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Year : 2015  |  Volume : 18  |  Issue : 3  |  Page : 257-260
Intra-canal calcium hydroxide removal by two rotary systems: A comparative study

1 Department of Endodontics, School of Dentistry, Islamic Azad University, Tehran, Iran
2 Department of Oral and Maxillofacial Pathology, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran
3 Dentist, Tehran, Iran
4 Department of Endodontics, School of Dentistry, Kermanshah University of Medical Sciences, Kermanshah, Iran

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Date of Submission16-Sep-2014
Date of Decision12-Feb-2015
Date of Acceptance30-Mar-2015
Date of Web Publication19-May-2015


Aim: The presence of calcium hydroxide (Ca(OH) 2 ) in the root canal interferes with the apical root canal sealing and may result in periapical lesions in the long run. The present study was aimed to compare the efficacy of two rotary systems of Race and Mtwo in the removal of Ca (OH) 2 aqueous-based from distobuccal canals of human maxillary molars.
Materials and Methods: A total of 44 distobuccal root canals of human maxillary molars were randomly distributed into two groups of 20 canals each and two control groups. Specimens in each group were instrumented with similar master apical rotary (MAR) and flexible files according to the manufacture's guidelines. The Ca (OH) 2 paste was placed in canals using # 20 lentulo and radiographs were taken from the two dimensions. The roots were incubated for 1 week at 37°C and 100% humidity and Ca (OH) 2 was removed from canals by MAR, afterward. Then, the roots were longitudinally split in halves by diamond disk and chisel without entering the root canals. Photos were taken from the canals' walls by a stereomicroscope with × 10 magnification. Next, according to a defined scoring system, photos were scored by four endodontists, so that scores 1 and 2 (nonvisible remnants or scattered remnants of Ca(OH) 2 ) were considered as acceptable and scores 3 and 4 (distinct mass or densely-packed mass of Ca(OH) 2 ) were regarded as nonacceptable.
Results: The obtained findings indicated that in coronal, middle, and apical portions of the root canal, 45, 60, and 65% of Mtwo specimens and 40, 50, and 55% of specimens prepared by the Race system acquired an acceptable score (1 and 2), respectively. Moreover, the results showed no significant difference between the two groups (P > 0.05).
Conclusions: Both Mtwo and Race rotary systems with acceptable removal efficiency (score 1 and 2) were similarly able to remove Ca(OH) 2

Keywords: Calcium hydroxide; mtwo rotary systems; race; race rotary systems

How to cite this article:
Dadresanfar B, Abbas FM, Bashbaghi H, Miri SS, Ghorbani F. Intra-canal calcium hydroxide removal by two rotary systems: A comparative study. J Conserv Dent 2015;18:257-60

How to cite this URL:
Dadresanfar B, Abbas FM, Bashbaghi H, Miri SS, Ghorbani F. Intra-canal calcium hydroxide removal by two rotary systems: A comparative study. J Conserv Dent [serial online] 2015 [cited 2022 Jul 6];18:257-60. Available from:

   Introduction Top

Existence of microorganisms, their products, or necrotic pulp tissue can cause pathologic changes, several lesions, and bone resorption in the periradicular tissues. Therefore, one of the most important goals of dentistry treatment is elimination of microorganisms. In a root canal therapy attempts should be made to eliminate microorganisms existing in root canal by different chemical and pharmaceutical methods. [1],[2] Calcium hydroxide (Ca(OH) 2 ) was first introduced into endodontics by Herman in 1920. [3] Todays, Ca(OH) 2 is widely used to disinfect the root canal system because of its alkaline pH. [4],[5] If the Ca(OH) 2 is not completely removed prior to obturation, then it has negative effect on root canal therapy success [6],[7],[8],[9] because it interferes with zinc oxide-eugenol (ZOE) based sealers and results in reduced setting time as well as crack in the sealer because it is loosened faster. Moreover, it prevents penetration of the sealer into porosities of the canal wall and reduces adjustment of sealer with canal, which results in microleakage in canal in the long time. [10] Previous studies have mostly investigated various irrigation techniques to remove Ca(OH) 2 . [10] Some studies, however, have compared the efficacy of manual files, ultrasonic systems, and rotary files; [11],[12] and have reported different results about the effect of irrigation techniques by mechanical instruments.

Rödig et al., (2011) conducted a study on ultrasonic system and Rinsendo system to remove Ca (OH) 2 inside the canal. [13] Further, Kuga et al., (2010) carried out a study in which he used a combination of rotary system and different irrigants. [14] With regard to the consequences resulting from Ca (OH) 2 left in the canal, different removal methods are recommended to be investigated in order to find the best and most efficient technique in order to ensure complete removal of this substance from the canal wall. Nowadays NiTi rotary system cause predictable shaping and adaptable to root canal system. Race and Mtwo are two of these systems' generation. These files are made from NiTi which are very flexible and without making fatigue in files. It can follow the root canal shapes and decrease the possibility file fracture. [15] Hence, the present study was conducted to examine the effect of Mtwo and Race rotary systems on the removal of Ca (OH) 2 aqueous-based within the canal at school of dentistry, Islamic Azad University.

   Materials and Methods Top

In this experimental study, 44 extracted maxillary molars were collected from different medical centers in Tehran. The teeth with external resorption, caries, root calcification, and undeveloped apex were excluded from the study. Scaling was done on other samples by a hand scaler. To prepare the canals more easily, the dental crown was cut by a diamond disk (D&Z, Diamant, Germany) along with a cooling spray, [16] so that all the samples had an equal root length of 12 mm. A # 10 K file (Maillefer Dentsply, Switzerland) was inserted in the distobuccal canal to the end of the root. The teeth were then fixed buccolingually on the wax and radiographs were taken using E speed film at radiation of 0.6 s and fixed distance of 15 cm. [17] All radiographs were taken by a trophy (Carestream Dental, GA, USA) with 65 kV/10 mA. Using these radiographs, the teeth with internal resorption and those with a curve outside the limit of 15-25° were excluded from the study. Schneider's technique was used to measure the canal curvature [18] and # 10 K file was used to determine the working length; # 15 K file, however, was used as the primary file. To prepare the canal, two rotary systems of Mtwo and Race were used for each group separately. To this end, the teeth were divided into Group A (Race system) and Group B (Mtwo system), each including 20 samples.

In all stages of preparation in Groups A and B, two positive samples (where Ca (OH) 2 was inserted in the canal, but was not removed) and two negative samples (where Ca (OH) 2 was not inserted in the canal after preparation) were used, 2 ml 2.5% sodium hypochlorite was used by 27-gauge needle (Iran, Supa) between filing procedures. During the filing intervals, # 10 K file was put through to ensure apical patency. Canal preparation was performed by Endo-Mate Dt electric motor (NSK, Japan).

In these two groups, based on the size of the files and their convergence, the filing sequence was selected so that the files' convergence and numbers were consistent in both systems. To this end, in the Race system, the file 35 with 8% taper, file 30 with 6% taper, and then file 25 with 6% taper, and files 25, 30, and 35 with 4% taper were used for the coronal, middle, and apical regions, respectively; where file 35 with 4% taper was considered as master apical rotary (MAR). In this group, low-speed handpiece with a speed of 300 rpm and a torque of 2/3 was utilized.

In Mtwo rotary system, the files 15 with 5% taper, 20 and 25 with 6% taper, 25 with 7% taper, 30 with 5% taper, and 35 with 4% taper were used. For more coordination and elimination of influential background variables, the last file used for apical (MAR) preparation as well as the speed and torque of the handpiece were the same as those of Group A.

Then to get a better visual in radiography, Ca (OH) 2 powder containing barium sulfate called Calci Pex (Tehran Etekal, Iran) was mixed with normal saline and a consistent paste was obtained. The obtained paste was inserted in the prepared canals counterclockwise using a # 20 lentulo. To ensure the canal is fully filled, two radiographs were taken buccolingually and mesiodistally. Then, the cotton ball and Cavizol dressing (Arya Dent, Iran) with minimum thickness of 3-4 mm were inserted. The samples were incubated at 37°C and 100% humidity for 7 days. Next, the dressings were removed by excavator and Ca(OH) 2 was removed by the Race rotary system using MAR file and Mtwo rotary system in Groups A and B, respectively. Also, 2 ml 2.5% sodium hypochlorite and # 10 K file were utilized in the filing intervals to ensure patency. In all samples, two longitudinal grooves were made in the buccal and lingual regions by a diamond disk and the roots were split into halves from the created groove by a chisel (Aesculap, Inc., PA, USA) without the disk entering the canal. [18] The samples were then analyzed by stereomicroscope (Olympus SZX9, Japan) at 10 × magnification and photographed by a digital camera (Alphaphot 2, YS-Nikon, Japan). To evaluate the remnants of Ca (OH) 2 on the canal wall, the following classification system was used.

Absence of remnants (score = 1), scattered remnants (score = 2), mass remnants (score = 3), and densely-packed remnants (score = 4). [19] Having made the longitudinal section and having taken the photo using stereomicroscope by four specialists, each sample was blindly scored. The photos were evaluated in three coronal, medial, and apical regions; so that the root length (12 mm) in all samples was divided into three equal parts. Scores 1 and 2 were considered as acceptable and scores 3 and 4 were regarded as unacceptable. The obtained data were analyzed by analysis of variance (ANOVA) statistical test and P < 0.05 was considered significant.

   Results Top

In the present study, various amounts of Ca(OH) 2 were found on the wall of the prepared canals in each testing group. Clean walls with no trace of Ca(OH) 2 were found in the two samples of negative control and Ca(OH) 2 sediment was clearly observed on the canal's walls. No significant difference was found between the overall performance of both systems in terms of the amount of residual (P > 0.05). Mtwo and Race groups indicated an acceptable ability to clean Ca(OH) 2 in all regions by obtaining 53.6 and 51.3% of total scores (1 and 2), respectively.

The findings obtained for the amount of the remnant in the coronal region showed that 45% of the Mtwo samples and 40% of Race samples gained an acceptable score (1 and 2); however, the difference between groups was not statistically significant (P > 0.05). In the middle portion of canal, four Mtwo samples and two Race samples from the total 20 samples acquired the score of 1. The findings of Race group indicated that half of the samples had been favorably cleansed, but the difference between groups was not statistically significant in terms of removal capability (P > 0.05). The amount of Ca(OH) 2 remained in the apical region of canals in both Race and Mtwo systems was less than 50% and more than half of the samples in this region obtained an acceptable score (1 and 2; Race = 55% and Mtwo = 65%); although, the difference between groups was not statistically significant (P > 0.05) [Table 1].
Table 1: Frequency of calcium hydroxide in terms of regions and testing groups

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   Discussion Top

The findings of present study indicated that 51.3% of samples in the Race group had been cleaned from Ca (OH) 2 and 53.6% of the samples prepared by Mtwo rotary file had been acceptably cleaned from Ca (OH) 2 , which showed no statistically significant difference between groups.

Nandini et al., (2006) reported that in the comparison between 17% ethylenediaminetetraacetic acid (EDTA) and 10% citric acid, the chelator in citric acid removed higher amount of Metapex (a kind of Ca(OH) 2 ) from the canal's wall. However, in this study only the canal irrigation techniques were used.

Further, De Faria et al., (2012) conducted a study to compare the effects of 2.5% NaOCl, 17% EDTA, 2% chlorhexidine (CHX) and polypropylene glycol on aqueous-based and oil-based Ca(OH) 2 removal. The results revealed that none of the substances was able to completely remove Ca(OH) 2 from the canal. [20]

The author, however, recommended the application of manual files, which led the authors to use this technique in the present study. [10]

Moreover, Lambrianidi and Margelos (1999) showed that using Gates Glidden drills is more effective than irrigation with NaOCl and EDTA to remove Ca(OH) 2 from the canal. However, they mentioned the risks of using this instrument in curved canals, so that they selected their samples in the curve range of 5-10° to access the whole length of canal without damaging the canal wall. [21] Kenee et al., found rotary instrumentation better than hand instrumentation for removal of Ca(OH) 2 . [22] In the present study, the curve range of 15-25° was taken into account to reduce the amount of error. Moreover, the higher capability of mechanical instruments made us to compare two rotary systems of Race and Mtwo. Several studies have reported that flute design and cross-section of the files are important factors in efficacy of debris removal. [23] Race rotary file has three cutting edges and is triangular in its cross-section. However, Mtwo rotary file has two cutting edges and wide empty space between cutting edges makes the instrument more flexible. This structure helps debris removal from the root canal. [23] The another characteristic of files effective in the performance is Rake angle, that is, the angle of dentin removal from the canal walls. The maximum performance of file is when that angle neutral or slightly positive. Race has negative angle but in Mtwo this angle is positive. [22] Pitch length is also an effective factor in collection and removal of material from the canal. Pitch is the number of torsion in unit length that the fewer this number, the wider the pitch length; therefore, the more space is available for collection of materials. [23]

In another study, Abou-Rass and Piccinino reported that low-gauge needle should be used to let the irrigant reach the end of canal and get a better irrigation performance. They argued that merely irrigation is not sufficient and other techniques such as reaming motions during filing and patency file should be used to constantly keep the canal open in order to enhance the irrigation efficacy. [24]

In addition, Kuga et al., (2010) compared different rotary systems in combination with various irrigants and reported that ProTaper was more efficient to remove Ca(OH) 2 inside the canal than K3 file. However, none of the techniques used in the study was able to remove Ca(OH) 2 from the canal wall, [14] which is in line with the findings of the present study in which none of the systems in combination with irrigator could fully remove Ca(OH) 2 in the canal.

Ca(OH) 2 is an intracanal pharmaceutical substance that has various clinical uses. To mix Ca(OH) 2 , the vehicle which is highly responsive for the velocity of ionic dissociation is used; [25] however, there's a debate on its difficulty removal influence. [10],[12],[20] The most important effect of Ca(OH) 2 is reduction of specific pathogens that lead to pulp necrosis. The success of this material depends on its base pH and quick bonding strength of its hydroxyl ions and calcium. The important point, however, is that this material should be fully removed before permanent filling of the canal, because the debris of Ca(OH) 2 in canal results in the increased ZOE base sealer setting and consequently disturbance in appropriate translocation of gutta percha and reduction of the bonding strength of the filling material when it penetrates into the porosities of the canal wall. In addition, Ca(OH) 2 is soluble and if it occupies some space, it can be dissolved over time and presence of an empty space causes microleakage and consequently endodontic treatment failure. [26] Hosoya et al., (2004) concluded that contact with Ca(OH) 2 left on the canal wall caused considerable changes to the sealing ability of sealers. [27]

Ricucci and Langeland reported a case with endodontic treatment failure due to incomplete removal of Ca(OH) 2 . [6] So far, no study has been carried out to compare two or more rotary files to remove Ca(OH) 2 . However, various studies have compared Race and Mtwo files to remove the debris in the canal such as the study conducted by Schafer et al., in which Race, Mtwo, and K3 were compared and the results showed Mtwo file was more efficient to remove debris than Race file, although the difference was not statistically significant. But, 53% of Mtwo samples in the present study obtained the scores of 1 and 2, which is similar to the findings obtained in the study performed by Schafer et al. In both studies, the apical portion of canal was effectively cleansed by Mtwo file. In the present research, Mtwo file with lower number of pitches, [23] positive cutting angle, [15] and S-form cross section [28] indicated a more cleansing strength than Race file, although the difference was not statistically significant.

   Conclusion Top

The results of the present study indicated that both Race and Mtwo rotary systems with acceptable removal efficiency were similarly able to remove Ca(OH) 2 . Moreover, there was no significant difference between the two rotary systems in removal of Ca(OH) 2 from the root canal.

   References Top

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Correspondence Address:
Dr. Shima Sadat Miri
Department of Endodontics, School of Dentistry, Kermanshah University of Medical Sciences, Kermanshah
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0972-0707.157268

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