Comparative evaluation of tensile strength of Gutta-percha cones with a herbal disinfectant.

AIM: To evaluate and compare the tensile strength values and influence of taper on the tensile strength of Gutta-percha (GP) cones after disinfection with sodium hypochlorite (SH) and Aloe vera gel (AV).
MATERIALS AND METHODS: Sixty GP cones of size 110, 2% taper, 60 GP cones F3 ProTaper, and 60 GP of size 30, 6% taper were obtained from sealed packs as three different groups. Experimental groups were disinfected with 5.25% SH and 90% AV gel except the control group. Tensile strengths of GP were measured using the universal testing machine.
RESULTS: The mean tensile strength values for Group IA, IIA and IIIA are 11.8 MPa, 8.69 MPa, and 9.24 MPa, respectively. Results were subjected to statistical analysis one-way analysis of variance test and Tukey post-hoc test. 5.25% SH solutions decreased the tensile strength of GP cones whereas with 90% AV gel it was not significantly altered.
CONCLUSION: Ninety percent Aloe vera gel as a disinfectant does not alter the tensile strength of GP cones.

INTRODUCTION

The primary objective of endodontic therapy is to maintain a complete aseptic condition in root canal treatment, right from access opening to the permanent coronal restoration of the tooth. Eliminating or decreasing the microbial count is of considerable importance for the success of endodontic treatment.

Several studies revealed that the selection of an ideal disinfectant for Gutta-percha (GP) cones is very important, because the disinfectant may affect the mechanical properties and surface texture of GP cones, thereby the outcome of obturation.

Current obturation techniques involve the use of several chemicals for GP cone disinfection. Among them, sodium hypochlorite (SH) was proved to be an effective disinfectant.[123] SH is a strong oxidizing agent and effective decontaminant that causes extreme topographic alterations and aggressive deterioration[4] in the cones, which inturn results in decrease of adhesion or bond strength of GP cones to endodontic sealer.[5] Moreover, there is decrease in tensile strength of GP cones and formation of cuboidal shaped crystals on the surface of GP with 5.25% SH, which could affect the sealing ability, reinforcement within the root canal, and outcome of endodontic treatment.[9] Therefore an effective, but safer chemical is desirable for disinfecting GP cones.

Aloe vera gel (AV) is bacteriostatic against Staphylococcus aureus, Streptococcus pyogenes, and Salmonella paratyphi and found to be an effective medium in decontaminating GP cones.[68] The purpose of the study was to evaluate and compare the effect of 90% AV gel and 5.25% SH on the tensile strength of GP cones.

MATERIALS AND METHODS

Sixty GP cones of size 110, 2% (Dentsply, Ballaigues, Switzerland) were included under Group I, 60 F3 ProTaper GP (Dentsply, Ballaigues, Switzerland) were included under Group II and 60 GP of size 30, 6% (DIADENT, Netherlands, Korea) were included under Group III. Each group was divided into three sub-groups (A, B, and C) of 20 each [Table 1].

Table 1

Experimental groups and sub-groups

GP cones were opened under sterile conditions from the sealed packets and divided in to three sub-groups of 20 cones each. Group IA was disinfected with 20 ml of 5.25% SH (Prime Dental, Thane, India) in a petri dish for 1 min, after which they were transferred individually and rinsed in 5 ml of distilled water for 1 min and allowed to dry in sterile petri dishes containing sterile filter paper pads. Similarly, Group IB was disinfected with 90% AV gel (Nature's Herbs, American Fork, USA) for 1 min. Accordingly II and III groups were sterilized. Group C was not disinfected and taken as a control group.

The tensile strength of all GP cones after disinfection was measured using computer controlled universal testing machine. Each cone was standardized to 14 mm length by cutting the cone from the base, 2 mm from each side of the cone was inserted into either ends of the holders of universal testing machine and load was applied at a crosshead speed of 1 mm/min, until maximum tensile failure was obtained and values were recorded. The data was compared for differences using one-way analysis of variance, followed by multiple comparisons using Tukey post-hoc test.

RESULTS

Results revealed that 5.25% SH would decrease the tensile strength of GP cones after 1 min of disinfection, which had a significant difference from the control group (C) and 90% AV (B) group. The results are considered as statistically significant at P ≤ 0.05. This was shown in Tables 2 and 3. 5.25% of SH decreases tensile strength and left a cuboidal crystal on the surface of GP cone after 1 min of immersion, conversely AV would not affect properties of GP cone.

Table 2

Comparison of mean tensile strength values of GP cones after disinfection with 5.25% SH and 90% AV gel

Table 3

Tukey Post-hoc test for multiple comparisons

DISCUSSION

The importance of GP decontamination to prevent any bacterial contamination of the root canal before obturation is now a widely recognized step in endodontic practice.[7] SH at 5.25% has been found to be rapid, reliable effective in disinfecting GP cones because of its strong antibacterial, oxidizing, and sporicidal activity.[9] AV has been used for the treatment of peptic ulcers and in cosmetics. Its antimicrobial activity is due to p-coumaric acid, ascorbic and cinnamic acid. Another major advantage is that AV gel has been found to be effective in decontaminating GP cones within 1 min.[8]

GP cone is one of the most popular materials used for obturating root canal space. Although GP cones are an essential factor within the aseptic chain, often little attention is paid to the microbiological cleanliness of the cones selected prior to their use in filling the canal. As root canal filling cones must remain in the root canal over a long period of time, they must be able to withstand rigorous sterilization procedures. Studies on the effects of disinfection on the mechanical properties and surface texture of GP cones have been reported,[1011121314] but they are limited and many remain unclear. The mechanical properties of GP cone were indicative of a partially crystalline polymeric material and found to obey the Hook's law.[1516] Several studies demonstrated that tensile strength was correlated to GP component of GP cone while modulus of elasticity and percentage of elongation were determined to be related to zinc oxide component of GP cones, and flexibility of the cone affected by wax and resin components of GP cone.[1516] As SH is known to be a strong oxidizing agent and has the potential to reduce the chemical stability of chain polymer, resin, and waxes of GP cones. Such, a chemical instability would adversely affect the mechanical properties of a GP cone.[10111213] Reduction in polymer component in GP cone by 5.25% SH might lead to a decrease in tensile strength. Furthermore, leaves multiple pitting on the surface of GP cones which might decrease adhesion or bond strength of GP cones to the endodontic sealer. Hence, all these thought to adversely affect sealing ability and reinforcement in the root canal, which were the main causes of endodontic failure.

The rationale behind selecting different size and taper of GP is to know whether there is any influence of taper of GP on tensile strengths. According to weine, minimum apical preparation should be till 30 size so master apical file size 30 was chosen. To simulate this, ProTaper F3 (Group II) and 30 size GP (Group III) were selected. To know the influence of taper, Group II with variable taper and Group III with 6% GP were selected. 110 size GP has been taken as a reference size according to the study done by Ismail et al.[9]

It is found in this study that the mean tensile strength values for Group IA, IIA and IIIA are 11.8 MPa, 8.69 MPa and 9.24 MPa, respectively. The mean tensile strength of experimental groups treated with 5.25% SH were significantly decreased when compared with control group (P < 0.05) whereas with 90% AV gel the value was not significantly changed. There was no statistical difference between tensile strength values of the control group and 90% AV gel group (P > 0.05). These results were in accordance with studies done by Ismail et al.[9] Irrespective of taper and size of the GP cones, the control group showed the highest tensile strength. Irrespective of taper and size of the GP cones, there was a significant reduction in tensile strength of GP cones upon disinfection with 5.25% SH. Irrespective of taper and size of GP cones, there was no significant difference in the tensile strength of GP cones in the control group and tensile strength of GP cones disinfected with 90% AV gel.

CONCLUSION

Within the limitations of the study, it is concluded that 90% AV is considered as safer GP disinfectant as it does not alter the tensile strength and topography of GP, which eventually will lead to enhanced sealing ability and reinforcement of the root canal. To establish AV as a GP disinfectant, further research has to be done exclusively on surface topography, modulus of elasticity and percentage elongation of GP cones on a larger sample size.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.