The Effects of Various Final Irrigants on the Bond Strength of Root Dentin Exposed to Chloroform: An In vitro Study.

AIM: The aim of the study was to assess the reaction of different final irrigants to the bond strength of root dentin exposed to chloroform.
MATERIALS AND METHODS: Fifty extracted maxillary central incisors were selected. Working length was determined, and canal was instrumented with ProTaper rotary system (Dentsply Maillefer) till F4 file. The specimens were then divided into five groups (n = 10). Group 1: not disclosed to any root canal solvent, Group 2: disclosed to chloroform for 5 min, Group 3: chloroform for 5 min followed by absolute alcohol, Group 4: chloroform for 5 min followed by chlorhexidine (CHX), And Group 5 - chloroform for 5 min followed by saline. The canals were obturated with F4 gutta-percha cones with AH Plus sealer. The samples will be sectioned horizontally into 1 ± 0.1 mm thick slices. The push-out bond strength was performed in a universal testing machine. Results were statistically analyzed by one-way analysis of variance.
RESULTS: There existed a significant difference between the mean push-out bond strength of different groups. Irrigation with chloroform negatively affected the bonding between root canal sealer and root dentine. Absolute alcohol significantly improved the bond strength values.
CONCLUSION: Exposure with chloroform during the retreatment will decrease the bonding between sealer (AH Plus) and root dentine. The use of absolute alcohol as a final irrigant improved the bonding between sealer and dentin. CHX and saline showed no improvement in bond strength. Copyright:

INTRODUCTION

A successful root canal treatment primarily depends on the complete cleaning and shaping followed by proper obturation of the root canal systems. There are always chances of posttreatment complications if these parameters are not achieved.[1] When a root canal treatment fails, retreatment is the choice to eliminate the infection.

Nonsurgical treatment demands complete removal of previously filled gutta-percha along with the sealer from the root canal system. Usually, mechanical removal is assisted by various chemical solvents.[2] The use of chemical solvents is aimed at the effective removal of the gutta-percha from the canal space. There are a wide variety of solvents that is available for retreatment procedures, out of which the most commonly used is chloroform because of its effectiveness in removal of the gutta-percha.[3]

Chloroform when used in retreatment will change the mineral composition of the dentinal walls and thus will adversely affect the bond strength of root canal sealer to root dentin.[4] Treatment with chloroform will leave a thin layer of softened gutta-percha that cannot be removed completely.[5] Hence, there is always a need for a final irrigant after the exposure of root canal walls to remove this residual gutta-percha and root canal solvents which was left behind. Effects of various final irrigants on the root dentin treated with chloroform have not been evaluated in any endodontic literature so far. Hence, our study was aimed to assess effects of different final irrigants on the push-out bond strength of root canal sealer to root dentin exposed to chloroform.

MATERIALS AND METHODS

A total of fifty extracted human maxillary central incisors were selected and stored in the distilled water until required. Criteria for tooth selection included a completely formed apex and absence of previous root filling, resorption, or calcifications. Access cavities were made with round burs (Diatech; Coltene Whaledent, Altstatten, Switzerland) using an airotor with sufficient water cooling. A No: 10 K-file (Dentsply Maillefer) was introduced into the canal till it was seen at the apical foramen. The working length was calculated by reducing 1 mm from this measurement. The samples were prepared with the Pro-Taper rotary system (Dentsply Maillefer) up to size F4 (master apical file). During biomechanical preparation, the root canal was irrigated with 5 mL of 2.5% sodium hypochlorite (NaOCl) solution between each instrument change.

The total of 50 teeth was assigned to five experimental groups.

Group 1 – not disclosed to any root canal solvent

Group 2 – disclosed to chloroform for 5 min

Group 3 – disclosed to chloroform for 5 min followed by irrigation with absolute alcohol for 5 min

Group 4 – chloroform for 5 min followed by irrigation with chlorhexidine (CHX) for 5 min

Group 5 – chloroform for 5 min followed by irrigation with saline for 5 min.

0.2 ml of each solvent was placed in the root canal space and left in place till the completion of the exposure time (5 min) and was then eliminated with paper points followed by irrigation with the abovementioned final irrigants.

The sealer used will be AH Plus (Dentsply DeTrey GmbH, Konstanz, Germany), and the canals were obturated with F4 gutta-percha cones (Dentsply Maillefer). 1 mm of filling material was then removed from the coronal area and spaces were filled with a temporary filling material. Radiographs were taken to conform complete filling. All the specimens were stored in 37° in 100% humidity for 2 weeks.

Push-out bond testing

The sections were horizontally sectioned into 1 ± 0.1 mm thickness serial slices from the middle third using a precision saw with adequate cooling. The thickness was confirmed using a digital caliper. Specimens were examined microscopically to confirm circular canal shape. The push-out test was carried out in a universal testing machine [Figure 1] (Tinus Oslen, USA).

Figure 1

(a) 50 extracted central incisor teeth, (b) 50 specimens of cross-sectioned teeth, (c) cross-sectioned slice of thickness 1 mm, (d) universal testing machine in action

Statistical analysis

Data were compiled on excel. Statistical analysis was done using SPSS software (V.17.0) (SPSS Inc., Chicago, IL, USA). The results were tabulated and analyzed statistically by one-way analysis of variance (ANOVA).

RESULTS

The highest value was recorded by the control group 1 with a mean push-out bond strength value of about 6.58 MPa [Table 1]. When the tooth samples were treated with chloroform, all the groups showed a significant decrease in bond strength values. Absolute alcohol-treated group showed a significant increase in bond strength values with a mean value of about 4.43 MPa. The push-out bond strength values of CHX (Group 4) and saline (Group 5) treated samples were 3.73 and 3.78, respectively.

Table 1

Push-out bond strength of root canal sealer to root dentin in mega Pascal (MPa)

Group 1 Not exposed to any solvent (n=10)	Group 2 Exposed to chloroform for 5 min (n=10)	Group 3 Exposed to chloroform followed by absolute alcohol for 5 min (n=10)	Group 4 Exposed to chloroform followed by chlorhexidine for 5 min (n=10)	Group 5 Exposed to chloroform followed saline for 5 min (n=10)
6.47	4.28	4.65	3.75	4.11
5.98	3.77	4.31	3.46	3.89
6.22	4.08	5.12	4.39	4.10
7.23	3.56	4.11	3.64	3.68
6.89	4.11	3.98	3.98	4.23
7.21	4.09	4.71	2.73	4.00
6.68	3.54	3.38	4.11	3.38
6.95	3.23	4.48	3.94	3.18
6.31	4.31	4.71	3.25	2.95
5.88	2.98	4.39	4.08	4.25

We compared a one-way ANOVA to compare the push-out bond strength of different root canal sealer after exposing it with chloroform followed by irrigation with different final irrigants. There existed a significant difference between the mean push-out bond strength of different groups with a f = 71.113 and significance level of 0.000 [Table 2].

Table 2

Push-out bond strength of Root canal sealer (MPa)

	Sum of squares	df	Mean square	F	Significance
Between groups	59.410	4	14.853	71.113	0.0001
Within groups	9.399	45	0.209
Total	68.809	49

DISCUSSION

Adhesion is one of the most important physical properties that is required by the root canal sealers.[6] It helps to obtain a tight seal, which is essential for attaining success in root canal treatment. AH Plus is a resin-based sealer available as a 2 paste system. Due to its excellent properties, such as low solubility, small expansion, adhesion to dentin, and very good sealing ability,[7] AH plus is considered as a benchmark “Gold Standard.” Hence, AH Plus was taken as the choice of sealer in our study.

In root canal retreatment procedure, we have to remove the gutta-percha that was previously obturated in the canal spaces and it requires a solvent. A root canal solvent is meant to dissolve as much as gutta-percha a possible.[8] Chloroform is an organic solvent and is effective in dissolving gutta-percha.[9] In fact, the gutta-percha was originally designed to get dissolved in chloroform and the mixture of chloroform and gutta-percha is called as chloropercha.[10] In clinical practice, chloroform still remains the most effective and widely used solvent for the dissolution of the gutta-percha.[11]

In a previous study, Shokouhinejad et al.[12] estimated the push-out bond strength Resilion/Epiphany self-etch system to radicular dentin after retreatment. They first obturated the canal and then removed the obturation with a combination of solvents and retreatment files. After the removal, the root canal space was again obturated with Resilion/Epiphany self-etch, but doing so will involve a lot of variables. Ring et al.[13] did a study, in which he compared the efficacy of different retreatment solvents and rotary files to remove the obturation material from the root canal space, and he concluded that it is unable to completely remove the obturation materials from the root canal space. In our study to reduce the variables involved, an initial root canal filling was not done.

In the present study, all the single-rooted maxillary central incisor specimens were obturated with the F4 gutta-percha. F4 size gutta-percha was selected because it matched the size and taper of the master apical rotary file that could fill the root canal space almost completely when used as a single cone.[14] Nagas et al.[15] compared the bond strength of master gutta-percha points with different tapers (0.02, 0.04, and 0.06) in canals instrumented with a 0.06 tapered master apical file and found that the highest bond strength was provided by 0.06 tapered single cone.

According to a previous study by Neelakantan et al.,[16] the bond strength values are greater in coronal followed by middle and apical third. In our study, to make the study more standardized and for the ease of sectioning, only middle third section of the root matching the plunger size of 0.8 mm was taken into account in testing the push-out values.

Kaufman et al.[17] showed that the calcium and phosphorus levels of human dentin were changed after treatment with the chloroform. The results of our study were similar to the one conducted by Topcuoglu et al.,[18] in which he concluded that bond strength was crucially affected by solvent type and time. The use of chloroform for 5 min in the root canal space reduced the bond strength of all sealers.

CONCLUSION

The highest push-out bond strength value was recorded by Group 1, which was not exposed to any root canal solvents with a mean push-out bond strength of 6.58 MPa

Exposure to chloroform significantly decreased bonding of epoxy resin-based (AH Plus) root canal sealer with root dentin with mean push-out bond strength values of 3.80 MPa (Group 2)

On irrigation with absolute alcohol, there was a gain in push-out bond strength after exposure to chloroform and Group 3 samples recorded a mean value of 4.48 MPa

Irrigation with CHX and saline (Group 3 and Group 4) samples recorded values of 3.73 and 3.78 MPa, respectively, indicating that it showed no improvement in bonding between root canal sealer and root dentin with these groups.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.