A Comparative Evaluation of Intracanal Calcium Hydroxide Removal with Hand File, Rotary File, and Passive Ultrasonic Irrigation: An In Vitro Study.

AIM: The aim of this study was to compare the effectiveness of hand file (K-file), rotary file (HERO shaper), and passive ultrasonic irrigation (PUI; U-file) in removing Ca(OH)2 from the root canal.
MATERIALS AND METHODS: Thirty single-rooted teeth were collected and decoronated to standardize the length to 14 mm. Cleaning and shaping were conducted using HERO shaper rotary files (up to no. 25, 4% taper). Ca(OH)2 powder was mixed with normal saline and filled into the canals using lentulo spiral and the orifice was sealed with zinc oxide eugenol. After 7 days of incubation, samples were divided into three groups of 10 samples each: Group I (hand files)-no. 20 K-file; Group II (rotary files)-no. 25, 4% HERO shaper; Group III (PUI)-no. 20 U-file. Ca(OH)2 paste was removed using 2 mL of 3% sodium hypochlorite solution followed by 1-minute activation of the respective file system. All the samples were finally irrigated with 17% ethylenediaminetetraacetic acid and flushed with distilled water.
RESULTS: Ultrasonic group was more effective in removing Ca(OH)2 followed by HERO shaper and hand file.
CONCLUSION: It was concluded that PUI had the highest ability to remove Ca(OH)2 from the root canal walls.

INTRODUCTION

In Endodontics, the use of intracanal dressing is important between treatment sessions for periapical periodontitis.[1] Calcium hydroxide (Ca(OH)2) was first introduced in Endodontics by Herman in 1920. It is alkaline in nature (pH of 12.5), inhibits tooth resorption, and even leads to hard tissue formation.[2] Because of these abilities, Ca(OH)2 has been recommended for use in several clinical situations, the most common indication being an antimicrobial agent in endodontic therapy.[3] Ca(OH)2 medicament should be completely removed from the canal walls before root canal fillings because any residues in the canal walls will negatively affect the quality of root canal filling. Furthermore, remnants of Ca(OH)2 may influence the dentine bond strength by interfering with the sealing abilities of the root canal sealers, resulting in potential reduction of sealer adaptation.[4] The removal of Ca(OH)2 residue from irregular canal walls is difficult. The most common method for removing Ca(OH)2 is the use of “master apical file” (MAF) at working length combined with copious sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (EDTA) solution for irrigating the canals.[56] The removal of Ca(OH)2 with hand files using irrigating solutions may be insufficient; hence, the use of rotary NiTi instruments has been advocated.[7] This study was conducted to compare and evaluate the efficacy of Ca(OH)2 removal from the root canals and canal walls using hand files (K-file), rotary files (HERO shaper), and passive ultrasonic irrigation (PUI). Stereomicroscope was used to evaluate the efficacy.

MATERIALS AND METHODS

Thirty single-rooted teeth, free of any cracks, caries, restorations, resorption, or open apices were selected for this study. The coronal portions of each tooth were sectioned using diamond disks to standardize the root length at 14 mm. K- file of size 10 was used to establish the patency, and cleaning and shaping were done using crown-down technique (HERO shaper no. 25, 4% taper). Using a syringe and a 27-G needle, the canals were irrigated with 2 mL of 3% NaOCl between each filling. The canals were finally rinsed with 3 mL of 17% EDTA and 2 mL of 3% NaOCl. The canals were dried using paper points. The apex was enlarged to taper MAF(HERO shaper no. 25, 4%). Ca(OH)2 powder was mixed with normal saline to form a paste, which was then carried into the canals using lentulo spiral. The orifices were then restored with zinc oxide eugenol (ZOE) cement. Teeth were stored in an incubator for 7 days at 37°C and 100% relative humidity. After this period, samples were randomly assigned into three groups as follows (n = 10).

Group 1: Hand file (no. 20, 2% K-file): The file was placed through the working length and moved up and down for 1 minute using 2 mL of 3% NaOCl. Finally, the root canals were irrigated using 3 mL of 17% EDTA for 3 minutes. Canals were then dried with paper points.

Group 2: Rotary file (HERO shaper): Under constant irrigation using 2 mL of 3% NaOCl, the same file system that was used for cleaning and shaping was placed through the working length and moved up for 1 minute. Finally, the root canals were irrigated using 3 mL of 17% EDTA for 3 minutes and were dried with paper points.

Group 3: PUI (U-file): 2 mL of 3% NaOCl solution was ultrasonically agitated using no. 20 U-file, which was attached to woodpecker ultrasonic irrigation device. Following this, the canal was finally rinsed with 3 mL of a 17% EDTA solution for 3 minutes and was dried with paper points.

Two longitudinal grooves were made in the buccal and lingual aspect of each root, with a diamond disk and then were split into two halves using a chisel. Each section was examined under a stereomicroscope (Lafco, India) at ×20 magnification [Figures 1-3], and photographs were taken with a digital camera (Nikon, Japan). The photographs were evaluated by a single person who was not associated with this study. The marked middle and apical portions were evaluated as per the following scores:

Figure 1

Group 1

Figure 3

Group 3

Group 2

Score 1 = absence of remnants;

Score 2 = scattered remnants; and

Score 3 = densely packed remnants.

Statistical analysis

The collected data were subjected to statistical analysis using one-way analysis of variance test using Statistical Package for the Social Sciences (SPSS, version 19.0) [Table 1].

Table 1

Statistical analysis using one-way analysis of variance

Source of variation	Sum of squares	df	Mean square	F	P value	F critical
Between groups	199	2	99.5	5.427273	0.100761	9.552094
Within groups	55	3	18.333333
Total	254	5

RESULTS

Minimal amount of Ca(OH)2 was found in Group 3 (average score of 0%) and maximum was found in Group 1 (average score of 70%). This difference between the groups was statistically significant [Table 2, Figure 4].

Table 2

Residual calcium hydroxide in apical third

Row labels	Score 1	Score 2	Score 3
Group 1 (K-file)	0%	20%	80%
Group 2 (HERO shaper)	60%	40%	0%
Group 3 (U-file)	80%	20%	0%

Figure 4

Residual calcium hydroxide in apical third

Group 2 displayed greater amount of residual Ca(OH)2 content as compared to Group 3 but lesser than Group 1. This difference among the groups was also statistically significant.

In the apical third, least amount of residual Ca(OH)2 content was seen in Group 3 (average score of 0%), whereas maximal amount was seen in Group 1 (average score of 70%) [Table 2, Figure 4].

In the middle third, minimal amount of Ca(OH)2 residual content was seen in Group 3 (average score of 0%), whereas maximal amount was seen in Group 1 (average score of 80%) [Table 3, Figure 5].

Table 3

Residual calcium hydroxide in middle third

Row labels	Score 1	Score 2	Score 3
Group 1 (K-file)	0%	30%	70%
Group 2 (HERO shaper)	0%	60%	40%
Group 3 (U-file)	60%	30%	10%

Figure 5

Residual calcium hydroxide in middle third

DISCUSSION

The results of this study showed that neither one of the techniques removed Ca(OH)2 completely. Despite the excellent antimicrobial characteristics, these remnants of Ca(OH)2 can reduce the canal permeability by promoting the formation of calcium carbonate particles and interfering with the sealing ability of endodontic sealers.[48] Therefore, different techniques have been proposed to improve Ca(OH)2 removal.[59]

In our study, PUI was found to be most effective in Ca(OH)2 removal whereas HERO shaper and K-file were least effective. The latter tends to release higher amount of hydroxyl ions within a short time, whereas the former, although effective for a longer duration, tends to release lower concentration of hydroxyl ions,[10] leading to diminished clinical effectiveness. The PUI is based on the transmission of energy from an ultrasonic oscillating instrument to the irrigant inside the root canal.[11] An irrigant solution in conjunction with ultrasonic vibration was directly associated with the removal of organic and inorganic debris from the root canal walls.[512] Thus, the effectiveness of irrigation depends on both the mechanical flushing action and the chemical ability to dissolve organic tissue.[48] In our study, the use of PUI improves the removal of Ca(OH)2 from the root canal when compared to the manual technique. The HERO shaper has triple-helix cross section, constant taper, positive rake angle, noncutting tip,[6] no radial land, variable flute helical angle or increasing helical angle from tip to shank, variable flute pitch, and works at a speed of 300–600 rpm.[1314] Positive rake angle cuts dentine effectively.[151617] The long pitch prevents the screwing in phenomenon, increases the cutting action, and facilitates the excision and evacuation of dentine chips. This could be a possible reason for better removal of Ca(OH)2 from root canal.[9] In this study, Ca(OH)2 was removed more effectively in the middle third of the root as compared to the apical probably because of more anatomical variations and constrictions being present in the apical third.[18]

CONCLUSION

Within the limitations of this study, none of these systems were able to completely remove Ca(OH)2 from root canal. PUI had the highest ability to remove Ca(OH)2 from the root canal walls when compared to the use of HERO shaper followed by hand file system.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.