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Year : 2019  |  Volume : 22  |  Issue : 9  |  Page : 1236-1240

Do separated instruments affect pH levels when using calcium hydroxide as intracanal dressing?

Department of Endodontics, Faculty of Dentistry, Trakya University, Edirne, Turkey

Date of Acceptance16-May-2019
Date of Web Publication6-Sep-2019

Correspondence Address:
Dr. B C Çanakçi
Department of Endodontics, Faculty of Dentistry, Trakya University, Edirne
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/njcp.njcp_180_19

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Background: The aim of this study was to evaluate the effect of intracanal separated instruments with different lenghts on periapical pH levels using calcium hydroxide (CH) as an intracanal medicament. Materials and Methods: In total, 60 teeth were used. Following root canal preparation, teeth were divided into four groups (n = 15). In Group 1, 2 mm and in Group 2, 4 mm weakened from the tip of Revo-S NiTi SC2 (Micro-Mega, Besancon, France) instruments were separated in the apical portion of root canals. In Group 3, there was no separated instrument. CH paste was placed in the first three groups. In Group 4, there was no separated instrument or CH paste. Teeth were placed in containers with deionized distilled water. After 1 h and 1, 2, 7, 15, and 30 days, the pH of the solution was measured. Results: At 1 h, Group 3 showed a significantly higher pH than Groups 1 (2 mm) and 2 (4 mm; P < 0.05). At the same time point, Group 1 (2 mm) showed a higher pH than Group 2 (4 mm) without significance. At 1, 2, 7, 15, and 30 days, Group 2 (4 mm) showed a significantly lower pH than Groups 1 (2 mm) and 3 (P < 0.05). At the same time points, Group 1 (2 mm) showed a lower pH than Group 3 without significance. Conclusions: Separated instrument may affect the rise in periapical pH level when using CH as the intracanal dressing. Therefore, 4 mm of separated instrument in the apical third showed a significant effect.

Keywords: Calcium hydroxide, intracanal medicament, pH, separated instrument

How to cite this article:
Çanakçi B C, Sungur R, Er &. Do separated instruments affect pH levels when using calcium hydroxide as intracanal dressing?. Niger J Clin Pract 2019;22:1236-40

How to cite this URL:
Çanakçi B C, Sungur R, Er &. Do separated instruments affect pH levels when using calcium hydroxide as intracanal dressing?. Niger J Clin Pract [serial online] 2019 [cited 2019 Sep 20];22:1236-40. Available from:

   Introduction Top

The separation of endodontic instruments may occur during root canal preparation [1] owing to the incorrect use or overuse [2] without any visible signs of file deformation,[3] even with unused new instruments.[4] NiTi instruments, which are more flexible and stronger than stainless-steel instruments,[5] may also separate, especially in narrow or curved canals;[6] this occurs in 1.3%-10.0% of cases.[3],[7] In several studies, separation was observed in every part of the root canal and frequently occurred in the apical third of the root canal.[3],[8],[9],[10]

Many techniques and systems have been suggested for the removal of separated instruments.[6] However, removing a separated instrument is challenging, especially from the apical third of the root canal. A lower removal success rate has been reported from the apical third versus the medium or coronal third of the root canal.[6] The management alternatives for separated instruments include bypassing the instrument, if not possible shaping and sealing the coronal part of the separated instrument, or retrograde endodontic surgery.[1],[11]

A retained instrument fragment may negatively affect prognosis by preventing adequate chemomechanical preparation, disinfection, or obturation of the root canal. In addition, the prognosis may be negatively affected if the root canal area harboring the instrument fragment is not cleaned sufficiently prior to separation.[12] A less favorable prognosis was reported in cases of separated instruments, wherein a preoperative periapical lesion was present.[7],[13]

Persistent infection or periapical inflammation may occur as a result of insufficient disinfection of the root canal system.[14] Therefore, calcium hydroxide (CH) has been widely used as an intracanal medicament. CH exerts antibacterial [15] and antiexudative effects,[16] induces mineralized tissue,[17] dissolves organic tissues,[18] absorbs CO2,[19] and inactivates bacterial endotoxin, both in vitro[20] and in vivo.[21] The effect of CH is directly attributed to its ability to dissociate into calcium and OH, resulting in locally increased pH.[22] In addition, the antibacterial effect of CH as an intracanal medicament is strongly associated with the direct contact between the medicament and microbial flora.[23] Therefore, CH must diffuse through the apical foramen, ramifications, accessory canals, and dentinal tubules, as well as areas contaminated by microorganisms and adjacent tissues, to reach the optimal pH level for its action.[22],[24] Several factors may affect the CH-induced pH level, such as the buffering effect of dentin [25] and the thickness of root canal dentin.[26] A decreased effect of CH might be attributable to a low pH level, limited solubility, and diffusibility of CH into the entire root canal system and dentinal tubules and, possibly, the presence of buffering ions in the tubules.[27] If the pH is inadequate, the intracanal dressing may not produce the expected effects or biological results.[28]

To the best of our knowledge, the relationship between separated instruments and the change in pH value caused by the application of an intracanal dressing has not previously been evaluated. In the present study, the effects of separated instruments, of different lengths, in the apical portion of the root canal, on apical pH while using CH as the intracanal dressing was evaluated. The null hypothesis tested was the presence of a separated instrument did not affect the apical pH level while using intracanal medicament.

   Materials and Methods Top

In total, 60 freshly extracted human mandibular central and lateral teeth were used. Radiographs were taken in the buccal and proximal directions to confirm the single root canal, mature apex, no resorption, no root canal calcification, and a root canal curvature of <10°.[29] External root surfaces were gently scaled to remove soft tissue remnants and calculi and rinsed with distilled water. Teeth with a width of 2–2.5 mm in bucco-lingual and mesio-distal directions at 2 mm far from the root tip were used. To standardize the length of specimens, all teeth were shortened to 12 mm by flattening the incisal edge, and a coronal access cavity was opened using a diamond bur (Diatech; Coltene Whaledent, Altststten, Switzerland) and a high-speed handpiece under water cooling. The working length (WL) was determined as 1 mm short of the length of a size 10-K file (Dentsply Maillefer, Ballaigues, Switzerland), so that the tip of the file was visible at the major apical foramen under an operating microscope (Opmi Pico; Carl Zeiss, Oberkochen, Germany). The teeth were coated with two layers of nail polish, except for the apical 3 mm region of roots.

The samples were randomly divided into four experimental groups (n = 15).

Group 1: Teeth were prepared with the Revo-S NiTi (Micro-Mega, Besancon, France) system using SC1 (#25, 0.06) in the coronal portion of the root canal and SC2 (#25, 0.04) to the WL, with rotating motion according to the manufacturer's recommendations. The apical canal patency was controlled with a 10-K file.

New Revo-S SC2 NiTi instruments were weakened 2 mm from the tip of files using a high-speed bur. The instruments were mounted into a handpiece and placed into the root canals to the WL; the handpiece was then activated. The instruments were separated at the weakened point by the rotating movement. The level and length of the separated instruments in the root canals were examined using radiographs. If the separated instrument was below or above the WL, the sample was replaced (In total, 9 replacements). After confirming the level of the separated instrument, the coronal part of the separated file was manually prepared to #50 with the step back technique up to #70.

During the instrumentation procedure, 5% NaOCl (Cerkamed Company, Stalowa Wola, Poland) was used for irrigation. For the final irrigation, 5 mL 17% EDTA (Cerkamed Company), 5 mL 5% NaOCl, and 10 mL distilled water were used. Then, the root canals were dried with paper points (VDW GmbH, Munich, Germany).

A CH paste mixed with propylene glycol, with a ratio of 1 g of powder to 0.4 mL of liquid, was placed into the root canals using a lentulo spiral size #30 (Dentsply Maillefer, Ballaigues, Switzerland) located 6 mm deep from the coronal tip of the root. The placement of intracanal dressing was confirmed with radiographs. Access cavities were sealed with composite resin, and the crowns were sealed with two layers of nail polish.

Further, teeth were placed in containers with 10 mL deionized distilled water. The containers were stored in an incubator at 37°C with 100% humidity. After 1 h and 1, 2, 7, 15, and 30 days, the pH of the solution in the containers was measured using a pH meter (Hanna 83141; Hanna Instruments, Woonsocket, RI, USA) that was calibrated before each measurement with known pH (4, 7, and 14) solutions. After every measurement, the teeth were placed in new containers with fresh deionized distilled water with a pH of 6.9.

Group 2: Same procedure as in Group 1, but the length of the separated instruments was set to 4 mm.

Group 3 (Positive Control Group): There was no separated instrument. Teeth were manually prepared to #50 using the step back technique up to #70 of the WL. Then, the CH paste was placed and pH measurements were taken, as in Group 1.

Group 4 (Negative Control Group): Same procedures as in Group 3 but without placement of CH paste.

Statistical analysis

Data were subjected to one-way analysis of variance and the Tukey test using SPSS software (ver. 22.0; SPSS Inc., Chicago, IL, USA). A P value < 0.05 was considered to indicate statistical significance.

   Results Top

[Table 1] shows the means and standard deviations of pH for the groups at different time points.
Table 1: Means and standard deviations for pH of the groups in the different periods

Click here to view

At all time points, Groups 1-3 showed a significantly higher pH than Group 4 (Negative Control; P < 0.05). At 1 h, Group 3 (Positive Control) showed a significantly higher pH than Groups 1 (2 mm) and 2 (4 mm; P < 0.05). In addition, at the same time point, Group 1 (2 mm) showed a higher pH than Group 2 (4 mm), but the difference was not significant (P > 0.05).

At 1, 2, 7, 15, and 30 days, Group 2 (4 mm) showed a significantly lower pH than Groups 1 (2 mm) and 3 (Positive Control; P < 0.05). In addition, at the same time points, Group 1 (2 mm) showed a lower pH than Group 3 (Positive Control), but the difference was not significant (P > 0.05).

   Discussion Top

The separation of endodontic instruments may occur without any visible signs [3], even with new instruments.[4] The attempt of removal mostly fails in the apical third of the root.[6] Separated instrument may affect the prognosis, especially in the presence of a preoperative periapical lesion.[1],[7],[30] The effect of CH as an intracanal dressing is related to its high pH.[22] No studies evaluated the effect of CH as intracanal dressing on periapical pH in the presence of seperated instruments. Thus, in this study, the effect separated instruments in the apical portion of root canal with different lengths, on periapical pH when using CH as intracanal dressing was evaluated.

In our study, NiTi files were used as separated files because they are more difficult to remove compared with stainless-steel instruments.[6],[31] In addition, the separated instruments were placed in the apical third of the root canal. Although instrument fracture may occur in any part of the root canal, it is most frequently observed in the apical third.[3],[8],[9],[10] In addition, lower success rates for removal of the separated instrument from the apical third of the root canal have been reported.[6] In our study, the lengths of the separated instrument parts were set to 2 and 4 mm; because in several studies, the NiTi files separated on average at 2-4 mm from the tip.[9],[10],[32] On the basis of the results from our study, after placing the CH dressing, the pH value increased rapidly in every experimental group at 1 h and 1 day, similar to the results of Zmener et al.[33] This rapid pH increase may be caused by the fast alkalinizing effects of CH, arising from its immediate contact with the root canal and resulting in instantaneous release of OH.

At 1 h, Group 3 (Positive Control) showed significantly higher pH values than Groups 1 (2 mm) and 2 (4 mm). The apical foramen is considered the main pathway for OH diffusion.[34] In the presence of a separated instrument, the instrument fragment may occlude the root canal pathway; thus, OH may not diffuse into the apical portion from the apical foramen.

At 1, 2, 7, 15, and 30 days, Group 2 (4 mm) showed a significantly lower pH values than Groups 1 (2 mm) and 3 (Positive Control). The pH on the outside of dentin is dependent on the distance that the OH have to breach.[35] Increase in the length of the separated instrument may cause the distance between the CH dressing and area outside of the root to increase. In addition, the increased distance to the apical delta may cause a decrease in ramifications and branching, which could, in turn, affect OH diffusion. Furthermore, in Group 2 (4 mm), the dentin in the root canal was thinner than in Group 1 (2 mm). Reportedly, increased thickness of dentin may decrease OH diffusion through dentin.[26] Moreover, the smear layer around separated instrument that may be formed during instrument separation procedure and cannot be removed by intracanal irrigation [36] may affect the OH diffusion. In addition, the smaller amount of CH dressing used in Group 2 (4 mm) may have caused less OH ionization.

At 1, 2, 7, 15, and 30 days, the pH levels in Group 1 (2 mm) were lower than those in Group 3 (Positive Control) without significance. Although the separated instruments in Group 1 may have inhibited diffusion of OH, as previously mentioned,[34] the complicated branching and ramification system in the apical delta may be an additional pathway for OH to reach the outer root surface.

In our study, pH reached peak levels within 30 days in every experimental group, possibly because CH requires 1-7 days to reach the outer dentin and pH requires 2-3 weeks to reach peak levels.[37] In addition, pH levels remained high for 30 days in every experimental group. Although dentin has a buffering effect that may inactivate the alkalinizing effect of CH,[37] this was not observed in our study, which was similar to the results of a previous study,[19] possibly owing to the strong alkalinizing effect of CH.

There are several limitations for this study. The thickness of cementum and dentine, the number of canal exits, and ramifications may affect the diffusion of OH ions. These can be determined using histological or micro-CT evaluations, which were not performed in this study. The snugness of fit between separated instrument and dentin affects the penetration of intracanal dressing. However, in this study, the instrument separation is artificial, so the squeeze can not totally duplicate a clinical instrument separation. In addition, the area of contact between the separated instrument and the prepared apical dentinmay affect the penetration of intracanal dressing, which was not evaluated in this study.

Within the limitations of this study, although there is no significant difference in the increase of pH between 2 mm of separated file group and positive control group at all time points (except 1 h), a significant difference is observed between 4 mm separated file group and other groups at all time points. Further investigations are needed to analyze the microbiologic activities of CH in the presence of separated instrument with prolonged intracanal dressing time.

   Conclusions Top

On the basis of the results from our study, 4 mm of separated instrument in the apical third of the root canal may affect the apical pH level when using CH as the intracanal dressing, which may negatively affect the prognosis. To obtain an adequate effect of CH as an intracanal dressing in the presence of separated files, extending the intracanal dressing time should be considered.

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Conflicts of interest

There are no conflicts of interest.

   References Top

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