Postspace pretreatment with 17% ethylenediamine tetraacetic acid, 7% maleic acid, and 1% phytic acid on bond strength of fiber posts luted with a self-adhesive resin cement.

Context: Pretreatment of radicular dentin with chelating agents improves the bond strength of fiber-posts luted with a self-adhesive resin cement. Aims: The aim of this study was to assess the effects of the three chelating agents as final rinse of the postspace on bond strength of fiber posts luted with a self-adhesive resin cement. Settings and Design: This is an in vitro laboratory study. Materials and
Methods: Forty-five mandibular premolars were prepared using MTwo rotary system and irrigation was done with 2.5% sodium hypochlorite. Three groups of teeth samples were considered for postspace preparation and irrigated with different solutions: Group 1: 17% ethylenediamine tetraacetic acid (EDTA); Group 2: 7% Maleic acid; Group 3: 1% Phytic acid. This was followed by the luting the posts with RelyX U200. After a week, from each sample, 2 mm thick slices were obtained from each third of the root and subjected to push-out bond strength testing. Statistical Analysis Used: One-way analysis of variance and Bonferroni's Post hoc analysis was used for assessing the results. The statistical significance level was set at P < 0.05.
Results: Bond strength values were improved with maleic acid and phytic acid pretreatment with slight or no significant difference between these groups. A final rinse of postspace with EDTA significantly reduced the bond strength. Conclusions: Maleic acid (7%) pretreatment of postspace improved the adhesion of fiber posts luted with a self-adhesive resin cement. Copyright:

INTRODUCTION

Teeth requiring root canal therapy presenting with significant coronal damage require posts to retain the core and the final crown [Supplementary Files].[1] While metallic posts have been traditionally popular, currently, fiber posts are preferred as they are more esthetic and can be adhesively bonded to the canal thus enhancing the longevity of postendodontic restorations. Fiber posts basically have an epoxy or methacrylate resin matrix reinforced with glass or silica fibers. They are more flexible as they have a modulus of elasticity closely mimicking that of dentin.[123]

Adhesive luting of fiber posts poses a greater challenge as they have to contend with the secondary smear layer (sealer and gutta-percha residues) created during postspace preparation.

Smear layer removal in endodontics is usually achieved by final irrigation using 17% Ethylenediamine tetraacetic acid (EDTA) followed by sodium hypochlorite (NaOCl). However, it has been reported that this approach may be detrimental to the adhesion of fiber posts.[4]

Presently, newer chelators like Maleic acid (7% conc.) and Phytic acid (1% conc.) are increasingly replacing EDTA as effective agents for smear layer removal.[56] However, there is limited research regarding their role in the adhesion of fiber posts.

Fiber posts can be adhesively bonded to the root canals using various adhesion strategies, such as total-etch, self-etch or self-adhesive systems. While total-etch adhesives have multiple clinical steps and are highly technique sensitive, self-etch adhesives are not capable of effectively penetrating the smear layer and bonding to the underlying dentin.[7]

Self-adhesive resin cements were introduced for the first time in the year 2002. They combine the properties of glass ionomers and resin cements.[8] Unlike the other two categories, they are simple and easy to use as they contain multi-functional methacrylated phosphoric acid esters that react with the mineral phase of dentin and also infiltrate and modify the smear layer.[9] Advantages of these cements include reduced technique sensitivity, less chair-side time, decreased contamination and improved retention.[169] Thus, self-adhesive resins are presently the material of choice for luting fiber posts. A literature search revealed limited information regarding the role of the newer chelating agents as a final rinse on the bond strength of self-adhesive resin cements.

The aim of this study was to assess the effect of postspace pretreatment with 17% EDTA, 7% Maleic acid and 1% Phytic acid on adhesion of fiber posts luted with a self-adhesive resin cement (3M ESPE RelyX U200).

MATERIALS AND METHODS

The study sample included 45 extracted human mandibular premolar teeth which were stored in thymol solution (0.1%). Atraumatically extracted intact premolars with minimal root curvature and devoid of caries or restorations were included in the study. After decoronation, biomechanical preparation was done with Mtwo (VDM, Munich, Germany) NiTi rotary instrumentation up to #25 file while rinsing with 2.5% NaOCl (Chemident, Delhi, India). Obturation was done using gutta-percha/AH Plus sealer (Dentsply Maillefer, Ballaigues, Switzerland). The samples were stored at 100% humidity.

Postspace preparation was done using peeso reamer (no. 3 = 1.1 mm tip diameter) leaving 4–5 mm of gutta-percha in the apical one-third. Later, the teeth were subdivided into 3 groups for final irrigation of postspace, using 30 gauge side vented needle.

Group 1: 5 ml of EDTA (17%) (Prime Dental Products Pvt. Ltd, India) for 1 min (n = 15)

Group 2: 5 ml of maleic acid (7%) (Leo Chemicals, India) for 1 min (n = 15)

Group 3: 5 ml of phytic acid (1%) (Leo Chemicals, India) for 1 min (n = 15).

The surfaces of the fiber posts (3M ESPE RelyX Fiber post) were treated with silane coupling agent prior to luting them with self-adhesive resin cement (3M ESPE RelyX U200).

After storage in distilled water for a week, 2 mm thick slices were sectioned using a low speed diamond disc from coronal, middle and apical third of the postspace. The samples were subjected to push-out bond strength testing in the universal testing machine. The posts were dislodged by applying the load at a crosshead speed of 0.5 mm/min to arrive at the bond strength values (MPa). Data were analyzed using one-way analysis of variance followed by Bonferroni's post hoc test to compare the mean pushout bond strength between the regions in each study group. The level of significance was fixed at P < 0.05.

RESULTS

The mean bond strength values in EDTA group for cervical 3rd were 52.96 ± 5.25, middle 3rd was 53.56 ± 5.09 and for apical 3rd region was 32.99 ± 5.17. Thus, the multiple comparisons revealed that the mean pushout bond strength significantly decreased from cervical to apical 3rd region at P < 0.001. Bond strength values were improved with maleic acid (cervical 3rd 62.44 ± 3.21, middle 3rd 72.48 ± 5.88 and apical 3rd was 67.43 ± 5.17) and phytic acid (cervical 3rd 60.98 ± 7.24, middle 3rd 70.60 ± 8.72 and apical 3rd was 65.52 ± 3.83) pretreatment with slight or no significant difference between these groups. A final rinse of postspace with EDTA significantly reduced the bond strength [Table 1 and Graph 1].

Table 1

Comparison of mean pushout bond strength between 3 different regions in each study group using repeated measures of ANOVA test followed by bonferroni’s post hoc test

Region	Groups	n	Mean±SD	Minimum	Maximum	P a	Significant different	P b
EDTA	Cervical	15	52.96±5.25	43.1	62.1	<0.001*	C versus M	<0.001*
	Middle	15	43.56±5.09	31.7	50.1		C versus A	<0.001*
	Apical	15	32.99±5.17	23.8	40.1		M versus A	<0.001*
Maleic acid	Cervical	15	62.44±3.21	57.9	68.2	0.001*	C versus M	<0.001*
	Middle	15	72.48±5.88	57.4	79.4		C versus A	0.11
	Apical	15	67.43±7.24	52.2	76.4		M versus A	0.22
Phytic acid	Cervical	15	60.98±7.24	42.5	70.8	0.02*	C versus M	0.04*
	Middle	15	70.60±8.72	60.3	93.9		C versus A	0.04*
	Apical	15	65.52±3.83	58.1	71.1		M versus A	0.28

*Statistically significant, aP-value derived by repeated measures of ANOVA, bP-value derived by Bonferroni’s post hoc analysis. C: Cervical 3rd region, M: Middle 3rd region and A: Apical 3rd region, SD: Standard deviation, EDTA: Ethylenediamine tetraacetic acid

Graph 1

Mean pushout bond strength between three different regions in each study group

DISCUSSION

A valuable means to evaluate the bond strength of fiber posts is the push-out bond strength test. It is considered to be highly accurate as it closely mimics the clinical situation and causes less errors during sample preparation.[710] In the present study, the testing was done using 2 mm thick specimens as this has been reported to distribute stresses more homogenously.[11]

During postspace preparation, the use of peeso reamers or proprietary drills creates an additional smear layer due to the smearing of the sealer cement and gutta-percha on the canal walls. Rinsing with chelating agents has been reported to eliminate this effectively.[12]

Optimal adhesion of self-adhesive cements is based on partial removal of smear layer followed by promoting micromechanical retention. In addition, they also demonstrate a chemical reaction between the acidic monomers of the resin cement and the hydroxyapatite of the radicular dentin. Dentin pretreatment with different chelating agents has shown varying effects on the bonding of self-adhesive resin cements. While most clinicians employ EDTA as the agent of choice for postspace cleansing, it may adversely affect the bond strength of some self-adhesive resin cements.[131415] Therefore the present research studied the role of two newer chelating agents, namely maleic and phytic acid on bond strength of a self-adhesive resin cement with EDTA being used as the control group. Final rinse was done for 1 min for all the irrigants to minimize demineralization and dentin erosion.[11]

Maleic acid is an effective smear layer removing agent at a concentration of 7% whereas increasing the concentration to 10% or more resulted in damage and demineralization of the intertubular dentin. Hence, Maleic acid in a concentration of 7% was employed in our study.[16]

Phytic acid, chemically known as inositol hexakisphosphate, is found in foods such as cereals, legumes, oilseeds, and nuts. Phytic acid etches the dentin, acts as a natural cross-linker by stabilizing the demineralized dentin matrix, and provides good resin dentin bonding. Irrigating the canals with 1% Phytic acid for 30 s to 1 min provides a clean, debris-free canal space and open dentinal tubules.[51718] Hence, phytic acid at 1% concentration was employed in this study.

Self-adhesive resin cements are currently popular to lute the fiber postdue to their simplified clinical procedure. While their major mode of retention is micromechanical, some may demonstrate additional chemical adhesion to hydroxyapatite.[1] RelyX U200, which is the self-adhesive resin cement used in the present research, is a dual-cure cement which exhibits both modes of retention.[1920] It has been reported to exhibit excellent bond strength even under wet conditions.[7921]

The present study revealed that the use of different chelating solutions as final rinse has a variable effect on bonding fiber posts to the radicular dentin. The following order was observed in the bond strength values: Maleic acid > phytic acid > EDTA.

Mean bond strength values for a maleic acid group in cervical 3rd was 62.44 ± 3.21, in middle 3rd was 72.48 ± 5.88 and in apical 3rd was 67.43 ± 5.17. For phytic acid group, the mean bond strength values in cervical 3rd were 60.98 ± 7.24, in middle 3rd was 70.60 ± 8.72 and in apical 3rd was 65.52 ± 3.83. For EDTA group the mean bond strength values in cervical 3rd were 52.96 ± 5.25, middle 3rd was 53.56 ± 5.09 and for apical 3rd region was 32.99 ± 5.17.

Numerous studies have revealed the superior performance of maleic acid as an agent to remove the smear layer. It has been reported that final irrigation with maleic acid enhances the bond strength of fiber posts as opposed to EDTA. It demonstrated an increased number of open dentinal tubules and minimal debris which promotes better adhesion of resin cement with the dentin, thus contributing to the high bond strength.[13141622] Other studies have shown that maleic acid at a low concentration of 7% has reduced demineralizing effect on the dentin.[16] These findings support the results of our study.[141722]

Shivanna demonstrated high bond strength of resin sealers to dentin after final rinse with maleic acid.[22] Ballal et al.,[13] reported that 7% maleic acid produced greater surface roughness of the root canal walls which was not the case with 17% EDTA. Furthermore, there is an increased collagen degradation seen with EDTA than with maleic acid.[17] All these additional factors may have a role in the superior performance of maleic acid in the present study.

Phytic acid is another mild chelating agent with a superior ability to deal with the smear layer than EDTA. Several mechanisms have been attributed to the high bond strength obtained after irrigation with phytic acid:

Mild etching effect of phytic acid without the significant depth of demineralization may facilitate better infiltration of resin monomers

It is a natural collagen cross-linker enhancing resin-dentin bond strength[23]

Interaction between phytic acid, collagen, and hydroxyapatite forms a complex structure combining collagen and calcium phytate that promotes adhesion with resin cement.[51721]

A significant increase in bond strength of RelyX U200 has been shown after final irrigation with phytic acid as compared to EDTA in a recent research.[6] This finding also corroborates with the results of this study.

On the other hand, studies have reported that EDTA interferes with the adhesion of RelyX U200 as it creates a partial apatite-depleted substrate.[1] It has also been speculated that residual EDTA interferes with the chemical curing of RelyX U200.[24]

Comparing the bond strength at all three levels of the root canal, final rinse with EDTA demonstrated higher bond strength at the cervical third (52.96 ± 5.25) of the postspace as compared to the apical 3rd (32.99 ± 5.17). Its reduced efficacy near the bottom of the postspace has been reported by other studies. Its higher surface tension compared to maleic acid may be a factor in this regard.[17] On the other hand, both maleic acid and phytic acid demonstrated high bond strength at all levels which is similar to the results of other investigators.[14] Their superior performance could be due to better interaction with the smear layer.[16]

Overall, the bond strength of fiber posts luted with the self-adhesive resin cement showed good results when the postspace was irrigated with maleic acid and phytic acid which was not the case with EDTA. Since these results were observed under ideal laboratory conditions, they cannot be directly applied to the clinical scenario. The present study assessed the push-out bond strength 1 week after treating with the chelating agents. Long-term bond durability was not assessed. This needs to be evaluated in a future study. Although self-adhesive resin cements can simplify luting of fiber posts, further research should focus on their adhesive mechanisms and associated factors.

CONCLUSIONS

The use of 7% Maleic acid as a final rinse prior to fiber postcementation using a self-adhesive cement (RelyX U200) significantly improved their adhesion.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.