Failed RCT UR6

The existing RCT in UR6 is symptomatic. The tooth is tender to percussion and the buccal sulcus overlying the mesiobuccal root is tender to palpation.

Radiographically the mesiobuccal canal is inadequately obturated and there is a screw-type post in the palatal canal. The material utilised for the core is either very radiolucent, or a core does not exist.

It was decided to provide an orthograde revision of the existing endodontic treatment.

Visualising The Existing Root Canal Filling X10

The crown was removed with a pneumatic crown remover and the post unscrewed without complication. No core material was present. The entire pulp chamber was filled with zinc phosphate cement. This was removed with ultrasonic instruments taking care not to damage the pulp chamber walls.

The pulp chamber is disinfected for one minute with hypochlorous acid to reduce the bacterial load [Sterilox]. Any secondary caries is removed with a combination of rotary and hand instruments. The pulp chamber is repeatedly disinfected during caries removal.

Removal Of Existing Root Canal Filling
Material X10

The coronal gutta percha is removed with a combination of heat, gates glidden drills and ProTaper rotary instruments. New glide paths are established with stainless files.

With the microscope a ledge of dentine can be seen to run from the mesio-buccal canal [MB1] towards the palatal canal. It is beneath this ledge that the second mesio-buccal canal [MB2] is located.

It is important not to destroy any anatomical landmarks when attempting to locate MB2. The floor of the pulp chamber provides guidance as to the location of the canal orifices. Careless use of a bur or ultrasonics will destroy such landmarks and make location of canals more difficult. The ledge or isthmus should investigated with a sharp DG16 explorer or micro-dedrider [Maillefer].

Location OF MB2 X10

Gently picking away at the ledge will eventually reveal and allow access to the first few millimetres of the MB2 canal.

It is important to realise that MB2 is only rarely located on a diagonal line from MB1 to the palatal canal. It is true that MB2 is palatal to MB1: However its position is most commonly found by locating it on an imaginary line that runs parallel to the mesial marginal ridge.

The location of a sclerosed MB2, such as those found in older teeth, can sometimes be difficult even with the use of a microscope. Tell tale signs of its location include bubbling around its orifice when using warm 5% NaOCl as the disinfecting solution.

With over 80% of maxillary first molars having two mesio-buccal root canals: It is important to assume there are always two canals: Unless careful examination reveals otherwise.

Instrumentation Of Canals X10

Instrumentation of MB2 is frequently much harder than MB1. Often the canal orifice is hidden beneath a calcified shelf and is of a smaller diameter and more sclerosed. Initial access is gained from a more distal approach than that for MB1 allowing for the safe removal of the calcified "roof" of dentine

To reduce the stresses on instruments it is important to refine the access cavity outline and canal orifice to facilitate straight line access to the coronal third of the root canal. In the majority of cases, the access cavity should be made more rhomboid in outline to assist in the palatal approach required for shaping of the canal.

Once access has been made to the middle third, instrumentation tends to revert to a more conventional approach along the long axis of the tooth.