Preparation of curved canals presents one of the greatest challenges in endododontics.  Improper management of those cases can lead to undersirable outcomes such as ledges, blockages, perforations, apical transportation and instrument separation.

To avoid the unwanted procedure errors, it is important to have a good understanding of  the root canal anatomy using properly taken radiographs.  To accurately determine the degree of the canal curvature, a straight-on radiograph with minimal distortion is essential.  Additional angle radiographs also elucidates useful information.  However, the conventional dental radiograph is limited because it can only tell the curvatures in the mesio-distal plane, but not the curvature in bucco-lingual plane.  Recently, cone beam CT (CBCT) radiograph was introduced to dentistry, and it might be a helpful tool in determining the actual canal curvature.

Proper instrumentation protocol is also important in preventing the procedure errors.  A successful endodontic therapy starts with access preparation.  The size and shape of the access cavity should be modified  based on the degree of curvature of canals so that straight-line access to the canals can be achieved.  Properly prepared access will eliminate many frustrations during the canal instrumentation.  The first file introduced in to the canal should be a smallest file such as #06.02, #08.02, or #10.02 K-type file.  Careful observation of the file after removing it from the canal can often elucidate many critical information regarding the canal curvature.  All hand files placed in to the canal should be pre-curved so that it would follow the original shape of the canal and prevent procedural errors such as ledge formation or apical transportation.  Excessive use of chelating agent such as EDTA or citric acid should be avoided because it tends to soften the dentin and increases the chance of ledge, perforation, or apical transportation.  Canal patency should be obtained at least up to #15.02 or #20.02 to provide a gliding path to the NiTi rotary file.  Pre-mature use of rotary file can lead to its separation.  Excessive reaming action with NiTi rotary file is another reason for file separation and canal transportation.

It is often wise to perform coronal flare-up before introducing the rotary file to the portion of the canal beyond the curvature.  This step will create a straighter access and reduce the file binding to the canal.  In some case, it is not feasible to use rotary file to instrument the canal beyond the curvature.  For example the acute canal curvature in the distal root of #30 (the above case) might prevent the rotary file from advancing further.  In addition, such acute curvature greatly enhance the file separation during the instrumentation.  For those type of cases, hand instrumentation might be a better approach and the apical size of the canal preparation should be kept small to retain the original canal shape. 

Mandibular premolars are one of the most challenging teeth to perform endodontic therapy because of the variations in root canal anatomy.  The goal of root canal treatment is to throughly instrument and obturate the entire root canal system to prevent and eliminate apical periodontitis.  Thus, failure to recognize the variations in root canal anatomy and properly treat them can lead to persistent root canal infection or symptom.

The canal morphology of mandibular premolar can be very complex.  Based on the literature, about 25% of the mandibular first premolars have 2 canals with 2 separate foramina.  Comparatively, about 5% of the mandibular second premolars have two canals with two foramina.  Only 0.5% of the first and second premolars have three canals with three foramina.  Although the incidence of the third canal in lower premolars is low, missing the canal can lead to endodontic failure.  The following points may help to identify the third canal in the mandibular premolars:

• careful evaluation of multiple preoperative radiographs (parallel, mesially and distally angulated films).  Multiple periodontal ligament space may indicate multiple roots.  A sudden change in radiographic density of a root canal space (fast break) might suggest a main canal branches in to multiple canals.
• off-centered canal on radiograph might indicate possible extra canals
• a third canal can also be suspected clinically when the buccal and lingual canal orifices do not follow the rule of symmetry.  If one of the canal orifices is larger than the othe, there might be two canals in the one with larger canal orifice
• Surgical operating microscope with high magnification

Recent literature shows that mandibular first molars have a 1-15% chance of a middle mesial canal.  Most of reported cases show the middle mesial canal join either mesiobuccal or mesiolingual canal.  It is rare occurence to have a true independent middle mesial canal as shown in this case. 

The third mesial canal is often located in the isthmus between MB and ML canals.  The isthumus is a narrow connection between two root canals that contains pulpal tissue.  Failure to instrument this area can potentially causes endodontic failure.  Careful observation of angle radiographs and understanding of tooth morphology is important in identifying those canals.  Today, with the use of the surgical microscope, we can predictably locate the middle mesial canal of a lower molar.

 The goal of endodontic therapy is to prevent and eliminate apical periodontitis. This is achieved by thorough intra-canal disinfection, three-dimensional fill of the root canal system, and good coronal restoration. Occasionally, even with our best effort, a root canal treated tooth might not heal as expected. Most common reasons are missing canal, coronal leakage, recurrent caries, poor quality of the previous endodontic therapy and tooth fracture. Once the tooth is determined to be non-healing, the options left are to save or extract the tooth.

To save the tooth, it could be accomplished by either endodontic retreatment or endodontic surgery. The decision of which option to choose should be based on fulfilling the biological requirement for successful endodontics. A recent systematic review study by Dr. Torabinejad* showed significantly higher success rate found for endodontic surgery at 2-4 years (77.8%) compared with nonsurgical retreatment for the same follow-up period (70.9%). However, at 4-6 years, this relationship was reversed, with nonsurgical retreatment showing a higher success rate of 83% compared with 71.8% for endodontic surgery. It appeared that the success for endodontic surgery declines progressively over time while it increases for the retreatment.

Since root canal infection is the cause of apical periodontitis, the biological aim of endodontic therapy is to eliminate root canal microbes. Endodontic retreatment has higher long-term success because it removes enough microbes from the root canal to ensure predictable success. On the other hand, endodontic surgery merely entombs the intra-canal microbes by placing retrofill after apicoectomy. Thus, depending on the seal and durability of the retrofill material, the success varies. If feasible, endodontic retreatment should be attempted first.

Orthograde endodontic retreatment yields hight incidence of tooth retention.  A recent epidemiologic study evaluated 4744 endodontically retreated teeth that were performed by endodontists participating in Delta Dental Insurance (that insures approximately 15million individuals in the USA).  Overall, 89% of teeth were retained in the oral cavity 5 year after the treatment.*

Endodontic surgery is often required if apical periodontitis does not heal or patient’s symptoms persist after nonsurgical retreatment. Some of reasons are persistent or refractory intracanal infection, extra-radicular infection, apical inflammatory cyst, and cyst or tumor of non-endodontic origin.

Due to the complex root canal anatomy, bacteria can potentially survive in the isthmus, lateral canals or dentinal tubules even after meticulous root canal instrumentation. In such cases, the only option is to seal the intracanal infection by performing endodontic surgery. Occasionally, surgical intervention is necessary because the source of the problem is outside the tooth. Bacteria can potentially survive in the lesion or forming biofilm on the apical root surface, which is called extra-radicular infection. Or there might be a cystic lesion or tumor that is not associated with root canal infection. Clearly, conventional root canal treatment can not address those problems.

Endodontic surgery involves three steps: apicoectomy (root resection), retro-preparation, and retrofil. The modern apical surgery is mostly done under a surgical operating microscope with ultrasonic instruments and retrofil materials such as MTA. It has shown that the modern technique has higher success than the traditional method. A meta-analysis study showed positive outcome in 59% of the cases for traditional root-end surgery and a 94% positive outcome for microscopic surgery*. Even with much improved success, endodontic surgery should not be considered the first option in case the primary root canal treatment fails for the reasons we mentioned earlier.

A carious pulpal exposure in a mature tooth is a good indication for root canal treatment because of its predictable long-term success. Research consistently showed an endodontic success rate of 90-95% for vital teeth in 5-10 follow-ups.* Other treatment options include direct pulp capping and pulpotomy. However, 10-year success rates are 20% and 50%, respectively, for direct pulp capping and pulpotomy.* Thus, root canal treatment is a preferred treatment option for adult patients in cases of pulpal exposure.

However, for a developing tooth, the root canal treatment can cause irreversible damage and result in the arrest of root development. Because of the thin root structure, there will be a higher risk of root fracture after the root canal treatment in immature roots. In addition, technical difficulty and patient compliance can further compromise the long-term prognosis for tooth retention. Therefore, for the immature roots, our treatment objective is to maintain pulpal vitality so that normal root development (apexogenesis) can continue. This is accomplished by removing of a portion of the affected vital coronal pulp tissue and preserving as much healthy pulpal tissue as possible. Therefore, direct pulp capping or pulpotomy should be considered.

Two of the most common materials that have been advocated to induce normal root development are calcium hydroxide and MTA. Both materials have high clinical success for direct pulp capping and pulpotomy procedures. However, MTA seems to produce a thicker dentinal bridge, less inflammation, less hyperemia and less pulpal necrosis compared to calcium hydroxide. Here, we present a case of MTA direct pulp capping for #19 with open apices.  Please note the closure of root apices at 1 year follow up evaluation.

An immature root with open apices often presents challenges to the routine endodontic therapy. Because it is difficult to create a good apical stop using the conventional method, canal overfill and poor apical seal frequently occur to compromise the long-term success of the treatment. Thus, an apexogenesis procedure is preferred if the tooth is vital. However, if the tooth is necrotic and infected, the only option left is to perform root canal treatment. To prevent the incident of overfill and allow adequate root canal seal, an apical barrier is desired.

Apexification is a procedure to create an apical barrier in a tooth with open root apex. Traditionally, a long-term calcium hydroxide therapy is used for this purpose and has shown clinical success of up to 95%*. However, this procedure usually requires 3-24 months for the hard tissue formation to complete at the root apex. In some cases, this might not be practical either due to patient’s non-compliance and increased chance of re-infection from loss of temporary restoration. In addition, some studies showed long-term use of calcium hydroxide intracanal dressing predisposes the tooth to fracture.

Recently, an alternative technique using MTA was introduced for the apexification procedure. Studies showed a 95% clinical success rate, which is comparable to calcium hydroxide apexification*. MTA is a biocompatible material that induces hard tissue formation in dental pulp and periradicular tissue. It also provides excellent seal against microleakage. On average, MTA takes 4 hour to set. Thus, most endodontic therapy using MTA apexification can be completed in 2 visits. Here we present a case using MTA apexification during the root canal treatment. 

Mandibular molars can have a supernumerary root called the radix entomolaris (RE). This additional root is often located distolingually in mandibular first molar. 

Instrument separation is one of the most troublesome incidents in root canal therapy. Depending on the clinicians’ skill levels, the incidence of fractured instruments in the canals range from 0.4% - 3.7%.* The most common reasons for the instrument separation include overuse, improper use, curved canals, manufacturer defect, and clinician’s technical skill.

Although the file separation within a root canal is an unpleasant experience, the prognosis of the endodontic treatment is not significantly reduced. A recent meta-analysis study showed 80.7% of the lesions healed when a periapical lesion was present, compared with 92.4% remaining healthy when no lesion was initially present*. Of course, the prognosis can be further compromised if effective canal disinfection cannot be achieved. Thus, the outcome of endodontic treatment is related to how well the canals are disinfected prior to the file separation and the prevention of recontamination during and after the procedure.

Several approaches to manage the separated instrument within the canals include removal of the file using an ultrasonic device or extractor such as an IRS instrument, bypass the file, or surgical removal of the file. Most of these procedures will require the use of a dental operating microscope and it is prudent to refer to a microscopic endodontist to manage these cases.

Nonetheless, the removal procedure might result in loss of considerable tooth structure. This could lead to clinical complications of root perforations, ledge, transportation, and possibility of root fracture in the future. Thus, the benefit of removing the instrument and the risk of damage has to be weighed before attempting file removal. For some situations, it might be in the patient’s best interest to leave the file alone.

Perforation is a mechanical or pathologic communication between the root canal system and the external tooth surface. A perforation that was not repaired or not successfully repaired can lead to serious periodontal problem. If possible, the repair of a perforation should be done immediately with materials of good sealing ability to minimize any further tissue damage.