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SUMMARY| INTRODUCTION | MATERIAL AND METHODS | RESULTS AND DISCUSSION | CONCLUSION | REFERENCES

SUMMARY
 

    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.

INTRODUCTION
 

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

    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.
ESTRELA 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.

MATERIAL AND METHODS

    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 containers.

    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.

RESULTS AND DISCUSSION

The 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 the membrane.

    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 growth; 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 reaction¹⁰

    The high pH of calcium hydroxide can activate alkaline phosphatase, which can start or favor mineralization^19,29 . 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 hydroxide^2-11,19-21 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 antimicrobial action.

    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 3.

    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.
 Another 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 containing.

    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.

CONCLUSION

    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 of observation.

REFERENCES

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