| Abstract|| |
Context: The use of intracanal medication aims to provide antimicrobial activity in the root canal system, leading to a more satisfactory condition for root canal obturation. However, it is important to evaluate whether such medication would affect the sealing-off from the main root canal of ramifications such as lateral canals.
Aim: Evaluate the influence of calcium hydroxide [Ca(OH) 2 ] paste on the filling of lateral canals.
Settings and Design: Ex vivo quantitative laboratory study.
Materials and Methods: Sixty single-rooted teeth with lateral canals created were used, 10 teeth per group. Group A was described respectively as lateral condensation technique (subgroup 1), thermomechanical compaction (subgroup 2), and continuous wave of condensation (subgroup 3). In Group B, subgroups 4, 5, and 6 were filled with Ca(OH) 2 for 7 days before filling using the techniques applied in subgroups 1, 2, and 3. Radiographic evaluation was performed to count the number of filled lateral canals in each group. The teeth were cross-sectioned over the lateral canals; thus, 180 specimens were obtained. Each specimen was immersed in a polyester resin. Digital images were obtained and specific software (Image Tool; ) was used to evaluate the number of obturated lateral canals and the filling length in each lateral canal of groups.
Statistical Analysis Used: Data were statistically analyzed using SPSS 12.0 for Windows (Descriptive statistical analysis and Newman-Keuls test).
Results: A greater number of simulated lateral canals were filled in Group A (91.1%). Group B had less filled lateral canals (33.3%). The sealing of lateral canals was statistically different between Group B (26.15%) and Group A (74.43%).
Conclusions: According to the radiographic analysis and the linear filling measurement, the use of Ca(OH) 2 decreased the number and the length of sealed lateral canals.
Keywords: Calcium hydroxide, root canal, root canal filling, root canal obturation
|How to cite this article:|
de Sousa BC, Gomes Fd, Ferreira CM, de Albuquerque DS. Filling lateral canals: Influence of calcium hydroxide paste as a root canal dressing
. Indian J Dent Res 2013;24:528-32
The anatomy of the root canal system in human permanent teeth is complex and is characterized by branches of the main channel. The sanitization and sealing of canal systems is often difficult to obtain because of the morphology and the extremely small dimensions of these branches, which prevents access to these areas with endodontic instruments. 
|How to cite this URL:|
de Sousa BC, Gomes Fd, Ferreira CM, de Albuquerque DS. Filling lateral canals: Influence of calcium hydroxide paste as a root canal dressing
. Indian J Dent Res [serial online] 2013 [cited 2019 Nov 14];24:528-32. Available from: http://www.ijdr.in/text.asp?2013/24/5/528/123357
The presence of ramifications communicating the root canal to periodontal ligaments allows the passage of bacteria and irritants from one site to the other, establishing so-called endodontic periodontal lesions.  Two studies found lateral canals in 45% of 74 teeth  and 27% of 1140 teeth, respectively.  As these branches represent areas of difficult access for endodontic instruments and antimicrobial solutions, these areas may allow the maintenance of sites of infection that can cause the onset or perpetuation of periradicular lesions, resulting in the failure of endodontic therapy. 
Although expressive decrease in microorganisms was found after root canal cleaning and shaping procedures, intracanal medication between sessions is necessary to increase the sanitization in the root canal system.  The use of calcium hydroxide [Ca(OH) 2 ] as an intracanal medication aims to provide antimicrobial activity in the root canal system, leading to a more satisfactory condition for root canal obturation. 
It is not possible to completely remove the Ca(OH) 2 paste in root canal dentin wall. Some studies have shown that the same cleaning techniques using irrigating solution activated by ultrasound could not completely remove the residue of Ca(OH) 2 paste. 
The use of Ca(OH) 2 paste as a root canal dressing or as an antimicrobial medication has been enshrined in the literature; however, it is important to assess whether this paste can affect the filling of the canal ramifications, such as lateral canals. If the Ca(OH) 2 paste affects the filling of the root canal system, being an unstable material physical-chemical, it can negatively influence the filling of root canals. 
The aim of this study was to analyze whether the application of Ca(OH) 2 paste reduces the amount of lateral canals filled and whether there is a reduction of the linear extent of filling of lateral canals.
| Materials and Methods|| |
Sixty extracted human single-rooted teeth were used in this study. All teeth were indicated for extraction due to advanced periodontal disease. A single operator performed all steps. Conventional endodontic access was prepared using round diamond drill (KG Sorensen, São Paulo, Brazil). The canal length was visually established by placing a size #10 K-file (Dentsply Maillefer, Ballaigues, Switzerland) through the entire length of the root canal until the file emerged from the apical foramen. The working length was established at 1 mm short of the apex. The coronal and middle thirds of each canal were flared using #4, #3, and #2 Gates Glidden drills (Dentsply Maillefer, Ballaigues, Switzerland). All teeth were instrumented to a working length of a size #40 K-file. A step-back preparation was performed with sizes #45, #50, and #55 K-files. The canals were irrigated with 3 ml of 2.5% sodium hypochlorite solution (Biodinâmica Química, Ibiporã, Paraná, Brazil) using a 27-gauge needle after each instrument.
The smear layer of the root canals was removed using irrigation with 10 ml of EDTA 17% (Biodinâmica Química, Ibiporã, Paraná, Brazil) through manual activation with a #40 K-file for 3 minutes for each canal, followed by a 5-ml flush with sodium hypochlorite. After that, canal patency was verified using a #20 K-file and dried by paper points (Dentsply Maillefer, Petrópolis, Rio de Janeiro, Brasil).
Three simulated lateral canals were then drilled on the mesial surfaces of the root (one in each third), perpendicular to the main canal at 3, 6, and 9 mm from the apex using a #15 engine reamer (Shein, New York, NY). ,
Sixty teeth were randomly assigned to six subgroups (n = 10). Grossman sealer (Endofill, Dentsply Maillefer, Petrópolis, RJ, Brazil) was used as the root canal sealer in all control and experimental groups.
Control group (A): Subgroups 1, 2, and 3
The sealer was mixed according to the manufacturer's instructions and was applied to the primary cone, which was inserted into the root canal. On subgroup 1 (lateral Condensation technique), subgroup 2 (thermomechanical technique), and subgroup 3 (continuous wave of condensation technique), filling was performed according to techniques specified for each subgroup.  Subgroups 1, 2, and 3 were defined as Group A (control group, without root canal dressing, before root canal filling).
Experimental group (B): Subgroups 4, 5, and 6
The root canals were filled with Ca(OH) 2 paste. Ca(OH) 2 P.A. (Biodinâmica Química, Ibiporã, Paraná, Brasil) was mixed with physiologic serum (Rimed, São Paulo, São Paulo, Brasil) and was inserted into the root canals with lentulo spiral (Dentsply Maillefer; Ballaigues, Switzerland) and size #40 file (Dentsply Maillefer, Ballaigues, Switzerland). Radiographs were taken to assess the quality of root canal dressing in main canals.
The access cavities were sealed with cotton and Cavit (Espe Gmbh, Seefeld, Germany), and the specimens were stored at 37°C and 100% humidity for 1 week. Afterwards, the Ca(OH) 2 paste was removed from the root canals using size #40 file and 20 ml of 2.5% sodium hypochlorite solution. The root canals were then rinsed with 17% EDTA solution for 3 minutes and were dried with absorbent paper points.
The root canals were filled according to the following experimental subgroups: Subgroup 4: Lateral Condensation; subgroup 5: Thermomechanical compaction; subgroup 6: System B + Obture II. Subgroups 4, 5, and 6 were defined as Group B (experimental group, with root canal dressing before root canal filling). Immediately after root canal filling, postoperative radiographs were obtained in the buccolingual direction, and chemically processed for developer and fixer in the darkroom. Then, radiographs were photographed on a light box by digital camera (Nikon Coolpix E5400, Japan).
Preparation for sample analysis
The teeth were cross-sectioned using a low-speed diamond saw (Ø 125 mm × 0.35 mm × 12.7 mm − 330°C) attached to an Isomet precision sectioning device (Buhler Ltd., Lake Bluff, NY, USA) under constant water cooling. The diamond saw was positioned perpendicular to the main canal at distances of 4, 7, and 10 mm from the apex so that 180 specimens were obtained. 
Each specimen was embedded in polyester resin (Cebtrofibra, Fortaleza, Brazil) to allow easier specimen manipulation. The blocks were wet-ground using 1000-grit SiC papers (DP-NETOT 4050014, Struers, Ballerup, Denmark) and with 4 μm to 1 μm diamond paste (SAPUQ 40600235, Struers, Ballerup, Denmark) to obtain a surface free of scratches and deformities, resulting in a highly reflective surface. 
Images were obtained [Figure 1] and [Figure 2] using stereoscopic lens (×40) (Lambda Let, Hong Kong, China) and digital camera (Nikon Coolpix E5400, Japan).
|Figure 1: Cross-section showing simulated lateral canal partially filled with sealer (Group B-cervical third)|
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|Figure 2: Cross-section showing simulated lateral canal not filled with endodontic filling material (Group B-coronal third)|
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X-ray analysis was performed by three experienced calibrated examiners (Kappa test 90%). The lateral canals were considered filled when completely filled with filling material.
Linear filling measurements were performed [Figure 3] using the Image Tool 3.0 software (University of Texas Health Science Center, San Antonio, USA). Measurements made in pixels provided by the software Image Tool 3.0 were converted into millimeters by using a millimeter ruler image, allowing the software calibration before each measurement of linear extension desired.
|Figure 3: Linear obturation measurements performed using the Image Tool 3.0 software (University of Texas Health Science Center, San Antonio, USA) (Group A-coronal third)|
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The operator performed two measurements for each lateral canal. The first measurement corresponded to the full extent of the lateral canal and the second corresponded to the extent of lateral canal filling.
The measures relating to linear extension of lateral canals and linear extent of filling of lateral canals were obtained by summation of 30 lateral canals in each third of the root canal in groups A and B.
Data were statistically analyzed using SPSS 12.0 for Windows (SPSS Inc., Chicago, USA), t-test, and Newman-Keuls test. Data obtained for the sum of lateral canals of each root third were compared statistically in the same group and between Groups A and B.
| Results|| |
[Table 1] shows the number of filled lateral canals for each root third in Groups A and B. The groups were statistically analyzed together with the help of t-test, where the difference was found between the groups (P = 0.0014). For the intragroup analysis, the Newman-Keuls test was used, demonstrating the number of lateral canals filled after using Ca(OH) 2 in Group B was lower than that observed in Group A (P < 0.01), regardless of the root third. Only 30 (33.3%) of the 90 lateral canals were filled following the use of Ca(OH) 2 . On the other hand, 82 lateral canals (91.1%) were properly sealed when Ca(OH) 2 was not used prior to root canal filling (Group A).
|Table 1: Number of filled lateral canals when calcium hydroxide was either avoided (Group A) or applied as intracanal medication (Group B) prior to root canal filling |
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[Table 2] exhibits the mean lateral canal length and the mean length of filled lateral canals for each root third.
|Table 2: Filling length (mm) in lateral canals either with or without the use of calcium hydroxide-based intracanal medication |
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The results in [Table 2] showed that the filling length in lateral canals when Ca(OH) 2 was not used prior to root canal filling (Group A) was higher than that observed when Ca(OH) 2 was applied as root canal dressing (Group B) (P < 0.01).
In Group A, the cervical third exhibited lateral canals with average length of 29.09 mm. The average length filled with gutta-percha was 22.52 mm (77.41%). On the other hand, the mean length of lateral canals was 28.8 mm, but only 4.04 mm (14.02%) were filled with gutta-percha when Ca(OH) 2 was used (Group B).
The middle third of Group A exhibited lateral canals with average length of 26.29 mm; 19.61 mm of that length were filled (74.59%). However, only 11.13 mm (41.25%) of 26.98 mm were filled when Ca(OH) 2 was used prior to root canal filling.
Regarding the apical third, Group A exhibited lateral canals with a mean length of 19.92 mm; 13.92 mm (69.87%) were filled. On the other hand, the apical third in Group B showed lateral canals of 19.31 mm in length, but only a length of 4.47 mm (23.14%) was filled.
The row corresponding to the total in [Table 2] showed a difference of 74.43% between lateral canal length and filling length in the experimental group without medication (Group A), and 25.24% between lateral canal length and filling length in the experimental group with medication (Group B).
| Discussion|| |
The current study evaluated the simulation of root lateral canals in natural teeth, following the strategy to create lateral canals.  Therefore, it was possible to create lateral canals of 150 μm in diameter. ,
This study used a radiographic analysis strategy to evaluate the filling of lateral canals. Radiographs may not show the filling of lateral canals. However, the pattern of radiopacity of the sealer used, and the fact that X-rays have been done without any other radiopaque structures overlap, as in X-rays performed in patients, allowed the visualization of the filling of lateral canals, as was observed in other studies, , which had demonstrated that this methodology was appropriate to conduct tests needed in this experiment.
Another strategy, the linear measurement of the filling, was used to assess the filling of lateral canals, optimizing the analysis of three-dimensional sealing of the root canal system.  This method proved to be adequate to evaluate lateral canal filling.
The flow capacity of the filling material through the dentin tubules, isthmus, and others ramifications in the root canal system is compromised by smear layer formation as a result of the post-instrumentation of root canal walls.  The smear layer blocks the entrance of areas that were previously patent, such as lateral root canals communicating with periodontal ligament, a fact that may have clinical importance depending on the clinical situation.  In this study, Ca(OH) 2 paste acts as a smear layer adhering to the root canal walls, blocking the entrance of the dentinal tubules and ramifications of the main canal, damaging him to adapt the filling material in the root canal walls, and preventing the penetration of branching areas such as lateral channels.
Smear layer formation during root canal instrumentation creates plugs composed of dentin debris that obliterate the entrance to lateral canals, as observed at the entrance of dentin tubules.  In the current study, 17% EDTA was used prior to the application of Ca(OH) 2 in specimens from Group B as well as in all specimens prior to root canal filling.
Different techniques have been used to remove the Ca(OH) 2 paste from root canals.  The enlargement of root canal with endodontic files associated with sodium hypochlorite irrigation could not capable of completely remove Ca(OH) 2 from root canal walls. 
Even variations in the technique and the technical sequence could not completely remove the Ca(OH) 2 paste from the root canal walls.  Perhaps, other techniques for removal of Ca(OH) 2 paste promote different patterns of removal; however, this study used endodontic files and copious irrigation with sodium hypochlorite, based on the results mentioned above and due to the fact that this is the most widely adopted technique by clinicians.
A study that evaluated the filling of lateral canals after the use of Ca(OH) 2 paste, showed a decreased number of filled lateral canals.  The authors found significant difference between the control group (95% of lateral canals were sealed) and the experimental group (21.7% of lateral canals were sealed).
The current study demonstrated, by radiographic analysis, that 91.1% of the lateral canals were obturated in the control group (without root canal dressing) and only 33.3% were sealed in the experimental group B (with root canal dressing).
Another study compared the quality of lateral canals filling as a result of six different techniques. The authors concluded that the methodology used to evaluate such parameters only allowed measuring of the amount of gutta-percha and cement in only one dimension, and they suggested that quality of filling would be better analyzed if the specimens were transversally sectioned. 
The current study evaluated transversal sections from the three root thirds, where lateral canals were simulated. The specimens were embedded in polyester resin to allow easier specimen manipulation and specimen polishing steps. The use of diamond pastes allowed easier visualization of the main root canal, the entire length of lateral canals, and the dentin limits. Therefore, it was possible to obtain reliable digital images to measure the length of lateral canals and the length filling. The analysis using a ×40 magnification microscope allowed evaluation of filling lateral canals, as well as of empty regions or regions filled with root canal dressing. Such findings would not be possible with radiographic analysis only.
The percent length of filled lateral canals gives us a more precise idea of the comparison between Groups A and B. In the current study, the analysis using Image Tool® software demonstrated that the lateral canals length filling corresponded to 26.15% of the whole length of lateral canals for the experimental group (Group B). Such a decrease in the lateral canals length filling in comparison to the control group (74.43% of the entire length) demonstrates that the use of Ca(OH) 2 affected the lateral canals filling in the current study. These data can be supported by statistical analysis comparing the results in the experimental and control groups. A statistically significant difference supports the conclusion of damage in lateral canals sealing by application of Ca(OH) 2 paste, both in number and extent.
Nevertheless, more appropriate to the use of techniques to allow better removal of Ca(OH) 2 paste would be to simply stop using them, as that would reduce the risk of branches sealing the main channel. The use of this medication has a purpose enshrined in literature and should not be subjugated by the results of this study.
Despite these findings, the present study was performed in vitro, and it is not possible to establish a direct correlation with clinical findings. Moreover, it should be noted that, although the results suggest the superiority of one technique over another, there is no scientific evidence proven through clinical studies.
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Bruno Carvalho de Sousa
Department of Endodontics, Ceará Federal University, Sobral
Source of Support: Committee for Postgraduate Courses Higher Education
Personnel (CAPES BRAZIL), Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]