Effects of Endodontic Sealers and Irrigation Systems on Smear Layer Removal after Post Space Preparation

Effects of Endodontic Sealers and Irrigation Systems on Smear Layer Removal after Post Space Preparation

Basic Research—Technology Effects of Endodontic Sealers and Irrigation Systems on Smear Layer Removal after Post Space Preparation Xuan Chen,* Haixia...

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Basic Research—Technology

Effects of Endodontic Sealers and Irrigation Systems on Smear Layer Removal after Post Space Preparation Xuan Chen,* Haixia Liu, MA,* Yuanli He,* Tao Luo,* and Ling Zou, PhD, MD*† Abstract Introduction: The aim of this study was to investigate the effects of endodontic sealer types and ultrasound on smear layer removal after post space preparation. Methods: Thirty-six bovine incisors were chemomechanically instrumented and randomly divided into 3 groups (n = 12) according to the endodontic sealer (AH Plus [Dentsply DeTrey, Konstanz, Germany], Apexit Plus [Ivoclar Vivadent AG, Schaan, F€urstentum Liechtenstein], or iRoot SP [Innovative Bioceramix, Vancouver, BC, Canada]) used during root canal obturation, and the groups were further subdivided randomly into 3 subgroups (n = 4) based on the post dowel irrigation systems (ultrasound, regular rinse, or control) used. The samples were examined under a scanning electron microscope and were scored for debris and tubule openings using a 3-scale grading system. The Friedman test, Wilcoxon signed rank test, Kruskal-Wallis analysis, and Mann-Whitney U test were used to statistically analyze the results (a = 0.05). Results: Samples in the AH Plus group were more easily debrided than those in the iRoot SP group (P < .05). The best tubule opening condition was presented in samples in the AH Plus group, whereas those in the iRoot SP group presented the worst (P < .05). The regular rinse and ultrasonic groups were similarly good at smear layer removal and tubule opening (P > .05) compared with the control group (P < .05). The samples using AH Plus in combination with ultrasound or syringe rinsing showed the best cleaning result among all of the subgroups (P < .05). Conclusions: AH Plus presented the easiest removal from the post space, whereas iRoot SP presented the most difficult removal. Ultrasound improved the cleaning efficacy of post dowels as did the regular rinse. (J Endod 2018;44:1293–1297)

Key Words AH Plus, Apexit Plus, iRoot SP, post space preparation, smear layer removal, ultrasonic irrigation

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ntraradicular posts are Significance generally required to Our study focused on observing whether the type improve the retention of of endodontic sealers and post irrigation systems an additional restoration would affect the post space smear layer removal, in endodontically treated providing novel insights into the appraisal of teeth having an extensive different endodontic sealers and post space irrigaloss of tooth structure tion systems. (1). Adhesively luted fiber-reinforced composite posts exhibit good physiochemical properties and biocompatibility and are widely used (1–5). Failure of adhesive luting fiber post restoration usually occurs because of bond deficiencies (4, 5). The binding mechanism of the luting systems to the post dowel dentinal walls is based on hybridization of the demineralized surface and on resin tags and adhesive lateral branches formation (2). Many factors can affect this micromechanical procedure (5); among these, removing or modifying the smear layer containing sealer and gutta-percha remnants (6) has been presumed to enhance the micromechanical retention of resin cements (5). It is well-known that endodontic sealers are used to obturate canal wall irregularities and seal the voids between gutta-percha and canal dentin (7). Different types of root canal sealers have been introduced into the endodontic field (8). AH Plus (Dentsply DeTrey, Konstanz, Germany) is an epoxy resin–based sealer and presents high bond strengths to dentin (9). Calcium hydroxide–based sealer exhibits alkalinity and sterilization ability (10). iRoot SP (Innovative Bioceramix, Vancouver, BC, Canada) is a novel bioceramic-based sealer with favorable physiobiological properties (9). Few parallel comparisons have been performed on the effects of these types of sealer on post space smear layer removal. On the other hand, ultrasound irrigation might enhance the dispersal of the irrigant and activate it (11) and was presumed to be effective in smear layer removal (1, 12). The aim of this study was to investigate the effects of endodontic sealer types and ultrasound on smear layer removal after post space preparation.

Materials and Methods Specimen Preparation Thirty-six freshly extracted, anatomically similar bovine incisors with fully developed apical foramens were selected and stored in 0.02% buffered thymol solution. The teeth were decoronated to standardize the root length at 15 mm. All the root canals were manually enlarged up to #40 file size (Dentsply Maillefer, Ballaigues, Switzerland) and were then instrumented up to F5 using ProTaper Universal rotary instruments

From the *State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, China; †National Clinical Research Center for Oral Diseases, Department of Endodontics, West China Hospital of Stomatology, Sichuan University, Chengdu, China. Address requests for reprints to Dr Ling Zou, State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, Department of Endodontics, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2018 American Association of Endodontists. https://doi.org/10.1016/j.joen.2018.05.014

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Basic Research—Technology (F3-F4-F5, Dentsply Maillefer) according to the manufacturers’ instructions. All experimental operations were performed by the same practitioner.

Root Canal Obturation After instrumentation, the teeth were randomly divided into 3 experimental groups (n = 12) according to the sealer type used: 1. The AH Plus group (G-AH); obturate root canals with gutta-percha and AH Plus 2. The Apexit Plus (Ivoclar Vivadent AG, Schaan, F€urstentum Liechtenstein), calcium hydroxide–based sealer group (G-AP); obturate root canals with F5 gutta-percha and Apexit Plus 3. The iRoot SP group (G-SP); obturate root canals with gutta-percha and iRoot SP All root canal sealers were mixed according to the manufacturers’ recommendations and were delivered into the canal using a spiral spreader (#40 21 mm; MANI, INC, Tochigi, Japan). A main guttapercha point (Dentsply Maillefer) with a tip diameter of 0.5 mm (#50) and a taper of .06 was inserted into the canal to the working length. Additional gutta-percha points (#25.02 tapered, Dentsply Maillefer) were introduced into the apical 5 mm of the canal using a #25 lateral condensation plugger (21 mm, MANI, INC) to reach an adequate apical sealing for warm vertical compaction. After sealing of the apical 5 mm, the standard warm vertical compaction procedure was followed to fill all the canals.

Post Space Preparation After obturation, a Pesso reamer (#5 28 mm, MANI, INC) was immediately applied to remove the coronal 10 mm of gutta-percha, leaving 5 mm of the apical sealing untouched. Post space preparations were completed with a #3 drill (3M ESPE; 3M Deutschland GmbH, Neuss, Germany), resulting in a post space with a 1.9-mm diameter at the coronal level.

Post Space Irrigation After post dowel preparation, the specimens within each group were then randomly subdivided into 3 subgroups (n = 4) according to the irrigation system used: 1. The regular rinse subgroup (RR): the post space was rinsed with 5 mL 2% chlorhexidine (CHX) for 1 minute followed by rinsing with 5 mL 17% EDTA for 1 minute and a final rinse with 5 mL distilled water for 1 minute. All rinse procedures were performed using 5-mL syringes and 23-G needles. 2. The ultrasonically irrigated (UI) subgroup: the post space was ultrasonically irrigated with 5 mL 2% CHX for 1 minute followed by ultrasonic irrigation with 5 mL 17% EDTA for 1 minute and a final rinse with 5 mL distilled water for 1 minute using ultrasonic agitation. All solutions were delivered by a 5-mL syringe and a 23-G needle and were activated by a size 25 ultrasonic K-file (Satelec Acteon, Merignac France), which was driven by an ultrasonic device (P5Suprasson, Satelec Acteon) at a power setting of 6 according to the manufacturer’s instructions. 3. The control subgroup (CT): the irrigants (CHX, EDTA, and distilled water) were successively flushed into each canal and left in place for 1 minute. During irrigant replacement, paper points were used to absorb the former irrigant from the canal. 1294

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Evaluation by Scanning Electron Microscopy Longitudinal grooves along the buccolingual direction were prepared in each specimen without penetrating the post space. The roots were split into 2 halves with a chisel and a surgical hammer to expose the dowel walls. The superior bisection of each pair was coded. The coded halves were then dried in a desiccator for 24 hours, mounted on metallic stubs, sputter coated with gold, and evaluated at the middle third (9–10 mm coronal from the apex) under a scanning electron microscope (Inspect F, FEI, Netherlands). Five serial microphotographs of the dowel walls were recorded continuously at 1000 magnification at 0.2-mm intervals and were rated by 3 blinded endodontic practitioners separately according to the criteria modified from the protocols of Guo et al (12) and Serafino et al (13). The amount of debris was scored from 0 to 2 as follows: 0, no debris particles or the remnant particles covered <25% of the canal walls; 1, few debris particles (the covered area was evident in 25%–50% of the canal surface) and a maximum particle diameter <20 mm; and 2, large amounts of debris particles (the covered area was evident in >50% of the canal surface) or a particle diameter $20 mm in any direction. The number of dentinal tubule openings was scored from 0 to 2 as follows: 0, the open dentinal tubules occupied >75% of the dentinal walls; 1, the open dentinal tubules occupied 50%–75% of the dentinal walls; and 2, the open dentinal tubules occupied <50% of the dentinal walls. Before scoring, 50 photographs were randomly selected, and the 3 examiners were asked to assess the photographs together for calibration purposes; then, the 3 examiners worked individually to rank all of the specimens, and for some specimens with less agreement levels, the final scores were determined by consensus. For each photograph, the mean debris and dentinal tubules opening scores were calculated. Statistical Analysis The Cohen kappa test was applied for the assessment of interexaminer agreement. The effects of sealer type and cleaning procedure on post wall cleanliness were statistically compared using the Friedman test, with a post hoc Wilcoxon signed rank test. For subgroup comparisons, Kruskal-Wallis analysis was used, with a post hoc Mann-Whitney U test. All tests were 2 tailed at a significance level of 0.05. The data were analyzed using SPSS software (Version 20.0; IBM Corp, Armonk, NY).

Results The Cohen kappa test showed that good agreement was obtained between examiners 1 and 3 (k = 0.742) and examiners 2 and 3 (k = 0.693). Excellent agreement was obtained between examiners 1 and 2 (k = 0.813). Complete removal of the smear layer and debris was found in the G-AH-UI group. Small areas of debris and moderate amounts of open tubules were discovered in the G-AH-RR, G-AP-RR, and G-AP-UI groups. All control groups and all samples in the G-SP group were covered by large areas of smear layers, and open dentinal tubules could hardly be found (Fig. 1). Distributions of the scores of debris and open tubules in all the tested subgroups are presented in Figures 2 and 3, and comparisons between groups are tabulated in Tables 1 and 2. Generally, samples in the G-AH group were more easily debrided than those in the G-SP and the G-AP groups (P < .01); the best tubule opening condition was presented in samples in the G-AH group (P < .05) followed by samples in the G-AP group (P < .05), whereas those in the G-SP group presented the worst condition (P < .05). Samples in the regular rinse and the ultrasonically irrigated groups exhibited similarly (P > .05) good smear layer removal and tubule opening results, which were better than that presented in the G-CT group (P < .01). JOE — Volume 44, Number 8, August 2018

Basic Research—Technology

Figure 1. Representative scanning electron microscopic photomicrographs showing the debridement and dentinal tubules opening results of all the tested groups (1000). (A, D, and E) Small areas of debris and moderate amounts of open tubules. (B) Complete removal of the smear layer and debris. (C and F–I) Large areas of smear layers and open dentinal tubules could hardly be found.

Statistical comparisons among the specific subgroups showed that the samples using AH Plus in combination with ultrasound or regular syringe rinsing showed the best cleaning result among all of the subgroups (P < .05) (Figs. 2 and 3).

Discussion According to our current results, iRoot SP was the most difficult to remove, whereas AH Plus was the easiest, and the cleaning efficacy fol-

Figure 2. Distribution of debris scores. Lines with * marks connect values that are statistically different. (*.01 < P < .05, **P < .01; Mann-Whitney U test).

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lowed the order ultrasonic irrigation = regular rinse > control. Loss of retention is considered 1 of the most frequent failure types in post restoration (4, 14). The adhesive bond of the post to the dentinal walls is based on the micromechanical retention created by the demineralized surface and resin tag formation (15). However, drilling a post space always creates a smear layer consisting of gutta-percha and sealer remnants that cover the dentin surface (16); this makes it difficult

Figure 3. Distribution of open tubules scores. Lines with * marks connect values that are statistically different. (*.01 < P < .05, **P < .01, ***P < .001; Mann-Whitney U test).

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Basic Research—Technology TABLE 1. Comparisons Between Groups According to Debris Removal Mean ± SD Comparison

First group

Second group

P value*

G-AH  G-AP G-AH  G-SP G-AP  G-SP G-RR  G-UI G-RR  G-CT G-UI  G-CT

1.38  0.89 1.38  0.89 1.73  0.67 1.62  0.72 1.62  0.72 1.38  0.90

1.73  0.67 1.88  0.42 1.88  0.42 1.38  0.90 2.00 2.00

<.01 <.001 >.1† >.06† <.0001 <.001

G-AH, AH Plus group; G-AP, Apexit Plus, calcium hydroxide–based sealer group; G-CT, control group; G-SP, iRoot SP group; G-RR, regular rinse group; G-UI, ultrasonically irrigated group; SD, standard deviation. *The Wilcoxon signed rank test. † P > .05, no statistically significant difference.

to etch the canal dentin, leading to deficient micromechanical retention and eventually hindering fiber post adhesive bonding (13, 15, 16). Hence, the dentin surface of the root canal needs to be effectively cleaned before fiber post cementation (15). Endodontic sealers are known components of the smear layer and can compromise fiber-post cementation (16). Because physicochemical properties vary with sealer type, it remains controversial whether the type of endodontic sealer used affects the efficacy of smear layer removal during post space irrigation. AH Plus is an epoxy resin– based sealer that has been widely accepted as the gold standard sealing material (8, 17). Resinous sealers can form covalent bonds with the dentin collagen (17) and can easily penetrate to collateral canals and dentinal tubules; thus, they are suspected to exert adverse effects on post space cleaning and post retention (9). However, our experimental results showed that AH Plus was the easiest to remove after post space preparation, confirming its excellence as a canal sealer. Calcium hydroxide–based sealers are widely used. Their alkalinization property has been shown to be bactericidal, and the released calcium ions from the sealer components can trigger calcium carbonate crystal generation, which can consequentially stimulate mineralized tissue formation and may have potential clinical benefits (18, 19). Some researchers have found that this type of sealer exhibits stronger adhesion to dentin and speculated that it would be difficult to remove them from the dentinal walls (20); several other studies directly compared the effects of sealer type on the fiber post bond strength (10, 21), but these conjectures and results could not explicitly measure the performance of calcium hydroxide–based sealers when it comes to post space cleaning. Furthermore, because the methodologies used in these experiments differed, it was difficult to achieve a unified and clinical beneficial result. Our study focused on observing whether the calcium hydroxide sealer could be easily removed from the dentinal walls, thus providing a new perspective from which to analyze the possible influences of sealers on the bond strength of posts. TABLE 2. Comparisons Between Groups According to Open Tubule Condition Mean ± SD Comparison

First group

Second group

P value*

G-AH  G-AP G-AH  G-SP G-AP  G-SP G-RR  G-UI G-RR  G-CT G-UI  G-CT

1.07  0.89 1.07  0.89 1.48  0.81 1.32  0.79 1.32  0.79 1.13  0.95

1.48  0.81 1.75  0.60 1.75  0.60 1.13  0.95 1.85  0.48 1.85  0.48

<.05 <.001 <.05 >.2† <.01 <.0001

G-AH, AH Plus group; G-AP, Apexit Plus, calcium hydroxide–based sealer group; G-CT, control group; G-SP, iRoot SP group; G-RR, regular rinse group; G-UI, ultrasonically irrigated group; SD, standard deviation. *The Wilcoxon signed rank test. † P > .05, no statistically significant difference.

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iRoot SP was the most difficult material to remove when compared with the other materials appraised in this study. iRoot SP is a newly introduced calcium phosphate silicate–based bioceramic sealer and is known for its outstanding biocompatibility and bioactivity (9, 22). This sealer type strongly adheres to the intracanal dentin, and its bonding strength has been reported to be stronger than those of some popular sealers (9, 22). The bonding strategy of this sealer is to first interact with dentinal fluids and then create intrafibrillar apatite deposits and form taglike structures within the dentin, which lays a foundation for further bonding between the sealer and the dentin surface (17). This strategy is even applied in the so-called monoblock concept in root canal obturation to completely eliminate interfacial gaps and produce perfect coronal and apical seals (23). We supposed that this unique bonding strategy made it difficult to remove iRoot SP from the post space in the current study. Although the singlecone filling method in combined use with iRoot SP has newly raised attention for its convenience (24), we chose warm vertical compaction to avoid unnecessary variables in this experiment. Regarding irrigation techniques, ultrasound has been used as an auxiliary technique to enhance smear layer removal (12). Ultrasonic irrigation uses acoustic streaming effects, and the small ultrasonic oscillating file used in this system has been proven able to deliver irrigants into the apical portion of the root canal; thus, ultrasonic activation is believed to be more beneficial to smear layer removal (11, 13). However, some studies contradict the notion that ultrasonic irrigation has similar efficacy to that of conventional syringe rinsing (12, 15), and this was confirmed by the present study. The discrepancies might be because of the different experimental designs used and the nonuniform sizes of the irrigated spaces. CHX was chosen as the endodontic irrigant used in this study for its credible antimicrobial effects, substantivity, and cytocompatibility (3, 16, 25). Unlike sodium hypochlorite, CHX does not trigger the release of oxygen, which can negatively affect resin polymerization; furthermore, CHX does not interfere with the dentin constituents to induce collagen denaturation, thus preserving the quality and integrity of the dentin substrate (1, 2). Moreover, CHX is a broad-spectrum inhibitor of matrix metalloproteinases and cysteine cathepsins in the hybrid layer (26) and can prevent endogenous proteolytic initiation and improve compositedentin adhesive bonding durability (1, 3). According to Perdigao et al (27), the cervical portion of the root canal is wider and always affords more access than the medium and apical thirds, making it easier for this portion to receive the treatment; this finding was corroborated by the study of Guo et al (12). On the other hand, the irregular structures and smaller number of dentinal tubules in the apical part of the root canal may hamper the cleaning and bonding process (4, 28). For these reasons, we chose the middle portion (9–10 mm from the apex) of the root canal to detect differences among the treated groups. We evaluated only cleanliness in this work, providing novel insights into the appraisal of different endodontic sealers and post space irrigation systems. However, further studies of the effects that these manipulations may have on the direct bonding strength, longevity, and thermal and mechanical fatigue of fiber-post adhesion are warranted.

Conclusions Within the limitations of this in vitro study, the following conclusions can be drawn: 1. AH Plus was the easiest material to remove from the post space. 2. Neither ultrasonic agitation nor regular rinse effectively removed iRoot SP from the dentinal walls of the post dowel. 3. Ultrasonic oscillation improved the smear layer removal after post space preparation and was as effective as regular syringe rinsing. JOE — Volume 44, Number 8, August 2018

Basic Research—Technology Acknowledgments Supported by grants from the National Natural Science Foundation of China (grant no. 81570974) and The Key Project of the Science and Technology Department of Sichuan Province (grant no. 2015JY0260). The authors deny any conflicts of interest related to this study.

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