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Year : 2012  |  Volume : 15  |  Issue : 2  |  Page : 113-117
Effect of the smear layer in the removal of calcium hydroxide from root canal walls

Department of Restorative Dentistry and Endodontics, Faculty of Dentistry, Ataturk University, Erzurum, Turkey

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Date of Submission09-Jun-2011
Date of Decision05-Nov-2011
Date of Acceptance09-Dec-2011
Date of Web Publication2-Apr-2012


Background: The aim of this study was to investigate whether the smear layer influences the removal of calcium hydroxide from the root canal with manual or rotary instruments.
Materials and Methods: The root canals of 48 freshly extracted single-rooted maxillary incisors were prepared to apical size 40 (n=40) and finally irrigated with sodium hypochlorite (group A), or ethylene diamine tetra acetic acid (EDTA) followed by sodium hypo chlorite (group B). 20 teeth were assigned to each group, while the remaining eight teeth served as positive and negative controls. Each group was divided into two subgroups of 10 teeth (subgroup I - calcium hydroxide was removed with master apical file; subgroup II - with profile file); and, in all removal procedures, citric acid was used for irrigation. The percentage of calcium hydroxide-[Ca(OH) [Ca(OH) 2 ] coated surface area was calculated by image processing analysis.
Results: Considering the root canal as a whole, the removal of Ca(OH) 2 from the dentinal walls in group B showed significantly better results (P<0.05) as compared to group A.
Conclusions: Under the conditions of this study, it can be concluded that the smear layer is important in the removal of calcium hydroxide.

Keywords: Calcium hydroxide removal; rotary instruments; smear layer

How to cite this article:
Arslan H, Topcuoglu H S, Karatas E, Barutcigil C, Aladag H, Topcu K M. Effect of the smear layer in the removal of calcium hydroxide from root canal walls. J Conserv Dent 2012;15:113-7

How to cite this URL:
Arslan H, Topcuoglu H S, Karatas E, Barutcigil C, Aladag H, Topcu K M. Effect of the smear layer in the removal of calcium hydroxide from root canal walls. J Conserv Dent [serial online] 2012 [cited 2022 Jan 17];15:113-7. Available from:

   Introduction Top

It is necessary to provide a sterile root canal for successful root canal treatment. The removal of debris by using mechanical instrumentation may not always succeed in complete cleaning because of morphological and physical barriers. Consequently, the use of numerous irrigating solutions and antimicrobial temporary dressing materials is recommended for additional benefit. [1],[2] Calcium hydroxide [Ca(OH) 2 ] has been used in dentistry for almost a century. [3] The routine use of Ca(OH) 2 as an inter-appointment intracanal medicament has become widespread [3],[4] owing to its bacteriological control of the canal environment, dissolution of soft tissue debris, promotion of the drying of weeping periapical lesions, and good biocompatibility. [3],[5],[6],[7] Ca(OH) 2 is kept into the root canal for various time periods (6 to 24 months for apexification and 1-4 weeks for intracanal medicament). [8] Regardless of the aim of its use, Ca(OH) 2 in the root canal has to be removed completely before the root canal filling.

Hosoyaet al. [9] demonstrated that the sealing ability of Sealapex improved with the Ca(OH) 2 , which influenced the physical properties of other sealers used in their study. The other previous reports have demonstrated that remnants of Ca(OH) 2 reduce the bond strength of a resin-based sealer to root canal dentin, [10] interfere with the sealing ability of a silicon-based sealer, [11] increase the dye apical leakage of gutta-percha root fillings when a zinc oxide-eugenol sealer is used, [12] interact with eugenol-based sealers, [13] and prevent penetration of the sealer into dentinal tubules. [14] Thus, complete removal of Ca(OH) 2 from the root canal becomes obligatory before root canal filling.

Several studies have demonstrated that Ca(OH) 2 removal was difficult or incomplete. [15] A range of products and techniques have been investigated for their efficacy in the removal of Ca(OH) 2 . The use of the recapitulation technique with the master apical file (MAF) in combination with irrigation resulted in better removal of Ca(OH) 2 when it was compared to an irrigant flush alone. [16] It was shown that rotary Nickel Titanium (Ni-Ti) instruments simplified the removal procedure from curved root canals. [17] Also, van der Sluis et al. [18] reported that passive ultrasonic irrigation was effective in the removal of Ca(OH) 2 ; however, it was concluded that it has no effect on the removal process. [19] Additionally, in the literature, there are many studies on the effects of chelators such as ethylene diamine tetra acetic acid (EDTA), citric acid, and EDTA-T in the removal of Ca(OH) 2. [16],[20]

Smear layer created during instrumentation is composed of inorganic particles of calcified tissue and organic elements. Studies analyzing whether the smear layer is beneficial or detrimental for the success of root canal treatment have been controversial. It may be beneficial because it reduces the permeability of the dentin and prevents or slows the penetration of bacteria into the dentinal tubules. [21] However, some authors have supported the removal of the smear layer because it prevents irrigants, medicaments, and filling materials from penetrating into the dentinal tubules and even from contact with the canal wall. [22] However there is no study that investigated the effect of smear layer on the removal of Ca (OH) 2 . Hence, the purpose of this study was to investigate whether the smear layer influences the removal of calcium hydroxide from the root canal with manual or rotary instruments.

   Material and Methods Top

Tooth selection

Single-rooted extracted maxillary incisors were chosen for this study. Teeth were stored in normal saline solution and the solution was changed daily. The teeth were then stored for two days in 5% sodium hypochlorite (NaOCl) at room temperature to remove organic debris. Consequently, they were cleaned with ultrasonic scaler. Following the preparation of the coronal access cavity, root canals allowing the introduction of instruments exceeding size 40 as well as teeth with fractures, cracks, or any other defects were excluded from the study. Consequently, 48 straight teeth were selected.

Root canal preparation

The lengths of the teeth were standardized at 18 mm from the apex (Digitall Slide Caliper, TchiboGmbh, Hamburg, Germany). The coronal portions of the canals were enlarged with Gates Glidden burs (Dentsply Maillefer, Ballaigues, Switzerland). The working lengths were established at 1 mm short of the apical foramen and then recorded for each canal. Each canal was instrumented using a combination of passive step back and rotary 0.04 taper nickel titanium files (Dentsply Maillefer, Ballaigues, Switzerland). The apical ends of the canals were enlarged to a size 40 file. The instruments were changed every five canals. One milliliter of 5% NaOCl delivered with a 31 gauge needle (NaviTip Sideport; Ultradent, Utah, United States of America) was used to irrigate the root canal between the use of each hand and rotary instrument. Before the final rinse, a size 20 file was passed 1 mm beyond the apex to remove any dentinal shaving plugs. The specimens were divided randomly into two groups of 24 teeth. The canals were treated with 5 ml of 5% NaOCl (group A). The canals were treated with 5 ml of 15% EDTA (Wizard; Rehber Chemical Co., Ltd, Istanbul, Turkey) for 1 minute, followed by 5 ml of 5% NaOCl (group B) [Table 1]. After that, two samples from both groups were stored as the negative control group and the canals were not filled. The remaining root canals were dried with paper points and then filled with Ca(OH) 2 (Metapex; Meta Biomed Co., Ltd., Cheongju, Korea) with a size 40 lentulo spiral until the material extruded through the apex. Two filled specimens from both groups were stored as positive controls. The access cavities were temporarily sealed with a cotton pellet and Cavit (3M ESPE, Seefeld, Germany). The teeth were stored at 37 o C and 100% relative humidity for 7 days. Then the temporary restorations were removed, and the teeth of each group were randomly divided in two subgroups that were treated as follows.
Table 1: Experimental groups in the study

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Removal of calcium hydroxide

Group A and group B were divided into 2 subgroups. In subgroup I, intracanal dressing was removed using MAF in a circumferential filing action and irrigation with 2.5 ml of 25% citric acid. In subgroup II, the dressing was removed using a Profile.04 file rotating at 300 revolutions per minute (MAF size) [Table 1]. Removal of the Ca(OH) 2 was performed as follows: First, a MAF (with circumferential filing action) or rotary instrument was introduced into the canal to the working length for seven seconds. Then the irrigation was performed with 0.5 ml of 25% citric acid. The MAF or rotary instrument was introduced to the canal again, and the instrumentation was performed for eight seconds with 0.5 ml of citric acid. Then the final flush of 1.5 ml of citric acid was performed. The total citric acid volume was 2.5 ml in each canal. After each technique, canals were irrigated with 5 ml of 5% NaOCl and then dried with size 40 paper points.


The teeth were split longitudinally along the bucco-palatal plane. To facilitate fracture into two halves, all roots were longitudinally grooved on the external surfaces using a diamond disk, avoiding penetration of the root canals, and sectioned longitudinally. After that, digital photographs of each half of the canal were taken using a digital camera mounted on a stereoscopic microscope at ×5 magnification. The digital images were imported into Adobe Photoshop (Adobe Systems, San Jose, CA). A pixel count of Ca(OH) 2 debris remaining on the canal walls was made and recorded as a percentage of the overall canal surface [Figure 1]. The two halves of each tooth were evaluated combined to represent each tooth. The teeth in the negative control group were dehydrated in a graded series of ethanol solutions, coated and viewed with a scanning electron microscope (Carl Zeiss, Gottingen, Germany) to confirm the presence/absence of smear layer according to the criteria reported by Torabinejad et al. [23]
Figure 1: Means and standard deviations of residual calcium hydroxideas seen in the study

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Statistical analysis

The means and standard deviations were calculated from the collected data, and the Kruskal-Wallis and Mann-Whitney U tests were then performed to determine the significance between the parameters (smear layer, the instrument type, and the region of the root canal).

   Results Top

Remnants of Ca(OH) 2 were found in all experimental groups regardless of the absence/presence of smear layer or the removal technique [Figure 2]. The positive control group revealed complete coverage of the canal walls with Ca(OH) 2 , in contrast to the negative controls. Considering the root canal as a whole, the removal of Ca(OH) 2 from the dentinal walls in group B (mean rank=54,18) showed significantly better results (P<.05) than the group A (mean rank=66,84). [Table 2] shows the mean ranks for the removal of Ca(OH) 2 for groups A and B within the variable coronal, middle, and apical thirds. The Mann-Whitney rank sum tests for pairwise comparisons found a significant difference between the apical and the middle/coronal thirds (P=0.017 and P=0.000, respectively) for group B; however, there was no significant difference between all canal sections for group A.
Figure 2: (a) Representative image in group B, coronal third; (b) Representative image in group B, middle third; (c) Representative image in group B, apical third; (d) Representative image in group A, coronal third; (e) Representative image in group A, middle third; (f) Representative image in group A, apical third. All images show the remnants of calcium hydroxide were seen in all the groups, regardless of the absence/presence of smear layer or the removal technique

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Table 2: Mean rank scores and statistically differences forcalcium hydroxide remaining within canal sectionsas seen in the study

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The Kruskal-Wallis tests found significant differences among the canal sections for each technique. The Mann-Whitney rank sum tests for pairwise comparisons found a significant difference between group AII and BII within the coronal and middle sections at P<0.05. Also, there was a significant difference between group AI and BI within the apical section at P<0.05. The removal technique with the profile in group B showed much better efficiency than the removal technique with a manual file in group A or the profile in group B (P<0.05). However, in group A, the manual technique was more effective in the removal process than the rotary file (P=0.016). For the negative control group the following results were observed: Group A was heavily smeared in all 3 sections. Most of dentinal tubules were closed and covered with smear layer. Group B showed complete smear layer removal in the middle and coronal sections. However, in the apical part, moderate smear layer was observed.

   Discussion Top

The techniques for measuring the residual materials in the root canals varied. One commonly used technique for measuring residual Ca(OH) 2 involves sectioning the teeth longitudinally and taking photos. [15],[19],[24] Additionally, the advantages of this technique are: (i) more accurate measurement of the complete canal area and (ii) confirming canals to be free of debris before a removal technique is employed. [17] Additionally, a radiographic analysis provides a 2-dimensional view and has proved less effective than the cleavage method. [25] However, if this method is not used correctly, the Ca(OH) 2 remnants could be displaced. This method should be done to avoid touching the root canal wall. In this study, the amount of remnant Ca(OH) 2 was evaluated by longitudinal cleavage measurements and quantitative analysis. Saline, water, NaOCl, EDTA, citric acid, and combinations of the substances have been used as irrigants for removing intracanal medicament. It is known that NaOCl and saline fail to completely remove Ca(OH) 2 from the root canal. [20] Citric acid and EDTA were found to be significantly more effective than NaOCl and water. [24] In contrast, Nandini et al. found that citric acid performed better in comparison to EDTA solution in removing Ca(OH) 2 containing silicone oil. Furthermore, they asserted that the EDTA chelates calcium ions in water; however, citric acid is able to penetrate the silicone oil better in comparison to EDTA and chelates the calcium ions. [20] In this study, citric acid was chosen as irrigant during removal because the vehicle used in the present study was silicone oil.

Balvedi et al. suggested that the interaction between Ca(OH) 2 and the root canal dentin is primarily mechanical. [19] The smear layer may be a risk factor that may inhibit the mechanical connection between the dentin and the Ca(OH) 2 . According to the hypothesis of this study, the mechanical connection will be deteriorated by the smear layer, and, in the smear-free group, the removal of the Ca(OH) 2 will be better than in the group without a smear layer. In other words, the absence of the smear layer will result in a better connection; thus, the Ca(OH) 2 removal will be more difficult. However, the results of this study demonstrated that the removal of Ca(OH) 2 was more effective in the group without a smear layer than in the group with a smear layer. The hypothesis was rejected according to this result. The results of this study demonstrated that the whole removal of Ca(OH) 2 from the canal walls was not obtained leaving up to 36.5% of the root canal covered remnants. This result is similar to the findings of previous studies, which showed sizeable amounts of Ca(OH) 2 persistent on the root canal walls, depending on the removal technique or irrigation solution used. [9],[15],[17],[18],[26]

The results of this study demonstrated that irrigating solutions with MAF or profile instruments were more efficient in the apical third of the root canal in comparison with the coronal and middle thirds in the smear-free group. In the literature, only one publication supports this finding. [24] These findings are in contrast to the results of other investigations that demonstrated Ca(OH) 2 remnants mainly in the apical third. [17],[20],[26] This difference may reflect different variables in the study design, such as: (i) the irrigation solution's volume, concentration, or contact time with the canal walls; (ii) ultrasonic agitation, using either an MAF or a rotary instrument; (iii) needle size; or (iv) root canal preparation size. Additionally, like our findings in previously published reports, it has been demonstrated that the smear layer in the apical third of the root canal has been not effectively removed when compared with the other thirds of the root canal. [27]

Within the limitations of this study, Ca(OH) 2 was removed more efficiently in the smear-free group compared with the other experimental group with smear layer. Thus, first, it can be concluded that smear layer is important in the removal of Ca(OH) 2. Second, the results of this study demonstrated that in the smear-free group rotary files were more efficient than manual files.

   Acknowledgment Top

The authors deny any financial affiliations related to this study or its sponsors.

   References Top

1.Wadachi R, Araki K, Suda H. Effect of calcium hydroxide on the dissolution of soft tissue on the root canal wall. J Endod 1998;24:326-30.  Back to cited text no. 1
2.Siqueira JF Jr, de Uzeda M. Intracanal medicaments: Evaluation of the antibacterial effects of chlorhexidine, metronidazole, and calcium hydroxide associated with three vehicles. J Endod 1997;23:167-9.  Back to cited text no. 2
3.Sjogren U, Figdor D, Spangberg L, Sundqvist G. The antimicrobial effect of calcium hydroxide as a short-term intracanal dressing. IntEndod J 1991;24:119-25.  Back to cited text no. 3
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20.Nandini S, Velmurugan N, Kandaswamy D. Removal efficiency of calcium hydroxide intracanal medicament with two calcium chelators: Volumetric analysis using spiral CT, an in vitro study. J Endod 2006;32:1097-101.  Back to cited text no. 20
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23.Torabinejad M, Khademi AA, Babagoli J, Cho Y, Johnson WB, Bozhilov K, et al. A new solution for the removal of the smear layer. J Endod 2003;29:170-5.  Back to cited text no. 23
24.Rodig T, Vogel S, Zapf A, Hulsmann M. Efficacy of different irrigants in the removal of calcium hydroxide from root canals. IntEndod J 2010;43:519-27.  Back to cited text no. 24
25.Takahashi CM, Cunha RS, de Martin AS, Fontana CE, Silveira CF, da SilveiraBueno CE. In vitro evaluation of the effectiveness of ProTaper universal rotary retreatment system for gutta-percha removal with or without a solvent. J Endod 2009;35:1580-3.  Back to cited text no. 25
26.Lambrianidis T, Kosti E, Boutsioukis C, Mazinis M. Removal efficacy of various calcium hydroxide/chlorhexidine medicaments from the root canal. IntEndod J 2006;39:55-61.  Back to cited text no. 26
27.Saito K, Webb TD, Imamura GM, Goodell GG. Effect of shortened irrigation times with 17% ethylene diamine tetra-acetic acid on smear layer removal after rotary canal instrumentation. J Endod 2008;34:1011-4.  Back to cited text no. 27

Correspondence Address:
H Sinan Topcuoglu
Department of Restorative Dentistry and Endodontics Faculty of Dentistry, Ataturk University, Erzurum, 25240
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0972-0707.94574

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