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Trabalho publicado na revista : BRAZILIAN ENDODONTIC JOURAL 3(2):24-30, July/Dec., 1998

Key Words: Calcium hydroxide, intracanal dressing, density

SUMMARY

Calcium hydroxide influences the enzymatic activity of bacteria which is reflected in growth, cellular division and bacterial metabolism. The chemical and biologic actions of calcium hydroxide on tissue and bacteria have made this medication indispensable in Endodontics. The correct filling of thc root canal is as important as the effectiveness of calcium hydroxide, because the lack of direct contact of this dressing interferes with its mechanism o faction. In order to better visualize the filling of the pulpal cavity, radiopaque substances, such as zinc oxide, iodoform and barium sulfate have been added to calcium hydroxide. However when the root canal is well filled, dentin and calcium hydroxide paste in association with saline solution clinically present themselves with the same radiopacity, causing the disappearance of root canal light. The aim of this work is to study the density of calcium hydroxide pastes with different vehicles, with no association with radiopaque substances and in comparison with dentin density. Considering the results of this work, it can be observed that it is not necessary to add radiopaque substances to calcium hydroxide pastes, because pastes used without them showed densities similar to dentin. In addition, when any substance is added to calcium hydroxide, even an inert one, it represents one more factor influencing biological processes and possibly of diminishing the amount of hydroxyl and calcium ions available, which represents one of the reasons for its use.

INTRODUCTION

Intracanal dressing continues to be the target of discussions. Considerations about thc real necessity of its use in pulpal necrosis and apical periodontitis, the selection of thc substance to bc used, the time it should remain in the root canal, its effect on different microorganisms found in endodontic infection and its influence on tissue healing are justifications for new research structured within adequate critical analysis and well established methodologies.

Considering the amount of research carried out, calcium hydroxide has withstood criticism and experimentation and has proven to be the best therapeutic option as na intracanal dressing. The principle action of calcium hydroxide involves the ionic dissociation into hydroxyl ions and calcium ions and its influence on tissue healing and microbial control ( 6-13). ESTRELA and PESCE (12) chemically analyzed the release of hydroxyl ions and calcium ions from calcium hydroxide pastes in connective tissue of dogs and demonstrated that when calcium hydroxide is placed within the root canal, 45.89% and 54.11% were dissociated into hydroxyl ions and calcium ions, respectively. HOLLAND (15) analyzed histochemically the biological process of tissue healing using calcium hydroxide, and reported the formation of five zones, clotting superficial necrosis zone, superficial grainy zone, deep grainy zone, proliferation zone and connective tissue zone. He also reported the importance of calcium ions in the mineralization process. The influence of calcium hydroxide on microorganisms was studied by ESTRELA et al. (13) who analyzed the action of hydroxyl ions on microbial enzymes in the cytoplasmic membrane, causing changes in the transport of nutrients and in the structure of organic components. This interference in biosynthetic processes that are essential to the life of microorganisms can also be analyzed through the process of lipid peroxidation and influenced by hydroxyl ions. Thus, the quantity of hydroxyl ions existing can lead to the enzymatic deactivation of bacteria.

Some studies have recommended the addition of other substances to calcium hydroxide, with the aim of improving some of its properties. Among these substances are vehicles that can speed up or slow down ionic dissociation, substances that aid the filling of the pulpal cavity by means of their consistency, substances that are used as antimicrobial medium and medium that enhance radiopacity.

The correct filling of the canal is as important as the effectiveness of calcium hydroxide because since the lack of direct contact of this dressing interferes with its mechanism of action (6-7). . In order to better visualize the filling of the pulpal cavity, radiopaque substances, such as zinc oxide, iodoform and barium sulfate have been added to calcium hydroxide. However, when thc root canal is well filled, dentin and calcium hydroxide paste in association with saline solution clinically present themselves with the same radiopacity, causing the disappearance of root canal light.

Considering these factors, the aim of this work is to study the density of calcium hydroxide pastes with different vehicles, with no association with radiopaque substances and in comparison with dentin density.

MATERIAL AND METHODS

This study was carried out on root canals (2nd and 3rd mandibular premolars) of dogs’ mandibles, divided into blocks. Samples were kept in saline solution for 7 days. Teeth were prepared until ISO #50 K-file (Maillefer, Switzerland), 1 mm short of the apical foramen, using the cervical preparation technique. The cervical third was enlarged with #2 Gates-Glidden burs. Three ml of 1% sodium hypochlorite was used for irrigation after each file, during instrumentation of the root canals. Root canals were then dried and filled and placed in 17% EDTA (pH 7.2) for 3 mim, and then dried again.

Twelve root canals were filled with a mixture of calcium hydroxide paste (Pró-analise, Quimis, Mallinkrodt Inc., USA) and one of the 3 vehicles: saline, propylene glycol 400 and camphoraled paramonoclorophenol (CPMC), with the consistency of tooth paste. Root canals were filled with the aid of the last file used in canal preparation. Simultaneously to the movement of penetration/removal and anti-clockwise rotation of file, pastes were condensed and compressed by means of a file and absorbent paper points, until the complete filling of cervical third could be observed

After placement of the calcium hydroxide paste, the teeth were radiographed together with an aluminum stepwedge (Alcan Alumínio do Brazil S.A., Porto Alegre, RS, Brazil) in order to evaluate the densities of teeth and dentin. After obtaining radiographs showing the image of the aluminum step-wedge, canals of each group were emptied using # 10 file K-file (Maillefer) and flushed with saline solution and radiographed again to confirm if they had been completely emptied, having in mind their reuse for the application of the two other pastes. After root canals had been filled with thc other pastes, teeth were radiographed again in order to verify if they had been completely emptied.

Analysis of density of calcium hydroxide pastes was performed using an aluminum step-wedge manufactured according to SCARPARO et al. . The chemical composition of the aluminum alloy was as follows: 6063 alloy; Al-base; Si- 0.60%; Fe-0.35%; Au- 0.10%; Mn 0.10%; Mg- 0.90%; Ar- 0.10%; Zn- 0.10%; Ti-0.10%; Others - 0.15%. This alloy was used to manufacture a 7- step wedge ranging from 4.0 to 10.0 mm in height; 3 cm in length and 3 mm in width. Its dimensions were adjusted to the size of film and to the contrast produced between steps of radiographic image. Thus, each radiograph showed the image of the aluminum stepwedge in the region of the tooth in which the optical density could be compared.

Three periapical radiographs (Kodak, UltraSpeed, USA) were taken of each tooth, as follows:

1^st initial, (2 ^nd . showing the root canal filled and densitometer and (3rd) final after complete emptying. All radiographs were taken using the same machine (Dabi-Atlante, Spectro II, 70KV, 10 mA, Ribeirão Preto, SP, Brazil), with a 4-em focus-film distance and 0,5-s exposition. Radiographic processing was performed at once for the three groups, through time temperature method. An acrylic support was used while the radiographs were taken, always holding the same position. All radiographs showed quality image, sharpness and contrast appropriate for analysis.

Parameters were established between the steps that ranged from l to 7, for dentin and for calcium hydroxide pastes, in order to assess density. With this objective, 3 appraisers individually observed each radiograph using a negative viewer located in an appropriated room and determined comparatively dentin density with calcium hydroxide pastes, in each root. The final parameter of assessment was quantified by the step (l to 7- density values were expressed in aluminum-equivalent rnm/A1/Eq.) corresponding to paste and to dentin density. A comparative and statistical analysis can be established by means of the average of the values corresponding to the wedge’s steps. The three thirds of root were analysed together. Figure 1 shows the aluminum step-wedge that was manufactured for this study; Figures 2 3, 4 to 5 show teeth after root canal preparation and after placement and complete filling of the canal with calcium hydroxide pastes, in which densities of dentin can be compared with densities of pastes used in the process.

RESULTS AND DISCUSSIONS
 
 

Some parameters for the use of intracanal dressing can be established from the better understanding of the mechanism of action of calcium hydroxide on tissues and microorganisms. The comparison of densities between different groups of calcium hydroxide pastes and between each group of calcium hydroxide pastes and dentin was performed in pairs using the Wilcoxon non-parametric test for paired observations, at a significance level of 5%. In terms of coincidence. there was no significant difference between thc three assessments performed by different appraisers. The comparison of the variation between appraisers revealed a coincidence of 89% in the assessment performed, and the Kappa values ranged from 0.60 100.65 for each pair of appraisers. The results of this study did not show statistically significant differences when the densities of calcium hydroxide pastes were compared between them nor when they were compared with dentin densities, as expressed in Table 1 and can be visualized in Figures 2 to 5.

The radiographic images provide important information. Different studies suggest methods of image analysis (1-5,14,19,20). . However, it is difficult to analyze a three-dimensional aspect presented in just one plane. CARVALHO (4) interpreting radiographs of bone lesions that were experimentally produced in dry human mandibles, reported that the deformities restricted to the cancellous bone were only observed in larger proportions. Images became clear when, by means of enlargement of deformities, jointed trabeculae and the inner surface of the lingual and/or buccal cortex were destroyed.

The methodology of this study using an aluminum step-wedge for density analysis has been used by others. SCARPARO et al.(20) developed au exploratory methodology to analyze bone density in the mandible, using an aluminum step-wedge as a numerical referential. PUPIN et al.(19) evaluating bone density through optical reading of the molar region in dry mandibles, observed that there were no statistically significant differences between bone density values of the right and left sides.

Within the context of this research, it is important to emphasize that the correct preparation of root canal is essential to thc cleansing process, also helping the filling with calcium hydroxide paste. Compression of paste relies on its appropriated consistency aided by the use of a suitable filling technique.

Considering the results of this study, it can be observed that it is not necessary to add radiopaque substances to calcium hydroxide pastes, because pastes used without them showed densities similar to dentin. In addition, when any substance is added to calcium hydroxide, even an inert one, it represents one more factor influencing biological processes and possibly of diminishing the amount of hydroxyl and calcium ions available, which represents one of the reasons for its use.

Knowing that the biological effects of calcium hydroxide lead to the activation of alkaline phosphatase, which, in turn, positively influences the mineralization process and favor the deactivation of bacterial enzymes aiding the antimicrobial effect, the importance of thc speed with which hydroxyl ions are released together with their availability in the environment in which their effectiveness is desired can be deduced.

Another factor to he analyzed is the possibility that calcium hydroxide is reabsorbed in the canal, with only the radiopaque substance remaining and giving the false idea that it keeps on acting. This factor should bc considered carefully, because has been no advantage of adding other substance to calcium hydroxide has been noted (6-13).

ESTRELA (6) analyzed the antimicrobial effectiveness of calcium hydroxide diffused by different substances. Microorganism tested were Streptococcus mutans, Streptococus faecalis, Staphylococcus aureus. Pseudomonas aeruginosa, Bacillus subtillis Candida albicans and a mixture of these microbial samples. Among the vehicles tested were: saline solution, CPMC, chlorhexidine. Fiagyl® (Metronidazole), Otosporim® and sodium lauryl sulfate. During the comparison of the results obtained in the experimental periods of exposition — 1 minute, 48 and 72 hours, and 7 days-the absence of antimicrobial synergy between calcium hydroxide and tested vehicles called the attention and supported the recommendation for the use of an inert and periapical-tissue-non-aggressive vehicle, such as saline solution and distilled water. These vehicles influence antimicrobial activity as they speed up ionic dissociation and diffusion and at the same time facilitate hydroxyl ions transportation and activity and activity in dentinal mass. Thus, the vehicle acts like an assistant in this process, giving calcium hydroxide chemical characteristics (dissociation, dissociation, diffusibility and filling) that are decisive to the antimicrobial potential and tissue healing capacity.

In this study, watery hydrosoluble (saline solution), viscous hydrosoluble (propylene glycol 400) and oily (CPMC) vehicles were compared, and it could be observed that the consistency of paste and filling technique were important factors, since there were no differences among their densities nor when their densities were compared to dentin densities, although research identifies advantages in the use of pastes with hydrosoluble vehicle, such as saline solution.

TABLE 1. Densities of pastes and dentin by steps (values expressed in aluminum/equivalent/mm)

CONCLUSIONS

Based on the results of this study, the following conclusions are made:

1. There were no statistically significant differences between optical reading values of densities of pastes analyzed or when they were compared to dentin density.

2. Addition of radiopaque substances to calcium hydroxide is not necessary, because calcium hydroxide paste density is similar to dentin density, provided that the root canal had been properly filled.

REFERENCES
 
 

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