Variable Smear Layer and Adhesive Application: The Pursuit of Clinical Relevance in Bond Strength Testing.

The removal or modification of smear layers that cover the dentin is critical to allow the penetration of adhesive molecules and to ensure a strong bond between resin and dentin. Aiming to establish a model for clinically-relevant dentin-bond testing, we evaluated the effects of smear layers created by abrasives having similar coarseness (180-grit SiC paper; fine-grit diamond bur) and application modes (single application; double application) on the microtensile bond strengths (µTBS) of two currently available universal adhesives (G-Premio Bond; Scotchbond Universal Adhesive) and a two-step self-etch adhesive (Clearfil Megabond 2). Sixty extracted human third molars were used for the µTBS test. Data were analyzed by three-way ANOVA and Tukey's test (α = 0.05). Fracture modes were determined using stereomicroscopy. An additional 24 third molars were prepared for observation of the resin-dentin interface by TEM and adhesive-smear layer interaction by SEM. µTBS was significantly affected by the adhesives and their application modes (p < 0.001), implying that the double application of universal adhesives should be recommended to improve their performance. The effect of smear layers was not significant (p > 0.05), indicating that 180-grit SiC papers could be used to prepare dentin as a substitute for fine-grit diamond burs for dentin-bond testing in laboratory settings.

Effect of peracetic acid used as single irrigant on the smear layer, adhesion, and penetrability of AH Plus.

The aim of this study was to evaluate the effect of peracetic acid (PAA) as a single irrigant on the smear layer, on the intraradicular dentinal bond strength, and on the penetrability of an epoxy-based resin sealer into the dentinal tubules. A total of 120 roots were distributed into 4 groups according to the irrigant used in root canal preparation: 1% PAA (PAA); 2.5% NaOCl followed by final irrigation with 17% EDTA and 2.5% NaOCl (NaOCl-EDTA-NaOCl); 2.5% NaOCl (NaOCl); and saline solution (SS). The smear layer was evaluated using scanning electron microscopy. The bond strength of an epoxy-based resin sealer (AH Plus) to root dentin was evaluated by the push-out test and penetrability of the sealer into dentinal tubules was observed by confocal laser microscopy. The results were analyzed by the Kruskal-Wallis and the Dunn post-test (α = 0.05). The use of 1% PAA as single root canal irrigant provided smear layer removal and improved the penetrability and bond strength of AH Plus to root dentin in a manner similar to that of the NaOCl-EDTA-NaOCl group (p > 0.05). The NaOCl and SS groups had higher values of smear layer and lower values of sealer penetrability and dentin bond strength than the PAA and NaOCl-EDTA-NaOCl groups (p < 0.05). Thus, 1% PAA has the potential to be used as a single irrigant in root canals.

Effect of peracetic acid used as single irrigant on the smear layer, adhesion, and penetrability of AH Plus

Abstract The aim of this study was to evaluate the effect of peracetic acid (PAA) as a single irrigant on the smear layer, on the intraradicular dentinal bond strength, and on the penetrability of an epoxy-based resin sealer into the dentinal tubules. A total of 120 roots were distributed into 4 groups according to the irrigant used in root canal preparation: 1% PAA (PAA); 2.5% NaOCl followed by final irrigation with 17% EDTA and 2.5% NaOCl (NaOCl-EDTA-NaOCl); 2.5% NaOCl (NaOCl); and saline solution (SS). The smear layer was evaluated using scanning electron microscopy. The bond strength of an epoxy-based resin sealer (AH Plus) to root dentin was evaluated by the push-out test and penetrability of the sealer into dentinal tubules was observed by confocal laser microscopy. The results were analyzed by the Kruskal-Wallis and the Dunn post-test (α = 0.05). The use of 1% PAA as single root canal irrigant provided smear layer removal and improved the penetrability and bond strength of AH Plus to root dentin in a manner similar to that of the NaOCl-EDTA-NaOCl group (p > 0.05). The NaOCl and SS groups had higher values of smear layer and lower values of sealer penetrability and dentin bond strength than the PAA and NaOCl-EDTA-NaOCl groups (p < 0.05). Thus, 1% PAA has the potential to be used as a single irrigant in root canals.

Evaluation of 17% EDTA and 10% citric acid in smear layer removal and tubular dentin sealer penetration.

The purpose of this study was to compare the efficacy of different chelating solutions (17% EDTA and 10% citric acid) on the smear layer removal, and their effect on tubular dentin sealer penetration. Sixty root canals were prepared and distributed into four groups (n = 15) according to the final irrigation protocol: G1, final irrigation with 2.5 mL of distilled water; G2, final irrigation with 2.5 mL of 2.5% sodium hypochlorite solution; G3, final irrigation with 2.5 mL of 17% EDTA; and G4, final irrigation with 2.5 mL of 10% citric acid. Five specimens from each group were not filled to assess smear layer removal by scanning electron microscopy. Ten specimens from each group were filled for analysis of sealer penetration into dentinal tubules by confocal laser scanning microscopy. Smear layer removal (Kruskal-Wallis and Dunn's tests) and sealer penetration (F and Tukey's tests) were statistically analyzed with 95% of significance level. G3 and G4 had greater smear layer removal rates in the cervical and middle thirds, in comparison with G1 and G2 (p < .05). G3 and G4 had the highest percentages of sealer penetration in all thirds, in comparison with G1 and G2 (p < .05). Smear layer removal was effective only at the cervical and middle thirds when the chelating solutions were used. Sealer penetration into the dentinal tubules significantly increased in all root thirds when the specimens were treated with both chelating solutions.

Smear layer-deproteinizing improves bonding of one-step self-etch adhesives to dentin.

OBJECTIVES: Smear layer deproteinizing was proved to reduce the organic phase of smear layer covered on dentin surface. It was shown to eliminate hybridized smear layer and nanoleakage expression in resin-dentin bonding interface of two-step self-etch adhesive. This study aimed to investigate those effects on various one-step self-etch adhesives. METHODS: Four different one-step self-etch adhesives were used in this study; SE One (SE), Scotchbond™ Universal (SU), BeautiBond Multi (BB), and Bond Force (BF). Flat human dentin surfaces with standardized smear layer were prepared. Smear layer deproteinizing was carried out by the application of 50ppm hypochlorous acid (HOCl) on dentin surface for 15s followed by Accel® (p-toluenesulfinic acid salt) for 5s prior to adhesive application. No surface pretreatment was used as control. Microtensile bond strength (µTBS) and nanoleakage under TEM observation were investigated. The data were analyzed by two-way ANOVA and Tukey's post-hoc test and t-test at the significant level of 0.05. RESULTS: Smear layer deproteinizing significantly improved µTBS of SE, SU, and BB (p<0.001). Hybridized smear layer observed in control groups of SE, BB, and BF, and reticular nanoleakage presented throughout the hybridized complex in control groups of BB and BF were eliminated upon the smear layer deproteinizing. SIGNIFICANCE: Smear layer deproteinizing by HOCl and Accel® application could enhance the quality of dentin for bonding to one-step self-etch adhesives, resulting in the improving µTBS, eliminating hybridized smear layer and preventing reticular nanoleakage formation in resin-dentin bonding interface.

Effects of smear layer removal agents on the physical properties and microstructure of mineral trioxide aggregate cement.

OBJECTIVE: To compare the effect of QMix (Dentsply Sirona), 7% maleic acid (MA), and 17% ethylenediaminetetraacetic acid (EDTA) on the microhardness, flexural strength and microstructure of mineral trioxide aggregate (MTA; ProRoot MTA, Dentsply Sirona). METHODS: Forty MTA specimens were divided into four groups: [I] QMix [II] 7% MA [III] 17% EDTA and [IV] distilled water (control). After treatment with 5mL of the respective solution for 1min, the specimens were tested for microhardness using a Knoop hardness tester. Forty additional specimens were similarly treated and evaluated for the flexural strength using a universal testing machine. For microstructure evaluation, MTA specimens were treated in a similar manner and examined by X-ray diffractometry and scanning electron microscopy (SEM). RESULTS: For microhardness, there were no differences between distilled water, QMix and EDTA groups. However, MTA exposed to distilled water had higher microhardness than MA. When compared with QMix and EDTA, MA had lower microhardness; there was no difference between EDTA and QMix. For flexural strength, distilled water group had higher flexural strength than the other agents. There were no differences between EDTA vs MA and EDTA vs QMix. Specimens treated with QMix had higher flexural strength than MA. X-ray diffraction indicated that EDTA inhibited hydration of MTA. For SEM, all the tested agents altered the microstructure of MTA when compared to distilled water. CONCLUSION: MA had more detrimental effect on the physical properties of MTA and EDTA was more detrimental to the hydration of MTA. CLINICAL SIGNIFICANCE: The present study highlights the effect of newer chelating agents on the physical properties and microstructure of MTA. Preventing the deterioration of MTA is important for its long term success in endodontic procedures.

The effect of dentine surface preparation and reduced application time of adhesive on bonding strength.

OBJECTIVE: This study evaluated the effects of surface preparation and the application time of adhesives on the resin-dentine bond strengths with universal adhesives. METHODS: Sixty molars were cut to exposed mid-coronal dentine and divided into 12 groups (n=5) based on three factors; (1) adhesive: G-Premio Bond (GP, GC Corp., Tokyo, Japan), Clearfil Universal Bond (CU, Kuraray Noritake Dental Inc., Okayama, Japan) and Scotchbond Universal Adhesive (SB, 3M ESPE, St. Paul, MN, USA); (2) smear layer preparation: SiC paper ground dentine or bur-cut dentine; (3) application time: shortened time or as manufacturer's instruction. Fifteen resin-dentine sticks per group were processed for microtensile bond strength test (µTBS) according to non-trimming technique (1mm(2)) after storage in distilled water (37 °C) for 24h. Data were analyzed by three-way ANOVA and Dunnett T3 tests (α=0.05). Fractured surfaces were observed under scanning electron microscope (SEM). Another 12 teeth were prepared and cut into slices for SEM examination of bonded interfaces. RESULTS: µTBS were higher when bonded to SiC-ground dentine according to manufacturer's instruction. Bonding to bur-cut dentine resulted in significantly lower µTBS (p<0.000). Shortening the application time resulted in significantly lower bond strength for CU on SiC and GP on bur-cut dentine. SEM of fractured surfaces revealed areas with a large amount of porosities at the adhesive resin interface. This was more pronounced when adhesives were bonded with a reduced application time and on bur cut dentine. CLINICAL SIGNIFICANCE: The performance of universal adhesives can be compromised on bur cut dentine and when applied with a reduced application time.

The comparison of penetration depth of two different photosensitizers in root canals with and without smear layer: An in vitro study.

BACKGROUND: The main objective of this study is to evaluate the penetration depth of suggested photosensitizers in the lateral wall of the human root canal. MATERIALS & METHODS: Forty extracted single-rooted human teeth with straight canals that extracted for periodontal reasons were collected and stored in the sterile saline until employment in the experiment. Teeth were decoronated to a standard 12mm root segment using diamond disc. After instrumentation of specimens, the external root surface was sealed with two layers of nail polish to avoid environmental contamination. The apical foramen was subsequently closed with composite material. Teeth were divided randomly in two major groups consist of indocyanine green solution (ICG) and tolonium chloride solution (TCH) with and without EDTA in their subgroups. Specimens in all groups grooved longitudinally with a diamond disc and split in two halves with a stainless steel chisel. The measurements were done by the stereo microscope under 20× magnification in three zones of each specimen and the penetration depth of dye was measured. RESULTS: The results of this study showed that the mean of lateral penetration depth of ICG (224.04µm) was significantly (P<0.05) higher than TCH (70.15µm). Regarding to the influence of EDTA, in ICG group without consideration to the different regions, the usage of EDTA improved the mean of lateral penetration depth of ICG, but this improvement was not statistically significant (P>0.05). CONCLUSION: Further to the findings of this study, it could be assumed that ICG could penetrate in deeper regions of the root canal wall.

Evaluation of antimicrobial effectiveness and dentine mechanical properties after use of chemical and natural auxiliary irrigants.

OBJECTIVE: To evaluate the effect of GSE, NaOCl, CHX and QMix as an antimicrobial agents against Enterococcus faecalis and their influence on flexural and ultimate tensile strength of root canal dentine. METHODS: Root canals were divided into five groups (n=10) according to the substances used: 2.5% NaOCl, 2% CHX, 6.5% GSE, Qmix and control group (distilled water) (DW). Final irrigation was done with 17% EDTA in all groups, except when DW was used. The number of colony-forming units was used to evaluate the antimicrobial activity. Dentine beams were used to assess the flexural strength after treatment with substances as described before (n=10). The UTS was evaluated after the treatment of root dentine hourglass shape sections with the same substances (n=30). RESULTS: The lowest bacteria contamination was observed for CHX and GSE, while NaOCl and QMix showed an intermediate antimicrobial activity (p>0.05). NaOCl and QMix significantly reduced the mechanical properties of dentine (flexural strength and UTS) (p<0.05) and no statistical difference was found among CHX, GSE and DW (p>0.05). CONCLUSION: CHX and GSE were more effective than NaOCl and QMix against E. faecalis. Furthermore, they did not harm dentine mechanical properties as observed for NaOCl and QMix. CLINICAL SIGNIFICANCE: The use of GSE can be recommended for endodontic procedures since it has good antimicrobial activity and does not interfere in the mechanical properties of dentine; similarly to CHX.