pH analyse of vehicles and calcium hydroxide pastes
publicado na Brazilian Endodontic Journal 3(2): 41-47, 1998
words: calcium hydroxide, intracanal dressing
INTRODUCTION | MATERIAL AND METHODS
| RESULTS AND DISCUSSION | CONCLUSION
Calcium hydroxide is one of the most used as intracanal medication in teeth
with apical periodontitis. Its success is due to its antimicrobial and
mineralizing properties, which are intrinsic to the dissociation and diffusion
of calcium and hydroxyl ions. The effect of pH on the transport
of nutrients and organic components through the cytoplasmic membrane determines
its toxic action on bacteria. This also activates the hydrolytic enzyme
alkaline phosphatase, which is closely related to thc process of tissue
mineralization. Considering that thc release of hydroxyl ions from calcium
hydroxide is essential to the mineralization and microbial control processes,
it is important to investigate thc necessity of using vehicles that favor
a quick ionic dissociation and, in addition, maintain a high pH during
the entire period of activity. Thc pH of thc following phenolic substances
was studied: paramonochlorophenol (PMC 5 g) associated to FuracinO
(28 ml) and camphorated paramonochlorophenol (CPMC), alone and associated
with 24 mg (0.12%) of calcium hydroxide P.A. Thc pH of thc following non-phenolic
substances was also studied: sodium lauryl diethylcnc ether sulfate (0,10%,
Tween 80 (0;1%) de-ionized distilled water, propylene glycol associated
with 24 mg (0.12%) of calcium hydroxide P.A., stored in plastic containers.
Pastes with non-phenolic vehicles (de-ionized water, propylene glycol,
sodium lauryl diethylene ether sulphate and Tween 80) showed a high pH
values (above 12). The paste, with CPMC as vehicle, showed a pH around
7.8 and CPMC alone remained at a pH of 5. PMC-Furacin showed a pH
of 7,0 and the paste containing this substance showed a pH of 10 during
the period of observation.
hydroxide is one of the most used as intracanal medication in teeth with
apical periodontitis. Its success is due to its antimicrobial and mineralizing
properties, which are intrinsic to the dissociation and diffusion of calcium
and hydroxyl ions
HEITHERSAY17 reported that calcium hydroxide has been extensively
employed in endodontic therapy since the use of calxyl by HERMAN 18,
in 1930. The action of hydroxyl ions from calcium hydroxide, producing
a high pH, represents an essential characteristic, since it induces the
formation of a mineralized barrier, as reported by HOLLAND 19
The effect of calcium hydroxide on bacteria and tissue is directly related
to its ionic dissociation into calcium and hydroxyl ions.
et al.10 reported this action explaining that its high pH inhibits
enzyme activities that are essential to bacterial life, i.e., metabolism,
growth and cellular division. The effect of pH on the transport of nutrients
and organic components through the cytoplasmic membrane determines its
toxic action on bacteria. This also activates the hydrolytic enzyme alkaline
phosphatase, which is closely related to the process of tissue mineralization.
Thus, this medication presents two fundamental enzyme properties: the inhibition
of bacterial enzymes leading to an antimicrobial effect and the activation
of tissue enzymes such as alkaline phosphatase leading to a mineralizing effect.
The effects of calcium, barium and strontium hydroxides on pulpal capping
used in dog dental pulps were assessed by HOLLAND et al.21 .
Sedimentation of strontium and barium carbonate grains occurred, similar
to the grains observed with calcium hydroxide. Since barium and strontium
do not exist naturally in the animal body, these grains were from the capping
material. Birefringents coarse grains are not observed with other hydroxides
such as magnesium or sodium hydroxide, due to the fact that sedimentation
only occurs with hydroxides whose solubility is similar to that of calcium
hydroxide. Magnesium hydroxide is insoluble and sodium hydroxide is highly
soluble in pulpal fluids. Barium hydroxide is slightly more soluble than
strontium hydroxide, which can be observed because barium hydroxide grains
are found deeper than strontium hydroxides grains.
GORDON and ALEXANDRE14 analyzed two properties of calcium hydroxide
on bovine pulpal tissue: variations in pH and calcium ion concentration.
Their results suggest that the effects of calcium hydroxide are mainly
pH dependent and its efficacy may result from lower solubility.
ESTRELA and PESCE4 chemically analyzed the release of hydroxyl
ions from calcium hydroxide in dog connective tissue. The percentage of
the existing ghydroxyl ions (45.89%) and calcium ions (54.11%) can be obtained
taking into account the molecular weigh of calcium hydroxide (74.08).
Much research 1, 9,11,13,-16, 18,24,26,30-33 has assessed the
pH of different materials and dental structures, pointing out the importance
of pH on tissues and microorganisms. Considering that be release of hydroxyl
ions from calcium hydroxide is essential to the mineralization and microbial
control processes, it is important to investigate thc necessity of using
vehicles that favor a quick ionic dissociation and, in addition, maintain
a high pH during the whole period of activity.
Thc purpose of this study was to evaluate the pH of different vehicles
and calcium hydroxide pastes.
The pH of thc following phenolic substances was studied: paramonochlorophenol
(5g) associated with Furacin O (28 ml) and camphorated paramonochlorophenol
(SS White, RJ, Brazil), alone and associated with 24 mg (0.12%) of calcium
hydroxide P.A. (Merck, USA). The pH of the following non-phenolic substances
was also studied: sodium lauryl diethylene ether sulfate (0.1%), Tween
80 (0.1%), de-ionized distilled water, propylene glycol associated with
to 24 mg (0.12%) of calcium hydroxide P.A. (Merck, USA), stored in plastic
After the active homogenization of the phenolic substances they were kept
inactive for 1 hour and then the initial pH of each one was determined
using tornassol paper (Merck, USA), allowing a gradual analysis of values
from O to 14. In this case, tornassol paper was chosen because, since it
is not possible to analyze concentrated organic substances with a reference-electrode
digital pH meter. The other substances were associated with 24 mg (0.12%)
of calcium hydroxide P.A. (Merck, USA) and the changes in their pH were
measured with of a digital pH meter (Digimed, SP, Brazil). The pH analyses
of vehicles and vehicles added to calcium hydroxide pastes were performed
1 60 days and the results were recorded on an electronic chart. Ali the
tests of this study were performed three limes.
basic principle for thc selection of any intracanal medication is the understanding
of its mechanism of action on the predominant rnicroorganisms in endodontic
infections. Thc antimicrobial substances from antibiotics and/or chemotherapeutics,
cause two kinds of effects on l microorgani sms: 1) inhibit growth or reproduction
2) induce cellular deactivation. These effects can he observed in
cellular wall synthesis, cellular wall structures, protein synthesis, chromosomal
replication and in the intermediate metabolism. The mechanism of action
of calcium hydroxide as an antimicrobial medication could be better understood
adopting as reference the knowledge of microbiological and pharmacological
properties of antibiotics/chemotherapeutics and their effects on microorgani
sins and, mole specifically, their sites of action. ESTRELA et al2
reported that it is important to analyze thc effect of pH on growth, metabolism
and bacterial cellular division, in isolation. However, thc existence of
a pH gradient through the cytoplasm membrane must be considered, which
is responsible for producing energy for the transport of nutrients and
organic components to the interior of the cell. This gradient can be affected
by a change in environmental pH, influencing chemical transport through
PUTNAM28 , describing thc adjustment of intracellular pH, reported
that pH influenced different cellular processes such as: a) cellular metabolism;
b) alteration of shape, mobility, adjustment of transporters and polymerization
of cytoskeleton components; c) activation of cellular proliferation and
d) conductivity and transport through the membrane; e) isosmotic cellular
volume. Thus, many cellular functions can be affected by pH and thc enzymes
essential to cellular metabolism are among them.
Considering all the reasoning on pH processes and isolated activities at
essential enzymatic sites, it is enlightening to associate calcium hydroxide,
a substance with a high pH, with harmful biological effects on bacterial
cells in order to explain mechanism of action
With this aim, ESTRELA et al8. studied the biological effect
of pH on the enzymatic activity of anaerobic bacteria. Since enzymatic
sites are located in the cytoplasmic membrane, which is responsible for
essential functions such as metabolism, cellular division and growth, and
take part in the last stages of cellular wall formation, biosynthesis of
lipids, transport of electrons and oxidative phosphorylation, the authors
believe that hydroxyl ions from calcium hydroxide develop their mechanism
of action in the cytoplasmic membrane. The effect of the high pH (12.6)
calcium hydroxide, influenced by the release of hydroxyl ions, is able
to alter the integrity of the cytoplasmic membrane by means of chemical
injuries to organic components and transport of nutrients, or by means
of the destruction of phospholipids or unsaturated fatty acids of the cytoplasmic
membrane, observed in the lipidic peroxidation process, which is a saponification
The high pH of calcium hydroxide can activate alkaline phosphatase, which
can start or favor mineralization19,29 . Two other calcium dependent
enzymes (adenosine triphosphate and pyrophosphate) can also favor the mechanism
of tissue healing.
Clinically, several substances have been used as vehicles for calcium hydroxide2-11,19-21
to enhance its antimicrobial action, speed of ionic dissociation and chemo-physical
properties. The use of hydrosoluble vehicles (distilled water or saline
solution) is controversial because when they are compared with camphorated
paramonochlorophenol (oily vehicle) doubts arise regarding calcium hydroxide
Much research has evaluated the pH of substances and structures and their
effects on tissues The present study observed the pH of pastes during a
period of time ranging from O to 160 days. The results showed that pastes
with non-phenolic vehicles (de-ionized water, propylene glycol, sodium
lauryl diethylene ether sulfate and Tween 80) presented a high pH value
(above 12), whereas the paste with CPMC as vehicle presented a pH around
7.8 during the entire period of observation. The vehicle CPMC alone maintained
a pH of 5. PMC-Furacin showed a pH of 7 during the period of observation
and the paste with this substance presented a pH of 10, as showed in Figures
1, 2 and
The importance of studying these vehicles is related to thc fact that they
are indicated for use in association with calcium hydroxide for different
reasons. In 1891, Walkhoff suggested the use of PMC based on the antiseptic
properties of phenol wich was associated to camphor with the objective
of minimizing its irritating potential. When camphorated paramonochlorophenol
(CPMC) is used in association with calcium hydroxide it acts as an oily
vehicle because camphor is considered an essential oil and presents low
solubility in water.
LEONARDO et al24 evaluated thc changes in the pH and in the
release of calcium ions in calcium-hydroxide based endodontic products.
Samples containing 1 .5 of material for each 6 ml of distilled water were
prepared for analyses of pH changes. During a period of O to 60 days, results
showed that the pH varied from 12.28 to 12.46 for calcium hydroxide hydrosoluble
pastes, from 10.94 to 12.33 for CalenO and from 10.80 to 12.5 1 h)r CalenO
with CPMC. In this paste the proportion was O. 1 5 ml of CPMC to 1 .75ml
propylene glycol to 0.05 g colofônia to 1.0 g zinc oxide P.A. and
2.5 g calcium hydroxide P.A.
NAUMOVICH26 analyzing the surface tension and pH of drugs used
in root canal therapy reported the pH of phenol-camphor pH to be 4.4.
ANTHONY et al1. , analyzing the effect of three vehicles on
the pH of calcium hydroxide, reported that the high potential for tissue
irritation by CPMC would make saline a logical choice for mixing with calcium
hydroxide powder to make a temporary paste filling.
study concerning the irritating potential of CPMC was carried out by FAGER
and MESSER12 who analyzed the systemic distribution and excretion
of camphorated monoclorophenol not lowing insertion into the pulp chambers
of cat canine teeth with or without periapical lesions. Cotton pellets
C-labeled CPMC were sealed into the four canine teeth of each cal, and
thc teeth and tissue were analyzed for radioactivity. Radioactivity was
detected in the blood within 30 mm and in urine within 2 hours of placing
cotton pellets into thc tooth. After 24 hours, more than 50% of thc CMCP
had been lost from the teeth and up to 20% had been excreted in thc urine.
CMCP was not concentrated in any tissues examined. Although CMCP passed
rapidly and extensively beyond the apical foramen and into the circulation,
the lack of binding in the tissues and the rapid urinary excretion are
likely to minimize systemic toxic effects. Taking into account the necessity
of hydroxyl ions in order to obtain the expected effects from calcium hydroxide
as an antimicrobial and mineralizing agent, it is crucial to choose pastes
that maintain high pH levels and that allow its dissociation and diffusion,
such as distilled water and saline solution
Chemical characteristics of vehicles, whether they are hydrosoluble or
oily, logether with their ionic dissociation and diffusion capability,
can be considered more important properties than thc antimicrobial action
of the vehicle, because calcium hydroxide alone already has this property,
which, in case of an association, might not show a synergic effect or might
even show na opposite reaction.
HOLLAND et al20. evaluated the effect of hydrosoluble and non-hydrosoluble
intracanal dressings in the healing process of dog teeth with periapical
lesions. Calcium hydroxide associated with saline solution and calcium
hydroxide associated with camphorated paramonochlorophenol (Frank’s paste)
were used. Six months after the obturation of root canals, the authors
observed the highest rates of healing with the used of intracanal dressing
with hydrosoluble paste containing saline solution. Thus way, the importance
of chemical characteristics of vehicles (their hydrosolubility) in regard
to antimicrobial power, is remarkable, since they influence thc speed of
ionic dissociation and diffusion. When calcium hydroxide is chosendue to
its antimicrobial effectiveness, the vehicle assumes a supportive role
in this process, giving calcium hydroxide some chemical characteristics
(dissociation, diffusibility and filling) that are decisive to the antimicrobial
potential and tissue healing capability. Based on these chemical properties,
the best vehicle to be added to calcium hydroxide is the one that presents
hydrosoluble characteristics such as distilled water or saline solution.
Pastes with non-phenolic vehicles (de-ionized water, propylene glycol,
sodium lauryl diethylene ether sulfate and Tween 80) showed high pH values
(above 12). The past with CPMC showed a pH around 7.8 during the period
of observation and CPMC alone a pH of 5. PMC-Furacin showed a pH of 7,0
and the paste containing this substance showed a pH of 10 during the period
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