Irrigation Materials
Instrumentation of the root canal system must always be supported by an irrigation
system capable of removing pulp tissue remnants and dentin debris. In modern
treatment systems the irrigation fluid is delivered with a fine-caliber needle in large
volume, and the debris is aspirated with a good suction device. The effervescence
created by mixing NaOCl with hydrogen peroxide has been used to remove debris
from the root canal, but this is not an effective method. Liberal irrigation is essential
for effective functioning of the files. Many anecdotal descriptions of the lubricating
effect of irrigation fluids are merely the mistaken effects of debris transportation.
Without irrigation, instruments rapidly become ineffective because of the
accumulation of debris. Irrigation also is essential for reducing the number of bacteria
in an infected root canal, but it has only a minimal antimicrobial effect on the infected
root canal walls. Consequently, the antimicrobial effect of an irrigation fluid should
not be the clinician’s only concern when choosing among suitable compounds.
Surface tension and cleaning effectiveness are equally important qualities.
Quaternary ammonium compounds with a low surface tension have been extensively
used as irrigation fluids. These fluids are detergents and therefore effective aids in
pulp space cleaning because they remove lipid pulp breakdown products. However,
they now are rarely used because of their toxicity. Quaternary ammonium
compounds are still used as additives to ethylene diamine tetra-acetic acid (EDTA) in
EDTAC (EDTA and cetrimide) to provide some antimicrobial effect. NaOCl has
become the irrigant of choice worldwide. Its strong proteolytic effect makes it an
excellent aid during instrumentation. Chlorhexidine has also been suggested as an
irrigant, but it has few advantages over NaOCl during instrumentation. A 2% solution
of chlorhexidine has proved more effective against Enterococcus faecalis than
sodium hypochlorite. Chlorhexidine also differs from sodium hypochlorite in that it is
relatively nontoxic and does not dissolve tissue. If applied to dentin, it binds
effectively to hydroxyapatite, providing a lasting reservoir of chlorhexidine after the
completion of treatment. Some have suggested that this long-term effect may be
helpful in reducing the effect of postoperative coronal leakage. One study showed
that combined use of chlorhexidine and sodium hypochlorite resulted in a greater
percentage of microbe reduction than was achieved with either used alone. New
irrigants are being developed in an attempt to address some of the shortcomings of
past and current materials. MTAD is a mixture of a tetracycline isomer (i.e.,
doxycycline), an acid, and a detergent. In an in vitro study, MTAD was found to be an
effective solution for killing E. faecalis.
Proteolytic Materials
The most commonly used proteolytic irrigation material is NaOCl, which became an
important agent for the treatment of infected wounds in the early twentieth century.
NaOCl dissolves necrotic tissues and debris through a complex biochemical process.
The amount of free chlorine is important for this breakdown of proteins into amino
groups. Higher temperatures also potentiate the antimicrobial and tissue-dissolving
effects of NaOCl. The original concentration suggested by Dakin was 0.5%, but
concentrations as high as 5.25% have been used in dentistry. A 1% concentration
provides sufficient tissue dissolution and antimicrobial effect if used freely. Higher
concentrations of NaOCl affect living tissue and do not improve the reduction of
bacteria during endodontic treatment. NaOCl has an antimicrobial effect as long as
free chlorine is available in the solution. Because free chlorine is the important
component consumed during tissue breakdown, the NaOCl must be replenished
frequently, especially when low concentrations are used. This becomes even more
important when the root canals are narrow and small.
Sodium hypochlorite does not effectively wet dentin, and small canals and canal
extensions are poorly irrigated. Attempts have been made to change the surface
tension of NaOCl but without significant success. NaOCl also has been shown to
deplete dentin of organic compounds and to increase the permeability of dentin
significantly. Pure NaOCl is a U.S. Pharmacopeia (USP) preparation and may be
purchased from a pharmacy. However, dentists commonly use commercial 5.25%
NaOCl (i.e., household bleach). At this concentration NaOCl is highly toxic, meaning
that it unnecessarily necrotizes wound surface areas that should remain unharmed.
The literature widely suggests that postoperative pain is no greater when high
concentrations of NaOCl are used. However, this lack of correlation proves little,
because tissue damage and clinical symptoms are poorly correlated.
Commercial NaOCl is buffered to a pH of approximately 12 to 13. This adds another
toxic component, making the solution even more caustic. Therefore if commercial
bleach is used as a base for preparing a 1% irrigation solution, it is better to use
sterile 1% sodium bicarbonate as a diluent rather than water. This helps to adjust the
pH to a less caustic level. Diluted, buffered NaOCl has a limited shelf life and should
be stored in a dark, cool place for no longer than 1 to 2 weeks. Few clinical
complications are associated with the use of NaOCl. The most common one is
accidental injection of NaOCl into periradicular tissue. This results in excruciating
pain, periapical tissue bleeding, and extensive swelling. The pain normally subsides
within 2 to 3 days. The swelling increases for the first day, after which healing occurs.
The prognosis is usually good if no critical tissues, such as the mental nerve, have
been damaged. Sodium hypochlorite and hydrogen peroxide are known to release
oxygen-free radicals and have the potential to reduce the bonding of resin to dentin.
Alcohol, chlorhexidine, saline, EDTA, anesthetics, and sodium ascorbate do not
seem to affect the bond strength of resin, and they may even remove or negate the
oxygenfree radicals. One study found that short-term use of calcium hydroxide
Ca(OH)2 did not affect dentin bond strengths when ethanol or acetone-based
adhesive resin was applied.
Detergents
Detergents are often used as irrigation solutions because they are effective at
removing the fatty tissue residues that are byproducts of tissue necrosis. Commonly
used materials are included in the family of quaternary ammonium compounds.
These compounds were once considered optimal for antimicrobial therapy and
effective in very low concentrations. However, this has been disproved, and the
preparations have been shown to have a toxicity comparable with that of other
irrigation solutions and a rather narrow bactericidal spectrum.Quaternary ammonium
antiseptics normally are used in a water solution at 0.1%
to 1%. Zephiran chloride has been commonly used as an endodontic irrigation
solution. However, in light of its toxicity and low antimicrobial effectiveness, no
reasons exist to use this detergent instead of a relatively less toxic irrigating solution
(i.e., 1% or less NaOCl solution). Another group of antimicrobial agents with
detergent effects are the iodophores. Wescodyne and Iodopax are common products
in this line of antiseptics. These organic iodine products are effective at low
concentrations. They are antimicrobially effective at an iodine concentration of 0.05%
(volume/volume). Detergents have also been mixed with calcium hydroxide for
irrigation.
Decalcifying Materials
A smear layer is formed during preparation of the root canal. No clear scientifically
based understanding exists on whether this layer must be removed or can be left.
However, a multitude of opinions have been offered on both sides of this question. In
addition to weak acids, solutions for the removal of the smear layer include
carbamide peroxide, aminoquinaldinium di-acetate (i.e., Salvizol), and EDTA. In
objective studies, carbamide peroxide and Salvizol appear to have little effect on
smear layer buildup.A 25% citric acid solution also failed to provide reliable smear
layer removal. EDTA is often suggested as an irrigation solution because it can
chelate and remove the mineralized portion of smear layers. It also can decalcify up
to a 50 μm layer of the root canal wall if used liberally. EDTA is normally used in a
concentration of 17%. It removes smear layers in less than 1 minute if the fluid is
able to reach the surface of the root canal wall. Reports suggest that under clinical
conditions, the fluid should be kept in the root canal for at least 15 minutes for
optimal results. The decalcifying process is self-limiting, because the chelator is used
up. To achieve continuous effect, the EDTA must be replaced through frequent
irrigation. For root canal preparation, EDTA has limited value as an irrigation fluid. It
may open up a hair-fine canal if given the time to soften the 50 μm it is capable of
decalcifying. This amount, at two opposite canal walls, results in 100 μm. This is
equivalent to the tip of a #010 file. The smear layer consists of both an organic and
an inorganic component. EDTA alone normally cannot remove the smear layer
effectively; a proteolytic component (e.g., NaOCl) must be added to remove the
organic components of the smear layer. Commercial products with such
combinations are available. EndoDilator N-Ø (Union Broach, York, PA) is a
combination of EDTA and a quaternary ammonium compound. Such an irrigation
fluid has a slight detergent effect in addition to the chelating effect. Two newer
irrigating solutions, MTAD (Dentsply–Tulsa) and Smear Clear (SybronEndo), have
recently been studied. Smear Clear, which is commercially available, is a clear,
odorless, water-soluble solution containing water, 17% EDTA salts, a cationic
surfactant (centrimide), and anionic surfactants.
Intracanal Disinfection Materials
Biomechanic instrumentation and irrigation with an antimicrobial solution are
essential for disinfection of the pulp space, but some suggest that these techniques
may not completely eradicate microorganisms in a necrotic pulp space and that
further disinfection with an effective antimicrobial agent may be necessary. Phenol
and phenol derivatives are the most commonly used intracanal disinfectants.
Antiseptics with a chlorine or iodine base are also common. In recent years more
attention has been given to the use of calcium hydroxide as an intracanal dressing
for the treatment of infected pulp necrosis. Conventional antiseptics generally are
toxic, and care must be taken not to cause undue tissue damage.
Phenolic Preparations
Phenol (C6H5OH), or carbolic acid, is one of the oldest antimicrobial agents used in
medicine. Despite the severe toxicity of phenolic preparations, derivatives of phenol,
such as paramonochlorophenol (C6H4OHCl), thymol (C6H3OHCH3C3H7), and
cresol (C6H4OHCH3), remain available. One survey noted a decrease in the use of
classic phenolic medicaments with a corresponding increase in the use of calcium
hydroxide or no medication. Phenol is a nonspecific protoplasm poison that has an
optimal antibacterial effect at 1% to 2%. Many dental preparations use much too
high a concentration of phenol (e.g., in the range of 30%). At such a concentration
the antimicrobial effect in vivo is lower than optimal and of very short duration.
Derivatives of phenol are stronger antiseptics and toxins than phenol. Phenolic
compounds are often available as camphorated solutions. Camphoration results in a
less toxic phenolic compound because it slows the release of toxins to the
surrounding tissues.
Studies in vitro have shown that phenol and phenol derivatives are highly toxic to
mammalian cells and that their antimicrobial effectiveness does not sufficiently
balance their toxicity. Experimentation in vivo also demonstrated that phenol and
phenolic derivatives induce inflammatory changes at much lower concentrations than
many other antimicrobial agents. Phenols are ineffective antiseptics under clinical
conditions. In one study, 2 weeks of intracanal dressing (in which the canals were
filled with camphorated phenol or camphorated parachlorophenol) failed to eliminate
intracanal bacteria in one third of the cases. Phenolic compounds are also unable to
release an effective antimicrobial vapor and therefore are ineffective when placed on
a cotton pellet in the pulp space.
Formaldehyde
Formaldehyde has been used extensively in endodontic therapy despite its high
toxicity and mutagenic and carcinogenic potential. The compound of interest when
discussing pulp space disinfection is formocresol. The formaldehyde component of
formocresol may vary substantially between 19% and 37%. Tricresol formalin,
another formaldehyde preparation, contains 10% tricresol and 90% formaldehyde.
Therefore all these preparations have a formaldehyde content well above the 10%
normally used for fixation of pathologic specimens. Formaldehyde is volatile and
releases antimicrobial vapors if applied on a cotton pellet for pulp chamber
disinfection. All these formaldehyde preparations are potent toxins with an
antimicrobial effectiveness much lower than their toxicity. The formaldehyde in
contact with tissue in the pulp and periapical tissues is transported to all parts of the
body. Considering the outright toxic and tissue destructive effects and the mutagenic
and carcinogenic potential, no clinical reason exists to use formocresol as an
antimicrobial agent for endodontic treatment. The alternatives are better antiseptics
with significantly lower toxicity. Clinicians who might still contemplate using
formaldehyde in practice are referred to Chapter 11 for a discussion of the legal
implications of this unwise decision.
Halogens
Chlorine has been used for many years to irrigate the root canals. It also is
sometimes used as an intracanal dressing in the form of Chloramine-T. Iodine, in the
form of iodine potassium iodide (IKI), is a very effective antiseptic solution with a low
tissue toxicity. One in vitro study showed that IKI (i.e., IKI 2%) penetrated deeper
than 1000 μm of dentin in 5 minutes. IKI is an effective disinfectant for infected dentin
and can kill bacteria in infected dentin in 5 minutes in vitro. Iodine potassium iodide
releases vapors with a strong antimicrobial effect. The solution can be prepared by
mixing 2 g of iodine in 4 g of potassium iodide; this mixture then is dissolved in 94 ml
of distilled water. Tincture of iodine (5%) has proved to be one of the few reliable
agents for disinfection of rubber dam and tooth surfaces during the preparation of an
aseptic endodontic workfield.
Calcium Hydroxide
Hermann introduced the use of calcium hydroxide in endodontics in 1920. Although
its use was well documented for its time, the clinical applications over the next 25
years were not well known. Calcium hydroxide cannot be categorized as a
conventional antiseptic, but it kills bacteria in the root canal space. It has been
routinely used by many clinicians over the past 40 years. The value of calcium
hydroxide in endodontic treatment of necrotic, infected teeth is now well documented.
Calcium hydroxide normally is used as a slurry of calcium hydroxide in a water base.
At body temperature, less than 0.2% of the calcium hydroxide is dissolved into Caand OH- ions. Because Ca(OH)2 needs water to dissolve, water should be used as
the vehicle for the calcium hydroxide paste. In contact with air, calcium hydroxide
forms calcium carbonate (CaCO3). However, this is an extremely slow process of
little clinical significance.
Calcium hydroxide paste with a significant amount of calcium carbonate feels
granular because the carbonate has a very low solubility. Some have suggested
using Cresatin or camphorated parachlorophenol as the mixing vehicle. Mixing with
Cresatin results in the formation of calcium cresylate and acetic acid, whereas mixing
with camphorated parachlorophenol results in calcium parachlorophenolate. In both
cases hydrolysis is inhibited, and the advantageous high pH is not reached. Calcium
hydroxide is a slowly working antiseptic. Direct contact experiments in vitro show that
a 24-hour contact period is required for complete killing of enterococci. In clinical
experimentation, 1 week of intracanal dressing has been shown to safely disinfect a
root canal system. A study of 42 patients found that sodium hypochlorite irrigation
reduced the bacteria level by only 61.9%, but use of calcium hydroxide in the canals
for 1 week resulted in a 92.5% reduction. These researchers concluded that
Ca(OH)2 should be used in infected cases to more predictably obtain healing.
In addition to killing bacteria, calcium hydroxide has the extraordinary ability to
hydrolyze the lipid moiety of bacterial lipopolysaccharides (LPS), thereby inactivating
the biologic activity of the lipopolysaccharide and reducing its effect. This is a very
desirable effect because dead cell wall material remains after the bacteria have been
killed and can continue to stimulate inflammatory responses in the periradicular
tissue. Calcium hydroxide may be mixed with sterile water or saline; this formula is
also available commercially from a number of manufacturers in sterile, single-dose
packages (e.g., Calasept [J.S. Dental, Ridgefield, CT]; SteriCal [Centrix, Shelton,
CT]; and DT Temporary Dressing, [Global Dental Products, North Bellmore, NY])
.The mixture should be thick to carry as many calcium hydroxide particles as
possible. This slurry is best applied with a lentulo spiral. For maximal effectiveness
the root canal must be filled homogeneously to the working length. Saturated calcium
hydroxide solution mixed with a detergent is an effective antimicrobial agent suitable
for irrigation.
Bioactive Glass
Research is underway in the use of bioactive glass as an intracanal medicament. In
one study the glass used was composed of 53% SiO2 (w/w), 23% Na2O, 20% CaO,
and 4% P2O5 and was prepared from reagent grade Na2CO3, CaHPO4, 2H2O,
CaCO3, and Belgian sand. When used in root canals, bioactive glass was found to
kill bacteria, but the mechanism of action was not pH related and dentin did not seem
to alter its effect. Some new obturating materials (e.g., Resilon [Pentron Clinical
Technologies, Wallingford, CT]) contain bioactive glass.
Superoxidized Water
Superoxidized water is saline that has been electrolyzed to form superoxidized water
(hypochlorous acid and free chlorine radicals, supplied as Sterilox [Sterilox
Technologies, Radnor, PA]). This solution is nontoxic to biologic tissues yet able to
kill microorganisms. A study investigating the cleaning of endoscopes found that the
solution killed microbes at a level equivalent to glutaraldehyde and superior to
ozonated water and 0.05% chlorhexidine. However, the solution’s effectiveness was
reduced by contact with albumin. These researchers concluded that superoxidized
water was effective only after the endoscopes had been mechanically cleaned. In
addition to its surface disinfection capability, superoxidized water has been shown to
have potential as an endodontic irrigating solution. However, additional work is
needed to confirm this result.