Pulp chamber access has always been a qualitative procedure. It was assumed that because pulp chamber height and overall tooth size were so variable, nothing relating to the morphology of the pulp chamber was consistent. A review of the dental literature regarding the morphology of the pulp chamber revealed very little information. Only 2 studies measured the distance from the floor of the pulp chamber to the furcation. Both studies found the distance to be approximately 3 mm in both maxillary and mandibular molars most of the time.1,2
|Figure 1. Standardized length of 6.5 mm for all No. 4 round burs.|
When I first started practicing endodontics, it quickly became apparent that using a qualitative approach made it much too easy to perforate into the furcation while gaining access. In looking for a standardized approach, I realized that the shaft length of a No. 4 round bur was the answer. For the next 25 years, the distance “L” of 6.50 mm would almost always place me at the ceiling of a molar pulp chamber (Figure 1).
|Figure 2. The molar line-up. Roots vary in length, but crowns are approximately the same height from cusps to CEJ.|
Several years ago while looking at molar teeth, we were shocked to see that although the root size varied considerably from tooth to tooth, the crowns of these same teeth were very nearly the same size (Figure 2). This led us to hypothesize that perhaps the pulp chamber anatomy also was consistent for molars.
|Figure 3. Key morphological measurements for molars and their anatomic placement in the tooth.|
We then identified and measured several key anatomic landmarks relating to the pulp chamber for maxillary and mandibular molars. These morphological measurements can be seen in Figure 3. One hundred maxillary molars and 100 mandibular molars were measured; the results are displayed in the Table.
Several important pulp chamber morphological measurements were noted.
|Figure 4a. Measurement “A” from pulpal floor to furcation was approximately 3.0 mm on all molars.||Figure 4b. The ceiling of the pulp chamber was found at the CEJ 98% of the time.|
The distance from the pulp chamber floor to the furcation was on average 3.0 mm for both mandibular and maxillary molars. This was in agreement with the 2 other previously published studies.1,2 Therefore, we have less than 3 mm clinically before irreversible damage is done. Concerning the ceiling of the pulp chamber, two important facts were discovered. The ceiling is at the level of the CEJ 98% of the time (Figures 4a and 4b). The height of a pulp chamber is between 1.5 to 2.0 mm (Figure 5a). This 1.5-mm to 2.0-mm measurement is the most variable due to calcifications because of aging, caries, and restorations.
|Figure 5a. For molars, pulp chamber height was between 1.5 to 2.0 mm.||Figure 5b. The distance from the cusp tip to the pulp chamber ceiling was close to 6.5 mm consistently.|
Lastly and most surprisingly, we found that the distance from any cusp tip to the ceiling of a molar was very consistent at approximately 6.3 mm (Figure 5b). This correlates very nicely with the empiric bur measurement of 6.5 mm from 25 years ago. The measurements from this published study were pointing to a more clinically safe and effective access technique.3
|Figure 6. Key morphological measurements for furcated bicuspids.|
Since molars were not the only teeth with furcations, we began to measure the morphological landmarks of bicuspid teeth. Figure 6 shows the location of the measurements for bicuspids with furcations.
We have recently had our second morphological research paper published in the 2005 Journal of Dental Research abstracts. We were a little fancier in this study and used the Trophy RVG digital imaging system to radiograph the bicuspids. Once the digital x-rays were processed, we measured them using the Digipan measuring mode of the Trophy system. The mean for the pulpal floor to furcation distance was 1.85 mm. The average height of a pulp chamber was 2.76 mm. When comparing these measurements to molars we found the following: The only measurement that was statistically the same across all 3 groups, (mandibular molars, maxillary molars, and bicuspids) was measurement “B”—chamber ceiling to furcation. However, we found that the smallest percentage variance for bicuspids and the second smallest for molars were found in measurement “D.” This is the critical measurement of cusp tip to pulp chamber ceiling. This measurement in bicuspids was 6.94 mm.4 Measure-ment “D” for both mandibular and maxillary molars was statistically the same, but it was different from furcated bicuspids. Although this number is statistically different from the average of 6.3 mm for molars, it is still very close on a clinical basis. In actual numbers, the difference between molars and bicuspids is approximately 0.60 mm.
|Figure 7a. You can feel the drop when the diameter of the ball is smaller than the height of the pulp chamber.||Figure 7b. You cannot feel the drop when the diameter of the ball is the same or larger than the height of the pulp chamber, as in calcified chambers.|
When all these measurements are taken together, they give us for the first time a quantitative approach to a clinical access technique as opposed to our standard qualitative approach. Qualitatively we rely on the feel of the “drop” when the bur goes through the pulp chamber ceiling and into the chamber itself. We go from cutting dentin to cutting soft tissue. We can feel this because the diameter of a No. 4 round bur is 1.35 mm and the height of the average pulp chamber is approximately 2 mm. We cannot feel this in calcified chambers when the diameter of the No. 4 round bur is larger than the height of the pulp chamber itself (Figures 7a and 7b). With only approximately 2 mm to 3 mm from the floor of the pulp chamber to the furcation, there is little room for error.
|Figure 8a. A stop at 7.0 mm places the bur in the middle of the pulp chamber in average-size chambers.||Figure 8b. A stop at 7.0 mm places the bur where the middle of the chamber used to be in calcified cases. This allows for easier orientation and locating of canals.|
We can now turn this once qualitative technique into a predictable, quantitative technique by standardizing the bur length to match the consistent cusp-to-pulp chamber ceiling height. We accomplish this goal when we set a fixed, nonmovable stop at 7 mm from the cutting tip of the bur. When we gain access with a fixed-stop 7-mm bur, we place ourselves into the pulp chamber in both molars and bicuspids (Figure 8a). This is done consistently without the risk of perforation into the furcation. In teeth with calcified chambers, the 7.0 mm depth will place us in the middle of the chamber before the calcification occurred. This gives a very accurate starting point to begin looking for canals (Figure 8b). Clinically, the time taken to find the canals is shortened.
|Figure 9. Smoothing and shaping of the access cavity with a non-end-cutting extracoarse, extralong, barrel-shaped diamond bur. Once the walls are smooth, it is easier to find the canals.|
Once the correct depth is predictably reached, we use a non-end-cutting coarse diamond to smooth and shape the axial walls of the access preparation (Figure 9).
The advantages even for someone who has been practicing endodontics for many years are twofold: (1) speed of operation is increased and (2) reliability and predictability become standard. Finding canals becomes more routine and easy.
So, the next time you read some scientific endodontic research, you may want to ask yourself, “How can I use this information to improve my clinical technique?”
|Table. Mean Measurements for the Key Morphological Landmarks.|
1. Sterrett JD, Pelletier H, Russell CM. Tooth thickness at the furcation entrance of lower molars. J Clin Periodontol. 1996;23:621-627.
2. Majzoub Z, Kon S. Tooth morphology following root resection procedures in maxillary first molars. J Periodontol. 1992;63:290-296.
3. Deutsch AS, Musikant BL. Morphological measurements of anatomic landmarks in human maxillary and mandibular molar pulp chambers. J Endod. 2004;30:388-390.
4. Deutsch AS, Musikant BL, Gu S, Isidro M. Morphological measurements of pulp chambers of human maxillary furcated bicuspids. J Dent Res. 2005;83(Special Issue):Abstract No. 2860. Available online at: www.dentalresearch.org.