Shaping Difficult Canals with 4 Instruments and No Chance of Breakage

Every now and then, endodontic cases come along that reinforce the need to follow principles that are safe for the instruments and the canals. These factors include high levels of calcification, significant curves and longer lengths than average. In the case above we see a combination of all three. The canals are barely visible in the apical third demonstrating a high degree of narrowing with unpredictable calcifications along their length. The two outer canals have s-shaped curves that along with their calcifications represent a challenge to reaching full apical length. Finally, the canals were between 24 and 25 mm in length.

Gaining access to the canals required the removal of calcifications filling the entire pulp chamber. No soft pulpal tissue was present. Determining the location of the canals was entirely dependent upon the overlying color of dentin as a guide to the proper direction for uncovering them. The best tools to accomplish this delicate task are imo Munce burs. Fabricated from tool steel, they are 34 mm in length and sized from a ? round to a 4 round. A light touch removes dentin creating a smooth floor where if a canal orifice is present, will be easily identified visually by the disruption in the smooth floor and confirmed with a sharp explorer.

Finding the canal orifices is no guarantee that the canals we are attempting to enter will be patent at this point, but at a minimum we now have visualization of where to remove more overlying secondary dentin to the level where patency is present. In pursuing this task, the smaller Munce burs give us the ability to stay centered on the orifice whether calcified or not with a minimal loss of supporting tooth structure. A catch with a sharp explorer is followed by the attempted insertion of an 06 tipped stainless steel twisted reamer (not ground) into the canal orifice and using a watch winding motion combined with a small amount of apically directed pressure lubricated with 17% EDTA, we attempt to advance the reamer the length of the canal.

Fortunately, even highly calcified canals present the greatest resistance coronally and tend to open as we negotiate apically. Small sized reamers (06 to 10) are not only quite flexible easily negotiating significantly curved canals, but also have adequate body to remove dentin when directed against any and all walls. These properties give the thinnest of reamers the ability to often widen the canals beyond their own dimensions allowing the dentist to skip sizes (say from an 06 to a 10 or a 10 to a 20) without excessive binding. It is this combination of flexibility and body that allows me to confine my instrumentation to 02 tapered stainless steel relieved reamers.

The initial thinnest twisted stainless steel reamers create the glide path through which the subsequent wider 02 tapered twisted reamers will follow. Each instrument in the sequence further prepares the canal space to accept without distortion the next larger size. Each subsequent reamer is slightly stiffer, but the pathway is that much more defined limiting the ability to deviate from the established path. Starting with a 15 the twisted reamers are relieved with a flat along their entire working length increasing their flexibility and creating two vertical blades that enhance the removal of dentin and minimizing the potential for any distortion.

Once the initial 06 tipped 02 tapered twisted stainless steel reamer is manually negotiated to the apex, its correct length confirmed with an apex locator, that initial reamer and all subsequent reamers in the sequence are used in a 30o handpiece oscillating at 3000-4000 cycles per minute generally resulting in rapid advancement to the apex eliminating all hand fatigue in the process. It should be stated that in cases like the one illustrated above, the initial manual negotiation to the apex may require using several 06 tipped 02 tapered twisted reamers before gaining full length, but once that length is achieved it is generally smooth sailing made far easier by incorporating the oscillating handpiece.

Specifically, the instrument sequence for this tooth after achieving full apical length in the 4 canals with an 06 tipped 02 tapered stainless steel twisted reamer was as follows:

. the same 06 tipped 02 tapered stainless steel twisted reamer used in the 30o oscillating handpiece.

. a 10 tipped 02 tapered stainless steel twisted reamer used in the 30o oscillating handpiece to the apex

. a 20 tipped 02 tapered stainless steel relieved twisted reamer used in the 30o oscillating handpiece to the apex. In the event that the 20 encounters resistance leaving it short a mm or two, I regain the lost length manually using a tight watch winding motion with increased apical pressure applied. This occurs rarely, but it effectively regains full length without distortion. Once that length is achieved in this manner, I place that instrument in the oscillating handpiece and working the canals predominantly in the bucco-liongual plane.

. a 30 tipped 02 tapered stainless steel twisted reamer used in the 30o oscillating handpiece to the apex. In a case like this, the 30 would be the last instrument to the apex.

. for the sake of coronal clearance I opened the coronal two thirds of the canal to a 35/02. This was the final preparation prior to obturation.

 I used a total of 5 instruments 4 of which went to the apex. All were made of stainless tell and anything beyond a 10 is relieved with a flat along their entire working length. By confining the arc of motion to 30o I virtually avoid the possibility of instrument separation. Because instrument breakage is not a concern, I am entirely comfortable in working these thin 02 tapered instruments aggressively against the buccal and lingual walls, a necessity given the highly oval isthmus-like anatomy most often found in the majority of teeth.

I fitted the canals with either medium fine or fine-fine points gaining apical tugback at the proper length. After coating the canals with an epoxy resin cement (EZ-Fill) I coated the points, placed them to length in each canal and seared them off at the canal orifice. One interesting point to note is that fine-fine and medium fine points are quite thin. Yet, the fills on x-ray do not appear anywhere near as thin as the points, a result of the significant instrumentation done in the bucco-lingual plane that was subsequently filled with cement.

This was an extremely difficult case in first finding the canals and then gaining full length with the thinnest reamers. Yet, only 4 instruments were required for full preparation of the canal with the 5th instrument used to simply widen the coronal aperture. It was made much easier because I know from years of experience that these instruments are virtually immune to breakage and can be used vigorously against all the canal walls in a technique that is accurately described as internal routing targeting all aspects of the pulpal anatomy throughout the length of the tooth.

The technique we developed and employed in this as well as far more routine cases is described as the SafeSiders. Confined to stainless steel relieved reamers (starting from 15) they offer a combination of safety , efficiency and effectiveness. From my perspective the only times greater tapered instruments should be employed are those cases where the canals are quite large in the mesio-distal plane to begin with. If one examines most x-rays prior to the initiation of endodontics you will find that this condition is indeed quite rare.

Regards, Barry