Can intra-radicular cleaning protocols increase the retention of fiberglass posts ?

Abstract: The presence of residues within the root canal after post-space preparation can influence the bond strength between resin cement and root dentin when using fiberglass posts (FGPs). Currently, there is no consensus in the literature regarding what is the best solution for the removal of debris after post-space preparation. This systematic review involved “in vitro” studies to investigate if cleaning methods of the root canal after post-space preparation can increase the retention of FGPs evaluated by the push-out test. Searches were carried out in PubMed (MEDLINE) and Scopus databases up to July2017. English language studies published from 2007 to July 2017 were selected. 475 studies were found, and 9 were included in this review. Information from the 9 studies were collected regarding the number of samples, storage method after extraction, root canal preparation, method of post-space preparation, endodontic sealer, resin cement, cleaning methods after post-space and presence of irrigant activation. Five studies presented the best results for the association of sodium hypochlorite (NaOCl) and ethylenediamine tetra-acetic acid (EDTA), while in the other 4 studies, the solutions that showed improved retention of FGPs were photoninduced photoacoustic streaming (PIPS), Qmix, Sikko and EDTA. The results showed heterogeneity in all comparisons due to a high variety of information about cleaning methods, different concentrations, application time, type of adhesive system and resin cements used. In conclusion, this review suggests that the use of NaOCl/EDTA results in the retention of FGPs and may thus be recommended as a post-space cleaning method influencing the luting procedure.


Introduction
In the rehabilitation of endodontically treated teeth with extensive dental structure losses, the use of fiberglass posts (FGPs) is a viable alternative.¹FGPs exhibit similar physical properties to dentin, such as elastic modulus, compressive strength, flexure, thermal expansion coefficient, and advantages, such as aesthetics and biocompatibility. 2,3,4he retention of the FGPs depends on the adhesive interaction and better adaptation between the resin cement and root dentin. 5Failures of FGPs occur by root fracture or debonding between post and resin cement while frequently occurring on the resin cement and root dentin. 4,6,7These interfaces could be affected by several factors, such as orientations of dentinal tubules, presence of residues, endodontic sealers, type of adhesive system and cementation strategies. 8,9esin-based luting cements are used to promote mechanical adhesion between the monomers of the material and the collagen fibers of dentin, with consequent formation of the hybrid layer. 10Cements and adhesive approaches have been proposed to bond FGPs to root dentin in the main available techniques, including conventional or self-adhesive resin cements.Dual polymerizing resin cements associated with previous dentin conditioning on etch and rinse adhesive systems have demonstrated good results; however, self-adhesive cements appeared as an alternative to avoid the critical drying step with less time for cementation because there is no requirement for pretreatment on root dentin. 11In this sense, the chemical interaction between the acidic hydrophilic monomers and hydroxyapatite modifies the smear layer, thus ensuring the adhesion of the self-adhesive cements to dentin. 11,12he presence of residues in root canal walls, composed of the remaining sealer, gutta percha and smear layer debris, must be removed to open dentinal tubules to enhance the intertubular penetration of the adhesive system and avoid weakened areas in the bonding interface as to increase bond strength. 8,9,13,14NaOCl, EDTA, phosphoric acid, and chlorhexidine are the most routinely used agents and have different chemical properties. 15Moreover, activation methods of irrigation solutions have been used as an additional method to increase their effectiveness, such as the use of ultrasonic systems and laser devices. 16,17,18espite the large number of in vitro studies in the literature, there is currently no consensus on the best solution for removing debris after post-space preparation, while it remains unclearif this can affect the bond strength of FGPs to root dentin. 19Therefore, the objective of this study was to systematically review the literature using in vitro studies to investigate if cleaning methods of root canal after post-space preparation can increase the retention of FGPs evaluated by push-out test.The null hypothesis was that cleaning methods of the root canal after post-space would not influence the bond strength of FGPs to root dentin.The following research question was investigated: Does the method of root canal cleaning after post-space preparation influence the retention of a fiber post evaluated by push-out tests?

Search strategy
This systematic review was conducted by following the guidelines of Transparent Reporting of Systematic Reviews and Meta-analyses (PRISMAstatement). 20The review question was formulated by the following PICO 21 framework (Patient Population, Intervention, Comparison, and Outcome).The following keywords and their combinations were used: "Root Canal Preparation"[Mesh] OR "Canal Preparation, Root" OR "Canal Preparations, Root" OR "Preparation, Root Canal" OR "Preparations, Root Canal" OR "Root Canal Preparations" OR "root canal cleaning" OR "root canal irrigation" OR "post-space cleaning" OR "post-space preparation cleaning" OR "mechanical cleaning root space" OR "intracanal cleaning"; AND "fiber post" OR "fiber glass" OR "Post and Core Technique"[Mesh] OR "Post-Core Technic" OR "Post-Core Technics" OR "Technic, Post-Core" OR "Technics, Post-Core" OR "Post and Core Technic" OR "Post Technique" OR "Post Techniques" OR "Technique, Post" OR "Techniques, Post" OR "Post Technic" OR "Post Technics" OR "Technic, Post" OR "Technics, Post" OR "Dental Dowel" OR "Dowels, Dental" OR "Dental Dowels" OR "Dowel, Dental" OR "fiber glass post" OR "glass fiber post"; AND "postspace preparation" OR "post-space preparation" OR "endodontic procedures root canal" OR "deep post-space" OR "post-space".

Eligibility criteria
Literature on the topic in the English language, published from 2007 to July 2017, was selected.All in vitro studies that evaluated the method of root canal cleaning tested by push-out were included.
The inclusion criteria were as follows: in vitro studies that used human teeth, the push-out test was included in the methods, a fiber glass post was cemented, resin cement was used to fill the canal, and some irrigant solution method to clean the canal was used, whether activated or not.The exclusion criteria were as follows: studies that did not use human teeth, the push-out test was not described, use of eugenol endodontic sealer, use of solutions for pretreatment after the post-space to improve adhesion, and use of dental canal surface treatment prior to cleaning methods.Duplicated and published studies that did not meet the inclusion/exclusion criteria were excluded from this systematic review.

Screening and selection
A comprehensive electronic search was performed through PubMed (MEDLINE) and Scopus databases up to July 2017.A hand searching process was applied based on the references of selected articles.Two endodontic specialist reviewers (L.V.O. and C.C.G.M.) independently ran the described search for eligibility.The lists were then compared, and a definitive consensus regarding the inclusion of articles was reached by discussing each individual article

Data extraction and risk of bias
A data extraction form was developed by the authors to collect general information (title, year of publication, journal, authors, impact factor, aim of study, number of samples, storage after extraction, root canal preparation, method of post-space, moment (time) of post-space before FGPs cementation, endodontic sealer, post resin cement, method of cleaning of root canal after post-space, groups analyzed, presence of final activation, storage/aging, methodology of analysis of samples, hypothesis accepted or rejected, statistical results, conclusion).The JADAD scale 22 assesses the methodological quality of the studies, reporting any potential risk for bias.Each question of this three-point questionnaire needed to be answered with either a yes or a no.Authors elected to exclude all papers on the topic with a JADAD score of 3 or less.Two endodontic specialist reviewers (L.V.O. and C.C.G.M.) evaluated all of the selected studies.

Results
Based on this systematic review objective, the lack of information and the heterogeneity of the selected studies, it was not possible to perform valid quantitative analyses of the data or a subsequent meta-analysis.Therefore, a descriptive presentation of the data was adopted.
A n i n it i a l e le c t r on ic s e a r c h ide nt i f ie d 473 studies (Figure 1), and the hand searching process identified 2 studies 8,23 (total of 475 studies).The initial screening of the titles and abstracts resulted in 20 full-text papers that were read in full.The characteristics of the 9 included studies are summarized in Table 1. 8,17,19,23,24,25,26,27,28Eleven studies that did not meet the inclusion criteria (Figure 1) were excluded. 29,30,31,32,33,34,35,36,37,38,392 did not used fiberglass post 29,30 3 did not used human teeth 31,33 1 used eugenol endodontic sealer 34 1 did not used push-out test 35 2 used solution for pre-treatment 36,37 1 used dental canal surface treatment prior to cleaning methods 38 1 the root canal was not obturated 39 To evaluate the effects of different post-space treatments on push-out bond strength of glass fibre posts.
To analyze the effects of five different irrigation protocols (IPs) on the bond strengths of fiber posts luted using three different adhesive strategies.
To evaluate the effects of different surface treatments on the bond strength of a fiber post to dentin.

Description of studies
All studies were in vitro, of which a high number of the selected studies had low methodological quality, revealing a high risk of bias, which precluded any statistical analysis of the data.
This systematic review included studies that analyzed the influence of cleaning methods of root canal after post-space preparation on the performance of FGPs evaluated with the biomechanical push-out test.For this investigation, all studies used a fiberglass post in a root canal that was filled with resin-based endodontic sealer.The studies used human teeth, of which the most frequent were premolars, canines or incisors.The most frequently resin-based endodontic sealer used was AH Plus (Dentsply, York, PA, USA).The timing of post-space after obturation revealed certain heterogeneity, where 4 studies were relieved after 7 days, 2 after 24 hours, 1 after 72 hours, and 1 after 2 weeks post-obturation.One study did not show the period for post-space preparation.Seven studies used the association of NaOCl/EDTA in some of their experimental groups. 8,17,23,24,25,26,27,28hlorhexidine appeared in 3 studies, 18,25,26 although in one of these studies, there was also the presence of chlorhexidine in the composition of a commercial solution called Qmix. 26Other solutions that were also tested included NaOCl and EDTA used individually, with some variations of time and concentration, 8,16,18,26,27 of which the most used concentrations were 5.25% NaOCl and 17% EDTA both for a maximum of 1 minute.Regarding the methods of activation of the irrigating solutions, 5 studies 18,23,24,27,28 reported using some type of activation method to potentiate the cleaning effect.Most failure modes were of the adhesive type at the junction of the root dentin and resin cement, which is the retention region of the FGPs.All studies were classified as having a high risk of individual bias.

Discussion
To the best of the authors' knowledge, this systematic review is the first to summarize in vitro data on the influence of cleaning methods on root canals after post-space preparation on the performance of FGPs luting by dual resin cements.The retention between root dentin and resin cement is a critical point for luting FGPs, since interference in the resin-dentin diffusion zone affects the longevity of the FGPs. 23,40,41lthough several studies have evaluated the effect of post surface treatments and cementation strategies on the retention of FGPs, the presence of the smear layer and debris along the post-space canal walls can also affect the optimal dentin adhesion. 8The role of cleaning methods after post-space supports clinicians in terms of evidence-based decision making.Therefore, the tested hypothesis was rejected.
For anatomical reasons, the apical third of the root presents deep, narrow irregular dentin and a fewer number of dentinal tubules, which are often sclerotic and render any adhesive application protocol difficult to control. 42In addition, another reason that explains the lower bonding potential at the deeper root canal dentin is the distance from the light activation, resulting in a lower monomer conversion and reduced resin cement polymerization. 8,41,43Endodontic sealer residues might also interfere with the polymerization of the resin cement. 44The presence of the smear layer impairs an adequate contact between the acidic methacrylates of self-adhesive resin cements and the underlying dentin during adhesive procedures, thus interfering with bond strength. 19The partial or total debris removal previous to resin cement insertion into the root canals might improve post retention and, consequently, the bond strength. 34Acidic solutions such as EDTA have shown good results in removing the smear layer but do not adequately demineralize dentin or enhance the contact of the self-adhesive resin cements with dentin. 45In contrast, NaOCl solution alone partially removes the smear layer, causing removal of dentinal proteins and making the dentin surface hydrophilic, which could impair resin cement polymerization. 46he current study was conducted by in vitro studies due to the difficulty of evaluating this parameter in vivo.Only human teeth were included in this study because they are closest to the clinical conditions in which the posts are installed.However, bovine teeth or artificial devices could be used to evaluate FGPs retention.8][49] To standardize the samples, only studies that performed the bond strength test by using push-out test were included, since it is a commonly used test to evaluate FGPs as it provides a better estimate of the bond strength. 50n relation to the treatment of the dentin surface for the removal of debris previous to FGPs cementation, there are several forms, such as aluminum oxide blasting, rotary brushes and irrigating solutions that are activated or not. 17Regarding the irrigation solutions, we verified the use of NaOCl, EDTA, chlorhexidine, distilled water, QMix (Dentsply Tulsa Dental), phosphoric acid, alcohol, Sikko Tim (VOCCO, Germany), and citric acid. 8These irrigant solutions promote flushing of the flue and dissolve the tissues, while theydisplay antimicrobial characteristics in the removal of the smear layer formed during the post-space of the root canal. 51Considering these criteria, only nine studies were included, of which five studies showed better results for the combination of NaOCl/EDTA, regardless of the sequence of the use. 17,23,25,27,28The increased FGP bond strength after the combination of NaOCl/EDTA solutions 17,23,25,27 may be attributed to the ability of the solutions to remove the smear layer, thus improving cement contact and penetration into dentinal tubules. 25ecently, the use of irrigation activated by ultrasonic, lasers, and negative apical pressure (Endovac) has been discussed. 52However, the activation does not necessary imply a better bond strength. 23,24n addition, the association of NaOCl/EDTA with ultrasonic agitation had a better performance when compared with non-activated NaOCl/EDTA on the removal of debris capacity. 28Ultrasonic application showed good results in the most important retention areas, since it is possible to reach the entire length of the root canal with irrigant solutions. 53In addition, distilled water was used frequently as the final irrigation. 17,24,25,27,28Boosting the effect of cleaning methods may reduce precipitate formation. 54The higher bond strength by using this protocol was explained by the removed smear layer and opened dentinal tubules. 28e association of non-activated NaOCl/EDTA also showed satisfactory results when using self-adhesive resin cement for FGPs cementation. 17However, when cemented with an etch-and-rinse adhesive system, the best results were assigned to NaOCl 1% with ultrasonic activation, 17 which leads us to believe that each adhesive strategy should be adapted to each irrigant procedure.Knowing that self-adhesive cement has been widely used because of its chemical or micromechanical retention on the dentin surface, 55 the association of NaOCl/EDTA can be considered as an excellent choice for root canal cleaning after post-space on self-etch and self-adhesive strategies involving adhesive cementation, as the acid-resin monomers of these cements may not be as effective as phosphoric acid in penetrating and modifying the smear layer of the root canal.The resin cement type and the composition can negatively interact with the cleaning agents.This aspect is more sensitive for the selfadhesive system, since it does not use phosphoric acid.The same irrigants may influence the polymerization reaction and, consequently, the bonding interaction. 23here is a scarcity of studies testing different irrigants with different self-etching resin cements.In general, the RelyX U200 is less sensitive with the use of NaOCl and EDTA irrigation. 23,45n the other hand, the isolated or alternate use of the NaOCl and EDTA solutions, intensified by some methods of activation, was not as effective as the distilled water activated with PIPS. 24PIPS is a novel laser agitation technique used with an erbium:yttrium-aluminum-garnet (Er:YAG) laser. 56,57he higher efficiency of this technique is based on photoacoustic and photomechanical action without the need to extend the root apex; each propellant reacts with the water molecules, constituting expansion and succession waves that create intermittent fluid. 56Such results support the use of Er:YAG laser activation or PIPS to improve the effectiveness of the final irrigation after post-space preparation; however, more studies are needed to confirm this finding. 24nother cleaning method option that also exhibited good results was a commercial product named Sikko Tim (VOCCO, Germany), which is an ethyl acetate and acetone-based cleaning agent.The group treated with Sikko showed the highest bond strength values compared to NaOCl/EDTA. 8 However, it could not remove the smear layer effectively and differed with an association of 17% EDTA for 60 s and 5% NaOCl for 15 s, which appeared to be satisfactory.The product Sikko did not show satisfactory results regarding the opening of the dentin tubules, as well as the removal of the smear layer and cement remnants, and thus has not been indicated for the self-etching system. 8herefore, more studies are needed to evaluate the use of this solution.Another study using NaOCl and EDTA independently found better GFP bond strength when 14% EDTA irrigation and the self-adhesive resin cement were used. 19This fact can be attributed to the low pH of EDTA, in addition to its ability to act as a chelator by removing the smear layer and cleaning the root canal. 58EDTA removes calcium from hydroxyapatite and is linked to non-collagenous protein.Thus, collagen fibrils are preserved, and they subsequently improve the infiltration of the resin material, resulting in higher adhesion strength between resin cement and root dentin. 59Chlorhexidine has also been used as a possible irrigation solution post-space preparation 17,25,26 .Three studies used chlorhexidine, but only one had satisfactory results by using a commercial formulation named QMix. 26It is composed of EDTA, chlorhexidine and a surfactant, supporting the removal of the smear layer while opening dentin tubules and simplifying the irrigation protocol. 26,60This solution decreases the surface tension of the root dentin, thus increasing its wett ability, as well as its capacity to contact the smear layer and the underlying dentin to improve irrigation. 19,60he result of the present systematic review should be interpreted with caution considering that in vitro studies have limitations regarding simulating in vivo conditions.The variety of cleaning methods, different concentrations, application time, type of adhesive system and resin cements used result in heterogeneous comparisons, which reduce standardization and demonstrate a high risk of bias.Therefore, more attention should be placed on the influence of root canal cleaning methods after post-space on the cementation of FGPs because the presence of residues may negatively interfere with the adhesion of the fiber post to the root canal. 8,13

Conclusion
Based on the findings of this systematic review, it is possible to conclude that root canal cleaning methods after post-space, whether activated or not, can affect the bond strength of FGPs.Despite the variability of irrigation protocols in most of these studies, the current findings may suggest that the use of NaOCl/EDTA could be recommended for post-space irrigation when luting a fiber post, since it demonstrated a better performance compared to other irrigation solutions.

Figure 1 .
Figure 1.Flow diagram of the systematic review according to the PRISMA Statement.

Table 1 .
Summary of the characteristics of the 9 included studies.