Variations in the Cross-Sectional Pulpal Anatomy of Teeth and How to Treat Them

As you can see from the micro CT scans of a mandibular molar, not all pulp tissue is configured as conical shapes. Quite often as illustrated here, pulpal inclusions are in the form of sheaths of tissue, much broader bucco-lingually than they are mesio-distally. Even when not broad bucco-lingually the pulp tissue tends to be flattened in the mesio-distal plane. Isthmuses often present in the mesial roots of mandibular molars are thin extensions of the larger mesio-buccal and mesio-lingual canals that join the two, sometimes through their entire length other times partially. 

 When performing endodontics, our goal is to remove all the pulp tissue and the bacteria that tissue may be supporting. To accomplish that goal, we must think three dimensionally. This is not an easy task when what is typically at our disposal are radiographic two-dimensional images. A periapical x-ray will tell us if we are short or long in our cleansing and obturation procedures covering two of the three existing dimensions, but give us little information on what we have accomplished  or not accomplished in the third (bucco-lingual) dimension. We value the images produced by our two dimensional radiographs so much that what appears to be a thorough job of instrumentation and obturation in these x-rays is taken as proof of a job well done and often that is exactly the case. We should appreciate, however, that that happy result is more a product of fortunate coincidence (the canals are indeed conical to start with) than the application of techniques that address anomalous anatomy.

So what is the best way to address anomalous anatomy in three dimensions? Let’s start with what doesn’t work, staying centered and removing pulp tissue from the widest portions of the canal. The results will look good on x-ray, but leave tissue in the buccal and lingual extensions. To remove tissue three dimensionally, we must do our best to physically shave it away from all the canal walls. To do that, the instruments must be thin enough to penetrate thin isthmuses and flat sheaths of tissue and flexible enough to easily negotiate any curvatures that may be present. Most importantly, the instruments must carry out these functions without any chance of separation, an iatrogenic event that strongly discourages the dentist from applying the techniques necessary to be effective.

 As you can see from the second illustration, two approaches were used to remove the tissue from a c-shaped canals. The first used a rotary system that left the bulk of the pulp tissue untouched, the result of the need to stay centered for the preservation of the instruments.. The second used a tool designed as a flexible hollow tube that conforms to the three-dimensional canal anatomy. This second instrument called the SAF (self-adjusting file) collapses upon itself and enters into canals already opened to a 20/02 using .4mm vertical oscillations of 5000/cycles per minute to sand the walls. As the flexible hollow tube that is wider than the canal collapses mesio-distally the bucco-lingual diameter can expand as much as 2.4 mm if space is available in this dimension. The differences in cleasning action are dramatic, proving the concept of a tool that can address pulpal anatomy in three dimensions.  

I tried this system for a while and thought it ingenious, but cumbersome to use. At some point I realized that the action that the SAF performed could be accomplished by an instrument thinner than the canal it enters into. By applying a thin stainless steel reamer, one as thin as an 06/02 in a 30o handpiece oscillating at 3000-4000 cycles per minute I can have all the advantages of the SAF with far less complexity. The reasoning is simple. A stainless steel reamer limited to a 30o arc regardless of frequency will not separate no matter how vigorously applied to any and all canal walls. Given this reality, I can routinely apply the reamer uniformly and circumferentially against all the canal walls removing a more or less equal amount of dentin from the canal walls, the result will be a cleansed version of the canals only slightly larger. The biggest advantage is I can introduce this advantage with the thinnest reamers rather than first have to open the canals to a minimum of a 20/02.

By opening the canals to no more than a 15/02 using the oscillating handpiece, I have removed most of the pulp tissue, created a space that provides for effective irrigation that is activated by the 3000-4000 oscillating handpiece. Instrumentation is not complete at this point, but the glide path is fully formed and the thinner portions of the canals need no further widening. In fact further widening of the thin portions should be avoided lest they undermine the external walls too much. Those portions of the canal that were wider to begin with and have a greater bulk of dentin supporting the roots are then further widened using the horizontally relieved rotary reamers that rarely require enlargement beyond a 30/04 and often to no more than a 30/02.

It was the realization that what I term “internal routing”, using stainless steel reamers in oscillation accomplishes the same function as the SAF far more simply, more quickly, less expensively and more safely. Once you know that the instruments are virtually free of breakage despite their vigorous usage, the application of their shaving flutes against the canal walls solves the problem of three-dimensional cleansing and shaping that is now entirely predictable. 

Regards, Barry