Utilising the anatomy in molar root canal retreatment

molar root canal treatmentJohn Rhodes presents another interactive practical and problem-solving solution in endodontics. This month he looks at how you can use root canal morphology advantageously during non-surgical root canal retreatment.


Non-surgical retreatment is often the preferred means of managing a molar tooth in which the previous attempt at root canal treatment has failed.

During retreatment the practitioner will have to remove the existing root canal filling material; there may also be other obstacles such as fractured instruments or silver points which should be removed. This is so that the root canal system can be thoroughly disinfected.

Ideally foreign objects are removed or bypassed so that the root canal can be instrumented and then disinfected.

If the canal is blocked by the object, retrieval may be difficult. The practitioner must always be wary of causing excessive iatrogenic damage in an attempt to achieve successful removal.

The unique morphology of molar teeth

The anatomical morphologies of the mesio-buccal root in maxillary molars and the mesial root of mandibular molars have similarities; there are nearly always two primary canals and an interconnecting isthmus.

The isthmus is often present in the apical third and can also be seen crossing the pulp floor between the orifices of the primary canals.

This interconnecting space can be utilised during retreatment to aid removal of root canal filling material, pieces of fractured instrument or firmly cemented silver points.


Ultrasonics are an excellent means of vibrating, loosening and removing filling material and foreign bodies from the root canals.

In order to be effective, the tip of the instrument has to be placed alongside the object that is being removed.

It is possible to trough around the head of a silver point or fractured file with a fine ultrasonic tip in order to achieve this. However, it is very important to conserve valuable dentine and not cause irreversible damage merely to remove an obstruction.

In molar teeth the isthmus is used to the operator’s advantage. This is done by troughing alongside the object that needs to be removed. This allows conservative removal of dentine and prevents iatrogenic damage.

Case example

Figure 1: A periapical radiograph with the root filled maxillary molar with a silver point in the mesial root and gutta percha in the palatal

A patient was referred for root canal retreatment of the maxillary right first molar. An attempt at root canal treatment had been made many years previously.

The general practitioner had recommended that the tooth was crowned but it had become symptomatic with an acute exacerbation of a chronic periapical abscess and the previous root filling was technically deficient.

Figure 1 is of a periapical radiograph showing the maxillary molar had been root filled with a silver point in the mesial root and gutta percha in the palatal. The tooth was restorable and non-surgical retreatment should have a favourable outcome.

Replacement with an implant would offer no better outcome.

Periapical periodontitis

Figure 2: A small volume CBCT was exposed that showed the disto-buccal root (DB) had not been instrumented

A small volume CBCT was exposed that showed the disto-buccal root (DB) had not been instrumented and was undoubtedly infected as there was associated periapical periodontitis (Figure 2).

The gutta percha filling was short in the palatal canal but there was no sign of periapical pathology. In the mesio-buccal root a silver point was visible in the first mesio-buccal canal (MB1) and there was also a previously uninstrumented second mesio-buccal canal (MB2); there was no periapical radiolucency present.

It is not uncommon to find silver point cases that appear to be working well, with no sign of pathology or symptoms; this may also mean that the point is well cemented and will be difficult to remove.

After infiltration of local anaesthetic and placement of rubber dam, the existing composite restoration was removed.

There was no tag available to grip the silver point and retrieval was going to be complicated. Rather than spending valuable time trying to retrieve the silver point immediately the other canals could be located and prepared first allowing more rapid irrigation and disinfection.

The second mesio-buccal (MB2) and disto-buccal (DB) canals were located. The gutta percha was removed from the palatal canal (P) with a Gates Glidden bur size 2 and all three canals prepared and tapered using an electronic apex locator for length estimation and Wave One Gold instruments (Dentsply Sirona) for tapering.

It was not possible to achieve patency in the palatal canal. It had probably been blocked during the first attempt at root canal treatment or had become completely sclerosed. As there was no evidence of pathology the outcome should not be affected.


Figure 3: The pulp floor after cleaning with ultrasonics

A fine ultrasonic tip (Endosuccess ET25, Acteon) was used to trough along the isthmus from the MB2 orifice towards the head of the silver point.

Low-power vibration was applied to the lateral aspect of the point with water-spray and after a few seconds movement was visible under the microscope. The point was retrieved with Stieglitz forceps and the MB1 canal prepared. It would also have been possible to remove it with the IRS system (Dentsply Sirona) or a loop technique.

After disinfection with 3% sodium hypochlorite agitated with an Endo-Activator the canals were obturated with a vertically compacted gutta percha technique and a core fabricated using a fibre post and dual-cure composite.

The pulp floor after cleaning with ultrasonics (Figure 3). The silver point is well cemented in the MB1 and the head is flush with the pulp floor. By preparing the MB2 canal first and irrigating, the silver point was loosened. Troughing along the isthmus and applying lateral vibration to the point aided removal.

The final radiograph shows a good apical-coronal seal (Figure 4). The tooth will be restored with a crown by the general practitioner. It will be reviewed at one year to confirm bony healing.

Figure 4: A good apical-coronal seal

Summary of treatment protocols

  1. Clinical diagnosis and restorability assessment
  2. Image including CBCT
  3. Canal location
  4. Removal of previous RCT materials
  5. Disinfection
  6. Apical-coronal seal,

To see how these steps are applied visit https://youtu.be/j8AIG3ri0bI or search Youtube for john rhodes endo for utilising the anatomy in molar root canal retreatment.

The author is happy to answer questions directly via Youtube @john rhodes endo.

This article first appeared in Endodontic Practice magazine. You can read the latest issue here.

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