Oral Health Group
Feature

Endodontic Principles That Govern

May 1, 2006
by Stace D. Lind, DDS


I would rather not give you another ‘how to’ article or another preaching ‘sermon’ telling you how to practice but would rather teach correct principles that govern endodontic success and allow you to govern yourself. A correct principle can and should apply to each endodontic system and not to just what I use in my practice. We must understand that the ‘chemistry’ of what we do is more important than the ‘company’. So our desire to be better and do better for each patient really lies in our becoming more aware of the chemistry advances, which will help the patients we serve. Even if you are one of those dentists who ‘really do not like doing endo’ the principles that follow may help you find enjoyment in an area of your practice, which, due to past experience, has been avoided.

With the new material science, techniques, and options of armamentarium, endodontics is most likely the top or one of the few areas of study that has changed the most since we attended dental school. In the next few decades we will see “more people (baby boomers), living longer while maintaining more teeth”, and have greater needs endodontically and periodontally.1 The demand will far exceed what the endodontist can handle so that each dentist will have the opportunity to perform endodontic treatments which are in his or her comfort level while still maintaining referrals for the specialists for those teeth which require additional expertise to perform. What has happened to create such changes in how we do endodontics and why so many new approaches? We have seen office incomes increase but have also witnessed increased issues with more endodontic failures, need for retreatments and serious concerns with broken files and poor apical sealing of teeth.2 I desire to say that any materials mentioned are for example and what I am familiar with and not meant to tell you what you must use. Remember Chemistry not Company. Numerous companies and many competitive products may accomplish each part of each principle that I will share with you. I prefer to use the best of materials and do not purchase based on any manufacturer or their representative.

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PRINCIPLE ONE: ACCESS

Many dentists skim past the topic of access because they think they ‘have it down’. Please ask yourself the following questions first.

1 How much time do you spend on finding canals? And how much time during the procedure do we spend looking for them again? This is what I call performing Morse code on the floor of the tooth. And again are you still probing with the master cone trying to again find that canal that should now be easy to find? This can all be summed up as true dental schizophrenia.

2 How often do you need to take the file or handpiece from the direction of the Uvula to come forward to find the canal? Or how often do you need to stretch that rubber dam to the soft palate to try to come forward in finding the angle of that mesial buccal canal?

Better yet, how often do you need to place your finger in the patient’s mouth trying to bend the file to find the angle for placement?

3 Problem with broken files, transported canals or ledging?

4 And the final question: Do you feel stressed out when you do endodontics? Are you impatient, stressing staff out, trying to hurry to obturate but everything is taking longer than it should?

If these previous questions ring familiar then endo access may be the most important area to work on. Just maybe re-working on the principle of access may change your practice of endodontics. You need a straight-line access to each canal and if there is a problem finding canals it is often due to improper access.3 I have found over the last 10 years since I have been tracking numbers and timing myself with techniques, accuracy and performance, that when I use an additional 3-5 minutes on the tooth access, I reduce the time spent for the whole procedure by a third and I end up with fewer problems arising during the procedure.

A few of my simple keys about access: First, I begin with the end in mind, meaning that if the tooth will end up with a crown then I take a pre-impression of the tooth for the crown temporary and then I will do my occlusal reduction prior to beginning my endo treatment. Why? Greater visibility of each canal, less bending of the file especially for a second molar, and a flat plane for more accurate measurement with each file. If the tooth already has a crown or you do not plan at this time to put a full coverage crown on the tooth, then we do an access which is more like a class 1 inlay design that has divergent walls from the floor of the chamber to the occlusal portion of the tooth. This allows better visability, lighting and straight line access. Effective removal of the areas of dentin in the access or coronal part of the canals will create an angular change in the canal and when the entry angle is altered then risk of file separation and instumentation problems decrease. There are many burs to use but I prefer a #2 or #4 round bur to access the pulp chamber, and then I use safe tip burs which prevents me from causing damage to the floor of the tooth. Once in the pulp chamber if there is a question as to where canals are, and especially in a crowned tooth which can create stress for you in worrying about a perforation, I have a suggestion. I know that many do not use microscopes in their operatories yet, and when searching for a canal we can use a safe chemistry to help us. I like using a green caries indicator at the bottom of the tooth because there is nothing else which is green, and I particularly do not like chasing red colors on the floor of the tooth for obvious reasons.

Upon rinsing the caries indicator it leaves green anywhere there is soft tissue or an orifice. It is safe to chase the green and this was the way for years prior to new innovations that I discovered so many mb2 canals in the upper first molars. I like the ‘Sable Seek’ made by Ultradent due to the ease of syringe placement anywhere in the mouth. There are other green indicators but placement to the floor of the tooth is the biggest problem. There are many ways to flare and open the coronal portion of the tooth so find one that will be safe and efficient in removing the overhangs, ledges, and pre flare the canal. There are other kits like the Endo-Eze Access Bur Kit from Ultradent.

PRINCIPLE TWO: BULK INSTRUMENTATION

The initial approximate length of the tooth is first determined whether using digital, film, or an apex locator. A few definitions first: The Crown Down Technique: Beginning with a larger file to remove coronal debris first and moving to smaller files as the files move closer to the apex. Step-Back Technique: Beginning with the smallest files and aiming just shy of the apex and moving back from that point while increasing the file size. The reason the Step-Back Technique has been popular over the years was solely to avoid ledges, or transporting the canal and thus blocking you from reaching the apex. Now with our current materials, techniques and methods it is much safer and also improves the quality of care for our patients to use the Crown Down Technique. Why? “The goals of endodontic treatment are to remove the canals soft tissue contents as completely as possible, eliminate as completely as physically possible any microbial elements, and create a situation within the canal that can prevent microbes or toxic substances from passing through the canal system to the apical supportive structures.”4

No two things can occupy the same space at the same time. With inflammation and diseased tissues or cells in the tooth we can help avoid the expulsion of inflamed pulp tissue and cellular debris out of the apex because once these toxic materials are pushed into the periodontal ligament space and bone they are no longer accessible and now unable to treat chemically without forcing the chemistry into the same area. As coronal tissues are removed, pressure is lessened apically and it is eaasier to get chelating agents and sodium hy
pochlorite to the infected tissues at that remaining apical plug. Now, if those materials escape out of the tooth, they have been soaked and treated chemically first so the body has a better chance to heal the area. With the crown down technique you will see a decrease in postoperative sensitivity, root canal failures, or need for apicoectomies.

We must always remember that it is the operator, not the instruments, that prepare the canals. Nickel titanium has been a wonderful blessing to endodontics and was needed, invented and designed for teeth, which had curved canals. So when I have canals which still have a high degree of curvature following my access I will use my Nickel Titanium files. Nickel titanium files are a softer alloy, which gives us the flexibility, but are more difficult to observe any stress or deformation in the metal and due to properties require more files and more instrumentation time for correct instrumentation.5 On the other hand stainless steel files have a greater cutting ability but lack the flexibility. Stainless files will show more observable deformation and are typically one-third the cost of their titanium counterpart, and can handle six times the torque of titanium.6

Normally with a straight line access into the tooth I will use a stainless steel reciprocating file for the bulk debridement due to each file cutting more efficiently (using less files), anticipating instrumentation sooner (less time), and using files which are both much less expensive and have a lower risk of separation. This is a difficult point to understand: Are we taking a step back if we use both titanium and stainless? No. Do we not have different instruments for the task of extracting a tooth? Why not use one instrument for everything? The instruments are for me, not me for the instruments. If I were to ask you what holds a sharper edge and cuts more efficiently; a flexible knife or a stiff knife? Of course we know that a stiff knife holds the edge. When I have a straight canal why would I use a file that costs 2-4 times more, takes more time, cuts less efficiently, and separates more easily?

The reason I use both rotary and reciprocating is that the morphology within the canals for all but the last 3mm (except for maxillary incisors) is elliptical or flat-ribbon shape in cross section. The reciprocating stainless steel files are more effective at following the anatomy and removing the debris from the walls of the tooth. It is interesting to note that “… After five years of steady increases in the use of Nickel Titanium files, the latest survey reflects a drop in use from 84% last year to 45.3% in 2002″7 The strength of the rotary files or hand files is in the area of the apex where the near roundedness more approaches that of the file.

Following removal of all debris in the tooth except the last three millimeters, I then can take the rotary or hand files and instrument the very apical portion of the tooth. As will be discussed in the next item, chemistry is always used prior to each new file that enters the canal. Clifford Ruddle stated, “When there is an irregular glide path, regardless of etiology or size of the foramen, then 0.02 tapered hand instruments should be used to prepare and finish the apical one third of the canal.”8 The importance of all instrumentation is we remove the pathology and clean the inside of the tooth large enough to obturate the tooth. It is paramount for the patient that we do not over treat the tooth with removing the healthy tooth structure.

PRINCIPLE 3: CHEMICAL TREATMENT IN THE CANAL

There are many variances of canal anatomy when using a dye or a clearing technique (making the tooth clear with chemical treatments) to see into the tooth. There are areas of multiple connections between canals and many areas, which no file can touch. It is interesting to note that “all instrumentation techniques with rotary nickel titanium left 35% or more of the canals surface area untouched… and this finding underscores the importance of irrigation of the root canal system since irrigants aid in the cleansing process and remove pulp tissue not contacted by files.”9 From numerous studies we know that sodium hypochlorite and an EDTA lubricating agent produces canals with less organic debris and are better being used together than either one alone.10 We also know that it has been shown that the cleansing power of sodium hypochlorite percentage concentration is not as important as repetitive irrigations and volume due to the short lived reaction of the freed chlorine.11

The canal is treated with an EDTA gel prior to file placement and then rinsed with sodium hypochlorite after the file is removed. Following final instrumentation of the canal, it is recommended to flood the canal with a citric acid or EDTA rinse and leave it for one minute followed by a final rinse of sodium hypochlorite or saline rinse. If an intracanal medication is needed then you can mix a calcium hydroxide powder with chlorahexidine liquid and leave for one week.12 I prefer to use ‘UltraCal’ from Ultradent Products Inc., which is in a syringe for easy delivery and has a pH of 12 and is very effective for calming teeth as well as for apexification. One final point on the principle of irrigation is that of getting the solution where you need it. I have not found a better tip for getting everything from calcium hydroxide to EDTA solution at the apex region of even a curved canal than the ‘NaviTip’ from Ultradent Products, Inc.

PRINCIPLE 4: CONSERVATION OF TOOTH STRUCTURE

How often have we seen endodontically treated teeth fail restoratively? How long does the tooth have to last to claim endodontic success? Too many times I have seen teeth that have been entirely gutted out internally in the name of endodontic treatment only to be extracted once the remaining tooth and post gave out just a few years later. One of the most important principles in our daily practice of dentistry is to help the patient the most by doing procedures and techniques that will alloy them to keep the treated tooth the remainder of their life. It has been documented that “reducing dentin width by all intracanal procedures, especially with rotary instruments, can be a predisposing factor for a subsequent vertical root fracture directly related to the amount of dentin removed”, and “…excessive removal of radicular dentin compromises the root… and the amount of remaining dentin is directly related to the strength of the root.”13

So we do the patient no service in over enlarging canals and removing all the supporting dentin, only to fill it with gutta percha. We best serve our patients by moving toward better chemistry in our materials and more conservative treatment approaches. There are many other areas of endodontics we could discuss, principles that should govern our conduct like the obturation materials which will strengthen the teeth and allow us to bond from the restoration to the apex. There have been great advances in endodontics in the moving away from lateral condensation of gutta percha to the new hydrophilic sealers and cements which are incredible new resin technologies that due to the chemistry are drawn in and seal each tubule and internal morphology. These new resins allow bonding from our composites and seal up the tooth better than the other sealers and cements and are biocompatible.14 I have used the product ‘EndoRez’ from Ultradent Products Inc. for eight years and have seen nothing but wonderful results.

There are other great resin products on the market from different companies but remember look at the studies, learn their chemistry and first practice on extracted teeth. But know this, that if you move to the new resin technology, there are two points that are fundamental to their chemistry. First, you must use peroxide free lubricants and irrigants as oxygen generated from peroxide can inhibit the set of resins, including EndoRez. Second, you must thoroughly rinse sodium hypoclorite from the canal before placing resins. I recommend using an EDTA solution as
a final rinse but if not an EDTA, then use bacteria free water or a local anaesthetic may be used. The resins with a single master cone placement will produce less voids, provide better adaptation to the tooth surface and will increase endodontic success and profitability. Read the literature, study the chemistry, most of all try it on the bench first–this is a good way to become the best at what you do and serve the most important person in your practice: the patient. Try staying in business without them. Serve the patient the best you can and the results are always good.

Dr. Stace D. Lind currently pratices in Littleton, Colorado and lectures at many national dental societies and dental schools in the U.S. and abroad. Dr. Lind is a graduate of the University of Louisville School of Dentistry. Dr. Lind may be contacted at stacelind@msn.com

REFERENCES

1.Endodontic Status in older adults JADA, Vol. 132, Nov.2001

2.Australian Dental Journal Vol. 34 (1), pp49-51, Feb 1989 International Endodontic Journal Vol. 20, pp276-281 no. 6 1987Journal Of Endodontics Vol. 21, No. 6 June 1995Journal Of Endodontics Vol. 25, No. 6 June 1999

3.Dental Economics Oct. 2002 pg 124 Dr. Dennis Brave and Dr Kenneth Koch

4.Journal Of Endodontics Vol. 11, No. 5 May 1985 Properties Of Endodontic Hand Instruments Used in Rotary Motion.

5.Compendium Vol. 21, No. 11 pg 984 Nov. 2000 Facts on Nickel Titanium Files

6.Journal of General Dentistry December 2000 pg 690 Facts on Stainless Steel files

7.Dental Products Report, November 2002 pg. 27

8.Ruddle, CJ Dentistry Today, May 2002

9.Int. Endod J. 2001: 34 (3) pg221-230. Also see Dentistry today Feb. 2004 pg119-126.

10.Journal of Endodontics Vol. 26 pg. 331-354 2000.

11.IBID

12.See: J Endod. Vol 29. Pp.340-345, 2003. Int. Endod J. Vol. 36. Pp. 100-105, 2003. And Cont. Endo Vol 1, No. 1, 2004 Protocol for the chemical treatment of canals.

13.Pilo, et al Journal of Endodontics, June 1998

14.See: Newcombe J., et al IADR/AADR/CADR March 2002 Microleakage of Root Canal Sealers Geurtsen W., Aust Endod J. Vol. 27 (1) pp 12-21 April 2001 Biocompatibility of Root Canal Filling Materials