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One of the main concerns and, consequently, one of the main objectives of endodontics is the accomplishment of thorough disinfection of the root canal system.

The presence of microorganisms and their endotoxins are the factors responsible for the appearance and maintenance of the periapical and pulp pathology.

Thus, endodontic treatment usually requires the use of an intracanal dressing between appointments in order to potentiate the root canal disinfection process and so favor periapical repair.

Calcium hydroxide is one of the most-used intracanal dressings as it acts on microbe control, organic dissolution, inflammation and resorption control, as well as on the process of mineralized tissue formation (Holland et al, 1995; De Souza et al, 2005).

However, some studies, such as Kim and Kim (2002), have questioned the difficulty in the complete removal of calcium hydroxide from the root canal walls. According to Calt and Serper (1999) and Khedmat and Shokoubinejad (2008), the presence of residual calcium hydroxide inside the canal during the obturation stage might hinder the penetration of endodontic cement in the dentinal tubules and interfere with the sealing quality of the obturating material.

With this in mind, the present study aims to analyze the performance of two methods for the removal of calcium hydroxide from the root canal walls.

Materials and methods
Thirty-five single-rooted teeth were used in this study, distributed randomly into two experimental groups of 15 each, according to the technique employed for removing the intracanal dressing. The third group, comprising five teeth, was considered control.

After determining the working length (WL), the canals were prepared by just one operator with a serial technique. For the preparation, instruments such as first series FlexoFile® (Dentsply/Maillefer Ballaigues, Switerzerland) were used, with the help of the Endo-Gripper oscillatory system (Moyco/Union Broach) with 16:1 speed reduction, where the final apical size was standardized at 40 ISO.

The root canal irrigants used were sodium hypochlorite solution at 1% (ULBRA School Pharmacy, Canoas, Brazil) alternated with EDTA at 17% (ULBRA School Pharmacy, Canoas, Brazil).

Once the preparation process was completed, the canals were dried using absorbent paper points (Tanari Industrial Ltd, São Paulo, Brazil), then the calcium hydroxide-based intracanal dressing (Calen, SS White, Rio de Janeiro, Brazil) was applied, according to the manufacturer’s instructions, followed by the coronal sealing with cotton and Coltosol® (Coltène Whaledent, Switzerland).

The teeth in the control group were prepared but did not receive the intracanal dressing. Periapical x-rays were taken in order to check whether the root canal had been completely filled with the intracanal dressing.

The teeth were then immersed in saline solution (ULBRA School Pharmacy, Canoas, Brazil), for 14 days at 37oC in an incubator (Fabbe-Primar Equipamentos e Serviços Ltd, São Paulo, Brazil) with a 100% average humidity environment.

The teeth were then opened and the dressing was removed as follows:

  • Group 1: Removal of the Calen paste with the help of 2 mL of sodium hypochloride at 1% + final apical file + 2 mL sodium hypochlorite at 1% final washout.
  • Group 2: Removal of the Calen paste with the help of 2 mL of sodium hypochlorite at 1% + final apical file + 2 mL of EDTA at 17%, which was agitated (stirred) for 3 minutes + 2 mL sodium hypochlorite at 1% final washout.

fig1In both groups, removal was considered completed when, during the washout process, vestiges of dressing were no longer observed.

After that, the teeth were sectioned in the lingual or palatal directions, and the best hemisection was selected and analyzed under a 4× enlargement magnifying glass (Bioart, São Paulo, Brazil) by two trained and calibrated examiners, regarding the presence or absence of calcium hydroxide on the walls of the canals at the apical, middle, and cervical third levels (Figure 1).

Kappa calculus was used for the examiners’ calibration, and the results obtained were submitted to statistical analysis using the Fisher exact test with 5% significance.

Results
The results obtained regarding the presence or absence of the intracanal dressing on the canal walls are presented in Tables 1, 2, and 3.table1

It was possible to show after analyzing the root canal walls at the cervical and middle thirds, that there was no significant statistical differences in the presence of calcium hydroxide between the two experimental groups (p = 0.651).

The analysis of the apical third showed a significant statistical difference between the two experimental groups (p = 0.028). Group 1 presented a higher percentage of cases with the presence of calcium hydroxide on the canal walls than Group 2.

Discussion
For a good seal of the obturating material, it is important that the surface of the root canal be free of residues, including the intracanal dressing (Holland et al, 1995).

With this in mind, the present study was designed to analyze the capability of two different methods of removing intracanal dressing from the root canal walls. According to the literature, there is no single technique to completely remove the calcium hydroxide from the root canal (Lambrianidis et al, 1999; Pécora et al, 2002; Lambrianidis et al, 2006).

table2Some studies have tested different methods for the  removal, such as using sodium hypochlorite solution and EDTA (Tatsuta et al, 1999; Kim and Kim, 2002; Silva et al, 2009) with rotary endodontic files (Souza, 2008) and the ultrasound system (Guerisoli et al, 2002; Sabins et al, 2003; Keene et al, 2006).

The results obtained showed that none of the methods tested managed to completely remove the intracanal dressing on the root canal walls, agreeing with the studies of Prokopowitsch (2000) and Silva et al (2009), who have verified the same situation.

In the present study, the analysis of the apical third of the canals demonstrates a greater presence of calcium hydroxide. This can be justified by the difficulty in removing the dressing in this region. This aspect has also been observed and pointed out in the studies carried out by Margelos et al (1997) and Lambrianidis et al (1999).

According to Silva et al (2009), as one gets closer to the apical third, there is greater difficulty and less efficacy in the removal of the intracanal dressing—often due to anatomical complexities in this region.

Improved efficiency in removing calcium hydroxide is achieved by combining sodium hypochlorite with EDTA. This is due to the power of the EDTA calcium ion in chelation.

For some authors (McComb and Smith, 1975; Meryon and Brook, 1990), EDTA is an excellent chelator as it removes smear layer, resulting in cleaner dentinal walls andScreen_shot_2011-07-05_at_3.24.27_PM more open dentinal tubules.

On the other hand, some studies, such as Lambrianidis et al (1999) and Silva et al (2009), observed that combining sodium hypochlorite with EDTA did not present any statistically significant difference regarding the capacity to remove calcium hydroxide from the root canal walls.

Thus, it is advisable to carry out further studies so that new techniques and chemical substances with a greater capacity of intracanal dressing removal can be found, so a greater probability of attaining chemical and biological success in endodontic obturation will result.

Conclusion
From the results of this study, it can be concluded that:

  • Neither of the two methods managed to completely remove calcium hydroxide from the root canal walls at all levels
  • The apical third presented the worst results as to the presence of calcium hydroxide on the root canal walls than the cervical and middle thirds
  • Regarding the method for the removal of calcium hydroxide, the association of sodium hypochlorite and EDTA appeared to be more efficient than the use of just sodium hypochlorite alone.

 

Authors

Elias Pandonor Motcy de Oliveira, PhD in endodontics, is a teacher at Universidade Luterana do Brasil – Canoas/RS, Brazil.

Mário Luiz Pinto de Queiróz, MSc in endodontics, is a teacher at Universidade Luterana do Brasil – Canoas/RS, Brazil.

Tiago André Fontoura de Melo, MSc in endodontics, is from the school of dentistry, Universidade Luterana do Brasil – Canoas/RS, Brazil.

Aline Michele Gallas is a dentist at the school of dentistry, Universidade Luterana do Brasil – Canoas/RS, Brazil.

Taline Silva Marchetti is a dentist at the school of dentistry, Universidade Luterana do Brasil – Canoas/RS, Brazil.

 

References

Calt S, Serper A (1999) Dentinal tubule penetration of root canal sealers after root canal dressing with calcium hydroxide. J Endod 25(6):431-433.

De Souza CA, Teles RP, Souto R, et al (2005) Endodontic therapy associated with calcium hydroxide as an intracanal dressing: microbiologic evaluation by the checkerboard DNA-DNA hybridization technique. J Endod 31(2):79-83.

Guerisoli DMZ, Marchesan MA, Walmsley AD, et al (2002) Evaluation of smear layer removal by EDTAC and sodium hypochlorite with ultrasonic agitation. Int Endod J 35(5):418-421.

Holland R, Murata SS, Saliba O (1995) Efeito a curto é médio prazo dos resíduos de hidróxido de cálcio na qualidade do selamento marginal após a obturação de canal. Rev Paul Odontol 17(2):12-16.

Khedmat S, Shokouhinejad N (2008) Comparison of the efficacy of three chelating agents in smear layer removal. J Endod 34(5):599-602.

Kenee DM, Allemang JD, Johnson JD, et al (2006) A quantitative assessment of efficacy of various calcium hydroxide removal techniques. J Endod 32(6):563-565.

Kim SK, Kim YO (2002) Influence of calcium hydroxide intracanal medication on apical seal. Int Endod J 35(7):623-628.

Lambrianidis T, Margelos J, Beltes P (1999) Removal efficiency of calcium hydroxide dressing from the root canal. J Endod 25(2):85-88.

Lambrianidis T, Kosti E, Boutsioukis C, et al (2006) Removal efficacy of various calcium hydroxide/chlorhexidine medicaments from the root canal. Int Endod J 39(1):55-61.

Margelos J, Eliades G, Verdelis C, et al (1997) Interaction of calcium hydroxide with zinc oxide-eugenol type sealers: a potential clinical problem. J Endod 23(1):43-48.

McComb D, Smith DC (1975) A preliminary scanning electron microscopic study of root canals after endodontic procedures. J Endod 1(7):238-242.

Meryon S, Brook A (1990) Penetration of dentine by three oral bacteria in vitro and their associated cytotoxicity. Int Endod J 23(4):196-202.

Pécora JD, Barbin LE, Spano JCE, et al (2002) Remoção de pastas de hidróxido de cálcio do interior dos canais radiculares. Rev Bras Odontol 59(1):133-135.

Prokopowitsch I (2000) Influência do uso do hidróxido de cálcio como medicação intracanal na permeabilidade e limpeza dentinária radicular em dentes portadores de rizogênese incompleta. Ecler Endod 2(1):1-78.

Sabins RA, Johnson JD, Hellstein JW (2003) A comparison of the cleaning efficacy of short-term sonic and ultrasonic passive irrigation after hand instrumentation in molar root canals. J Endod 29(10):674-678.

Silva JM, Cruz HM, Araújo LM, et al (2009) The evaluation of removal of calcium hydroxide using different irrigation methods. Rev Odontol UNESP 38(1):37-43.

Souza SSB (2008) Análise comparativa entre as limas Kerr manuais e limas rotatórias profile para remoção de hidróxido de cálcio dos canais radiculares. [Monografia]. Petrópolis: Associação Brasileira de Odontologia – Regional Petrópolis.   

Tatsuta CT, Morgan LA, Baumgartner JC, et al (1999) Effect of calcium hydroxide and four irrigation regimens on instrumented and uninstrumented canal wall topography. J Endod 25(2):93-98.

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Research has shown that irrigants are more effective when they are electro-mechanically activated.

Acoustic streaming and cavitation have been proven to significantly enhance cleaning of difficult anatomy. Studies have shown that low frequency (Sonic) oscillation (160-190Hz) was not sufficient to create acoustic streaming or cavitation within the canal space.

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