Braz Dent J (1990) 1(1): 17-24 ISSN 0103-6440
| Introduction | Material and Methods | Results | Discussion | Conclusion | References |
The permeability of the dentin of the pulp chamber floor of lower molars with separate roots was studied, after instrumentation of the root canals by manual or ultrasonic techniques. The dentinal permeability was evaluated by the degree of penetration of copper ions in the tissue and quantified by methods used in morphometry. None of the combinations of irrigating solution/instrumentation technique caused an increase in the permeability of dentinal tissue in the pulp chamber region, probably because the dentin is reparative dentin, which is more amorphous and less tubular than primary dentin.
Key words: dentinal permeability, pulp chamber floor.
Moss (1965), using stains, investigated the dentinal permeability of this region, in deciduous teeth and concluded that the dentin is more permeable in teeth with necrotic pulp.
Macchetti and Campos (1975) studied various drugs used in pediatric dentistry, comparing their action on permeability of the dentin of the floor of the pulp chamber in deciduous teeth. For this investigation, they used 131I as the detector of dentinal permeability, concluding that formalin, cresol formalin, and tricresol formalin increased this permeability. '
Sasso et al. (1966), studying the dentin of human molars, verified the presence of reparative dentin on the floor and the roof of the pulp chamber, observing that this dentin was directly related to the defensive capacity of the pulp against caries. They also noted that the reparative dentin presented hypocalcification, with fewer tubules irregularly distributed, even loosing their tubular configuration.
The lack of research on the permeability of dentin in the pulp chamber floor in permanent molars prompted the present investigation, not only to test the permeability of dentin when it is submitted to the action of irrigating solutions during the instrumentation of root canals, but also to verify the type of dentin present in this region.
Two instrumentation techniques were used in the root canals - manual and ultrasonic - associated with irrigating solutions - distilled water and Dakin's solution. The Dakin's solution, prepared at the Endodontic Laboratory of the School of Dentistry of Ribeirão Preto, University of São Paulo, was 0.58% chloride at pH 9.20.
The 40 teeth were divided into four groups: 1) manual instrumentation with distilled water; 2) manual instrumentation with Dakin's solution; 3) ultrasonic instrumentation with distilled water; 4) ultrasonic instrumentation with Dakin's solution.
The outer surface of the teeth was impermeabilized with cyanacrylate, with the exception of the occlusion surface and the apex of the roots. The access to the pulp chamber was performed by a routine clinical technique.
The manual instrumentation was performed as follows: localization of the canals, determination of the working depth in the apical limit, use of three files in sequential increasing size from that which determined the anatomic diameter. The irrigating solution used was 10 ml per canal. The final cleansing was performed by irrigating each canal with 10 ml distilled water.
The ultrasonic instrumentation was done with the Brazilian ultrasonic unit Profiendo (Dabi-Atlante, Ribeirão Preto, SP, Brazil), using only two files of sequential increasing size, for 11/ 2 minutes per file. The irrigating rate was 3 ml/minute. The final cleansing was performed with distilled water energized by ultrasound, with a number 15 file in the root canal.
After the instrumentation of the canals, the teeth were immersed in a container with 10% copper sulfate solution for 30 minutes, in a vacuum for the first 5 minutes. After this time, the teeth were dried with absorbent paper and placed in a 1% rubeanic acid solution. The same time periods in solution and vacuum were observed as above. The rubeanic acid reveals copper ions, forming a stained compound ranging in color from deep blue to black, depending on the quantity of copper ions present (Feigl, 1958).
Upon completion of this reaction revealing the extension of the penetration of copper ions, the teeth were placed in acrylic blocks and 500- mm mesiodistal longitudinal sections were obtained with a diamond disk. During this process, the disk and acrylic block were cooled with jets of water to avoid burning the dental tissue. From each tooth, about 5 sections were obtained from which only those that passed through the central region of the furcation were used.
These sections were filed to a thickness of approximately 200 mm, washed in running water for 4 hours and then dehydrated in an increasing alcohol solution series, cleared in xylene, and mounted on glass slides for microscopic examination. The quantification of the penetration of copper ions was done using morphometric methods, with a 400 point grid inserted into the microscope eyepiece. The number of points in the stained and non-stained areas of the dentinal furcation were counted.
This region, of triangular shape, was outlined as follows: the vertex was the upper external concave point of the region of the furcation and, from this point, two orthogonal lines were drawn until they reached the inner floor of the pulp chamber.
Once the number of points in the stained and non-stained areas were determined, the percent of copper ion penetration in the dentin was calculated by the following equation: where PC indicated the points in the stained dentin and PN, the points in the unstained area.
An arc sine transformation of the original data was necessary in order to make the sample distribution normal and the variance homogeneous to allow for the application of parametric statistical tests.
The analysis of variance (Table 2) was statistically non-significant for the main factors of variation (solutions and instrumentation techniques) as well as for their interactions.
In spite of the non-significance indicated by the parametric statistical analysis, the non-parametric Kruskal-Wallis test (Table 3) was also applied for comparison and confirmation.
The Kruskal-Wallis test confirmed the results shown by analysis of variance that there was no significant difference in the degree of copper ion penetration of the dentin of the pulp chamber floor, in the furcation region between the roots, either between the two solutions (distilled water and Dakin's solution) or between the two instrumentation techniques of root canals (manual or ultrasonic) or even between their interactions.
The histological sections, examined by an optic microscope, magnified 40, 1W, 2W, and 400 X, showed the presence of reparative dentin in most of the pulp chamber floors examined (Figures 1 and 2).
The use of the identification method of copper ions is justified by its high reproducibility (Pécora, 1985; Zuolo et al., 1987; Silva, 1988), by the fact that copper ions are much smaller than the stained molecules, and by permitting the sections to be diaphanized for microscopic examination.
Water was used as the irrigating solution because it does not increase the dentinal permeability during root canal instrumentation (Marshall et al., 1960; Pécora, 1985). Dakin's solution was chosen because halogenic solutions increase dentinal permeability (Pécora, 1985) besides dissolving organic tissue (Moorer and Wesselink, 1982) and provide cleaner root canals when energized by ultrasound (Ahmad et al., 1987; Vansan, 1988).
The quantification of copper ion penetration, by the use of a point grid, offers security and objectivity in calculation and comparison of the areas, as well as ease of use (Pécora, 1985; Zuolo et al., 1987; Silva, 1988).
The comparison of the two techniques of root canal instrumentation was done to verify if the agitation of liquid in the pulp chamber, during ultrasonic instrumentation, offers a better result in the increase of permeability of the dentin of the pulp chamber floor than manual instrumentation, in which the irrigation solution only wets the walls of the floor.
The statistical analysis of the results obtained in this study shows that there was no significant difference in the degree of penetration of copper ions in the dentin of the pulp chamber floor, either with the use of water or Dakin's solution, or with manual or ultrasonic instrumentation, or with any combination of these factors.
The histological examination showed the presence of reparative dentin in the pulp chamber floor in the analyzed teeth, amorphous dentin with a reduced number of tubules, proving the findings of Sasso et al. (1966).
Sasso et al. (1966), Mjör (1972) and Seltzer and Bender (1975) report that the irregular (or reparative) secondary dentin forms more on the floor and the roof of the pulp chamber than on the lateral walls; and that, while the regular (or physiological) secondary dentin forms during the entire life of a tooth as a response to physiological stimuli, irregular (reparative)- secondary dentin forms as a response to injury to the pulp organ.
Due to the fact that the reparative dentin appears more amorphous, less tubular and less regular than primary dentin, the passage of liquid is hindered, since the reduction in the number of available dentinal tubules leaves this dentin without its principal path of penetration.
When the pulp chamber floor consists of primary dentin and regular secondary dentin, the penetration of copper ions is more uniform than in the presence of reparative dentin.
I. Distilled water and Dakin's solution as irrigating solutions are equal in relation to the permeability of dentin of the pulp chamber floor of lower molars with separate roots. .
2. The two techniques used in the instrumentation of root canals (manual and ultrasonic) were not significantly different statistically in relation to the degree of copper ion penetration in the dentin of the pulp chamber floor of the molars studied.
3. The interaction of instrumentation techniques and irrigating solutions did not show statistical significance in relation to the degree of copper ion penetration of the dentin of the area studied. .
4. The statistical non-significance of the irrigating solutions and the instrumentation techniques as well as the interaction of the solutions and techniques can be attributed to 2 factors: .
a) the fact that the floor of the pulp chamber consists of reparative dentin, more amorphous, less tubular, and less regular than primary dentin, which hinders the passage of copper ions;
b) the fact that only the irrigating solution comes in contact with the floor of the pulp chamber, leaving the cleaning of this region to only the hydraulic movement of the irrigating solution.
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Correspondence: Professor Jesus Djalma Pécora, Departamento de Odontologia Restauradora, Faculdade de Odontologia de Ribeirão Preto, Universidade de MO Paulo, 14050 Ribeirão Preto, SP, Brasil.
Accepted September 20, 1990
Eletronic publication: august 1997