|Year : 2014 | Volume
| Issue : 6 | Page : 698-701
|Micro-computed tomography and bond strength analysis of different root canal filling techniques
Juliane Nhata1, Ricardo Machado2, Luiz Pascoal Vansan1, Antonio Batista2, Gilson Sidney2, Tiago Pereira Rosa3, Emmanuel João Nogueira Leal Silva4
1 Department of Restorative Dentistry, Ribeirão Preto Dental School, University of São Paulo - FORP/USP, Ribeirão Preto, São Paulo, Brazil
2 Department of Endodontics, Paranaense University - UNIPAR, Francisco Beltrão, Paraná, Brazil
3 Campinas State University - UNICAMP, Piracicaba, São Paulo, Brazil
4 Grande Rio University - UNIGRANRIO, Duque de Caxias, Rio de Janeiro, Brazil
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|Date of Submission||11-Jan-2014|
|Date of Decision||31-Mar-2014|
|Date of Acceptance||22-Jan-2015|
|Date of Web Publication||02-Mar-2015|
| Abstract|| |
Introduction: The aim of this study was to evaluate the quality and bond strength of three root filling techniques (lateral compaction, continuous wave of condensation and Tagger's Hybrid technique [THT]) using micro-computed tomography (CT) images and push-out tests, respectively. Materials and Methods: Thirty mandibular incisors were prepared using the same protocol and randomly divided into three groups (n = 10): Lateral condensation technique (LCT), continuous wave of condensation technique (CWCT), and THT. All specimens were filled with Gutta-percha (GP) cones and AH Plus sealer. Five specimens of each group were randomly chosen for micro-CT analysis and all of them were sectioned into 1 mm slices and subjected to push-out tests. Results: Micro-CT analysis revealed less empty spaces when GP was heated within the root canals in CWCT and THT when compared to LCT. Push-out tests showed that LCT and THT had a significantly higher displacement resistance (P < 0.05) when compared to the CWCT. Bond strength was lower in apical and middle thirds than in the coronal thirds. Conclusions: It can be concluded that LCT and THT were associated with higher bond strengths to intraradicular dentine than CWCT. However, LCT was associated with more empty voids than the other techniques.
Keywords: Bonding, endodontics, micro-computed tomography
|How to cite this article:|
Nhata J, Machado R, Vansan LP, Batista A, Sidney G, Rosa TP, Leal Silva EJ. Micro-computed tomography and bond strength analysis of different root canal filling techniques. Indian J Dent Res 2014;25:698-701
Obturation is a critical step to perform a successful endodontic therapy. , The filling of the root canal system prevents bacterial and toxins infiltration and creates suitable environment conditions for apical tissues repair. ,,
|How to cite this URL:|
Nhata J, Machado R, Vansan LP, Batista A, Sidney G, Rosa TP, Leal Silva EJ. Micro-computed tomography and bond strength analysis of different root canal filling techniques. Indian J Dent Res [serial online] 2014 [cited 2019 Aug 24];25:698-701. Available from: http://www.ijdr.in/text.asp?2014/25/6/698/152164
Over the years, several filling techniques have been suggested in order to accomplish a hermetic sealing of the root canal system. Cold lateral condensation is the most used technique and it is a reference for assessing other techniques. In 1984, Tagger et al.,  suggested an hybrid filling technique associating the lateral condensation technique (LCT) and the "Gutta-percha (GP) thermomechanical condensation technique" proposed by John T. McSpadden in 1993.  Other techniques as warm vertical condensation involve a thermoplasticized ﬁlling material compacted vertically with heat pluggers. As finger spreaders are not used, root fractures during the filling procedures are less frequent.  Warm vertical condensation techniques demonstrate better adaptability of the ﬁlling material to the canal walls,  but may also result in extrusion of the ﬁlling materials to the apical tissues.  An interesting variation of this philosophy is the continuous wave condensation technique (CWCT),  in which a well-ﬁtted master apical cone reduces the apical extrusion of the ﬁlling material, while heat pluggers are used to thermoplasticize and downpack the ﬁlling material in the apical third. The remaining part of the canal is backﬁlled with injectable thermoplasticized material and then vertically compacted.
During the obturation, some variables may affect the GP adherence on the root canal walls including the dentin surface treatment, the GP surface energy, the cement surface tension, the type of filling material, and the used methods. 
However, the purpose of this study was to evaluate the quality and bond strength of three root filling techniques (lateral compaction, continuous wave of condensation and Tagger's Hybrid technique [THT]) by micro-computed tomography (CT) and push-out tests, respectively. The null hypothesis of the study was that there is no difference regarding the analyzed variables.
| Materials and methods|| |
The study protocol was approved by the Institutional Ethics Committee (Process #2011.1.373.58.6). Thirty mandibular human incisors with completely formed apices and roots with curvature angle ≤10π (mild curvature) according to Schneider's method  were used. Therefore, buccolingual and mesiodistal radiographs were taken to confirm that all teeth had no internal calcifications, resorptions, or previous endodontic treatment. The crowns were removed at the cemento junction with a water-cooled diamond disc (KG Sorensen, Barueri, SP, Brazil) at low speed to obtain a standardized root lengths of 18 mm. A size 15 K-file (Dentsply Maillefer, Ballaigues, Switzerland) was passively introduced into each canal until its tip was just visible at the apical foramen observed with an × 4 magnifier. The working length (WL) was established by subtracting 1 mm from this length.
Root canals were prepared using Hero System (MicroMega, Besanηon, France) up to 45/0.02 apical size. Throughout the chemomechanical preparation, the canals were irrigated with 2 mL of 1.0% NaOCl at each change of file. After preparation, the canals were filled with 3 mL of 17% EDTA for 3 min followed by flushing with 10 mL of distilled water and drying with absorbent paper points (Dentsply Ind. E Com. Ltda. PetrÓpolis, RJ, Brazil).
The filling procedures were performed using standardized GP cones (Dentsply, Petrσpolis, Rio de Janeiro, Brazil) in association with AH Plus sealer (De Trey, Dentsply, Konstanz, Germany). The 30 roots were divided in the following groups according to the filling technique.
Lateral condensation technique
After the sealer insertion with a 15K-file, the master cone was adapted into the WL. Medium-fine accessory cones (Dentsply, PetrÓpolis, Rio de Janeiro, Brazil) were placed with the aid of a #30 finger spreader (Dentsply/Maillefer, Ballaigues, Switzerland) until this one did not penetrate beyond the coronal third.
Continuous wave of condensation technique
Continuous wave of condensation was performed with Beefill system. First, a fine-medium GP cone was selected as the master cone and after the sealer insertion with a 15K-file was gently inserted into the canal and vertically condensed leaving only the apical thirds filled. Then, 3 mm long segments of GP were backpacked in the cervical and middle third until the canal was completely filled.
Tagger's hybrid technique
All initial procedures were performed as described previously for LCT group. However, after the placement of the master cone, only two medium-fine accessory cones were inserted. Then, a #55 McSpadden compactor (Dentsply/Maillefer, Ballaigues, Switzerland) calibrated 4 mm short of the WL was used for 10 s.
All specimens were radiographed in mesiodistal and buccolingual views to verify the quality of the fillings and stored at 37°C and 100% relative humidity for 2 weeks to allow the sealer to set. All clinical procedures were performed by the same operator with clinical experience.
Five randomly chosen samples of each group were mounted on a custom attachment and scanned in a micro-CT scanner (SkyScan 1174v2; SkyScan N.V., Kontich, Belgium) at an isotropic resolution of 22.6 mm. Exposure parameters were set at 70 kV, 140 μA and 80 W. The areas of the spaces within the filling material were measured on the cross-sectional images by the CTAn v. 1.12 software (Bruker-MicroCT, Kontich, Belgium). NRecon V1.4.0 software (SkyScan, Kartuizersweg, Kontich, Belgium) was used to make the three-dimensional (3D) reconstruction of the obtained images.
For push-out tests, the roots were fixed on acrylic plates with wax (Kota Import, Sγo Paulo, SP, Brazil) and then sectioned in a precision cutting machine (Isomet 1000; Buehler, Lake Forest, IL, USA) at 300 rpm. Twelve 1-mm-thick slices were obtained from each root (4 per root third). Both apical and coronal aspects of each sample were photographed and carefully examined to select only root sections with a uniform sealer layer (<50-mm thickness) and absence of voids. The diameters of the canal in each aspect were measured using a ×20 magnifying glass and a digital caliper. Two slices of each third were selected for the push-out test in a universal testing machine (Instron 3345, Instron Corporation, Canton, MA, USA) at a crosshead speed of 0.5 mm/min. Cylindrical steel punch tips ranging in size from 0.5 to 0.9 mm in diameter were used, matching the smaller (apical) diameter of the canal for each section with the punch diameter corresponding to approximately 90% of the canal diameter. The force needed to dislodge the filling material (kN) was converted to push-out bond strength (MPa), and the mean values were analyzed statistically. As the samples tested showed abnormal distribution, Kruskal-Wallis and Dunn Multiple comparisons tests were applied to assess the differences between the filling techniques. To analyze the root canal thirds, Tukey's test was used (SPSS 17.0 for Windows, Chicago, IL, USA).
| Results|| |
Micro-CT scans of specimens provided a good visualization of tooth dentin, sealant material, and GP. The two-dimensional (2D) and 3D images of flattened root canals showed ramifications and isthmus areas filled only by sealer in all experimental groups. The images also revealed the presence of voids at the interface between the root canal dentin and the filling material in all filling techniques investigated. Less empty spaces were observed when GP was heated within the root canal on continuous wave of condensation and THTs when compared to LCT [Figure 1]. The middle third was the root canal region with more voids and gaps. [Table 1] presents the filling voids for each third.
|Figure 1: Proximal view of three-dimensional micro-computed tomography (CT) reconstruction images and two-dimensional transversal micro-CT images. (a) Lateral compaction technique; (b) Continuous wave of condensation; (c) Tagger's hybrid technique; (Arrows) Show voids and gaps spots|
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|Table 1: Mean values and standard deviation of the filling voids for each third (mm2)|
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Bond strength was affected by the filling technique. The displacement resistance on CWCT was significantly lower (P < 0.05) than lateral condensation and THT, which presented similar bond strength mean values. Regarding the displacement resistance on root canal thirds, no statistically significant differences were observed between the coronal and middle thirds, however, was statistically lower on apical third (P < 0.01). The load profiles are shown in [Table 2].
|Table 2: Mean values in megapascals and SD of the push‑out bond strength necessary to dislodgement the filling material comparing the groups|
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| Discussion|| |
The success of endodontic therapy is related to interdependent procedures to allow the healing of apical tissues. These procedures include a thorough debridement of the root canal, the reduction of pathogenic organisms and a complete 3D filling to prevent ingress of bacteria from the oral environment and spread to the periapical tissue. , A variety of filling techniques based on the principles of vertical compaction of warm GP have been extensively investigated over the years with good results regarding filling of the root canal system, homogeneity of the filling material and apical seal.  In this study, were analyzed the quality and push-out bond strength of three root canal filling techniques using micro-CT images and push-out tests, respectively.
Micro-CT analysis is a highly accurate and nondestructive method for the evaluation of root canal fillings and its constituents. The 2D scans and 3D reconstructions provided different gray scale levels allowing to distinguish all the different components of the root canal filling such as GP, sealer, and surrounding hard tissues.  Studies about the quality of different root ﬁlling techniques have been inconsistent. De-Deus et al.,  for example, found that the GP ﬁlled areas were signiﬁcantly higher for all the thermoplasticized techniques than cold LCT. On the other hand, Martins et al.,  observed less voids on LCT when compared to Tagger and Thermafil techniques. A recent study, using micro-CT, also assessed the quality of root canal filling using different techniques (LCT with GP, EndoRez, Resilon, and GuttaFlow) in different thirds of the root canal. GP filled canals showed the lowest mean volume of voids in the coronal and middle thirds, whereas GuttaFlow showed the lowest volume of voids in the apical third. However, none of the tested materials provided a void-free canal filling.  In the present study, none of the tested root canal fillings were without voids and/or gaps which is in accordance with previous studies. , LCT presented the highest area of empty spaces within the filling material, especially in the middle thirds. The discrepancy between studies might be explained by use of different instrumentation protocols and the difficulty of filling effectively a very complex and irregular space. 
The push-out test used in this study has been applied to compare the bond strength of different types of root canal sealers with or without different core materials and root dentin pretreatment procedures. , Although bond strength testing may not be a completely reliable predictor of the clinical behavior of the sealers,  it is suitable for ranking root filling materials  and is considered the best methodology to perform adhesiveness measurements.  The less sensitivity to small variations among specimens and variations in stress distribution during load application are advantages of this method over tensile and shear bond strength tests. 
In the present study, depending on the technique used to fill the root canal, there were differences in the material displacement resistance. Among the experimental groups, the highest values observed after push-out tests were obtained by the specimens filled with LCT and THT. This outcome is in agreement with previous studies. , Carneiro et al.,  evaluated the bond strength to human intraradicular dentine of root canal filling materials with adhesive properties (AH Plus/GP, Sealer 26/GP, Epiphany SE/Resilon and Epiphany SE/GP) using either LCT or THT by push-out tests. Among the root filling materials evaluated in their study, the use of LCT associated with AH Plus with GP cones presented the highest mean values.
Specimens filled with CWCT presented the lowest mean values of bond strength. Interestingly, micro-CT images showed better results regarding the filling quality. The lower bond strength values found in CWCT group might be explained by the presence of a thin sealer layer observed on micro-CT. Previous studies have shown that thin layers of sealer are preferred in modern endodontics because the sealer may shrink during setting and dissolve over time.  On the other hand, a thin sealer layer might be more inclined to cohesive failures. It is possible that the resin matrix material preferentially penetrated the dentinal tubules, leaves a sealer layer that is enriched with filler particles that are larger than the dentinal tubules diameter. This leaves a sealer with a resin-depleted layer and a filler particle enriched interface. An excessively high particle ratio in the sealer layer might result in a weak cohesive strength. 
| Conclusion|| |
It can be concluded that LCT and THT were associated with higher bond strength to intraradicular dentine than CWCT. However, LCT was associated with more empty voids than the other techniques.
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Department of Endodontics, Paranaense University - UNIPAR, Francisco Beltrão, Paraná
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2]
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