Objective: Measure root and canal diameters and ratios, canal tapers and wall thickness.
M&M: Thirty human premolars with single canals were selected. Specimens were scanned using Micro CT and cross-sections analyzed at the following levels: 1,2,3,4,5,7,9,11 and 13mm from the radiologic apex.
Take aways:
1) At all levels, the BL (bucccolingual) diameter of the canal was greater than the MD (mesiodistal) diameter. This means that the canal diameter the dentist typically sees on the x-ray (MD view) was always smaller than the size of the canal they don’t see (BL view). For example, the data shows that at 1mm from the apex, the canal diameter as seen by the dentist averaged 0.32mm. However, in the view they don’t see, the canal diameter was much larger, 0.45mm. If one prepares the canal with a size #35 instrument the canal would be under prepared at the 1mm level because in reality one would have to go two sizes larger to a size #45 to properly clean the canal, 3-dimensionally.
2) The canal’s taper, in the BL dimension is much greater than the MD dimension. So the taper you don’t see is much larger than the taper you do see. Measurements taken in the MD dimension showed tapers ranging from (0.03 to 0.06 mm/mm) but in the BL dimension they were significantly greater (0.13 to 0.27mm/mm)! If one prepares the canal to a common taper (let’s say .04 taper) it more often than not under prepared in BOTH dimensions, particularly in the BL dimension (.04 vs. 0.18 average).
This puts serious doubt as to the efficacy of tapered preparations in general. Can one expect to effectively clean canals, with 0.04 or 0.06 tapered instruments, when the canal’s dimensions (at a minimum) are 0.45mm diameter with a 0.13 taper?
August 20, 2008 at 12:23 am
Yes, this is a good one–along with others that say pretty much the same thing.
Yes, we have been saying the same for many years but few are listening. (Jim Roane, Balanced Force, has also been doing that.) The reason few have taken note of the facts is that money and advertising power dominate. Our competitors advocate small apical preps because their instruments would cause major mishaps if used to larger apical sizes. It’s that simple–money talks.
So, what’s the solution? That’s simple also, in my opinion. A lot of apical greater and lesser diameter studies should be done around the world so that even powerful dental companies can’t refute the facts.
I have developed a protocol for doing such a study that has been used by a University in Mexico and was submitted to the JOE last week for publication. I would make the following changes of the M &M’s; (1) 25-30 teeth per tooth type (centrals, premolars, molars, etc.) instead of 40 and (2) cross-sectioning also at 3 mm, 4 mm and 5 mm.
What are we waiting for?
Regards to all,
Dr. Steve
August 20, 2008 at 12:26 am
Here’s a copy of the protocol referenced above by Dr. Senia:
Materials and Methods
Two hundred extracted maxillary and mandibular anterior teeth ranging in age from 20 to 60 years were used. All had a single canal and were free of apical resorption. The teeth were placed in 6% NaOCL for 15 minutes to dissolve any remaining tissue and then the crowns were removed at the cervical line.
Methylene blue dye was applied to the margins of the apical foramen to ensure maximum clarity and the foramen was photographed (40X) with a Wolf Stereomicroscope (Carolina Biological Supply Co., Burlington, North Carolina). Then a #10 K-file was advanced in the canal until the tip was at the foramen. The file’s rubber stop was positioned at the coronal root surface reference point, the file withdrawn and the canal length (CL) of the tooth carefully measured.
The 1 mm level (from the foramen) was located by repositioning the stop 1 mm less than the CL and reinserting the file into the canal to this length. The file was secured with light-cured resin and the handle cut off. Starting at the tip of the root, root structure was carefully removed perpendicular to the canal with a high speed handpiece and using a light skimming motion. This cutting was constantly viewed with a microscope to ensure that it terminated when it reached the tip of the file (1 mm level). To avoid distorted and inaccurate measurements of the canal diameters resulting from an angled cut, careful attention was given to obtaining a cross-section that was perpendicular to the canal and not to the long axis of the root. The root was swirled in 6% NaOCL to clean the cut surface, methylene blue was applied to the canal margins for maximum clarity and photographed (40X).
The K-file was removed, its stop repositioned to the 2 mm level (CL minus 2 mm) and reinserted to that level. After the file was secured with resin, root structure was removed to the file tip as previously described for the 1 mm level. The canal margin was cleaned, colored with methylene blue and photographed.
A total of 600 photographs were taken (3 per tooth) of the apical foramen and 1 mm and 2 mm levels. The photographs were digitized and their margins were electronically outlined in green for enhanced visibility. The areas of the foramen were electronically colored red and two black lines were added to designate the greater and lesser diameters that were measured using the Image Proplus Program version 3.1 (Media Cibernetics, Silver Spring, MD 20910) and recorded in Tables 1 and 2.