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REASONS FOR ROOT CANAL FAILURES
David S. Wan, DDS,MS and Lisa C. Selem, DDS
Although the success rate of root canal treatment is quite high, it is
possible for root canals to heal improperly, becoming painful or dis-
eased months or even years after initial treatment. The leading causes
of failure or re-infection of endodontically treated teeth include:
1) Calcified or curved canals that were not negotiated to
apical terminus
2) Complicated canal anatomy that went undetected and
untreated during initial treatment
3) The final restoration was delayed and /or the restoration did
not prevent coronal leakage (bacterial recontamination)
4) New caries or compromised restoration allowing coronal
leakage
5) Root fracture allowing exposure of root canal filling material
to bacteria
There are two treatment options the endodontist performs that correct
endodontic failure and/or re-infections. With the advancements of
digital imaging, microscopes, biocompatible materials, ultrasonic and
micro instruments the success of retreatments and microsurgeries
are higher than ever before.
14 HOUSTON DENTISTRY | www.houstondentistrymagazine.com
Endodontic Retreatment Procedure
Retreating root canals requires a specialized armamentarium which
should include the endodontic microscope and cone beam computed
technology (CBCT) imaging. The microscope allows the clinician to
better visualize the contents of the canals and to maintain a conserva-
tive access by providing magnification and illumination. CBCT scans
provide 3D images which help the clinician to make assessments of
previous treatment such as the quality of the obturation, missed
canals, and potential perforations, as well as to identify calcified
canals, resorptive lesions and, in some cases, root fractures. “Expect
the unexpected” is a general saying during retreatments and the clini-
cian must be able to adapt to each unique clinical presentation.
Beyond access, removal of existing obturation materials, cleaning and
shaping the canal system, and obturation, endodontic retreatment also
encompasses repair of existing perforations, removal of metal or plas-
tic carriers, locating missed anatomy, removal of fractured instru-
ments, and negotiating ledged or blocked canals.
The first step in the treatment procedure is to gain access to the canal
system and to the existing obturation material which may require disas-
sembly of complex restorative materials such as various types of
crowns, posts, and core materials. Removal of obturation materials
from the canals may be accomplished with a combination of rotary in-
struments, heat, solvents and endodontic rotary and hand files. Frac-
tured instruments or carriers may be removed with ultrasonics or
various other micro-endodontic instruments. Repair of perforations is
done with bioceramic materials that are biocompatible and provide an
excellent seal. The canals are mechanically debrided and chemically
disinfected with the use of and activation of various irrigants (sodium
hypochlorite, chlorhexidine, ethylenediaminetetraacetic acid, and/or
mixture of tetracycline isomer, acid, and detergent [MTAD]). Finally, the
canals are then obturated using a themoplasticized technique. The
access cavity is restored and, if needed, a new full coverage restora-
tion is placed. Follow up evaluations are done at 6 to 12 months to
assess healing.
Contemporary Endodontic Microsurgery (Apicoectomy)
Endodontic Microsurgery is the treatment of choice when non-surgical
options have been exhausted or have poor predictability or when non-
surgical orthograde treatment would put complex restorations at risk.
Apictoectomy is performed on the root apices of an infected tooth.
Conventional techniques performed in the past were done with an air
driven handpiece with a bur for the retrograde preparation and with
amalgam as a root-end filling material. Advances over the past
decades have led to the refinement of techniques, materials, and
instruments and have significantly increased the overall success rate.
The contemporary microsurgical procedure involves reflecting a full
thickness flap under the magnification and illumination of an endodon-
tic microscope. The periapical lesion is debrided with microsurgical
hand instruments and, once the root end is resected, the canal is retro-
prepared with ultrasonic instrumentation. The preparation is then retro-
filled with bioceramic materials that are biocompatible and provide an
excellent seal, such as mineral trioxide aggregate (MTA) or root repair
putty. In some cases allograft bone is placed along with a bioactive
membrane. After the initial post-operative visits, recalls are done, usu-
ally one year after surgery to assess the periapical healing.