INTRODUCTION
Three-dimensional obturation of the root canal system is the final objective of non-surgical root canal therapy. The most commonly used core-filling material is gutta-percha, but it has the disadvantage of being non-adherent to canal walls. In addition presence of canal irregularities and the size of the dentinal tubules a root canal sealer is essential to enhance the seal during compaction and to penetrate into small, normally inaccessible areas, i.e., the dentinal tubules. The penetration of sealer cements into dentinal tubules is considered to be a desirable outcome for a number of reasons: It will increase the interface between material and dentin thus improving the sealing ability and retention of the material may be improved by mechanical locking. Sealer cements within dentinal tubules may also entomb any residual bacteria within the tubules and the chemical components of sealer cements may exert an antibacterial effect that will be enhanced by closer approximation to the bacteria. Therefore, it is important that the percentage of the sealer/dentin interface that is covered by the sealer and the degree of tubule penetration by the sealer be as great as possible in all cases, whether previously infected or not.
Placement of a sealer into the root canal system should be done in a manner which is predictable and completing covers the dentin walls.[1] Accepted means of sealer placement include the use of endodontic files or reamers, lentulospirals, gutta-percha cones, paper points, and recently ultrasonic files.[2] In the ultrasonic system properties of irrigant activation, cavitation, and acoustic streaming are apparently responsible for the enhanced canal system cleaning. The same actions may be responsible for the more thorough placement of a root canal sealer.[1]
Recently, the Endoactivator system (Densply Tulsa Dental Specialities, Tulsa, OK) was introduced. It is a sonically driven canal irrigation system that comprises a portable hand piece and three types of disposable flexible polymer tips of different sizes. It is designed to safely and vigorously energize the hydro dynamic phenomenon without cutting root dentine. This hydrodynamic activation serves to improve the penetration, circulation, and flow of irrigant into the more inaccessible regions of the root canal system.
The analysis of the dentin/sealer interface allows the determination of which filling technique could obturate the root canals with less gaps and voids. Several microscopy techniques are currently used to evaluate the sealer/dentin interface, including stereomicroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and confocal laser scanning microscopy (CLSM).[1,3]
In comparison to conventional SEM, CLSM has the advantage of providing detailed information about the presence and distribution of sealers or dentinal adhesives inside dentinal tubules in the local circumference of the root canal walls at relative low magnification and non-dehydrated samples through the use of fluorescent Rhodamine-marked sealer.[3] Therefore, the purpose of this study was to compare the depth and percentage of dentinal tubule sealer penetration with four different placement techniques using CLSM as the evaluative tool.
MATERIALS AND METHODS
Thirty single-rooted human maxillary teeth stored in normal saline solution containing 0.1% sodium azide were used in this study. A dental operating microscope (Global Surgical Corp., St. Louis, MO) was used to verify the selected teeth were free of cracks or apical resorption. Radiographs were exposed from facial and proximal views to ensure the presence of a single canal. The coronal portions were cut by using water cooled, high-speed drained bur, and the root canal length standardized at 10 mm.
Root canal preparation
A size 10 K-file was introduced into each canal until it could be seen through the apical foramen and the length measured. Working length was established by subtracting 0.5 mm from that length. Then, the roots were instrumented by using the Protaper technique to a size of F3. The hand piece was used with an electric engine (X-smart, Densply-Maillefer, Ballaigues, Switzerland) at 250 rpm.
A solution of 2.5% sodium hypochlorite was used continuously during the root canal shaping, 2 ml for each file used. A final irrigation with sodium hypochlorite was performed for 1 minute using a 20 K-file attached to the hand piece of an ultrasonic unit set to the “endo” mode with intension adjusted to level 5 (in a range of 1-10). To eliminate the smear layer, 2-ml 17% EDTA for 3 minutes was used followed by a final rinse of 2-ml distilled water. Each root was then dried with paper points. The roots were randomly divided into three groups according to the sealer placement technique used: Ultlrasonic (Woodpecker Dte-D5 Ultrasonic Scaler, China), lentulo spiral (Densply Maillerfer) and Endo activator (Densply Tulsa Dental Specialities).
Sealer placement
AH 26 sealer was mixed according to manufacturer's instructions. To allow analysis under the CLSM, each sealer was labeled with Rhodamine B (Sigma-Aldrich, St. Louis, MO) to an approximate concentration of 0.1%.
Each group of 10 roots had sealer applied by one of three methods. Four different methods of sealer placement used were: Group 1, ultrasonic file; group 2, lentulo spiral and group 3, Endoactivator. A single mix of sealer was used for all teeth. A 1-ml tuberculin syringe was used to dispense 0.05 ml of sealer with each placement technique. No additional sealer was used. In group 1, the ultrasonic unit was used with a # 20 tapered file. Sealer was placed on the apical portion, and the file was placed into the canal to working length and ultrasonically activated for 5 seconds. In group 2, a # 2 lentulo spiral was selected that would not bind in the prepared canal and that would reach the prepared working length. After the hand piece was set to enable the lentulo spiral to spin material apically, the 0.05 ml of sealer was placed into the canal and was gently rotated to working length and worked gently up and down within the canal for at least 5 seconds.
In group 3, endoactivator tip was set to reach within 1 mm of working length 0.05 ml of sealer was placed into the canal, and endoactivator was slowly rotated for 5 seconds. In each group, after sealer placement a standardized protaper gutta-percha cone was placed to length, laterally condensed with finger spreader, and accessory cones were added as needed. Extruded sealer from apical foramen, if present, was wiped off with moist cotton. Three millimeter of gutta-percha and sealer was removed with a heated plugger from the coronal end of root canal and Cavit was placed. All the roots were stored in container at 100% humidity and 37°C for 7 days to allow the sealer to set.
Sectioning and image analysis
The roots were sectioned using a diamond disc at 200 rpm and continuous water cooling to prevent frictional heat. Horizontal sections were done at the 3 and 6 mm levels from the apical foramen. Then, the surface were polished using sand papers number 500, 700, and 1200 under running water to eliminate debris product of the cutting procedure. The samples submitted to confocal laser microscopy had 2 mm thickness. The dentin segments were examined on a confocal microscope (Olympus Fluoview FV 1000). The respective absorption and emission wave lengths for the Rhodomine B were 540 nm and 590 nm. Dentin samples were analyzed using the 10× lens.
To calculate the percentage of sealer penetration around the root canal, first each image was imported into the IOB software and the circumference of root canal measured. Next, areas along the canal walls in which the sealer penetrated into dentinal tubules were outlined and measured using the same method. Subsequently, the percentage of root canal sealer penetration in that section was established. Statistical significance for the percentage of root canal was determined for each level of the root canal using analysis of variance (ANOVA) followed by Tukey test; the level of significance was set at P < 0.05.
Using the ruler tool of the IOB software (Olympus), depth of sealer penetration was measured and recorded at four standardized points of each 10× picture as described by Gharib et al.[4] The canal wall served as the starting point and sealer penetration into dentinal tubules was measured to a maximum depth of 1,000 μm. These data points were averaged to obtain a single measure for each section. Statistical significance for the mean of depth penetration of root canal sealers was determined for each level of the root canal using ANOVA followed by Tukey test; the level of significance was set at P < 0.05.
RESULT
From the three placement techniques 60 sections were evaluated at the 3 and 6-mm levels. A consistent fluorescent sealer ring was seen around the canal wall in all 10× sections. In each section sealer penetration was seen. The mean and standard deviation of sealer penetration depth and percentage of sealer penetration are presented in Table 1. Gr-1 showed maximum mean depth of penetration (810 μm) and maximum mean percentage of sealer penetration (64.5) while Gr-3 showed minimum mean depth of penetration (112.7 μm) and minimum mean percentage of sealer penetration (26.7). Results also demonstrated that the mean depth of penetration and percentage of penetration was less at 3 mm level (496.33 μm and 43.23%, respectively) than at 6-mm level (653.36 μm and 52.4%, respectively). A statistical significant differences among Gr-1, Gr-2, and Gr-3 were found at 3 mm and 6-mm level (P < 0.05; ANOVA-Tukey tests) for the depth and percentage of sealer penetration [Table 2] except for GR-1 and Gr-2 at 3-mm level. Figure 1 shows representative pattern of sealer penetration around root canal walls. Sealer displayed different amount of penetration into dentinal tubules, but in all samples various methods of sealer application failed to show a total adaptation, as shown by sealer penetrating into dentinal tubules around the total extent of root canal walls. Figure 2 shows representative interfaces of the evaluated methods of sealer placement, with sealer tags penetrating into dentinal tubules visible with sealer AH plus.
DISCUSSION
It is currently accepted that the major goal of root canal filling is to prevent any interchange between the oral cavity, the root canal system, and the periradicular tissues, providing a barrier to canal infection and re-infection. Sealers are used to attain an impervious seal between the core material and root canal walls. Most of the studies have shown that use of sealer along with core material results in significantly less leakage than when it is not use. The fact that the sealer penetration into the dentinal tubules increases the interface between the filling material and the dentin might influence the sealing ability of the obturation the removal of the smear layer from the root canal walls is regarded as an essential step of root canal treatment.[5,6]
The clinical implication of increased sealer penetration into the dentinal tubules is that it may kill the bacteria that remain inside the dentinal tubules and may influence the quality of treatment. Sealer containing antibacterial-active ingredients might be more effective through a closer contact with isolated bacteria by penetration into the dentinal tubules.
The sealer penetration depth in the dentinal tubules depends on many factors like smear layer removal, dentinal permeability (the number and the diameter of tubules), root canal dimension, presence of water and the physical, and chemical properties of the sealer.[7,8] The flow is one of the main physical factors to influence the tubular penetration and is defined as the ability of a sealer to penetrate in irregularities, lateral canals, or dentinal tubules of the root canal system.[9] The flow is determined by the consistency, particle size, shear rate, temperature, time, internal diameter of the root canal, and the rate of insertion.[10] Of these factors, the particle size and consistency of the sealers were typical for the sealers used and therefore not standardized during the experiments. In the present study temperature, amount and time for placement are kept constant to minimize the errors.
The apical 5 or 6 mm of a root canal is a critical area for placement of sealer. It is important for successful obturation because it is in this area that accessory canals are most often found. Since accessory canals communicate with the periodontal membrane, they can create a periodontic-endodontic pathway for potential bacterial penetration to and from the periodontium.[10,11] A complete sealing of the canal seems difficult when using a combination of gutta-percha and a root canal sealer that is in a general use clinically. Thus the apical third of root canal was chosen for the evaluation of sealer.
There are very few studies have been done to evaluate the efficacy of different methods of sealer placement.[12,13,14] Among these previously conducted studies on sealer placement techniques few shortcomings were observed for e.g., either there was no standardization of amount of root canal sealer applied or the method of evaluation was not cleared or percentage of canal covered after obturation was not calculated. In addition, one study utilized plastic blocks; the plastic canals were visible during sealer application, which does not correlate well with the clinical situation or their evaluation technique (radiograph or colored slice of cleared specimens) lacked sensitivity.
Clinically, rapid insertion of a pseudoplastic sealer into the canal would decrease viscosity and increase the flow of sealer. Various studies have advocated use of ultrasonics for sealer placement.[1,15,16] Like Ultrasonics, EndoActivator Systems are also used for activation of root canal irrigants. The difference between the two is that Endoactivator system is used by application of sonic energy. The Activator tips are used in conjunction with the hand piece Driver to provide the energy for tip oscillation and vibration. To best of our knowledge none of the study had utilized this system for sealer placement. Thus in the present study all the three rapidly placement techniques (ultrasonics, lentulo spiral, and endoactivator) were chosen and the sealer distribution was analyzed.
Several microscopy techniques are currently used to evaluate the sealer/dentin interface, including stereomicroscopy, SEM, TEM and, CLSM. Stereomicroscopy has drawback of not being sensitive for too thin sealer along canal walls, thus more sensitive detection techniques are used. CLSM offers several advantages over conventional SEM. It provides detailed information about the presence and distribution of sealers or dental adhesives inside dentinal tubules in the total circumference of the root canal walls at relative low magnification through the use of fluorescent Rhodamine-marked sealers and artifacts could practically be excluded.[17,18] In addition it uses non-decalcified or hard tissue samples that do not require a specific section technique (sputter coating).
Thus the present study was carried out to assess the sealer-dentin interface and compare the percentage and depth of dentinal tubule sealer penetration by using 10× CLSM. In all the canals, the technique was directed with an attempt to duplicate the in vivo use of sealer. The same method of obturation techniques and the same volume of sealer was placed into each canal.
The results of this study indicate that all three methods of sealer placement may not consistently and completely cover dentin walls after lateral condensation. Although sealer was present in the majority of the areas examined, the 3-mm level demonstrated significantly less (P < 0.05) sealer coverage than 6-mm level which corroborates the findings of Weimann and Wilcox. Not only the coverage but also the penetration of the sealer into the dentinal tubules was greater significantly more (P < 0.05) at the 6-mm level than 3-mm level of the root canal irrespective of method of sealer placement. This is in support of other studies.[17,18] This could be because of the fact that the number as well as diameter of tubules decreases on descending apically in the root canal. Furthermore, the apical portion of roots shows pronounced variations in structures, for e.g., primary dentinal tubules are irregular in direction and density; some areas are devoid of tubules.[19] Also, cementum-like tissue can line the apical root canal wall, occluding any tubules.[20] Also the effect of smear layer removal of irrigant decreases towards apical direction liming the flow of sealer in dentinal tubules. Furthermore, some moisture is left in root canal even after drying with absorbent papers due to capillary action in narrow apical third of canal, limiting the flow of sealer in the apical third.[21] Thixotropic property of the sealer explains the results of the study in which there was a significant difference between the depth of sealer penetration at 3 and 6-mm levels of all the groups due to the fact that less amplitude of vibration would be possible in apical third of canal than in the middle or coronal third. Over all ultrasonic group (Gr-1) showed better depth and percentage of sealer penetration than lentulospiral (Gr-2) followed by endoactivator group (Gr-3). The ultrasonic and sonic energy apparently propels the relatively viscous sealer along the length of file to appropriate depth[1] while lentulo spiral centrifugally pushes the sealer.
Sonic energy generates significantly higher amplitudes and lesser frequency or great back and forth tip movement[22] compare to ultrasonically driven instruments. Contact between the tip and dentine results in diminished amplitude and undesirable decrease in streaming velocity. Also sonic energy produces just one single node and antinode over the entire length of vibrated instrument so the streaming velocity is less than the ultrasonic devices. Node production along activated file is an important part of acoustic streaming[23,24] resulting in a strong current produce along the activated instrument.[25] Ultrasonic energy has the ability to create several nodes along the length of file.[24] Poor percentage of sealer penetration and depth of sealer penetration in the more apical region might be due to the activated file touching the canal wall in the more constricted area and not being able to produce the necessary nodes for acoustic streaming and cavitation.[25] If ultrasonic instruments with their constant power supply and increased node production cannot effectively clean the more apical region, it is likely that endoactivator with its battery power and sonic energy will have the same problem. The insert in the ultrasonic system is made of metal alloys, while endoactivator has polymer-based tips. The difference in material might have also influenced the displacement of sealer. Significantly better percentage of sealer penetration and depth of sealer penetration was observed in ultrasonic group, substantiating the findings of previous studies.[1,15,16] All these studies concluded that use of ultrasonics results in better sealer placement than other compared techniques utilized in their studies.
Within limitations of this study it can be concluded depth and percentage of sealer penetration of sealer is influenced by the type of placement technique and by the root canal level with penetration decreasing apically. All the analysed placement techniques failed to show a consistent adaptation of sealer to the total circumference of the root canal wall. Further studies could be concluded to analyze the entire canal rather than a portion with bigger sample size as depth and percentage of penetration of sealer may be important in future nonsurgical endodontic outcomes.
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Source of Support: Nil
Conflict of Interest: None declared
Keywords:
Confocal laser scanning microscopy; endoactivator; lentulospiral; sealer penetration; ultlrasonics
