Assessment of the wetting behavior of three different root canal sealers on root canal dentin.

AIM: The objective of the present study was to evaluate and compare the wetting behavior of three different root canal sealers on the root canal dentin surface treated with irrigants and their combination.
MATERIALS AND METHODS: Decoronation and apical third resections of 27 extracted single-rooted human mandibular premolars were done. The roots were then split longitudinally into two halves, and randomly assigned into three treatment groups (n=18). The root dentin surfaces in Group1, Group 2 and Group 3 were treated with 17% ethylene diamine tetra acetic acid (EDTA), 3% sodium hypochlorite (NaOCl) and combination of 17% EDTA and 3% NaOCl, respectively. Each group was subdivided into three subgroups of 6 specimens each, depending on the the sealer used, i.e. sub group A. zinc oxide (ZnOE), sub group B. AH plus, subgroup C. Guttaflow sealer, respectively. The contact angle was measured using First Ten Angstroms (FTA) 200 dynamic contact angle analyzer.
RESULTS: The contact angle values for AH Plus sealer were significantly lower when compared to the other two sealer groups.
CONCLUSION: The wettability of AH Plus sealer on the root surface dentin was found to be better than Gutta-Flow and ZnOE sealer.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

The achievement of a fluid-impervious seal within the root canal system is important for the long-term success of an endodontic treatment.[12] A fluid-tight seal will also stop bacteria and their products from entering the periapical tissues and thus prevent re-infection.[3] Root canal sealers have been used along with solid core obturating materials to enhance the fluid-tight seal. Solid-core root filling materials do not usually reach the irregularities of the root canal system such as the accessory and lateral canals, fins, ramification and deltas. Therefore, root canal sealers are used along with the solid core obturating material to fill these irregularities. This also aids in filling the empty spaces present between the core material and the root canal walls.[4] Various root canal sealer formulations are available in the market, such as, zinc oxide-eugenol based, epoxy resin based and silicone based root canal sealers. Zinc oxide eugenol based sealers have been traditionally the most commonly employed sealants. They have served as the benchmark with which other sealers are compared, as they reasonably meets most of Grossman's requirements for sealers.[5] Of the resin based sealers, AH Plus sealer (Dentsply, De Trey, Konstanz, Germany) has shown favorable properties.[6] Gutta-Flow (Colténe/Whaledent, Altstätten, Switzerland) is a recently introduced injectable silicone based root canal filling material. This new root canal filling paste is a modification of RoekoSeal, sealer and it contains gutta-percha particles as a filler material.[7-9]

Proper adaptation of the root canal sealer to the root canal wall is an important factor in the attainment of a fluid-tight seal.[1011] Wettability of the root canal sealers influences its adaptability to the radicular dentin. Contact angle is a useful indicator for the wetting behavior of any liquid tested. This angle is formed by a liquid at a three-phase boundary where a liquid, gas and solid intersect. Low contact angle values (<90°) indicate good wetting characteristics of the liquid, whereas higher values (>90°) indicate a poor wetting. The surface tension of the sealer and the presence or absence of smear layer on the root canal walls can have an effect on the contact angle.[12] Smear layer is an amorphous film composed of inorganic and organic debris and is produced during the mechanical instrumentation of the root canal. There is a controversy over whether to remove or maintain the smear layer. However, a recent systematic review and meta-analysis of leakage studies concluded that removal of the smear layer improves the fluid tight seal of the root canal system.[13] The smear layer may prevent the penetration of the root canal irrigants, intra canal medicaments and root canal sealers.[14] Its presence is also said to affect the surface energy of the dentin. The smear layer is shown to have a hydrophobic character.[15] Hence, complete removal of the smear layer from the root canal surface is recommended. Goldman et al.[16] showed that root canal irrigation with 17% EDTA followed by NaOCl is effective for the removal of the smear layer. These chemical agents are used as irrigants during the chemomechanical preparation of the root canal system, and may affect the characteristics of the dentinal substrate.

The purpose of the present study was to evaluate the contact angle of zinc oxide-eugenol sealer, AH Plus sealer and Gutta-Flow on the root canal dentin treated with 17% EDTA, 3% NaOCl and a combination of 17% EDTA and 3% NaOCl.

MATERIALS AND METHODS

Sealers tested

Zinc oxide-eugenol (ZnOE) sealer (DPI, India, Ltd.), AH Plus (Dentsply, De Trey, Konstanz, Germany) and Gutta-Flow (Colténe/Whaledent, Altstätten, Switzerland) were tested in this study.

Sealer preparation

The root canal sealers were prepared in accordance with the manufacturer's instructions, immediately before dispensing the sealer for the contact angle measurement, as given below:

ZnOE sealer: Powder and liquid were manually mixed on a glass slab with a spatula according to manufacturer's instructions.

AH plus: Paste A and paste B were mixed on paper pad with a spatula in accordance with the manufacturer's instructions.

Gutta-flow R: was prepared by vibrating the capsule for 30 seconds on a vibrating device (SDI Ultramat, Victoria, Australia).

Sample preparation

Twenty seven intact single-rooted human mandibular premolars extracted for orthodontic purpose were used in the present study. The teeth were stored in saline after the tissue remnants present on the root surface of these teeth were cleaned using an ultra-sonic scaler. Decoronation and apical third resections of these teeth were done using high-speed diamond abrasives, (Diatech, Swiss Dental Instruments, Heerbrugg, Switzerland) with water spray cooling. The remaining root segments were then split longitudinally through the root canal in a bucco-lingual direction with a diamond disk (Diamant, Horico, Berlin, Germany) at low speed. The inner dentinal portions of the 54 root halves thus obtained were smoothened with Soflex disks (3M ESPE, St Paul, MN, USA). The samples were then stored in normal saline solution until use.

Sample treatment

The samples were randomly assigned to three experimental groups of 18 specimens each:

Group 1: The samples were immersed in 10 ml of 17% EDTA (B. N. Laboratories, Mangalore, India) for 5 minutes, and then rinsed with 10 ml of saline.

Group 2: The samples were immersed in 10 ml of 3% NaOCl (Novo Dental Products Pvt. Ltd., Mumbai, India) for 5 minutes, and then rinsed with 10 ml of saline

Group 3: The samples were first immersed in 10 ml of 17% EDTA for 5 minutes and thereafter immersed in 10 ml 3% NaOCl for the next 5 minutes. The samples were then rinsed with 10 ml of saline solution. After the surface treatment, each group was subdivided into three subgroups of 6 specimens each depending on the sealer used, i.e. sub group A: Zinc oxide eugenol based sealer; sub group B: AH plus sealer; and, subgroup C: Guttaflow.

Contact angle measurement

Once the specimens were blot dried, they were stabilized on a flat glass surface using cyanoacrylate glue. The contact angle was measured 30 minutes after a controlled volume of the sealer was dispensed on to the treated root canal dentin surface through a nozzle. The measurements were made using a dynamic contact angle analyzer, FTA 200 (First Ten Angstroms, Portsmouth, VA, USA), by imaging the sealer dispensed onto the surface being characterized. The captured images were analyzed using FTA software to determine the contact angle.

Statistical analysis

The contact angle values obtained on each root dentin surface with different sealers were tabulated and the data were analyzed using Tukey's honestly significant difference (HSD) test. The level of statistical significance was set at 95% (P=0.05).

RESULTS

The mean values and standard deviation of the contact angles for each sealer on root canal dentin surface treated with various irrigating solutions is shown in Figure 1. The statistical analysis between the groups is summarized in Tables 1 and 2. Statistically significant lower contact angle values were recorded for AH Plus as compared to the other two sealers, irrespective of the root canal dentinal wall treatment. The contact angle of ZnOE sealer and Gutta-Flow showed no statistically significant results except in Group 3 [EDTA+NaOCl], where Gutta-Flow showed statistically significant lower contact angle value compared to the ZnOE sealer (P<0.001) [Table 1]

Figure 1

Comparison of mean values of the contact angles for each sealer on root canal dentin surface treated with various irrigating solutions in the study

Table 1

Multiple comparison of sealers tested

Table 2

Multiple comparison of irrigants tested

Within the ZnOE sealer group, there was no statistically significant difference seen in the contact angle values between any of the surface treatment groups. On the contrary, in the AH Plus group, NaOCl treated surface [Group 2] showed a significantly higher contact angle value, as compared to the other two groups (P<0.01). Whereas in Gutta-Flow, the root canal dentin surface treated with EDTA+NaOCl [Group 3] showed statistically significant lower contact angle value compared to the root canal dentin treated with EDTA alone [Group 1] (P <0.03) [Table 2].

DISCUSSION

Reliability of the experimental procedure followed in the present study was tested in a previous study done by Kontakiotis et al., and found to be particularly high. In this study, the contact angle was measured using the mixed sealer paste to mimic the clinical situation, because the wetting behavior and specifically the contact angle could be different between the individual component and the mixed sealer paste. The contact angle results from the establishment of the equilibrium of surface energy at the liquid- solid interface. The factors affecting the contact angle on the liquid side include the surface tension, and those on the solid side include the hydrophobic effect caused by changes in the porosity as a result of surface roughness, and the surface energy effect based on the changes in the 3-dimensional structure of the surface molecules.[17] With the contact angle method, it is very difficult to differentiate the contribution of surface roughness from the amount attributed to the real changes in the energetic state. The aim of polishing the inner dentin surface of the root halves with Soflex was to reduce the influence of the roughness on the surface energy of the radicular dentin wall, and thus reduce its influence on the contact angle.[15] The state of hydration of the dentin surface is also shown to affect the contact angle.[18] Hence, the specimens were blot dried to keep the dentin surface sufficiently hydrated after the final rinse with saline, to simulate the clinical scenario.

The surface with lower contact angle (greater surface free energy) presents high wettability, that is, in a solid with high surface free energy, the sealer spreads and interacts better with the surface, and thus forms a lower contact angle. In the present study, AH Plus sealer was shown to wet the root dentin surface better than the other two experimental sealers tested, as it showed statistically significant lower contact angle values. This result is in agreement with the study by Kontakiotis et al.,[19] where AH26, the predecessor of AH Plus, showed better wetting than Gutta-Flow. Superior wetting of AH Plus sealer on the root dentin surface could be because of its ability to penetrate into the micro-irregularities better. The good adhesive property of AH Plus sealer as shown in the investigations by Nunes et al.[20] and Eldeniz et al.,[21] support the result in the present study. AH plus sealer showed better surface wetting in the group where root dentin surface was treated with both, EDTA and NaOCl. The reason for this could be the intimate contact of the sealer with the dentin surface and the penetration of the sealer into the dentinal tubules as a result of the complete removal of the smear layer.[20] Dentin surface treated with EDTA also showed good wettability as compared to the surface treated with NaOCl alone. The reason for this could be better dissolution of the smear layer by EDTA.

In the present study, ZnOE sealer showed no statistically significant difference in the contact angle within any of the treatment groups. The poor surface wetting of zinc oxide-eugenol (ZnOE) sealer could be due to the increased viscosity of the sealer. Gutta-Flow also showed poor wetting on the root dentin surface because of the presence of silicone, which possibly produces high surface tension forces, making the spreading of these materials more difficult.[17] Gutta-Flow showed good spreadability in the group where root dentin surface was treated with both EDTA and NaOCl. The reason for this could be the increase in the surface energy of the root dentinal wall which was free of the smear layer. On the contrary, dentin surface treated only with EDTA showed high contact angle value, suggesting the poor wettability of Gutta-Flow. The high concentration of EDTA could have caused mild etching of the dentin surface leading to the exposure of collagen fibers, and the exposure of this hydrophobic moiety could have resulted in the increased contact angle.[15]

Under the experimental conditions of the present study, the results showed that wettability of root canal sealers depends on the surface treatment of root dentin by various irrigants. The wettability of AH Plus sealer on the root surface dentin was found to be better as compared to others. The complete removal of the smear layer was shown to result in better wetting of AH Plus sealer and Gutta-Flow; however, it showed no improvement in the ZnOE sealer. Further studies are necessary to analyze the wettability of the root canal sealers on the root canal dentin surface treated with various irrigant combinations, and confirm the observed data.