unopposed molar

Afinal error in maxillary molars is perforation of the palatal canal, commonly caused by theassumption that the palatal canal is straight (Figure 53). In more cases than not, the palatalcanal curves to the buccal aspect, a fact that does not appear in the standard buccolingualradiograph. Careful exploration with fine-curved files should reveal the presence and.direction of the curve

MANDIBULAR MOLAR TEETHAll mandibular molar teeth are entered through the occlusal surface. Initial penetration ismade in the exact center of the mesial pit, aimed for the orifice of the distal canal, the largestcanal. Round carbide burs (no. 4), end-cutting, tapering fissure burs, or diamond stones(. are used to enter the chamber and to remove the roof of the chamber as well (Figure 54

B

Figure 53 Operative errorsmaxillary molars. Perforation of a palatal root is commonlycaused when theclinician assumes the canal is straight and fails to explore and enlarge the canal with a fine,curved instrumentRemember, roots that curve buccally appear to be straight in buccolingual.radiographic projections

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Figure 54 Mandibular molar teeth. Entrance is always gained through the occlusal surfaceof posterior teeth. Initial penetration is made in the exact center of the mesial pit, with the bur.directed distallyOnce the chamber has been entered, the bur is used to enlarge the opening orifice bycutting away the roof of the pulp chamber. This allows for the entrance of exploring.instrumentsEndodontic explorers or files are used to locate the orifices of the canals and to determinethe direction convenience extensions must be made (Figure 55). One must carefully explorefor a possible fourth canal in the distal root

Figure 55 Mandibular molar teeth. An endodontic explorer is used to locate the orifices of thedistal, mesiobuccal, and mesiolingual canals. Special care is taken to explore for a

possible fourth canal in the distal root. Tension on the explorer indicates how much of the.walls must be removed to gain unchallenged access to the canals full lengthNon-end-cutting, tapering fissure burs or stones are best used to expand the outline formto accommodate unimpeded use of the enlarging instruments (Figure 56). The final outlineform is dictated by the size and shape of the pulp chamber plus the convenience extensionsneeded to free the enlarging instruments from interference (Figure 57). Severe extensionsto the mesial are not uncommon. The final outline form, from occlusal to apex, provides(. unobstructed access for all enlarging instruments and filling materials (Figure 58

Figure 56 Mandibular mol teeth. Final finishing and funneling of the cavity walls are.completed with a fissure bur or a diamond

Figure 57 Mandibular molar teeth. The square outline form reflects the anatomy of the pulp

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chamber modified for convenience form, mostly flared to the mesial to allow easier access.to the mesial canals. Four canals are shown in this il lustration

Figure 58 Mandibular molar teeth. The final preparation provides unobstructed access tothe canal orifices and should not impede the enlarging instruments; there should be a freeflow to the apical third of all canals

Operative ErrorsPerforation into the furcation is commonly caused by using a surgical- length bur andunknowingly passing through the narrow pulp chamber (Figure 59). Depth to the pulpchamber should be measured on the radiograph and marked on the shaft of the bur withDycal. Perforation at the mesiogingival aspect is caused by the failure to orient the bur to the(. long axis of a mandibular molar severely tipped mesially (Figure 60

Failure to locate a second distal canal occurs because of a lack of exploration for a fourth(. canal hidden by inadequate outline form (Figure 61Perforation of a curved, distal root is caused by using a large, straight instrument in aseverely curved canal (Figure 62). Such a curve should be observed in a radiograph, and.fine, curved or flexible instruments should be used

Figure 59 Operative errors mandibular molars. Perforation into the furcation is caused bythe use of too long a bur and a failure to recognize on the radiograph the depth of recessionof the pulp. The bur should be measured against the radiograph and the depth marked on.the shaft. This is a common error

Figure 60 Operative errors mandibular molars. Acommon error is perforation at themesiogingival aspect caused by a failure to recognize the severity of the tilt of the lowermolar. The bur must be oriented with the long axis of the tooth

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Figure 61 Operative errors mandibular molars. Failure to locate a second distal canal iscaused by theoverhanging dentin wall and a lack of exploration for a second canal

Figure 62 Operative errors mandibular molars. Perforation of the curved, distal root iscaused by the use of a large, straight instrument in a large but severely curved canal

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: Dr Bassam in Endodontics

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