The case to be presented and also deconstructed pertains to a maxillary first premolar. The UR4 belonged to a retired engineer; it had undergone endodontic treatment some 12 years earlier and was the mesial abutment of a three unit fixed bridge (UR6-UR4). The UR6 had failed five months previously and so had been extracted and the bridge sectioned at the distal margin of the UR5. This now resulted in a gap and an occlusally-unfavourable distal cantilever. To compound matters further the patient began to feel a deep-seated ache, which became unresponsive to his analgesic efforts, high in the buccal sulcus adjacent to the UR4. A referral for pain relief and restoration of the space was sought.
After thorough examination and history taking, a digital periapical radiograph was taken, which revealed a poorly filled palatal root short of the apex and a periapical radiolucency centred around the mesial root. The mesial root filling was of good length but skewed in direction in relation to the centre of the root (Figure 1).
Figure 1: Pre operative view
Cutting into the abutment
Maxillary first premolars usually have two canals, the incidence of three canals is rare, about 1.6%. If there are three canals, the buccal root usually houses the extra canal in a separate root form or as two fine roots fused into one. An aberrant canal missed could harbour necrotic pulpal tissue. In retreatment cases mysterious causes of pain are usually down to pulpal remnants hidden in extra canals or isthmuses, fins or anastomoses.
Returning to the case in question, there appeared to be two to three millimetres of uncharted mesial canal space to the existing root filling. After discussing the radiographic findings with the patient it was felt worthwhile to investigate further and so, after adequate anaesthesia and rubber dam placement, a slot-like access was cut into the existing crown. The parameters of the outline form were the tip of the working palatal cusp and two millimetres shy of the buccal non-working cusp tip. Upon penetration of the porcelain bonded abutment, recurrent caries was encountered and removed, and the access to the pulp chamber continued with the XLTD (extra-long tapered diamond) burr from the LA Axxess Kit (Sybronendo, California, USA). At this point exhibit one was found, a separated file fragment, lying amidst the mass of gutta percha (Figure 2).
Figure 2: A separated file fragment was found lying amongst the gutta percha
Clinical access and canal location is hugely dependent on the quality of the magnification and lighting utilised. Surgical length or extra-long diamond or carbide burrs also help to keep the visual field clear of obstruction by the handpiece. The LA Axxess burr is invaluable in roughing out the shape of the pulp chamber and removing obstructive triangles of dentine by dropping into the canals and marrying them to the axial line angles. Any further, deeper searching for canals may be completed with ultrasonics – the Start-X tips (Dentsply Maillefer, Ballaigues, Switzerland) being the author’s weapons of choice. Again, ultrasonic instrumentation facilitates investigation of the depths of the pulp chamber by optimising vision.
Very quickly the tell-tale burr marks of previous searches were uncovered and the MB (mesiobuccal) and DB (distobuccal) canals were found. A partially vital and purulent MB canal presented itself and the access cavity was refined to a T shape. A central dividing burr scorch between the two mesial canals shows how close the previous operator was to uncovering the MB canal and with it success or indeed perforating the pulpal floor and imminent failure. An elegantly finished access cavity allows the smooth path of a hand-file from the coronal access to the entrances of all canals without the need for direct vision (Figure 3).
Figure 3: An elegantly finished access cavity
All canals were negotiated to their physiologic termini with a size 8K file and patency was ensured and verified with the aid of an electronic apex locator. A glide path was established with size 10 and 15K files in an M4 Safety handpiece (Axis/Sybron Endo, Coppell, Texas) – a reciprocating device turning a hand file through 30 degrees of clockwise and counter-clockwise rotation in an oscillating movement.
The working length was confirmed with a size 15K file in the presence of a viscous chelator such as Glyde (Dentsply), again with an apex locator until the reading obtained was static for three seconds. The canals were medicated with calcium hydroxide and temporarily sealed with sterile cotton wool and Cavit (3M Espe). The patient was scheduled to return five days later.
Shaping of the canal system
At the second visit the buccal tenderness had resolved, but the reluctant cantilever bridge had debonded the night before. Clinically, this allowed the opportunity to scrutinise the UR4 for adverse signs before placement of the rubber dam.
Shaping of the canal system was carried out exclusively in the presence of EDTA (Edetic Acid) (17%) using the novel TF Adaptive system (Sybronendo, Orange, USA) utilising SM1, SM2 and SM3 files corresponding to 20 .04, 25 .06 and 35 .04 ISO sizes respectively. Each file was cleaned with isopropyl alcohol after use and patency ensured before the use of the next file in the series. The TF adaptive system uses patented, complex algorithms to switch between continuous rotation and reciprocation, rather like an automatic gearbox. The finer buccal canals were prepared to a 25 .06 shape and the palatal canal to a 35 .06 after using appropriate K files to gauge the apical terminal diameter, rather like a feeler gauge.
At this point, heated (38°C) sodium hypochlorite (5%) was introduced into the canal system and was refreshed every six minutes for a total of 40 minutes (the author prefers a 20 minute ‘soak’ for non-vital cases and 40 minutes for vital cases – this case was treated as vital due to the bloody remains found in the MB canal). Ultrasonic agitation of the reagent was performed with the Irrisafe file (Satellec Acteon, France) 1mm short of working length for three minutes.
Filling the canals
After the EDTA solution has removed the smear layer and any dentinal mud created by mechanical or hand filing, the sodium hypochlorite has the best chance to dissolve organic matter deep into the dentinal tubules. It is the only currently used solution that can do this and is of utmost importance in removing necrotic tissue remnants as well as biofilm.
With the case almost closed, all that remained was to fill the canals using a polyester fibre called Resilon (Realseal, Sybronendo, Orange, USA). Master cones were fitted 0.5mm short of full working length in a wet canal containing EDTA (17%) and the System B Elements unit (Sybronendo, Orange, USA) was used to downpack through the polyester core material using the continuous wave technique. A syringe backfill technique was employed to fill the canals 1mm below the canal orifices (Figure 4).
Figure 4: A syringe backfill technique was emplyed to fill the canals 1mm below the canal orifices
The Resilon was light cured for 40 seconds and any remnants from the pulp chamber walls and floor was cleaned with isopropyl alcohol before an etched and bonded restoration was placed to form a strong coronal seal (Figure 5).
Figure 5: The Resilon was light cured for 40 seconds and any remnants from the pulp chamber walls and floor was cleaned with isopropyl alcohol
In summation, the initial failure of the case may be attributed to a
- Lack of adequate vision: magnification/lighting
- Failure to appreciate the nuances of variant tooth anatomy
- Inadequate access form – resulting in an over stressed file
- Inadequate management of the ‘glide path’.
This, however, does tend to hold true for the majority of our failures.
Figure 6: Post operative view
Mohit qualified from the Birmingham School of Dentistry in 1997. He holds a position as a key opinion leader for Sybronendo and regularly holds hands-on endodontic workshops for the busy general dental practitioner. He is a founder and director of Modus and accepts referrals for all aspects of endodontics.