(Editor’s Note: This article is the second in a series and continues the discussion on this topic. The first in the series was published in November 2019 in Dentistry Today.)
As soon as we pick up the handpiece, we are faced with a procedural difficulty: How deep do we drill to get into the pulp chamber in order to find the canals? For at least half of my career, I was under the assumption that the depth of the pulp chamber had to be different for each tooth in every different patient. Early on in my practice, I devised a crude depth gauge to help in finding the pulp chamber. It turned out that when you put any manufacturer’s No. 4 round bur over a radiograph of a molar tooth and line the tip of the round bur up to the ceiling of the pulp chamber, the junction of where the cylindrical part of the shaft meets the conical part of the shaft lined up at the cusp tip (Figure 1). This distance equals approximately 6.5 mm. More than 20 years later, we measured and published the morphological distances in molar teeth.1-3 We found that a distance of 7.0 mm from any cusp tip of a molar tooth will place you somewhere between the middle of the chamber and the floor of the chamber; a clinician will never perforate the floor at this distance. Knowing this distance does several things. Firstly, it eliminates perforations of the floor of the pulp chamber. Secondly, it greatly increases the speed of finding the canals. I make the outline of the access cavity and drill down to 7.0 mm without stopping. I then wash and dry the chamber and look for canals. Usually, I find the canals within seconds. If the canals are calcified, the 7 mm places you where the canals used to be. This makes finding them a lot quicker and easier.
The next anatomic difficulty occurs because we have not achieved straight-line access. Straight-line access means the instrument does not have to curve around any dentin impingement to get into the canal. We must create an access into the canal that is totally on the floor and not on a wall (Figure 2). If we do not have straight-line access, the instrument must bend around dentin to get into the canal, and this increases instrument stress, consequently increasing the chance of instrument breakage.4
Lastly, there are 2 morphological anatomic formations that must be recognized and dealt with. Firstly, C-shaped canals. These are usually found on teeth Nos. 18 and 31, the mandibular second molars. The MB, ML, and distal canals are usually all connected via a sheath of tissue down to the apex. These teeth are difficult to clean, shape, and obturate. Luckily, we can identify them on a radiograph. On radiographs, they do not have a furcation. They appear as a single root shaped like a cone (Figure 3). If you see this morphology, the decision is to try to treat or refer to a specialist.
The other anomaly is called Radix Entomolaris (RE). It occurs as a totally separate DL root and mostly on mandibular first molars (Figure 4). The occurrence of a separate RE in the first mandibular molar is associated with certain ethnic groups and is as follows:
- Africans, 3%
- Eurasians/Indians, < 5%
- East Asians, Southeast Asians, and people of the Arctic region of North America, 5% to 30%
- Caucasians, 4.2%
- Taiwanese, 21% (normal anatomy)5-7
It is often difficult to see this root on a preoperative periapical radiograph (Figure 5). The canal is usually detected clinically, and when the distal canal is found to be skewed heavily to the buccal, there is usually another distal canal skewed to the lingual. This other disto-lingual canal is the RE. Once found, it is usually not difficult to treat (Figure 6).
Doing Endo in One Visit
In the more than 40 years that I have been an endodontist, there has always been a controversy about treating patients endodontically in one visit. However, the literature seems to be very clear about this dilemma. The amount of literature that has been published on this choice in treatment is quite large. The conclusion from these studies all determine that single and multiple visits showed similar repair or success rates, regardless of the preconditions of the pulps and periapicies. Not only are the success rates not statistically different, but the postoperative complications are fewer with single-visit endodontics.8-17 Over the almost 30 years that I have been doing one-visit endodontic treatments, I have personally found that post-op complications and pain were significantly less than those of multiple-visit treatments. I only do multiple-visit root canal treatment if I cannot find the canals or if I simply do not have the time in my schedule to complete the endodontic treatment.
It is interesting to note the general emphasis placed on instrumentation. The reality is that instrumentation only cleans 35% to 50% of the canals, no matter what system or technique is used.18,19 The remaining debris removal and bacterial reduction is accomplished through the irrigation regime. So if all endodontic instrumentation systems clean equally well, what are we looking for in using a particular type of instrument? There are several instrument factors and features that are important when deciding which instrument system to use to lessen the procedural errors associated with instrumentation of the canal. We must consider:
1. Safety of the instrument (breakage)
2. Ease of use (iatrogenic mistakes)
3. Cutting efficiency
The ability of the endodontic instrument to effectively clean and shape the canal and yet be resistant to breakage is affected by many factors. One main factor is the metal the instrument is composed of. Stainless steel instruments break less often and are kind enough to give us a warning before they break. If you see a shiny spot or small knots on the instrument, it means the instrument is distorting (Figures 7 and 8). Distortion will soon become breakage if the endodontic instrument continues to be used. Examine the stainless steel instrument after each usage in the canal and discard immediately if you see a shiny spot or knotted threads.
New Instrumentation System Recently Introduced
NiTi instruments are not as forgiving as stainless steel ones when it comes to breakage. They do not give us a warning. They just break! The more engagement with the canal dentin and the longer they are used both lead to increased breakage. A recently introduced patented development in rotary instrument design has greatly reduced the incidence of NiTi instrument breakage. TheSafeSiders HF instrumentation system (Essential Dental Systems) incorporates a non-interrupted helical-flat design, which combines the safety and durability of the original SafeSiders instruments with the added benefit of quicker apical access. The helical relief of the instrument reduces dentinal engagement and, consequently, the resistance of the instruments within the canal, shortening the time for canal preparation without instrument fatigue or breakage. The key advantage of the new SafeSiders HF design is a non-cutting, helical flat wrapped around a series of cutting flutes, which reduces engagement along the length of the instrument (Figure 9). The unique non-cutting-to-cutting-edge ratio of this design significantly minimizes the amount of torsional stress that SafeSiders HF instruments are exposed to within a canal. When used in rotation, the new NiTi SafeSiders HF instruments encounter far less resistance, which is of critical importance in reducing the risk of instrument breakage while ensuring excellent cutting efficiency. This is particularly true for the instrumentation and shaping of curved root canals, which are often encountered in clinical cases. The heat-treated NiTi SafeSiders HF instrument design features 16 cutting flutes with 2.5 turns of a helical, non-cutting flat portion oriented in the opposite direction of the cutting threads. This design allows for effective cutting and navigation of curved canals (Figure 10). The design also results in the removal of debris coronally and reduces the number of rotations required to gain apical access to the full length of a root canal. The instruments are also easy to use and operator-friendly. Advancement to the apex is achieved with a 1- to 2-mm apical pecking motion while the instrument is rotating at approximately 300 rpm. When using very slight apical pressure, the instrument will self-advance toward the apex very quickly. The heat-treated NiTi alloy is more flexible and is now bendable for easier entrance into a curved or calcified canal. This helps in reducing iatrogenic mishaps like transportation and ledging of the canals.
Taken together, the SafeSiders HF design minimizes both torsional stress and cyclic fatigue and results in effective, safer, and easier endodontic therapy with far less incidence of instrument breakage, root fractures, iatrogenic failures, and injury to the patient20 (Figure 11) (Deutsch AS et al, unpublished material, January 2020).
- Deutsch AS, Musikant BL. Morphological measurements of anatomic landmarks in human maxillary and mandibular molar pulp chambers. J Endod. 2004;30:388-390.
- Lee MM, Rasimick BJ, Turner AM, et al. Morphological measurements of anatomic landmarks in pulp chambers of human anterior teeth. J Endod. 2007;33:129-131.
- Deutsch AS, Musikant BL, Gu S, et al. Morphological measurements of anatomic landmarks in pulp chambers of human maxillary furcated bicuspids. J Endod. 2005;31:570-573.
- Pedullà E, Maria La Rosa GR, Virgillito C, et al. Cyclic fatigue resistance of nickel-titanium rotary instruments according to the angle of file access and radius of root canal. J Endod. 2020 Jan 3. [Epub ahead of print]
- Bains R, et al. The radix entomolaris: a case report. Endo (Lond Engl). 2009;3:121-125.
- de Pablo OV, Estevez R, Heilborn C, et al. Root anatomy and canal configuration of the permanent mandibular first molar: clinical implications and recommendations. Quintessence Int. 2012;43:15-27.
- Chen YC, Lee YY, Pai SF, et al. The morphologic characteristics of the distolingual roots of mandibular first molars in a Taiwanese population. J Endod. 2009;35:643-645.
- Penesis VA, Fitzgerald PI, Fayad MI, et al. Outcome of one-visit and two-visit endodontic treatment of necrotic teeth with apical periodontitis: a randomized controlled trial with one-year evaluation. J Endod. 2008;34:251-257.
- Sathorn C, Parashos P, Messer HH. Effectiveness of single- versus multiple-visit endodontic treatment of teeth with apical periodontitis: a systematic review and meta-analysis. Int Endod J. 2005;38:347-355.
- Su Y, Wang C, Ye L. Healing rate and post-obturation pain of single- versus multiple-visit endodontic treatment for infected root canals: a systematic review. J Endod. 2011;37:125-132.
- Fleming CH, Litaker MS, Alley LW, et al. Comparison of classic endodontic techniques versus contemporary techniques on endodontic treatment success. J Endod. 2010;36:414-418.
- Figini L, Lodi G, Gorni F, et al. Single versus multiple visits for endodontic treatment of permanent teeth: a Cochrane systematic review. J Endod. 2008;34:1041-1047.
- Deutsch AS, Cohen BI, Musikant BL, et al. A study of one visit treatment using EZ-Fill root canal sealer. Practical Endodontics. 2001;4:29-36.
- Vieyra JP, Enriquez FJJ, Acosta FO. Frequency of postoperative pain in one- versus two-visit endodontic treatment. Endodontic Practice. 2015;8:34-39.
- De-Deus G, Canabarro A. Strength of recommendation for single-visit root canal treatment: grading the body of the evidence using a patient-centered approach. Int Endod J. 2017;50:251-259.
- Moreira MS, Anuar ASN, Tedesco TK, et al. Endodontic treatment in single and multiple visits: an overview of systematic reviews. J Endod. 2017;43:864-870.
- Fernández R, Cardona JA, Cadavid C, et al. Survival of endodontically treated roots/teeth based on periapical health and retention: a 10-year retrospective cohort study. J Endod. 2017;43:2001-2008.
- Peters OA, Laib AL, Göhring TN, et al. Changes in root canal geometry after preparation assessed by high-resolution computed tomography. J Endod. 2001;27:1-6.
- Vaudt J, Bitter K, Kielbassa AM. Evaluation of rotary root canal instruments in vitro: a review. Endodontic Practice. 2007;1:189-203.
- The effect of cyclical fatigue on rotary endodontic instruments made of nickel titanium. Essential Dental Systems, Inc. Data on file.
Dr. Deutsch co-operates an endodontic practice in New York City. He holds 18 patents for co-inventing endodontic products for Essential Dental Systems. He is one of the leading authorities in endodontics, having lectured in more than 150 worldwide locations, and has co-authored more than 200 dental articles. He can be reached at (800) 223-5394, via email at email@example.com, or via the website essentialseminars.org.
Disclosure: Dr. Deutsch is vice president of Essential Dental Systems.