Filling of simulated lateral canals with gutta percha or resilon when using thermomechanical compaction.

AIMS: To evaluate the filling of simulated lateral canals with gutta-percha or Resilon when using thermomechanical compaction. SETTING AND
DESIGN: Forty-five human single-rooted teeth were subjected to tooth decalcification and clearing.
MATERIALS AND METHODS: After root canal preparation, artificial lateral canals were made at 2, 5, and 8 mm from the working length (WL), corresponding to the apical, middle, and cervical thirds, respectively. The specimens were divided (n = 15) according to the filling material: Dentsply gutta-percha (GD), Odous gutta-percha (GO), and Resilon cones (RE). Root canals were obturated by thermomechanical compaction using a #45 compactor and no sealer. Lateral canals were analyzed by digital radiography and digital images after tooth decalcification and clearing using the Image Tool software. STATISTICAL ANALYSIS USED: Data were subjected to the Kruskal-Wallis and Dunn tests at 5% significance.
RESULTS: In the coronal third, RE and GO presented more filling ability than GD (P < 0.05). In the middle and apical thirds, RE presented the best results.
CONCLUSIONS: Resilon demonstrated filling ability as material for root canal obturation by using thermomechanical compaction.

INTRODUCTION

Root canal filling of the root canal system (RCS), including the ramifications and anatomical complexities, is essential for the success of endodontic therapy and periapical tissue healing.[1] Although the gutta-percha presents dimensional stability,[2] it can be plasticized when heated.[3] Due to these properties, gutta-percha is the solid core material most widely used for root canal filling. Some root canal filling techniques are based on application of heat, which can favor the long-term microleakage.[24]

Resilon/Epiphany system consists on a dual-cure resinous sealer (Epiphany - Pentron Clinical Technologies, LLC, Wallingford, CT, USA) and solid core polymer-based Resilon cones (Resilon Research, LLC, North Branford, CT, USA).[5] Resilon is composed of a synthetic polyester polymer and is available as cones in ISO sizes with physicochemical property similar to gutta-percha.[67] Resilon has thermal plasticity greater than gutta-percha,[8] reducing the bacterial leakage.[9]

Several thermoplastic root canal filling techniques have been developed aiming to achieve effective filling of the RCS.[10] Thermomechanical compaction is a technique introduced by Mc Spadden and modified by Tagger et al.[11] In this technique, thermomechanical compactors are used to promote heat and plasticize the gutta-percha, while exerting apical and lateral pressure. Previous studies have demonstrated that thermomechanical compaction is able to fill irregularities and also simulated lateral canals.[1213] Sant Ánna Júnior et al.[14] reported that Resilon and gutta-percha present similar thermal behavior when subjected to thermomechanical compaction.

Complete filling of the root canal system (RCS) is the main goal of endodontic obturation.[15] Assessment of the percentage of simulated lateral canals filling has been carried out in natural[121617] and artificial teeth.[1819] Using decalcified and cleared human teeth, Tanomaru-Filho et al.[20] evaluated the ability of gutta-percha and Resilon to fill simulated lateral canals by using the Obtura II system and observed that gutta-percha and Resilon are solid core materials with lateral canal filling ability.

So, the aim of this study was to evaluate the filling of simulated lateral canals with three different solid core endodontic materials (two types of gutta-percha and Resilon) when using thermomechanical compaction. The null hypothesis is that root canal filling with Resilon is different from that obtained with gutta-percha when thermomechanical compaction technique is used.

MATERIALS AND METHODS

Specimen preparation

Forty-five single-rooted human teeth were selected for this study. Root canal anatomy was standardized using round/oval root canals without the presence of isthmus and ramifications observed after radiographic evaluation. The specimens were stored in saline solution after kept for 48 hours in a 1% sodium hypochlorite solution. Teeth were decoronated, and their root length was standardized at 15 mm. All specimens had a single root canal with apical diameter corresponding to a #20 or smaller K-file. The root canal length was measured by introducing a #10 K-file (Dentsply-Maillefer, Ballaigues, Switzerland) up to the apical foramen. The working length (WL) was established by subtracting 1 mm from the total length of the root canal.

Root canal preparation was carried out using a crown-down technique. The instruments used were K3 nickel-titanium rotary files (Sybron Endo, Orange, CA) sizes 25/.12, 25/.10, 25/.08, 25/.06, and 25/.04 until resistance and 25/.02, 30/.04, 35/.04, and 40/.04 to the WL. Root canals were irrigated during the chemo-mechanical preparation with 5 ml of 2.5% sodium hypochlorite solution (Instituto de Química, Araraquara, UNESP - Brazil) using 2 ml at each change file. For removal of the smear layer, 17% EDTA (Odahcam Dentsply, Petrópolis, RJ, Brazil) was used in the root canals for three minutes. Then, the root canals were irrigated with 5 ml of saline.

Once the root canals were prepared, the specimens were subjected to a tooth decalcification and clearing protocol. Specimens were decalcified in a solution of 5% hydrochloric acid (Hexis Cientıfica, Jundiaı, SP, Brazil), which was changed every 24 hours for 5 days. Teeth were demineralized until they achieved a rubber-like consistency. Then, #8 and #10 K-files were inserted through the buccal and lingual root surfaces at 2, 5, and 8 mm from the WL until they reached the main root canal, creating the simulated lateral canals. The patency and standardization of lateral canals were tested with a #8 or #10 K-file. After that, teeth were washed in running water for 4 hours and dehydrated using increasingly concentrated serial dilutions of alcohol. Finally, specimens were immersed in methyl salicylate (Vetec Química Ltda, Rio de Janeiro, RJ, Brazil) in order to render the tissues transparent.

Root canal filling

Each specimen was removed from the methyl salicylate and wiped with gauze soaked in alcohol, which was also used to irrigate the canals and remove residual methyl salicylate. The specimens were handheld with gauze, and the same operator filled the root canals using the thermomechanical compaction technique. Teeth were divided into 3 groups (n = 15) according to the root canal filling material used: Group GD: Dentsply 40/.04 gutta-percha cones (Dentsply Ind. e Com. Ltda., Petrópolis, RJ, Brazil); Group GO: Odous FM (fine medium) thermoplastic gutta-percha cones (Odous De Deus Ind. e Com Ltda., Belo Horizonte, MG, Brazil); and Group RE: Resilon 40/.04 cones (Resilon Research, LLC, North Branford, CT, USA).

Cones were fitted to the WL, and the Odous cones were trimmed with a #15 surgical scalpel (BD – Becton Dickinson Indústrias Cirúrgicas Ltda., Rio de Janeiro, RJ, Brazil). The canals were then filled by thermomechanical compaction based on the hybrid technique described by Tagger et al.[11] After placement of the master cone, lateral condensation was performed with finger spreaders (Dentsply-Maillefer, Ballaigues, Switzerland), and two accessory cones of the respective material were inserted into the canal. After that, a #45 compactor (Gutta Condenser, Dentsply-Maillefer, Ballaigues, Switzerland) rotating at 8,000 rpm was inserted for 10 seconds up to 3 mm from the WL. The material was vertically compacted up to the entrance of the root canal using #4 and 5 Schilder pluggers (Odous De Deus Ind. e Com Ltda., Belo Horizonte, MG, Brazil). Since the goal of this study was to evaluate the filling ability of solid core materials, no sealers were used.

Methods of analysis

After root canal filling, radiographs (Kodak RVG 6100, Kodak Dental Systems, Atlanta, GA, USA) were taken using a Spectro 70X Electronic X-ray unit (Dabi-Atlante, Ribeirão Preto, SP, Brazil). Positioning of the roots and focus-film distance were standardized, employing a standardizing device coupled to the X-rays device. Following that, specimens were soaked once again in methyl salicylate, and after that, standardized digital photographs were taken (Nikon D80, Tokyo, Japan).

The radiographic and photographic images showing the root canal fillings in each specimen were imported into the Image Tool software (UTHSCSA Image Tool for Windows version 3.0, San Antonio, TX, USA). The amount of filling material visualized in each lateral canal was calculated and expressed as percentages of linear extension (length of the lateral canal that was filled, in relation to its entire length in mm) and of filled area (area occupied by the filling material inside the lateral canal, in relation to its entire area in mm2). Data were not normally distributed and were analyzed using the Kruskal-Wallis and Dun tests at 5% significance (GraphPad Prism 5.0, California Corp.).

RESULTS

Tables 1 and 2 show the percentages of lateral canal filling achieved by each material. In the coronal third, the results of the cleared specimens did not show significant differences between Resilon and the Odous gutta-percha cones (P > 0.05), with Dentsply gutta-percha presenting the lowest percentage of filling among the materials tested (P < 0.05). Resilon had better results than both types of gutta-percha (P < 0.05) in the middle and apical thirds in both analyses. Figure 1 shows the radiographic and photograph images of the decalcified and cleared specimens.

Table 1

Radiographic analysis of filling material penetration into the simulated lateral canals made in each third (mean percentages)

Table 2

Analysis of filling material penetration into simulated lateral canals made in each root third - photographs of decalcified and cleared specimens (mean percentages)

Figure 1

Images from the radiographic (a) and photographic (b) analyses of the decalcified and cleared specimens. Radiographic and photographic evaluation of lateral canals filling was performed by using image software

DISCUSSION

The obtained results confirmed the null hypothesis, once, the lateral canal filling with Resilon, when using thermomechanical compaction, presented better results than gutta-percha, especially in the middle and apical thirds.

The use of decalcified and cleared natural teeth[1721] allows three-dimensional analysis of the RCS while preserving the specimen's characteristics.[17] Radiographic analysis associated with analysis of decalcified and cleared specimens has also been performed by Almeida et al.,[16] who evaluated the flow of endodontic sealers after lateral condensation and reported that 8% of the fillings not visualized by radiographs could be detected in the cleared teeth. The artificial lateral canals had a diameter ranging from 80 to 100 μm, which is compatible with the range of 50 to 150 μm reported in other studies.[1115161819] These small differences in diameter did not affect the flow of the solid materials evaluated in the present study. After clearing and fabrication of lateral canals, teeth were subjected to dehydration and immersion in methyl salicylate. Thus, the root canal filling was performed on teeth with a resistant dentin.

In the present study, root canal sealer was not used to provide the filling ability of the root canal filling solid materials (gutta-percha and Resilon). Tanomaru-Filho et al.[20] evaluated the ability of gutta-percha and Resilon to fill simulated lateral canals by using the Obtura II system, and a similar methodology was used without the use of root canal sealer.

Among the materials evaluated, Resilon demonstrated the best ability to fill simulated lateral canals. These results are similar to those found in other studies that used different methodologies for lateral canals filling analysis using the Obtura II technique.[82022] Resilon showed results similar to Odous (thermoplastic) gutta-percha only in the coronal third, and both materials performed better than Dentsply (conventional) gutta-percha. In the apical third, Resilon presented filling percentages near 100%. The flow and plasticization of gutta-percha when filling lateral canals by thermomechanical compaction can be influenced by the manufacturing process. Michelotto et al.[19] evaluated thermomechanically compacted gutta-percha using endodontic sealer and observed greater lateral canal penetration for thermoplastic gutta-percha in the middle third, and for conventional gutta-percha in the apical third. In the present study, the ability to fill lateral canals by conventional gutta-percha cones (Dentsply) was lower than observed to thermoplastic gutta-percha cones (Odous), but no differences between these materials were observed in the middle and apical thirds.

Within the present study, the mean percentage of penetration into simulated lateral canals was 62.73%. Carvalho-Sousa et al.[12] observed a percentage of 62.70% using gutta-percha alone, similarly to the results from the present study.

Karr et al.[23] observed that gutta-percha and Resilon present similar ability to fill lateral grooves and depressions in natural teeth by warm vertical compaction. Contrastingly, Karabucak et al.,[24] using a thermoplastic delivery system, reported that Obtura Flow 150 gutta-percha was more effective in filling simulated lateral canals than gutta-percha. The present study shows that thermomechanical compaction was able to promote satisfactory lateral condensation of Resilon, as previously reported for gutta-percha.[3]

Introduction of the compactor up to 3 mm from the WL allows filling of the lateral canals placed at 2 mm from the WL, since the compactor is able to plasticize and compact material from 1 to 2 mm beyond its tip.[11] In the apical third, the temperature achieved by thermomechanical compaction is higher than on the coronal third.[14] This may explain the greater flow of Resilon in the apical third compared with both types of gutta-percha, despite the fact that both materials present similar melting points.[25] Therefore, the greater thermoplasticity of Resilon compared to that of both types of gutta-percha[7] results from its higher heat-induced flow rate.

CONCLUSION

Our findings showed that Resilon had better results than both types of gutta-percha, especially in the middle and apical thirds and, therefore, may be considered to be used as solid core material for root canal filling by thermomechanical compaction. However, further studies should be carried out in order to evaluate other properties.