Evaluation of flow and filling of root canal sealers using different methodologies

materiais dentários; microtomografia por raio-X. Abstract Introduction: Flow and filling ability of root canal sealers are indispensable for hermetic sealing of four metal for glass plate/sealer set was scanned using micro-CT. The flow was calculated by linear measurement of the material in the grooves. The central filling (mm 3 ) was calculated in the central cavity and the lateral filling was measured up to 2 mm from the central cavity. Data were


INTRODUCTION
A complete root canal filling is substantial for long-term success of endodontic treatment 1 . The obturation is classically performed using gutta-percha and different types of root canal sealers 2 . The root canal sealers fill the gaps between gutta-percha cones and the dentine walls 3 . Therefore, these materials should present adequate physical properties 4 .
Among the important physical properties to a proper obturation, the flow of endodontic sealers allows their deeper penetrability into the irregularities of the root canal system, which contribute to own interlocking between sealer and dentine 5 . Therefore, the flow of endodontic sealers may be evaluated by the ISO 6876/2012 6 standard, which recommend that the materials have a minimum of 17 mm of flow. However, the main limitation of this conventional test is its incapability to evaluate also the filling ability of the materials 7 .
A previous study 7 proposed the micro-computed tomography (micro-CT) as a reliable method to assess the flow and filling of root-end filling materials using a single test, in a 3D way. The authors used glass plates in a similar manner to the conventional ISO test, and observed an absence of correlation between the flow and filling properties. Up to now, there is no study applying this method to evaluate root canal sealers.
Endodontic sealers are divided according to their main components 8 , and their properties are directly related to their composition 9 . AH Plus (Dentsply DeTrey, Konstanz, Germany) is an epoxy resin-based root canal sealer that is considered the gold standard for physical properties 10 . Fill Canal (Technew Com. e Ind. Ltda., Rio de Janeiro, RJ, Brazil) is a zinc oxide and eugenol-based sealer that is routinely used in the Brazilian dental practice 11 . Sealapex (SybronEndo, Glendona, CA, USA) is a root canal sealer based on calcium hydroxide 12 . Previous studies showed flow in accordance with the ISO 6876 for sealers based on calcium hydroxide, epoxy resin and zinc oxide and eugenol 12,13 . However, the comparison between flow and filling of these sealers was not assessed yet.
Based on this gap in the literature, the aim of this study was to evaluate the flow and filling ability of root canal sealers based on different components by using conventional tests and micro-CT. The null hypotheses were that there is no difference between the sealers, and the properties of flow and filling ability are associated.

MATERIAL AND METHOD
The endodontic sealers used in this study, their respective manufacturers, and compositions are described in Table 1.

Flow (mm and mm 2 )
The flow test was performed based on ISO 6876:2012 standard 6 ( Figure 1). After mixing of the sealers, 0.05 mL of the material was placed in the center of a glass plate using a graduated disposable syringe (n = 10). Then, another glass plate (20 g) and a metal weight (100 g) were placed over the sealer, and kept for 10 minutes. So, the diameters of the sealer disks were measured using a digital caliper. The materials were photographed on the plate with a millimeter ruler for evaluation of the flow in area (mm 2 ), according to Tanomaru-Filho et al. 14 The flow area of the sealers was obtained using Image Tool 3.0 software (UTHSCSA, San Antonio, TX, USA).

Flow and Filling Ability Evaluated by Micro-CT
A glass plate was manufactured with a central cavity (1 × 1 × 2 mm) (length, width, and height) and grooves extending out horizontally and vertically to the 4 sides 7 (Figure 2A). Another dimension (1 × 1 × 1 mm -length, width, and height) was proposed for comparison. In a similar manner to the ISO 6876 6 test, an amount of 0.05 mL of each sealer was placed in the central cavity of the bottom glass plate, and another glass plate (20 g) and metal weight (100 g) were placed on the sealers and kept for 10 minutes ( Figure 2B). The glass plates/sealer set was scanned with the SkyScan 1176 micro-CT system (SkyScan, Bruker, Kontich, Belgium) ( Figure 2C). The micro-CT parameters were 9 µm voxel size, 90 kVp, 278 mA, 0.1 mm copper filter, and 360° scanning. The linear flow (mm) on each side of the grooves (horizontal and vertical) was analyzed. The filling in volume (mm 3

Statistical Analysis
The normality of the data was tested using the Kolmogorov-Smirnov test. Statistical analysis was performed with ANOVA and Tukey parametric tests. The level of significance was set at p<0.05.

Flow (mm and mm 2 )
All the sealers evaluated had a flow above the minimum (17 mm) recommended by the ISO 6876/2012. Although AH Plus had the highest flow value, there was no statistically significant difference among the materials (p>0.05). The assessment in area also showed similarities between the sealers (p>0.05). The results are represented in Table 2. There was no statistically significant difference between the sealers (p>0.05).

Flow and Filling Ability Evaluated by Micro-CT
The results are showed in Table 3. Independently of the test model used, there was no statistically significant difference between the linear flow (mm), central and lateral fillings (mm 3 ) observed for AH Plus, Sealapex and Fill Canal (p>0.05). All the sealers had a central filling above 80% and a lateral filling above 75%, in both diameters of test models. There was no statistically significant difference between the sealers and between the different test models (p>0.05).

DISCUSSION
This study evaluated the flow and filling properties of endodontics sealers based on different components to compare the difference between the materials, besides differences between the properties evaluated. Our null hypothesis was accepted since there was no difference between the sealers and the flow and filling properties were also similar.
An appropriate flow ability of the root canal sealers is a desired property in order to fill irregularities 15 . Moreover, for the endodontic sealers to exert their antimicrobial properties, a proper flow able their diffusion into the complex anatomy of the root canal, which is difficult to access and disinfect 16 . Therefore, the root canal sealers could aid in the elimination of the remaining microorganisms, increasing the success rates of the endodontic treatment 17 . In this study, as previously performed, two methods of analysis were used to conventional evaluation of the sealers flow 12 . We used the method preconized by the ISO 6876/2012, which record the diameter of the sealers after to put a glass plate and a metal weight on the material. After that, we evaluated all the area occupied by the sealers, as an additional analysis 14 .
All the sealers evaluated in the current study showed flow in accordance with the ISO 6 standard, which recommends a minimum value of 17 mm. Zinc oxide and eugenol-based materials are widely used in Endodontics 11 . However, in the best of our knowledge, there is no study evaluating the flow property for Fill Canal. Nevertheless, many studies evaluated other sealers based on zinc oxide and eugenol, such as Endofill (Dentsply-Maillefer, Dentsply Indústria e Comércio Ltda., Petrópolis, RJ, Brazil). Marin-Bauza et al. 13 attributed the high flow of Endofill to the presence of hydrogenated resin on its formula. This component is also present in Fill Canal. Although the flow value of AH Plus was numerically higher than Sealapex and Fill Canal, the sealers had a statistically similar flow. The high flow of AH Plus was described in previous studies 12,13,[15][16][17][18] . The greater concentration of epoxy resin in AH Plus is considered the reason for its high flow rate 18 . The flow of the materials is also affected by the size of their particles, whereas small particles allow greater flow ability 18 . Chang et al. 19 showed similar flow diameter for AH Plus and Sealapex, in accordance with our findings. However, the authors found that the complex viscosities of these sealers were significantly different. Therefore, they stated that the flow of root canal sealers evaluated using the conventional test provides limited information, leading to the search of new methodologies to complement this assessment.
Micro-CT is an innovative tool that provide high-resolution 3-dimensional evaluation of root canal fillings, allowing further exploration of precise internal structures of the sealers in a nondestructive way 20 . For this reason, micro-CT is considered as the gold standard for the filling analysis 21 . Based on this important characteristic to an accurate evaluation, Tanomaru-Filho et al. 7 proposed a new technique for assessing flow and filling of root-end filling materials using micro-CT imaging. The authors stated that the test model proposed showed proper and reproducible results and could improve flow analysis. Moreover, this previous study observed an absence of correlation between the flow and filling properties. When using this technique to evaluate root canal sealers, and adding another diameter of test model, our results did not show difference between the sealers and the test models. These results probably occurred since no difference was observed in the flow property of the materials evaluated.
Araujo et al. 21 used micro-CT to evaluate AH Plus, Sealapex and Endofill regarding their volume in the 1 mm apical third after obturation of the teeth. In this study, the lowest volume of sealer was observed in teeth filled with Sealapex and Endofill. The authors considered this fact as a better sealing ability for these materials and related this characteristic to the greater flow rate of these sealers. AH Plus was also related to a good filling ability ** , besides a low percentage of voids *** .

CONCLUSION
Based on the methodologies used and the results obtained, we could conclude that AH Plus, Sealapex and Fill Canal have adequate flow and filling capacity, suggesting their clinical application. Micro-CT can be used to assess the flow and filling of root canal sealers by means of a single test.