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It is well-recognized and universally accepted that asuccessful outcome in endodontic treatment

essential-ly depends on three factors:1) cleaning and shaping2) disinfection3) three-dimensional

obturation of the root canal sy-stem. Although it is impossible to determine which of thethree factors

is the most important, it is obvious thatgreater importance should be given to the rst; anold axiom in

endodontics states that what you remo- ve from the root canal is more important that what you place inside.

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Proper cleaning and shaping esta-blish the necessary conditions for the success of thenext two factors.

It would be mistaken to try to disin-fect and three-dimensionally obturate a root canal thathad not been

previously cleaned and shaped.However, there is one other step that precedes the-se three. It affects all

three and therefore should ab-solutely not be undervalued or neglected. An errorin this preliminary

step would compromise all subse-quent work.This preliminary step is the preparation of the

accesscavity, the opening in the dental crown that permitslocalization, cleaning, shaping, disinfection, and

three-dimensional obturation of the root canal system.The success of the endodontic treatment

depends en-tirely on precise, proper execution of this step. Anaccess cavity that has been prepared

improperly interms of position, depth, or extent will hamper theachievement of optimal results.

REQUIREMENTS OF THE ACCESS CAVITY

The access cavity must make the succeeding steps ea-sier and safer. It must

therefore meet the following re-quirements:60,761) Permit the removal of all the chamber contentsAs stated above, one of the rst steps for a favorableoutcome in Endodontics isproper cleaning of the en-dodontic space, which comprises not only therootcanal, but also the pulp chamber and its pulp horns.Cleaning should be asthorough as possible.Good endodontic cleaning, therefore, begins with theremovalof the endodontic contents from the pulpchamber and its horns.To accomplish this, itis necessary to completely re-move the chamber roof. This allows the removal ofallthe pulp tissue, any calci cations, and all residue ortraces of old lling material.If the chamber roof is not completely removed, it willnot be possible toperform proper cleaning of thepulp horns. There are two consequences:

contamination or infection of the endodontic spacethat the dentist is trying toclean. discoloration of the endodontically-treated tooth(especially the frontteeth).To ensure adequate removal of the roof above thepulp horns, one can usea small, curve probe, suchas a # 17 (Fig. 11.1A), as Lasfargues et al.58suggest.It is used to probe the walls of the access cavity forthe presence ofoverhangings. Ardines probes3(Fig.11.1B) are also useful for this purpose.2) Permit complete, direct vision of the oor of the pulp chamber and canalopenings

The entire extent of the oor must be visualized, as itslandmarks help in

identifying the canal openings. Thisapplies particularly to the posterior teeth: the

oor fre-quently has natural grooves, at the end of which thecanal ori ces are

located (Fig. 11.2).To meet this second requirement, the access cavi-ty must

sometimes be slightly modi ed to give it theso-called convenient shape.

Following complete re-moval of the roof, it is necessary to orient the cavity

slightly toward the dentist, particularly when dealing with the molars and patients

with limited mouth ope-ning. This gives the walls a slight anterior inclinationthat

facilitates inspection of the oor and thus locali-zation of the canal openings

60

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(Fig. 11.3).Inspection and localization are facilitated by the use of the endodontic probe(Fig. 11.4), which is to the en-dodontist what the periodontal probe is to theperio-dontist.17By reaching, feeling, and frequently movingthe hard tissue, this probe functionsas an extensionof the dentists ngers.The natural anatomy of the oor frequently indica-tes the site of the ori ces. Sometimes, however, re-storations,dentinal neoformations, or dystrophic cal-ci cations may alter the originalcon guration and hi-de the root canal ori ces. Using the endodontic probeto explore the chamber oor, one can enter the ca-nal openings and sometimesdisplace calci c deposits that obstruct them.

Lastly, the endodontic probe can be used to determi-ne the angle between theroot canals and the oor of the pulp chamber.3) Facilitate the introduction of canal instruments into the root canal openingsAs stated above, the pulp chamber oor of the poste-rior teeth frequently hasgrooves that serve as guides,not only to nd the ori ces of the root canals, but

alsoto the introduction of endodontic instruments withinthem.The oor is alsofrequently convex and forms an acu-te angle with the chamber walls. It seems asthoughNature had considered the work that the endodon-tist would have to do.

Thus, if the access cavity hasbeen well made and, especially, if the chamberoor has not been affected by the cutting action of the bur,the instruments will enter

the canals easily without en-countering any obstacles. It suf ces to slide thecanalinstrument along the wall at the point where the canalopening is located. The wallsprepared by the endo-dontist and the oor created by Nature will guidetheinstrument toward the apex (Fig. 11.5).If the anatomy of the oor has beenmodi ed, resul-ting in attening or irregularities, each introduction of an instrument must be checked with a mirror with thepulp chamber free of anyirrigating solution, to allow visualization of the canal ori ce.

4) Provide access as direct as possible to the apical one third of the canal forboth preparationinstruments and canal lling instrumentsEndodontic instruments should not be de ected by any obstruction in the crown. When working in thecanal, they should move freely, particularly in the api-cal onethird (Fig. 11.6).For a variety of reasons, the endodontic instrumentsshould nevertouch the walls of the pulp chamber: They must be able to work on the entirecircumfe-rence of the canal. An access cavity that is too nar-row will force thedentist to work on only one wallof the canal, while the other remains completelyuntouched (Fig. 11.7). Deformations of the apicalforamen may result.39,50,60

The friction of the instruments shaft against the co-ronal obstructionswill have to be overcome. Theforce required to do so impairs theendodontistsability to sense how much the working portion ofthe instrument is engaged against the canal walls.60

This could easily lead to fracturing of the instru-ment.To avoid both of thesecomplications, the access ca- vity must be wide enough to permit the endodon-ticinstruments unhindered entry; there must not evenbe minimal contact with thewalls of the access cavi-ty. This is particularly important with the use of rotaryNickel Titanium instruments.The cavity need not necessarily remainunalteredthroughout treatment; rather, it should be consideredsubject to

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modi cation at any time, if the need arises.If any hindrance arises in mid-preparation becauselarger and more rigid instruments are called for, oneshouldput down the canal instruments, pick up thehigh-speed handpiece, and enlarge thecavity as nee-ded untilthe hindrance has been removed, even if thisrequiresremoving a cusp.To prevent any fragments of dentin or, worse, amal-gam or other

lling material, from falling into the ca-nal being prepared or into theneighboring canals thathave already been cleaned and shaped, it suf cestoplace small cotton pellets into the canal openings (Fig.11.8). One principleshould never be forgotten: it isalways advisable to prepare wide access cavitiesandgenerously remove old metallic restorations to avoidhaving to enlarge thecavity intraoperatively. Such en-largement carries the risk that the handpiecespray will obstruct the canals that have already been pre-pared or are in thepreparation phase by forcing frag-ments into them.In markedly curved canals, butparticularly in the cur- ves of the coronal one third, obstructions that can re-ducethe tactile sensitivityof the instruments in theapical one third are encounterednot only in the wallsof the pulp chamber, but also in the coronal one thirdof the canalitself. Such curves must be prophylac-tically eliminated following the

anticurvature -ling method as suggested by Abou-Rass, Frank, andGlick.1Obviously, if the access to the apical one thirdis straight for instruments used incanal preparation, itis also so for materials and instruments used for obtu-rationof the root canal system (Fig. 11.9).Fig. 11.8. An access cavity made through a prosthetic restoration has been en-larged mesially after the distal canal had already been prepared. The sprayof thehigh speed handpiece has causedmetallic lings to fall into the distalrootcanal.Fig. 11.9. A correctly-made access cavity permitsstraight-line access to theapical one third of theroot canal, even to instruments necessary for ca-nal lling.5) Provide a positive support for temporary llingsWhen the access cavity is temporarily obturated to seala medication within, the

temporary cement must forman hermetic seal to avoid contamination

of the

cavity.The cement must be unaltered for the entire period of time required (Fig.11.10), and it must not collapse in-to the chamber (Fig. 11.11). To prevent this,the wallsof the access cavity must be ared slightly in the sha-pe of a funnel, sothat the occlusal surface is slightly wider than the oor.

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5) Provide a positive support for temporary llingsWhen the access cavity is temporarily obturated to seala medication within, thetemporary cement must forman hermetic seal to avoid contamination of thecavity.The cement must be unaltered for the entire period of time required (Fig.11.10), and it must not collapse in-to the chamber (Fig. 11.11). To prevent this,the wallsof the access cavity must be ared slightly in the sha-pe of a funnel, sothat the occlusal surface is slightly wider than the oor.