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1. CALCIUM HYDROXIDE
CONTENTS
Introduction
Biochemical Actions
Initial Mineralization
Calcium Hydroxide Induced Mineralization
The Dentine Bridge
Direct Pulp Capping
Direct Pulp Capping
Pulpotomy
Histology
Replantation of the Teeth
Perforative Types of Resorption
Apexification
Root Resorption
Idiopathic:
Repair of Iatrogenic Perforations
Types of Vehicles
Aqueous Vehicles
Proprietary Brands
Mechanisms of Antimicrobial Activity of Calcium Hydroxide
Mechanisms of Antimicrobial Activity
1. Damage to the bacterial cytoplasmic membrane
2. Protein denaturation
3. Damage to the DNA
Root Canal Dis-Infection

2. Influence of the Vehicle on the Antimicrobial Activity
Physical Barrier
INTRODUCTION
Since the introduction of calcium hydroxide Ca (OH)2 to dentistry
by Hermann (1920, 1930), this medicament has been indicated to
promote healing in many clinical situations. However, the initial
reference to its use has been attributed to Nygren (1838) for the treatment
of the 'fistula dentalis', while Codman (1851) was the first to attempt to
preserve the involved dental pulp.
According to Cvek (1989) calcium hydroxide became more widely
known in the 1930s through the pioneering work of Hermann (1936) and
the introduction of this material in the United States (Teuscher & Zander
1938). The first reports dealing with successful pulpal healing using
calcium hydroxide appeared in the literature between 1934 and 1941.
Since then, and mainly after the Second World War, the clinical
indications for its use were expanded and now this chemical is considered
the best medicament to induce hard tissue deposition and promote healing
of vital pulpal and periapical tissues (Garcia 1983).

3. Although the overall mechanisms of action of calcium hydroxide
are not fully understood, many articles have been published describing its
biological properties, which are achieved by the dissociation in the Ca
and OH ions. The role of the high pH and the ionic activity in the healing
process, diffusion through dentinal tubules, influence on apical
Microleakage and some clinical topics, such as the importance of the
interappointment restoration, are examples of how this material has been
evaluated since its introduction.
Many substances have been added to the powder to improve
properties such as the antibacterial action, radiopacity, flow and
consistency.
BIOCHEMICAL ACTIONS
Initial mineralization
Before considering the specific effects of calcium hydroxide, it will
be helpful to describe briefly the theories of mineralization within
mesenchymal tissues. It is now widely accepted that an epitactic
mechanism operates following the initial seeding of a collagenous tissue.
Only certain types of collagen such as those found in dentine and bone,
mineralize in this way. The process is probably the result of juxtaposition
of charged groups on adjacent macromolecules which give rise to the

4. epitactic centers. These centers require a nucleation site from which
hydroxyapatite crystal growth can proceed. Chondroitin sulphate as the
seed whilst others, conversely considered it to be an inhibitor of
mineralization. Other substances which have been postulated as initiators
of mineralization include a Vitamin D dependent protein which is capable
of binding calcium, phosphoproteins and phospholipids.
One safety factor may be the presence in the blood and tissue of
substances such as pyrophosphate ions which pyrophosphates are
metabolized at the mineralization sites by pyrophosphates.
Pyrophosphates are a member of the alkaline phosphates group, which
many explain why these enzymes are invariably present in mineralizing
tissues.
Calcium hydroxide induced mineralization
It seems that calcium hydroxide has the unique potential to induce
mineralization, even in tissues, which have not been programmed to
mineralize (Mitchell & Shankwalker 1958, Binnie 1967). However,
Rasmussen & Mjor (1971) could not verify that calcium hydroxide
induced mature bone formation under these circumstances, but found that
when the material was placed in direct contact with host tissue it induced
the formation of fibrous tissue, with the occasional formation of areas of

5. immature bone. These workers also found that when calcium hydroxide
was separated from host tissue by Millipore filters, no significant
reactions occurred, indicating that the material did not have any effect
once it had diffused some distance.
It is also likely that the calcium ions present in the applied calcium
hydroxide do not become incorporated in the mineralized repair tissue,
which derives its mineral content solely from the dental pulp, presumably
via the blood supply. These observations indicate that calcium hydroxide
is an initiator rather than a substrate for repair.
The high pH may also activate alkaline phosphate activity, which is
postulated to play an important role in hard tissue formation. The
optimum pH for alkaline phosphates activity is 10.2 a level of alkalinity,
which is produced by many calcium hydroxide preparations.
The dentine bridge
There appears to be some variation in the way in which a dentine
bridge is formed depending on the pH of the material that is used to dress
the tooth. I the case of a high pH material such as Pulpdent a necrotic
zone is formed adjacent to the material and the dentine bridge then forms
between this layer and underlying vital pulp. The necrotic tissue
eventually degenerates and

6. Hydroxide. Nirschl et al reported that a high rate of success
(94.4%) can be seen in cases done with calcium hydroxide.
The mode of action of Ca(OH)2 on bacteria is not yet completely
understood. Yet, it is able to practically avert the caries process.
Direct pulp capping
Involves the application of a medicament to the exposed pulp in an
attempt to pre-care vitality. Observe has described the histopathology of
the pulp and concluded that the cells of the pulp are the same as those of
loose comparative tissues and that these cells could differentiate and that
healing could occur in the dental pulp.
In 1930, Hermann introduced calcium hydroxide as a successful
pulp-capping agent.
In 1938, Tauscher and Zander introduced calcium hydroxide in the
United States and historically confirmed complete dentinal bridging with
healthy radicular pulp tissues leading to degeneration.
According to Mo Walter et al, the advantage of calcium hydroxide
is when applied to exposed pulp, it does not exert a persistent stimulating

7. effect on reparative dentine, which would lead to eventual pulp
obliteration.
When calcium hydroxide is applied directly to (Stanley and Landy)
showed that pulp adjacent to each appeared to be chemically cauterized)
pulp tissue, there is necrosing on the adjacent pulp tissue and an
inflammation of the contiguous tissue. Certain formation occurs at the
junction of the necrotic tissue and the contiguous vital inflamed tissue.
Although calcium hydroxide works effectively, the exact mechanism is
not yet understood. The compounds of similar alkalinity cause
liquefaction when applied to pulp tissue.
Direct Pulp Capping
A study was done by the University if Michigan to understand the
cellular changes taking place in the pulp following direct capping with
calcium hydroxide. The study showed an increase in the number of cells
in the odontoblritiz and the cell free Fones over time, with an concurrent
decrease in the number of cells in the center of the pulp, suggesting that
this was where the cells were originated from. The study also showed that
at least 2 DNA Replications had occurred between initial treatment and
the final odontoblast-like cell differentiation. The study was done in
Primater after injecting them with thymidine.

8. In some case internal resorption is seen following caprior with
calcium hydroxide. In others complete dentin mineralization of the
remaining pulp takes place so that the camels are occluded. However,
due to the low incidence of those assurances, it does not seem to be
justified to avoid calcium hydroxide.
It was postulated that calcium would diffuse 'rom' dwening into the
pulp and participate in the formation of reactive dentin. Experiments with
radioactive ions however have shown that calcium ions from the dressing
do not enter into the formation of a new ideation and that the calcium for
the dentin bridge comes from the blood stream. The pulpal response
varies under different commercial form of calcium hydroxide.
Dycal or life: here the dentin forms directly under the dressing.
The chemically altered tissue created by the calcium hydroxide is
resorbed first and the bridge is then formed in contact with the capping
material.
Pulp dent: With calcium hydroxide powder (pulp dent) the bridge
forms at the junction of the chemically altered tissue and the vital
inflamed pulpal tissue. The altered tissue degenerates and leaves a void

9. between the capping material and the bridge. So radiographically the
bridge would be better appreciated with pulp dent than with Dycal or life.
The quality of the dentin bridge was found to be good. Reolit (hard
setting CaOH2) has a neutral pH and has proved to be unsuccessful for
pulp capping while hydreax (hard setting CaOH2) has been giving
conflicting reports.
PULPOTOMY
The pulpotomy procedure involves removing pulp tissue that has
inflammatory or degenerative channels leaving behind the remaining vital
tissue, which is then covered with a pulp-capping agent to promote
healing at the amount site or an agent to cause fixation of the underlying
tissue.
In young permanent teeth, CaOH2 pulpotomy is the treatment or
choice. The use of hard setting materials is the best. For Teener
amputations, CaOH2 powder is carefully beard against pulp stem. Care
must be taken not to pack the powder into the pulp tissue as this will
cause greater inflammation and failure or in the case of success, there will
be increase calcification of the remaining pulp tissues around the particles
of calcium hydroxide. Doyle et al have compared calcium hydroxide and

10. for increased pulpotomies in primary teeth and found a better rate of
success with form.
HISTOLOGY
Superficial part of the pulp, just beneath the coach is necrotic,
under this a layer of calcium proteinate was formed. Initially a 3 one of
inflammation was seen under the necrotic layer which then transforms
into a dentinal bridge. Systemic calcium is used. CaOH2 helps in
maintaining alkalinity, which is necessary for optimum hard tissue
formation. Pulpal merenchymal cells differentiate into odontoblasts,
forming the dentinal bridge. CaOH2 is also used in deep pulpotomy.
In a study done on dogs, immature teeth in the Tokyo Dental
College and published in 1990, a calcium hydroxide iodoform paste was
found to be very effective for pulpotomies on immature permanent teeth.
Calcium hydroxide paste are used is root canal sealers and calcium
hydroxide plugs produce a periapical response that overall is
indistinguishable from that produced by dentin plugs.
However another study shows that the calcification observed with
dentin plugs is more complete than that observed with calcium hydroxide
plugs. In an in-vivo study done in the University of Sanis Cataria, Brazil,

11. canine teeth roads were cleaned, shaped and filled with CaOH2 sealer.
Partial closure of the apices was seen and all over filled specimens
showed chronic inflammatory reaction on the periapical region.
Study done by Verdon and Holz shows that CaOH2 sealer shows
almost complete resorption of over fillings in Ist
year and a slight
improvement in the radiologic appearance of the periapical legions was
also seen is Ist
years.
In cases of root fracture, where the apical segment of the root is
vital and the coronal section is non-vital and a space exists between the
coronal and radicular segment, CaOH2 can be used to fill in the coronal
segment and promote healing. After a healing period of about 6 months,
calcium hydroxide can be replaced by Gutta Percha.
The indications are:
1. There is no evidence of a periapical radiolucency at the end of the
apical section
2. The apical segment of the pulp seems vital as evidenced by bleeding
on a paper point
3. A radial space is evident between or adjacent to the fractural
segments.

12. 4. There is evidence of internal or external resorption in the coronal
segment.
5. A wide root-canal space makes a fitting of the root canal with gutta-
percha difficult, with a strong possibility of extrusion of the gutta-
percha or cement into the fracture site.
6. There is no communication between the fracture site and the oral
cavity.
REPLANTATION OF THE TEETH
Anderson first reported the use of calcium hydroxide in the
treatment of inflammatory root resorption, which follows the re-
implantation of teeth. The tooth is re- implant and splinted in position
before the pulp is extirpated and the access is sealed using o temporary
restoration.
Placement of calcium hydroxide should be delayed by 1 to 2 weeks
following re implantation. Anderson has shown that immediate insertion
of calcium hydroxide in re implantation teeth causes noticeably more
replacement resorption that is seen in teeth with extenuated pulp or Gutta-
Percha fillings. He postulated that calcium hydroxide diffuses out through
the apical foramen. Further injuring the periodontal ligament. He has also
pointed out that inflammatory resorption is initiated at around 2 weeks

13. about the time that the periodontium is healing which is the ideal time for
the placement of calcium hydroxide fillings.
The mode of action of calcium hydroxide is uncertain. Tornstad. L
et al have shown an increase in the Ph of dentin in teeth in which the
canal has been filled with calcium hydroxide. They speculate that the rise
in Ph stimulates repair while reducing osteoclasts in an acidic
environment is necessary for osteoclastic activity.
Since CaOH2 is an absorbable material, it will eventually dissipate
out of the canal in some teeth so these cases will have to be reviewed
every 2 or 3 months and the CaOH2 filling replaced if necessary. After a
minimal period of 1 year, the CaOH2 can be removed and gutta-percha
placed.
PERFORATIVE TYPES OF RESORPTION
CaOH2 in a suitable vehicle such as can promote healing and
formation of in the same manner it can be used for the treatment of
accidental perforations.
The rationale is
1. CaOH2 has an antibacterial effect.
2. It has an alkaline pH, which causes osteoclastic activity and
promotes repair, which was demonstrated by Tronsted et al.

14. APEXIFICATION
Kaiser first reported the use of calcium hydroxide for apexification
in 1964 and the technique was popularized by the work of Frank.
Calcium hydroxide alone or in combination with other materials
has been the most clearly accepted material to promote apexification.
This procedure is done in non-vital teeth the pulp tissue is extirpated the
canals are cleaned and filled with a paste temporality to promote
calcification at the apex. The calcium hydroxide powder has been mixed
with camphorated chlrophenol (CMCP), metacresyl acetate, cresanol
(a mixture of CMCP and Metacresylacetate), physiologic saline ringer's
solution distilled water, LA solution. All have been reported to stimulate
apexification. Tricalcium Phosphate and collagen-calcium phosphate gel
has been reported to also produce apexification in both humans and
animals.
ROOT RESORPTION
Idiopathic:
Calcium hydroxide is frequently used as a dressing for the
treatment of both internal and external inflammatory root resorption in
order to halt the progress and encourage re-mineralization. It is doubtful
weather the materials has any real beneficial effect on internal resorption,

15. as this is now considered to be sustain by infection within the dentinal
tubules coronal to the resorptive process.
Following the replacement of an avulsed tooth or transplantation of
a tooth Once avulsed tooth has been splinted in position for 2 weeks the
root canal should be thoroughly cleaned and dressed with calcium
hydroxide for a period of 3-6 months, prior to the placement of a
conventional root filling. Although it has been shown calcium and
hydroxyl ions do not diffuse through the dentin, the calcium hydroxide
may still penetrate through lateral canals. Calcium hydroxide treatment
has no effect on replacement resorption (ankylosis) once it has become
established. The principle of managing transplanted teeth once pulpal
necrosis has been confirmed, are essentially the same as those that relate
to replantation.
REPAIR OF IATROGENIC PERFORATIONS
The calcium hydroxide sealer, Sealapex, was used by Beavers et al
1986 to treat root canal perforations. They observed bone healing and in
growth of trabeculae into the perforation after 42 days, there was also
reparative cementum formation and ankylosis.

16. TYPES OF VEHICLES
Aqueous vehicles
Water: some chemicals characteristics of such a paste were
evaluated by different authors, including its pH (Conrado et al 1965,
Leonardo et al 1992), ionic dissociation and its diffusion through dentin.
The antibacterial effect was studied by martins et al while the solvent
action was evaluated by Hasselgern et al 1988.
This paste has been evaluated for the tissue reaction when
implanted in rat subcutaneous connective tissue for its ability to induce
hard deposition in apexification procedure in non- vital dogteeth and in
replacement resorption in replanted rat teeth.
In human clinical studies this paste has been indicated for capping
of vital pulp tissue after pulpotomy (Russo et al ) as a long term dressing
in cases of non-vital teeth associated large periapical lesions and in
apexification procedures.
Sterile water. In humans this paste has been indicated for direct
pulp capping, pulpotomy and apexogenesis, Goldmen 1974 Sheehy and
Roberts 1997, Apexification procedure. And as an apical plug before

17. Gutta Percha filling in non-vital teeth with an open apex and in cases of
internal resorption with perforation of the dentinal wall.
Distilled water. It is important to highlight that Crabb (1965) was
the first to use this paste in the treatment of large periapical lesions he
said " perhaps the locally destructive action of calcium hydroxide with its
high pH, acting as chemical cattery, might effect breakdown of the
epithelium"
Clinically, it has been employed for the induction of hard tissue
deposition in apexification procedure (Saad 1988, Yang et al 1990), in
pulpotomy of deciduous or permanent teeth as a temporary dressing after
vital pulp extirpation and in non-vital teeth with associated chronic
periapical disease, in internal resorption, in perforation and to arrest
external cervical resorption after bleaching of pulpless teeth (Santos
1996).
It has been suggested that iodoform or bismuth carbonate should be
added to improve the radiopacity of the paste (Holland et al 1981,
Rezende 1982).

18. An old suggestion proposed by Yacometti (1952) was to add
penicillin to a calcium hydroxide-distilled water paste to be used as a pulp
capping material.
4. Sterile distilled water: This paste was evaluated for human direct pulp
capping in apexification procedures and in animal studies, for its intra-
dentinal calcium diffusion.
5. Bidistilled water: According to Laurichesse (1980) it was Albou who
first used bid stilled water as the vehicle of the paste in normal clinical
cases. However, in cases of infected non-vital teeth, some drops of
camphorated parachlorophenol were added to the paste.
6. Sterile bidistilled water: This vehicle was recommended by Breillat et
al (1983 a.b) for human apexogenesis and specification procedures.
7. Saline or sterile saline: According to the United States Pharmacopea
(1989) saline is prepared by dissolving 9 g of sodium chloride in water to
make 1000ml. When this paste was implanted in vital tissues, the
reactions were evaluated by Pissoitis & Spangberg (1980). In animal
studies, the paste was evaluated in direct pulp capping and in the

19. apexification of immature non-vital dog and monkey teeth and to arrest
inflammatory resorption in replanted dogteeth.
Clinically, it was evaluated in human non-vital immature teeth
(Cvek 1972), in preparations (Bogaers 1997), in internal resorption at the
site of an intra-alveolar root fracture in external inflammatory root
resorption, in infected teeth with associated cutaneous sinus tract, in
endodontic re-treatment after endodontic and surgical failures and as a
dressing partial pulpectomy.
Recently, Yoshiba et al (1994) proposed a new formulation, adding
a Tricalcium phosphate to the calcium hydroxide powder and saline for
capping amputee pulps. Sazak et al (1996) have suggested adding
Ledermix to a calcium hydroxide-saline paste to be used after pulpotomy
with the purpose of reducing postoperative pain and inflammation
8. Anaesthetic solutions: It is interesting to note that most these solutions
have an acid pH, but when mixed with the calcium hydroxide powder, the
final paste has a high pH which is maintained over time. Further more,
they promote a rapid ionic release.

20. As the final paste lacks radiopacity, some authors add barium
sulphate (one part) to calcium hydroxide powder (four parts) (Dumsha &
Gotmann 1985). Marasis (1996) believes this proportion is not necessary
for a high radiopacity and usesa 1:8 ratio to increase the antibacterial
property of the paste. Teplitsky (1986) suggested adding one drop of
camphorated chlorophenol when used as a dressing in infected non-vital
cases.
9. Ringer's solution: United States Pharmacopeia (1989) sodium chloride
(8.6 g), Potassium chloride (0.3 g), calcium chloride (0.33 g) and water to
1000 ml.
Historically, it was Granath (1959) who was the first to describe
the use of such a paste in cases of traumatic injuries, although some
authors believe he was also the first to employ a calcium hydroxide paste
in root-end induction procedures. This is not correct because the oldest
reference in which a calcium hydroxide paste was used for root-end hard
tissue deposition is Marmasse (1953).
10. Methylcellulose and carboxymethylcellulose: Maisto & Capurro
(1964) introduced a paste composed of equal volumes of calcium

21. hydroxide powder and iodoform mixed with a 5% aqueous solution of
Methylcellulose.
Laurichesse (1980) proposed the following modification of the
original formula; calcium hydroxide and iodoform in a ratio 2/3:1/3, two
drops of camphorated parachlorophenol and a 3% aqueous solution of
Methylcellulose as the vehicle.
More recently, Giro et al (1993) proposed the use of carboxy
methyl cellulose or according to the United States Pharmacopeia (1989),
polycarboxymethylether of cellulose as the vehicle in the following
formula: 0.5 g of calcium hydroxide to 0.5 ml of a 1.66% solution of
carboxymethylcellulose.
11. Anionic detergent solution: It is well known that detergents decrease
the surface tension between two surfaces and facilitate substance
penetration. This is perhaps the reason why calcium hydroxide powder
has been mixed with an aqueous detergent solution to increase the action
of the v deeper into the tissues.
Unfortunately, only two studies have appeared in the literature
dealing with these substances. Barbosa et al. (1994) tested the

22. antibacterial effect of a paste composed of calcium hydroxide and sodium
lauryl diethyleneglycol ether sulphate and Peniche et al (1996) evaluated
the pH of a paste containing calcium hydroxide and sodium lauryl
sulphate.
PROPRIETARY BRANDS
Calyxyl: This paste is the oldest manufactured calcium hydroxide
paste and was introduced by Hermann (1920). Employed as a dressing
with the purpose of maintaining vital pulp tissue and inducing healing by
the formation of a calcified
MECHANISMS OF ANTIMICROBIAL ACTIVITY OF CALCIUM
HYDROXIDE
Mechanisms of antimicrobial activity
Most of the endodontopathogens are unable to survive in the highly
alkaline environment provided by calcium hydroxide (Heithersay 1975).
Since the pH of calcium hydroxide is about 12.5, several bacterial species
commonly found in infected root canals are eliminated after a short
period when in direct contact with this substance (Bystrom et al 1985)
Antimicrobial activity of calcium hydroxide is related to the release
of hydroxyl ions in an aqueous environment. Hydroxyl ions are highly

23. oxidant free radicals that show extreme reactivity, reacting with several
biomolecules. This reactivity is high and indiscriminate, so this free
radical rarely diffuses away from sites of generation. Their lethal effects
on bacterial cells are probably due to the following mechanisms:
1. Damage to the bacterial cytoplasmic membrane
The bacterial cytoplasmic membrane possesses important functions to the
survival of the cell, such as (1) selective permeability and transport of
solutes; (ii) electron transport and oxidative phosphorylation in aerobic
species; (iii) excretion of hydrolyticexoenzymes; (iv) bearing enzymes
and carrier molecules that function in the biosynthesis of DNA, cell wall
polymers, and membrane lipids; and (v) bearing the receptors and other
proteins of the chemotactic and other sensory transduction systems.
Hydroxyl ions induce lipid peroxidation, resulting in the
destruction of phospholipid structural components of the cellular
membrane. Hydroxyl ions remove hydrogen atoms from unsaturated fatty
acids, generating a free lipidic radical. This free lipidic radical reacts with
oxygen, resulting in the formation of lipidic peroxide radical, which
removes another hydrogen atom from a second fatty acid, generating
another lipidic peroxide. Thus peroxides themselves act as free radicals,

24. initiating an auto catalytic chain reaction and resulting in further loss of
unsaturated fatty acids and extensive membrane damage.
2. Protein denaturation
Cellular metabolism is highly dependent on enzymatic activities.
Enzymes have optimum activity and stability in a narrow range of pH,
which turns around neutrality. The alkalinization provided by calcium
hydroxide induces the breakdown of ionic bonds that maintain the tertiary
structure but the polypeptide chain is randomly unraveled in variable and
irregular special conformation. These changes frequently result in the loss
of biological activity of the enzyme and disruption of the cellular
metabolism. Structural proteins may also be damaged by hydroxyl ions.
3. Damage to the DNA
Ions react with the bacterial DNA and induce the splitting of the
strands. Genes are then lost. DNA replication is inhibited and the cellular
activity is disarranged. Free radicals may also induce lethal mutations.
It is difficult to establish in a chronological sense which is the main
mechanism involved in the death of bacterial cells after exposure to a
strong base.

25. It has been suggested that the calcium hydroxide to absorb carbon
dioxide may contribute to its antibacterial activity. Hence, carbon dioxide
supply to remaining bacteria in the root canal system may be maintained
from the outside. In addition, bacteria located in ramifications have direct
access to carbon dioxide from the periradicular tissues. There is little
reason to consider that calcium hydroxide impedes the carbon dioxide
supply to bacteria.
ROOT CANAL DIS-INFECTION
Several studies have demonstrated that calcium hydroxide exerts
lethal effects on bacterial cells. These effects were observed only when
the substance was in direct contact with bacteria in solution. In such
conditions, the concentration of hydroxyl ions is very high, reaching
incompatible levels to bacterial survival. Clinically, this direct contact is
not always possible.
Bases of alkaline metals, such as NaOH2 and KOH show high
solubility and thereby may diffuse more than calcium hydroxide across
the culture medium. Both bases have pronounced antibacterial activity.
On the other hand, high solubility and diffusibility increases the cytotoxic
effects of these substances, they are not indicated for use in endodontic
practice.

26. Killing of bacteria by calcium hydroxide will depend on the
availability of hydroxyl ions in solution, which is higher where the paste
is applied. Calcium hydroxide exerts an bacterial effects in the root canal
as they retain a very high pH.
Bacteria inside dentinal tubules may constitute an important
reservoir from which root canal infection or reinfection occurs during and
after endodontic treatment (Oguntebi 1994). Occasionally, these
remaining bacteria may cause a persistent infection that jeopardizes the
outcome of endodontic therapy. Therefore, treatment strategies that are
directed towards the elimination of tubule infection are necessary and
must include medicaments that penetrate dentinal tubules and kill
bacteria.
To act effectively as an intracanal dressing, the hydroxyl ions must
be able to diffuse through dentine and pulpal tissue remnants. Studies
have revealed that hydroxyl ions derived from a calcium hydroxide-
medication do diffuse through root dentine.
To be effective against bacteria located inside the dentinal tubules
the hydroxyl ions from calcium hydroxide should diffuse into dentine at
sufficient concentrations. It has been reported that dentine has buffering

27. ability because of the presence of proton donors, such as H2PO4,
H2CO3, HCO3-, in the hydrated layer of hydroxyapatite, which furnish
additional protons to keep the pH unchanged (Wang & Home 1998,
Nerwich et al. 1993). Therefore, in order to have antibacterial effects
within dentinal tubules, the ionic diffusion of calcium hydroxide should
exceed the dentine buffer ability, reaching pH levels sufficient to destroy
bacteria. After short-term use of calcium hydroxide, microorganisms are
probably exposed to lethal levels of hydroxyl ions at the tubule orifice.
Another factor can also help to explain the inefficacy of calcium
hydroxide in disinfecting dentinal tubules. The arrangement of the
bacterial cells colonizing the root canal walls can reduce the antibacterial
effects of v since the cells located at the periphery of colonies can protect
those located more deeply inside the tubules.
A short dressing with calcium hydroxide appears to eliminate
mainly bacterial cells in direct contact with this substance, such as
bacteria located in the main root canal or in the circumpulpal dentine.
These areas are also commonly affected by the chemomechanical
procedures.

28. Bacteria may survive after intracanal medication for several
reasons. First, bacterial strains present in the root canal infection may be
intrinsically resistant to the medicament. Secondly, bacterial cells may be
enclosed within anatomical variations inaccessible to the medicament.
Thirdly, the medicament may be neutralized by tissue components and by
bacterial cells or products, losing its antibacterial effects. Fourthly,
medicaments may remain the root canal system for insufficient time to
reach and kill bacterial cells. Finally, bacteria may alter their pattern of
gene expression after changes in the environmental conditions. This
alteration may allow them to survive in unfavourable environments.
INFLUENCE OF THE VEHICLE ON THE ANTIMICROBIAL
ACTIVITY
Most of the substances used as a vehicle for calcium hydroxide
don’t have significant antibacterial activities. They include distilled
water, saline solution and glycerin. Other substances such as camphorated
paramonochlorophenol (CMCP) and metacresylacerate are known to
posses this property. Frank (1996) recommended mixing v with CMCP in
apexification procedures. Some authors criticized this by considering it
unnecessary to add antimicrobial agents to calcium hydroxide, especially
those that have been shown to be tissue irritating (Cvek et al. 1976,
Anthony et al 1982).

29. Calcium hydroxide CMCP glycerin paste effectively killed bacteria
in the tubules after 1 h exposure, except foe E. faecalis that required 1 day
of exposure. Studies using an agar diffusion test have revealed that the
calcium hydroxide /CMCP paste had pronounced antibacterial activity
against facultative and anaerobic bacteria which was superior to pastes
containing calcium hydroxide in entire substances.
1. The small concentration of released paramonochlorophenol (MCP).
Calcium hydroxide plus CMCP yields calcium
paramonochlorophenolate, which is a weak salt that progressively
releases MCP and hydroxyl ions the surrounding medium
(Anthony et al. 1982). It is well known that a substance may have
either beneficial or deleterious effects, depending on its
concentration.
2. The denaturing effect of calcium hydroxide on connective tissue,
which may prevent the tissue penetration of MCP reducing its
toxicity (Siqueira 1997).
3. The fact that the effect on peri radicular tissues is probably
associated with the antimicrobial effect of the paste, which allows
natural healing to occur without persistent infectious irritation.

30. PHYSICAL BARRIER
In addition to eliminating remaining viable bacteria unaffected by
the chemomechanical preparation of the root canal intracanal
medicaments have been advocated for other reasons. They should also act
as a physicochemical barrier, precluding the proliferation of residual
microorganisms and preventing the reinfection of the root canal by
bacteria from the oral cavity (Siqueira 1997). Canals filled with calcium
hydroxide/saline solution and calcium hydroxide/CMCP/glycerin showed
entire recontamination within an average of 14.7 and 16.5 days,
respectively. Calcium hydroxide pastes were significantly more effective
than CMCP in preventing root canal recontamination by bacteria from
saliva.
The filling ability of calcium hydroxide pastes is probably more
important in retarding root canal recontamination than the chemical
effect. Because calcium hydroxide has low water solubility, it is dissolved
in saliva, remaining in the canal for a long period, delaying the bacterial
progression towards the apical foramen. Despite the vehicle used,
calcium hydroxide seems to act as an effective physical barrier.
Medicaments that act as a barrier can kill remaining microorganisms by
withholding substrate for growth and by limiting space for multiplication.