May 1, 2012
by Filippo Santarcangelo, DDS
The traditional irrigation method still used by the great majority of clinicians is represented by the Positive Pressure irrigation technique.
It is based on delivering irrigant solutions into the root canals using syringes and irrigation needles by effect of the thrust (Positive Pressure) that the operator exercises on the piston of these syringes.
A careful examination of the literature shows some of the limits of this method which concern:
• Controlling the flow of the irrigant solutions;
• The effectiveness of the biochemical debridement.
A) CONTROLLING THE FLOW OF IRRIGANT SOLUTIONS IN THE ROOT CANAL SYSTEM
From a clinical viewpoint dentists who irrigate with a syringe and needle cannot know precisely where they are delivering the irrigant and more specifically cannot know if they are pushing too much or too little.
In the former case there is a risk of the irrigants extruding from the periapical tissue, in the latter case they might not even reach the apical third.
The traditional method of irrigation thus seems operator-dependent, in other words it is difficult to standardize and control.1
The literature has highlighted how sodium hypochlorite at the recommended concentration of 5.25% or 6% is the irrigant of choice in as much as it is capable of dissolving organic substances and eliminating the presence of bacteria and biofilm from inside the canal.2-7
Having established the essential need for sodium hypochlorite, it is easy to understand how its non or insufficient delivery to the apical third may thus compromise the outcome of the whole canal treatment, due to the presence of bacteria and their ideal pabulum, organic material, inside the root canal system.
In light of the cytotoxicity of the sodium hypochlorite, its extrusion from the root canal and affecting the periapical tissue may cause the patient a series of complications of a variable clinical significance,8-10 beginning with the “simple” post-operative pain whose various causes include the extrusion of chemical irritants.
By using a Positive Pressure technique, the patient is subjected to a greater risk of NaOCI extrusion into the periradicular tissue which occurs more frequently and with greater intensity compared to techniques using Negative Pressure.11
That long-lasting and annoying post-operative pain might, be explained as the undesirable consequence of using NaOCI with Positive Pressure even when the clinician does their best to irrigate in a correct and dignified manner.
Unfortunately post-operative pain is the least important complication caused by the extrusion of the irrigants and particularly of sodium hypochlorite.
Undoubtedly the most feared is represented by the so-called “hypochlorite accident” which can be manifested with:
— severe and sudden pain, in spite of the patient being under anaesthesia;
— swelling of the area;
— interstitial hemorrhages;
— spreading of the tissue swelling reaction to nearby areas but also to other areas away from the dental element in question;
— intraoral hemorrhage through the tooth12 (Figs. 1-2);
— temporary and permanent muscular paralysis.
Fortunately most hypochlorite accidents will resolve on its own in due time but in a few unfortunate cases neurological and mimetic muscle damage can be permanent13,14 (Fig. 3).
B) EFICACY OF BIOCHEMICAL DEBRIDEMENT
In order to perform its work, an effective irrigant like sodium hypochlorite needs not only to reach the apical third but also to be frequently renewed so that it does not lose its effectiveness.15,16
Hypochlorite delivered in the traditional way using syringes and needles has problems reaching into the whole root canal system and also in removing debris from the more remote portions of the canal systems.17,18
These difficulties limit the effectiveness of the irrigation with the positive pressure technique, but this is not all.
A very important technical aspect concerns penetration of an irrigant according to the irrigating needle diameter and the canal preparation size.
Since the canal irrigant only moves a millimetre beyond the tip of the irrigation needle, only canal preparations which allow the needle to reach within a millimetre of the canal length can effectively deliver disinfectants along the whole canal length.19,20
It is worthwhile remembering that the closer an irrigating needle gets to the apical foramen, the greater the risk of extrusion of the disinfecting solutions into the periapical tissues.
Unfortunately the different designs and needle gauges do not prevent hypochlorite accidents.21,22
Another factor which may have a negative influence on the fluid dynamics within the canals is that of gas (ammonia and carbon dioxide) which form following the hydrolysis reaction between sodium hypochlorite and pulp tissue.
In-vivo the gases formed inside the canals are trapped in the apical third and form a fluid barrier better known as “apical vapour lock.” When this occurs, fluids cannot reach the full working length and this barrier cannot be broken with a hand or rotary files.23
This apical vapour lock has been suspected in endodontics for many years but only recently has it been described and demonstrated.24-26
Insufficient delivery of the irrigants to the apical third may explain the failure of cases which seem to be well treated radiographically but the periapical radiolucency remains.
THE APICAL NEGATIVE PRESSURE IRRIGATION TECHNIQUE: THE ENDOVAC SYSTEM
The introduction of apical negative pressure to Endodontics is the logical response to unsolved problems connected to the above mentioned Positive Pressure technique.
The device which develops apical negative pressure is called EndoVac (SybronEndo, Orange, CA) and was invented by an endodontist from California named Dr. G.J. Schoeffel. EndoVac has the unique capability to deliver irrigants up to the apical foramen without the risk of forcing them into the periapical tissue.27
Its uniqueness lies in the concurrent work of two components, the first releases the irrigant inside the pulp chamber and the second (an aspirating cannula) which draws it by aspiration (negative pressure) down the canal walls to the very end of the canal before aspirating it into the High Volume Evacuation line by means of a Multi-Port Adapter (MPA) (Fig. 4). 28
The first component is the Master Delivery Tip (MDT). The MDT is designed for both irrigation delivery and evacuation. It allows one to deliver solution (normally NaOCl) to the pulp chamber in abundant quantities while concurrently evacuating any excess solution through a built-in hood (Fig. 5). The delivery tip extends 2.0 mm past the evacuation hood and is “hooked” on the wall of a posterior tooth or set just inside the access opening when working on an anterior tooth. By doing so, the dental assistant can do without an aspirator which would be essential in the traditional technique with syringe and needle.
The tip’s short length is designed to prevent the clinician or assistant from placing it into the orifice of a root canal. This is an important safety feature which when used properly prevent a powerful force of irrigant to be driven through the canal and into the periapical tissues. The flow of irrigant from the MDT should always be directed into a side wall of the chamber and never directly into an orifice.
It is extremely simple to use and can be delegated to the dental assistant with a significant reduction of operating times, regulations permitting (Fig. 6).
The MDT can also be used during instrumentation to evacuate the gross debris present in the chamber as it guarantees an abundant reserve of fresh irrigant.
FINAL IRRIGATION PROTOCOL
After completion of all rotary preparations, the second component
of the system, the MacroCannula, comes into play. It is made of polypropylene and fits into the EndoVac Handpiece for operator convenience.
The MacroCannula suctions the macro debris produced by the action of the rotary file from the coronal and middle third of the canal (MACRO-EVACUATION).
It is used in conjunction with the MDT to “pressure flush” the coronal two thirds of the canal system. The clinician places it into the canal as far as possible. Then, while the assistant delivers NaOCI from the 20-cc syringe the clinician moves the MacroCannula quickly up and down from the canal orifice to its apical extent for 30 seconds per canal (Fig. 7).
The third and last component, a thin stainless-steel cannula called MicroCannula, now comes into play. The MicroCannula is placed into the EndoVac Fingerpiece to make it easier to use.
In the micro evacuation phase, the assistant delivers hypochlorite passively into the pulp chamber with the MDT, while the dentist places the MicroCannula to the working length confirmed by the placement of a rubber stop set to the working length previously determined by x-ray and electronic apex locator (Fig. 8)
The development of the apical negative pressure technique undoubtedly represents the greatest step forward for endodontics in the last few years.
It is the first time in endodontic irrigation history that a clinician can control the flow of solutions within the canals with precision and safety from orifice to foramen.
Thanks to the Endovac system irrigation has now become much more predictable.
Many endodontic failures can be attributed to insufficient irrigation.19 In spite of employing state of the art technology for shaping and obturation procedures, radiographically well treated cases may develop or maintain the periapical pathology (Fig. 9).
Ineffective biochemical debridement is commonly found in retreatment cases. The presence of necrotic debris, bacteria and their by-products prove that commonly used techniques are insufficient to rid the canal of harmful materials (Fig. 10). The failure of the irrigants to reach the apical third or the insufficient exchange of fresh irrigant may be the cause of the failure leading to the need for retreatment.
Infected debris remaining inside the root canal system also prevents gutta-percha and cement from sealing hermetically and thus provides another possible explanation for the persistence of the periapical pathology.
In view of this, an irrigation device which ensures reaching the apical foramen safely and allows for an abundant exchange of effective irrigating solutions is undoubtedly a critical weapon to have in one’s endodontic armamentarium (Figs. 11-14).
ENDOVAC AND SHAPING PRODCEDURE
Since apical negative pressure should be ideally placed at the very end of the root canal, to be most effective the MicroCannula must be positioned at the working length.
The MicroCannula’s diameter is 0.32 mm and thus the EndoVac system requires a minimum canal shape of at least a No. 35 instrument with a 4% taper, or with a non-tapered system like LightSpeed, a size #45 at full working length.29
As widely demonstrated in the literature, root canal apical diameters are frequently equal to if not greater than 0.35 mm. Thus in theory, there should be few canals where positioning the MicroCannula at full working length would not be practical.30
In practice, several factors may make it difficult to shape canals to these larger sizes. In these cases, the use of non-tapered instruments such as LightSpeedLSX become invaluable.
Indeed, the presence of multi planar curvatures, mid root curvatures, apical third curvatures, constrictions of the canal lumen, gives the operator the wrong perception of a small apical foramen and a narrow root canal lumen when the impediments are really before the foramen itself.
From a strictly practical viewpoint this leads many dentists to perform minimally invasive preparations because they fear that the attempt to widen the root canal lumen may lead to breaking the rotary instruments or to iatrogenic damage of the anatomy like blocks and ledges.
These are the fears and perplexities of those who are faced with this new method of irrigation for the first time and of those who have never used it and inexplicably prefer to keep to the traditional technique.
Therefore the risk of insufficient debridement increases greatly whenever instrumentation is not performed to allow for deep biochemical debridement whatever irrigation technique is employed.
The author’s experience of having used the EndoVac for more than five years has led to the development of a logical operating strategy and thus to classify three types of clinical situations (A-B-C).
Each canal should be shaped with the preferred technique and instruments with complete respect and preservation of the original anatomy, thus complying with the mechanical and biological objectives outlined by Professor Schilder in 1974.31
At the end of the typical shaping procedure, almost 50% of the cases (A) are already large enough in the apical third to place a MicroCannula to the foramen; upper central incisors, canines, a good number of premolars, distal roots of lower molars, palatal roots of the upper ones are a constant example (Figs. 15-17).
In another high percentage of cases (B) which approaches 30%-40%, it is possible to obtain those diameters necessary for positioning the MicroCannula at working length of notoriously difficult canals like the mesial lower molars and the buccals of upper molars by using a technique which the author calls Safe Apical Enlargement (SAE).
SAE is performed after typical shaping techniques. Three NiTi rotary files with tip sizes 25, 30 and 35, all .02 taper, are taken in sequential order to working length.
They enlarge the last few millimetres to a size suitable for the EndoVac technique (Figs. 18-22).
Approximately 85-90% of all cases fall into the A or B category where the MicroCannula can be taken to the working length. That leaves the remaining 10% of cases (C) where apical enlargement is problematic.
Consider the narrow second mesiobuccal canal of an upper molar or severely curved canals or those which bifurcate. In these cases — which show the limits of the EndoVac technique — the MicroCannula shall be positioned as far as the canal permits it (Figs. 23-29).
It should be pointed out that complex cases from an anatomic viewpoint limit not only the EndoVac technique but also the traditional techniques of irrigation.
ENDOVAC AND ANATOMIC LIMITATIONS
The difficulty with endodontics is generally the last few millimeters of the canal, in other words the apical third where more than 90% of the portals of exit are located.
The apical third is by its very nature narrow and deep and complex making it difficult to instrument. Therefore the need for irrigation is even more critical.
However, this is not easy. One of the critical success factors of endodontic irrigation is the replenishment of used irrigant with fresh irrigant because the irrigant loses its effectiveness and has to be renewed.13,14
The deeper one goes into the root canal the more difficult this becomes.
So not only does the irrigant have to reach the last few millimetres it also has to be renewed. Apical canal anatomy is a complicating factor in this endeavour.
The canal anatomy limits every part of the root canal treatment, including irrigation. Indeed the difficulty is compounded if the apical third is found at the end of a long or narrow canal or worse still after a curve. In other words, with anatomy like this, where shaping and obturation are both difficult, irrigation is difficult too.
Successful treatment of these cases really depends on the operator’s ability to shape, cleanse and obturate the entire root canal even if the canal is curved, narrow or long.
In long canals like those typically found in the upper canines, a 31mm MicroCannula is available. By placing it at working length one can be assured of delivering and renewing the irrigants right to the very end of the canal. In this way the anatomical limitation represented by the canal length is eliminated (Figs. 31-35).
In curved canals, once the MicroCannula reaches the very end of the canal, the irrigants will flow the entire canal length.
It will thus be possible to perform excellent cleansing in spite of the presence of this anatomical limitation represented by the canal curve (Figs. 36-38).
The MicroCannula can be pre-curved for getting around curves.
Special pliers made for pre-curving files, Endobender (SybronEndo, Orange, CA) are helpful for doing this. The operator must pay great attention when pre-bending the MicroCannula because, being hollow, it might collapse, weaken and break (Figs. 39-46)!
Another limitation to endodontic procedures is represented by the narrow canals (Figs. 47-49).
Large canals with large foramen pose a greater risk for extruding the irrigants into the periapical area if traditional irrigation techniques are used. However, this is easily avoided if the EndoVac system is adopted.
In the case of physiologically or pathologically large foramen (immature apical anatomy or root resorption), irrigation by EndoVac be accomplished without worry given that the sodium hypochlorite is contained within the root canal space thus guaranteeing the patient’s safety and the dentist’s peace of mind (Figs. 50-53).
ENDOVAC AND “VITAL CASES”
When irreversible pulpitis or inflammation of the pulp tissue is present, the irrigants must be counted on to dissolve any organic material residue which remains in the canal after the shaping process.
Several techniques have been proposed to improve the effectiveness of the tissue dissolution action of the sodium hypochlorite. These include heating solutions and activating them through ultrasonics and subsonics means. Regardless, to be effective these techniques require that the solution reach working length in a safe manner.33-36 Therefore, their use can be supplemented with EndoVac because it is both a safe and effective method for getting the solution down to the end of the canal safely (Figs. 54-56).
ENDOVAC AND “INFECTED CASES”
Effective elimination of microbes by apical negative pressure microbial control is the key to bringing about painless and rapid recovery (Figs. 57-63).
ENDOVAC AND RETREATMENT
In 1983 Chow defined the three criteria necessary for successful mechanical endodontic irrigation. He showed that irrigation efficacy depends on three critical success factors, such that irrigants must: (1) reach the apex, (2) create a current flow, and (3) carry particles away.18
The EndoVac system satisfies all three criteria and in particular the removal of debris is particularly evident when performing a retreatment.
In canal retreatment, one must remove the obturation material of the previous treatment.
Until now, this work has been carried out mechanically (sometimes with the aid of solvents) using only manual and rotary files.
Experience has shown that the EndoVac system can save time and effort in removing intracanalar material including sealers, temporary dressing and gutta-percha.
The mechanical efficacy of this system is clinically witnessed by all the types of debris that it is capable of aspirating (Figs. 64-89).
Over the years the author has found numerous other helpful uses for EndoVac.
For example, the MicroCannula is useful as a foramen locator. This is because the 12 aspirating micro holes are positioned in the last mm of the MicroCannula. When the tip of the MicroCannula is placed through the foramen the system stops aspirating the irrigants.
Then, the flow starts again when the tip is pulled back inside the canal. This technique is described in detail in the following clinical case (Figs. 90-95).OH
Dr. Filippo Santarcangelo graduated from the University of Bari School of Medicine and Surgery in 1996. He maintains a clinical practice limited to endodontics in Bari, Italy, and is also an Active Member of the Italian Endodontic Society. firstname.lastname@example.org
Oral Health welcomes this original article.
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