SRM Journal of Research in Dental Sciences

ORIGINAL ARTICLE
Year
: 2021  |  Volume : 12  |  Issue : 3  |  Page : 117--121

Comparative assessment of long-term bond strength between fiber post and root dentin with and without 6.5% cocoa seed extract pretreatment – An in vitro study


Shilpi Tiwari, Chethana S Murthy, Meena Naganath, Anitha Kumari Rangappa 
 Department of Conservative Dentistry and Endodontics, Vokkaligara Sangha Dental College and Hospital, Bengaluru, Karnataka, India

Correspondence Address:
Dr, Shilpi Tiwari
Department of Conservative Dentistry and Endodontics, Vokkaligara Sangha Dental College and Hospital, Room No. 6, V. V. Puram, K. R. Road, Bengaluru - 560 004, Karnataka
India

Abstract

Background: Cocoa seed extract (CSE) is a natural cross-linker or biomodifier, which contains proanthocyanidin that increases the immediate resin-dentin bond strength as well as reduces the dentinal matrix degradation. There are very few studies which shows the long-term effects of the cross-linking agents on radicular dentin. Aim: The aim of this study was to assess and compare the effect of 6.5% cocoa seed extract (CSE) on long-term push out bond strength between fiber post and root dentin cemented by using two different adhesive systems – total etch adhesive system and self-etch adhesive system. Materials and Methods: Sixty extracted permanent maxillary central incisors were decoronated to standardize the root length. Root canal preparation followed by postspace preparation was done. Specimens were then randomly divided into four groups according to the adhesive technique and CSE pretreatment – Group 1: Total-etch adhesive + without 6.5% CSE treatment, Group 2: Total-etch adhesive + with 6.5% CSE treatment for 10 min, Group 3: Self-etch adhesive + without 6.5% CSE treatment, and Group 4: Self-etch adhesive + with 6.5% CSE treatment for 10 min. Fiber posts were cemented with resin cement, and then, specimens were stored in an incubator for 180 days. Specimens were then tested for pushout bond strength using the universal testing machine. Statistical analysis was performed using the one-way ANOVA followed by Tukey's post hoc analysis. Results: CSE-treated groups showed higher bond strength than nontreated group. Group 2 showed significantly higher bond strength among all groups. Conclusion: The pretreatment with Proanthocyanidines containing CSE can be a natural alternative to improve the long-term resin–dentin bond strength.



How to cite this article:
Tiwari S, Murthy CS, Naganath M, Rangappa AK. Comparative assessment of long-term bond strength between fiber post and root dentin with and without 6.5% cocoa seed extract pretreatment – An in vitro study.SRM J Res Dent Sci 2021;12:117-121


How to cite this URL:
Tiwari S, Murthy CS, Naganath M, Rangappa AK. Comparative assessment of long-term bond strength between fiber post and root dentin with and without 6.5% cocoa seed extract pretreatment – An in vitro study. SRM J Res Dent Sci [serial online] 2021 [cited 2021 Dec 4 ];12:117-121
Available from: https://www.srmjrds.in/text.asp?2021/12/3/117/326207


Full Text



 Introduction



Fiber posts have been widely indicated in root canal-treated teeth where coronal structure is compromised, mainly because the elastic modulus of fiber post is almost near to radicular dentin which minimizes the incidences of vertical root fractures.[1],[2]

Resin luting cements are used to bond a fiber post to the root dentin in conjunction with either total etch adhesives or self-etch adhesives.[3] However, a stable and reliable resin-dentin interface is still a challenge in adhesive dentistry.[4],[5] The loss of retention of resin-dentin bond with time is because of the hydrolytic degradation of resin component[6] and degradation of tooth collagen derived through the host enzymes.[7]

Synthetic matrix metalloproteinase (MMP) inhibitors such as chlorhexidine (CHX) have been documented to inhibit the enzymatic degradation of activated MMPs and prevent the resin – dentin bond degradation.[8] Cross-linking agents like proanthocyanidines, carbodiimide, genepins, and glutaraldehyde [GA] increases interfibrillar, intrafibrillar, and intermicrofibrillar cross linking of collagen fibrils.[8]

The use of CHX has shown to be an effective way to inhibit MMPs as well as cysteine cathepsins (CTs).[9] However, CHX is a water soluble compound which may leach out from the hybrid layer over a period of time, hence affects its long-term anti-MMP effectiveness.[9] Other cross linkers such as formaldehyde, GA, and carbodiimide also have been used in various studies, but these materials present several drawbacks such as toxicity, instability, and difficulty in controlling their cross-linking rate.[10] Hence, an ideal cross-linking agent should have low toxicity and should be biocompatible as well. Proanthocyanidins which are the specific group of polyphenolic compounds can fulfil this criteria, hence appears the most promising agents to improve the long-term resin dentin bond stability. These compounds can be procured naturally from fruits, vegetables, nut, seeds, and barks as a plant metabolite.[10] Epasinghe et al. showed that proanthocyanidines inhibits the MMPs and also found that proanthocyanidines reduces the degradation of dentin matrix more efficiently than chlorhexines.[11]

Cocoa seed extract (CSE) and grape seed extract are natural cross linkers or biomodifiers, which contains proanthocyanidin (PA) that increases the immediate resin-dentin bond strength as well as reduces the dentinal matrix degradation.

Most of the studies that evaluated the effect of cross-linking agents have shown the short-term beneficial results on coronal dentin,[12],[13] but there are very few studies which shows the long-term effects of these cross-linking agents on radicular dentin. Hence, the aim of this study was to assess and compare the effect of 6.5% CSE on long-term push out bond strength (180 days) between fiber post and root dentin cemented by using two different adhesive systems – total etch adhesive system and self-etch adhesive system.

 Materials and Methods



Preparation of 6.5% cocoa seed extract

6.5 g of CSE powder (Sattvic foods, India) was mixed in 100 ml solution of 95% ethanol and distilled water (1:1 ratio). The pH of the prepared solution was adjusted to near neutral followed by filtration using Whatman Filter Paper.[12]

Specimen preparation

Sixty permanent maxillary central incisors with fully developed apices were decoronated below CEJ to standardize the root length to 14 mm. Root canal preparation was done 1 mm short of the apex, followed by postspace preparation to a length of 10 mm till size #3 Peeso Reamer (Mani™). Afterward, specimens were randomly divided into four groups according to the adhesive technique used in bonding procedure and pretreatment with 6.5% CSE – Group 1: Total Etch Adhesive System (Adper Scotch Bond Multipurpose 3M™) without 6.5% CSE Pretreatment, Group 2: Total Etch Adhesive System (Adper Scotch Bond Multipurpose 3M™) with 6.5% CSE pretreatment for 10 min, Group 3: Self-Etch Adhesive System (Clearfil SE Bond–Kuraray™) without 6.5% CSE pretreatment, and Group 4: Self-Etch Adhesive System (Clearfil SE Bond–Kuraray™) with 6.5% CSE pretreatment for 10 min

In total etch adhesive Group 2, CSE was applied with the help of applicator tip after the acid etching and before primer application, while in self etch Group 4, CSE was applied before primer application.[13]

60 Fiber Post (Size 3, Angelus Reforpost, Brazil) were cleaned with 95% ethyl alcohol and then Silane Coupling Agent (Silano Angelus™) was applied for 1 min,[15] followed by Scotch Bond or Clearfil SE™ bonding agent application and light cured for 20 s. The dual-polymerizing resin luting cement: ParaCore (Coltene™) was injected into the prepared root canal by automix syringe and light cured for 40 s. Specimens of all four experimental groups were placed in saline and stored in an incubator at 37°C and 100% humidity for 180 days to simulate the oral environmental conditions.

Push-out test

Each root was cut horizontally with a low-speed, water-cooled diamond saw (Minitom – Struers™) to produce three slices of 2-mm thickness [Figure 1]. The first coronal slice was discarded. Hence 2 slices were taken from each root canal (total 120 slices obtained) for push out test.{Figure 1}

Universal Testing Machine (Mecmesin™) was used to perform the push-out test. Test was performed by applying a cross head speed at 1 mm/min from apex to crown until the fiber post was separated from the tested slice [Figure 2]. The applied load was divided by the bonded area (A) to convert the maximum failure load (Newton) into Megapascal (Mpa).{Figure 2}

Statistical analysis

Statistical analysis was done using the Statistical Package for the Social Sciences for Windows Version 22.0 Released 2013. Armonk, NY: IBM Corp. One-way ANOVA test followed by Tukey's honest significant difference (HSD) post hoc analysis was used to compare the mean push out bond strength (in MPa) between four study groups at 180 days' time interval. The level of significance was set at P < 0.05.

 Results



[Table 1] shows the mean, standard deviation, minimum, and maximum values for each group. The mean and standard deviation was calculated for each group as it gives a collective measure of the distribution of all values throughout the group and also for the purpose of comparison between the groups.{Table 1}

The difference in the mean push out bond strength between the four groups was statistically significant at P < 0.05.

[Table 2] shows the multiple comparison of mean differences between experimental groups at 180 days' time interval using Tukey's HSD post hoc analysis. The multiple comparison of mean push out bond strength between the four groups demonstrated that Group 2 showed significantly highest mean push out bond strength as compared to Group 1, Group 3, and Group 4 at P < 0.001. Similarly, Group 1 showed a higher mean push out bond strength as compared to Group 3 and Group 4 at P < 0.001. Finally, Group 3 showed a significantly lesser mean push out bond strength as compared to Group 4 that is statistically significant at P < 0.001.{Table 2}

The results of this study infer that Group 2 demonstrated highest mean push out bond strength followed by Group 1, Group 4, and the least by Group 3.

 Discussion



Dentin organic matrix is made up of 90% Type I collagen fibrils and 10% noncollagenous proteins. The physiologic cross linking between the collagen fibrils is a key factor which provides stability and strength to dentin matrix.[15] However, studies have established that the loss of integrity between resin and dentin interface occurs, due to the activation of MMPs and CTs which results in collagen fibrils degradation over a period of time.[7],[10] Therefore, it was hypothesized that if exogenous cross-linking agent is applied on dentin surface, it induces additional cross linking between collagen fibrils and make it more stable and resistant against the host derived enzymatic degradation.[2]

Exact mechanism of additional cross linking is unknown, but it was suggested that PA interacts with the collagenous proteins and form hydrogen bonds, covalent bonds, ionic bonds, and hydrophobic interactions between them.[14],[15],[16] Balalaie et al. (2018) suggested that PA treatment provides protection to collagen fibrils against collagenases through allosteric inhibition, i.e. masking the cleavage sites of collagen matrix.[16] It also decreases the swelling ratio which indicates the reduced absorption rate of collagenase enzyme.[15] Hence, all these unique properties of PA as a exogenous cross-linking agent justify its use in the prevention of long-term degradation of resin dentin interface.

The results of the present study showed that 6.5% CSE treated group had higher push out bond strength between resin-dentin interface after 180 days of storage as compared to nontreated group. These results are in corroboration with Cecchin et al. and Epasinghe et al.[2],[12] These results can relate to the ability of PA to increase the intermolecular and intramolecular cross linking of dentin collagen fibrils and also the ability to resist degradation against MMPs and CTs by deactivating these enzymes. The nontreated group showed significantly less bond strength after 180 days of storage, indicating resin – dentin interface degradation which might be suggestive of hydrolytic degradation of resinous components as well as collagen degradation as a result of MMPs and CTs activation.[2],[3]

Total etch adhesives versus self-etch adhesives

Although in this study 6.5% CSE treatment showed improved bond strength for both the adhesive system, the bond strength was lower in self-etch group as compared to total etch group. The reason could be because of greater susceptibility of self-etch group toward water sorption[17] and its more hydrophilic composition.[18] Hashimoto et al suggested that self-etch adhesive systems showed a lower degree of conversion due to the presence of excess water at the resin-dentin interface.[19] This could result in the presence of uncured monomers that might leach out over a period of time creating nanosized channels, these channels further increases the permeability of water as well as its movement through the interface.[20] These reasons could be the cause of lower bond strength of self-etch adhesive system.

Effect of solvent in preparing 6.5% cocoa seed extract solution

Hansen solubility parameter (δH) which represents the amount of probable hydrogen bonding, i.e. lesser the value of δH, less will be the hydrogen bonding.[21] Hence more unbonded hydrogen sites will remain available in PA molecules for interaction with collagen. δH is lower in cases of polar solvents (acetone, ethanol, etc.,) than nonpolar solvents (distilled water). Hence, ethanol used as a solvent for procuring 6.5% (w/v) CSE.

In the present study, preconditioning time with CSE considered was 10 min, which is not feasible clinically, as it will increase the technical sensitivity as well as valuable chair side time. However, Liu et al. demonstrated that by increasing the concentration of PA to 15%, the treatment time can be reduced to 1 min, which is clinically feasible.[15]

Furthermore, preconditioning with PA introduces a burden of one additional step. These limitations can be negated by incorporation of proanthocyanidines into the etchant adhesives system.[15] Thus, several aspects need further research such as preparation and storage of the CSE solution, appropriate PA concentration to reduce the treatment time, method of PA application, incorporation of PA into adhesive system, other novel modifications in use of PA while maintaining the quality of resin dentin hybrid layer without affecting degree of conversion and curing properties of adhesives. Hence, the subject is open for research in some of these areas of PA application and its use.

 Conclusion



The pretreatment with proanthocyanidines containing CSE improves the long term resin – dentin interface bond strength. Cocoa seed treated groups showed significantly higher long-term bond strength of resin-dentin interface than nontreated group. Total etch adhesives showed significantly higher bond strength than self-etch adhesives in both CSE-treated and nontreated group.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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