Micro-tensile bond strength of adhesives to pulp chamber dentin after irrigation with Ethylenediaminetetraacetic acid.

AIM: The aim of this study was to evaluate the influence of different concentrations of Ethylenediaminetetraacetic acid (EDTA) solution on adhesion, that is, the bond strength of the different adhesive systems, to the pulp chamber dentin.
MATERIALS AND METHODS: Recently extracted, sound, human, third molars were cut horizontally to expose the pulp horn. The roof of the pulp chamber and pulp tissue was removed. The teeth were then divided into five main groups. The teeth in each group were treated as follows: group 1, irrigated with saline; group 2, with 5% EDTA for 5 minutes; group 3, with 15% EDTA for 5 minutes; group 4, with 17% EDTA for 5 minutes and group 5, with 19% EDTA for 5 minutes. Treated specimens were dried and divided into 2 subgroups for adhesives; bonded with a total-etching adhesive (Adper Scotchbond Multi-purpose - ASB) or a one bottle of self-etch adhesive system (Clearfil S3 Bond - CS3). After the bonding procedure and composite restoration, teeth were sectioned and dentin sticks were obtained from each group for micro tensile testing (n = 10). Micro tensile testing was performed and scanning electron microscope (SEM) photographs were taken for each irrigated group.
RESULTS: In the ASB group, saline showed statistically higher bond strength values at the different concentrations of EDTA, while the micro-tensile bond strengths of the different concentrations of EDTA were not statistically different. In the CS3 group, saline and 5% EDTA showed statistically higher bond strength values than 17% and 19% EDTA, while the micro-tensile bond strengths of 15% EDTA compared to saline and 5% EDTA and 15% EDTA compared to 17% EDTA and 19% EDTA, were not statistically different.
CONCLUSION: This study showed that EDTA irrigation can affect the bond strength of adhesive systems on pulp chamber lateral walls. Clinically, low EDTA concentrations can be recommended if self-etch adhesives have been selected.

INTRODUCTION

In the recent years, more attention has been focused on procedures performed to obtain an effective coronal seal following the completion of root canal treatment, in spite of the fact that apical leakage is still considered an important factor in endodontic failures.[12] Coronal leakage has a negative influence on the prognosis of root canal treatment,[2] and plays a significant role in multirooted teeth, where accessory canals may be present in the furcation area.[3] Specifically, inflammatory changes can occur in the periodontal tissues because of a direct spread of microorganisms from the pulp chamber through these accessory canals.[4] Adhesive systems have been suggested for the restoration of endodontically treated teeth,[5] and they have many advantages over non-adhesive materials, such as reducing micro leakage[6] and reinforcing the weakened tooth structure.[7] However, achievement of a bond between adhesive resin and dentin relies upon the penetration of the primer and adhesive resin into the conditioned dentinal surface to generate micromechanical interlocking between the dentin collagen and resin, thus forming a hybrid layer.[6] Multiple bonding systems are available for good hybridization and adequate bonding. The first of the two most used systems among these is the “total etch” technique, with separate applications of an etchant, a primer, and adhesive resin. The second is the self-etching-priming technique, with the application of an adhesive resin to the conditioned dentin surface.[89]

The net influence of pulpal floor features on bond strength is difficult to predict, and the structure of pulp chamber walls is complicated as it contains predentin, regular and irregular secondary dentin, and high tubule density with large tubules.[8] On the other hand, accessory canals reported to occur frequently on the pulpal floor of molars may also assist in mechanical retention.[3] The bond strength between the pulp chamber walls and adhesive systems is affected by the irrigants used during the root canal treatment. Although the bond strength after irrigation with Ethylenediaminetetraacetic acid (EDTA) was demonstrated in previous studies,[10] the effect of different concentrations of EDTA has not been studied. Thus, the purpose of this study was to compare the effect of different concentrations of EDTA solution on resin-bond strength and to evaluate the bond strengths of two adhesive systems (total etch and self-etch adhesives) to the pulp chamber walls. The null hypothesis of this study was that the bond strength of adhesives would not be affected by different concentration of EDTA irrigations.

MATERIALS AND METHODS

Recently extracted sound human 15 third molars were selected for this study. The teeth were stored in distilled water at room temperature before their usage. The teeth were sectioned through the pulp chamber roofs using an Isomet saw under water lubrication (Buehler, Lake Bluff, IL). Pulp tissue was carefully removed without touching the inner surface of the pulpal wall. The teeth were divided into five main groups. Group 1: An unirrigated control group (immersed in 0.9% saline); Group 2: 5 minutes 5% 10 ml EDTA; Group 3: 5 minutes 15% 10 ml EDTA; Group 4: 5 minutes 17% 10 ml EDTA; Group 5: 5 minutes 19% 10 ml EDTA. After irrigation with EDTA, all teeth were rinsed with saline for 2 minutes as the final irrigation. Then, all the groups were divided into subgroups as shown in Table 1. The adhesive systems, a total etch (Adper Scotchbond Multi-Purpose) and a self-etch (Clearfil S3 Bond) were applied to the pulp chamber walls according to the manufacturers’ directions. The resin composite was condensed into the pulp chamber and cured in 2 mm layers on the the bonded surface (3M ESPE Elipar FreeLight 2 LED, Germany). The output of the curing light was checked with a radiometer (Hilux UltraPlus Curing Units, Benlioglu Dental Inc., Turkey). The adhesive systems and composite resins used in this study are shown in Table 2.

Table 1

The micro-tensile bond strengths of adhesives to pulp chamber lateral walls with different Ethylenediaminetetraacetic acid concentration

Table 2

Materials used in this study

All restored specimens were immersed in distilled water at 37°C for 24 hours, after which the teeth were sectioned vertically using the Isomet saw, and the samples were fixed to a sectioning block. Three thin rectangular sticks (1 ± 0.02 mm2) were prepared using the Isomet saw, with resin composite on one side and pulpal wall dentin on the other side. A digital slide caliper was used to check the thickness and width of the bonded area (Digital Slide Caliper, Tchibo GmbH, Hamburg, Germany). Every subgroup had three teeth, and after the sectioning process, approximately five or six dentin sticks could be obtained from each tooth. Finally, for micro-tensile testing, the sample size for each subgroup was ten. (n = 10)

Ten dentin sticks were obtained from each group. The ends of each stick were attached to a micro-tensile device (Bisco Microtensile Tester, USA) using a cyanoacrylate adhesive (Zapit, DVA, Corona, CA, USA) and stressed in tension at a speed of 1 mm/min. The microtensile bond strengths data were determined (MPa), and all data were analyzed by one-way analysis of variance (ANOVA) and for comparison with the differences in the subgroups, Duncan's multiple post-hoc test was performed for ASB and CS3 groups separately. After the test, fractured surfaces were examined under a stereomicroscope (SZ-PT Olympus, Japan). Failures were classified as adhesive failure (failure between resin and dentin interface), cohesive failure (failure in dentin or composite resin) and mix failure (mixture of adhesive failure and cohesive failure same time). In order to observe the samples under a scanning electron microscope (SEM), five recently extracted sound human third molar teeth were used. The pulp chamber dentinal walls were treated as: 1) saline; 2) 5 minutes 5% EDTA; 3) 5 minutes 15% EDTA; 4) 5 minutes 17% EDTA; and 5) 5 minutes 19% EDTA; after which all the teeth were rinsed with saline for 2 minutes. All the disks were then coated with a thin film of gold in a vacuum evaporator (Polaron SC500 Sputter Coater, VG Microtech Inc., Japan) and observed under SEM (JSM-5600, JEOL Ltd, Tokyo, Japan).

RESULTS

The mean micro-tensile bond strength values in MPa and standard deviations are shown in Table 1 for all groups. In the ASB group, saline showed statistically higher bond strength values than the different concentrations of EDTA (P < 0.05), while the micro-tensile bond strengths of the different concentrations of EDTA were not statistically different (P > 0.05). In the CS3 group, saline and 5% EDTA showed statistically higher bond strength values than 17% and 19% EDTA (P < 0.05), while the micro-tensile bond strengths of 15% EDTA compared to saline and 5% EDTA compared to 17% and 19% EDTA were not statistically different (P > 0.05). All statistical results are shown in Figure 1, and failure types are represented in Figure 2. In the SEM observations of the pulp chamber lateral walls, there was no smear layer in any group because all procedures were performed without touching the dentinal walls. An irregular dentin surface was observed in the specimen irrigated with saline and with 5% EDTA. SEM photographs of pulp chamber wall dentin after rinsing with saline only revealed smooth, open dentinal tubules with few remnants of pulp tissue. The SEM observations of the specimens irrigated with 15%, 17%, and 19% EDTA revealed the absence of irregular dentin surface [Figure 3].

Figure 1

The micro-tensile bond strength mean values and results of Duncan post hoc test (P < 0.05) for the different groups

Figure 2

Failure type of bonding agents after different Ethylenediaminetetraacetic acid irrigations.

Figure 3

Scanning electron microscope photographs of the specimens (a: Irrigated with saline, b: Irrigated with 5% Ethylenediaminetetraacetic acid (EDTA), c: Irrigated with 15% EDTA, d: Irrigated with 17% EDTA, e: Irrigated with 19% EDTA)

DISCUSSION

Endodontic chemical irrigants’ have different effects on the bonding of pulp chamber dentin. EDTA has been used extensively in root canal treatment in identifying the entrance of calcified root canals and in removing smear layer. Also, although there is no scientific study for this usage, paste form of EDTA has especially been used as a lubricant.[11] Currently, there is no consensus on the optimal time a chelating agent must be in contact within the root canal to adequately bond. In addition, the time needed for good cleaning efficacy of EDTA was recommended at between 1 and 5 minutes in several studies.[12] The present results indicate that, when a total etching or a self-etching adhesive system was employed, the use of EDTA for 5 minutes, especially in high concentrations, had an adverse effect on the strength of the bond to the pulp chamber. However, further studies need to be conducted to determine the effects of EDTA on bond strengths of adhesives at different time intervals.

In previous studies, EDTA was used either alone or in combination with Sodium hypochlorite (NaOCl) irrigation, and it was indicated that EDTA lessened the calcium/phosphorus (Ca/P) ratio of dentin significantly.[13] EDTA is popular as a Ca2+ chelating agent not only because it can extract Ca2+ ions from dentin, but because it can also produce demineralization lesions following extended contact with dentin, including “non-mineral” areas near the surface.[14]

It is known that any change in the Ca2+ ratio may cause a change in the original proportion of organic and inorganic components of dentin, which results in a change in the microhardness, permeability, and solubility characteristics of dentin.[15] It may also influence the sealing ability and adhesion of dental material dentin.[1516] Dentin adhesion actually relies upon the presence of residual Ca2+ on the bonding area,[16] as evidenced by a significant reduction in the bond strength of some adhesive materials caused by the partial depletion of surface Ca2+.[16] Garcia-Godoy et al. indicated that EDTA caused a collapse of the dentin matrix structure, which impeded sealer infiltration and formation of high quality hybrid layer bonding.[17] It is also thought that EDTA leads to changes in the mechanical properties of dentin, such as reduction of micro hardness, wettability, and increase of surface roughness,[18] which can also contribute to a decrease in the micromechanical interaction between adhesive resins and EDTA-treated dentin. The micro-tensile bond strength test was introduced by Sano et al.[19] This test method permits measurements of tensile bond strength on very small surfaces, measurement of high bond strengths without cohesive failure of dentin, and has the advantage of producing many specimens from the same tooth. As such, the micro-tensile bond strength test has become the most used dentin bond test today.[20] However, no correlation between bond strength and micro leakage has been observed, thus the micro-tensile bond strength data is not sufficient alone to evaluate the sealing ability of resins.[21]

In the present study, Clearfil S3 bond was preferred as a self-etch adhesive in accordance with the previous study.[22] On the other hand, ASB total etch bond has previously been used in many comparative studies.[2324] Self-etch adhesives and composites may offer some advantages over the use of total etch adhesives. Self-etch adhesives have weak acids in their primer composition, which results in less change in the dentinal wall structure than with the strong acids of total etch systems. The application of primer without air-drying does not cause collapse of collagen fibrils at the dentinal structures.[25] Also, self-etch adhesive systems simplify the bonding procedures and decrease the time needed for application.[8] From the results of this study, it can be affirmed that self-etch adhesives still preserve their advantages over total etch adhesives. Within the limitations of this study, it can be concluded that there is a significant reduction in the bond strengths of both ASB total etch adhesive and CS3 self-etch adhesive to the pulp chamber walls after the application of different EDTA concentrations. From a clinical point of view, low EDTA concentrations can be chosen if self-etch adhesives are used.