The Journal of Adhesive Dentistry, 01/2009

Purpose: To compare scanning electron microscopic (SEM) and confocal laser scanning microscopic analyses (CLSM) of hybrid layer thickness and the number of dentinal tubules penetrated with composite resin inside the root canal on identical samples. Materials and Methods: Central maxillary incisors were restored using fiber posts (FRC Postec) inserted with a chemically curing composite resin (Clearfil Core/New Bond). Two different fluorescent dyes were used to respectively label adhesive and composite resin. Each root was sectioned into two slices starting 2 mm below the cementoenamel junction. SEM (low vacuum mode) and CLSM (dual fluorescence mode) analyses of 18 samples were performed. Hybrid layer thickness was measured at five characteristic points of each sample and the number of dentinal tubules penetrated with composite resin was counted on both corresponding images by two independent observers. Correlation coefficients as well as pairwise comparisons were calculated for both parameters. Results: SEM and CLSM measurements of hybrid layer thickness were positively correlated (r2 = 0.772; Pearson), and thickness was significantly higher after evaluation with CLSM (p 0.0005; Wilcoxon). The observed number of dentinal tubules penetrated with composite resin revealed a nonsignificant correlation (r2 = 0.111; p = 0.193). Significantly lower tag numbers were counted when using SEM (p = 0.010; Wilcoxon). Conclusion: With respect to the variability of the hybrid layer measurements, the two methods yielded comparable results. CLSM provided more detailed information regarding the penetration and distribution of resin cement and adhesive than did SEM imaging. Keywords: scanning electron microscopy, confocal laser scanning microscopy, correlation, hybrid layer, root canal dentin

Purpose: This study evaluated the differential composition of resin/dentin interfaces of indirect restorations created by the application of 4th and 5th generation dual-curing luting systems (bonding agents/resin cements), when each material was either light cured or allowed to self-cure. Materials and Methods: Occlusal flat dentin surfaces of 60 human third molars were assigned into 12 groups (n = 5) according to curing mode and dual-curing cementing system: 4th generation All Bond2 (AB2)/Duolink (Bisco) and 5th generation (B1) Bond1/Lute-it (Pentron). Fluorescein-labeled dextran (FDx) was mixed with the bonding agents, while rhodamine-labeled dextran (RhDx) was incorporated into resin cements and Pre-Bond resin from AB2. Resin cements were applied to 2-mm-thick, precured resin composite disks (Z250, 3M ESPE), which were fixed to dentin surfaces containing adhesive resin in either cured (light cured; LC) or uncured (self-cured; SC) states. The restored teeth were light activated (XL3000, 3M ESPE) according to the manufacturers' instructions (LRC) or allowed to self-cure (SRC), were stored for 24 h, and then vertically, serially sectioned into 1-mm-thick slabs, which were analyzed using confocal laser scanning microscopy. Fluorescent additives indicated where individual components of the bonding/cement systems were located. Additional specimens were prepared and analyzed using a conventional scanning electron microscope. Results: AB2/LC and B1/LC exhibited nonuniform primer/adhesive layer thickness. AB2/SC showed adhesive resin penetration within the primed dentin, and resin cement penetration at the entrance of the dentin tubules. B1/SC/LRC demonstrated resin cement penetration within the hybrid layer and into the dentin tubules. More resin cement penetration was observed in B1/SC/SRC groups than in its LRC equivalent. Conclusion: The morphological features and component interactions among materials at resin/dentin interfaces are related to the activation modes of the primer/adhesive layer and of the resin cement used. Keywords: confocal laser scanning microscopy, dual-curing adhesive systems, dual-curing resin cements, adhesive interfacial morphology, indirect restorations

Purpose: The aim of this study was to investigate whether an electrical device for dental adhesive application (ElectroBond) influences bonding of two-step etch-and-rinse adhesives. Materials and Methods: Human teeth were selected and cut perpendicularly to their long axis to expose middle/ deep dentin. Specimens were then longitudinally sectioned into halves (experimental and control halves) to create two similar bonding substrates. Experimental halves were bonded using an ElectroBond-assisted application, while control halves were bonded with disposable sponges. The adhesives tested were Adper Scotchbond 1XT and XPBOND. Bonded specimens were submitted to the microtensile bond strength test. Additional adhesive interfaces were prepared and processed for nanoleakage investigation involving TEM examination. Results: The microtensile bond test revealed higher values (p 0.05) for both adhesives if ElectroBond was used during layering (55.5 ± 7.9 MPa for Adper Scotchbond 1XT and 54.7 ± 7.1 MPa for XP-BOND) compared to the conventional mechanical adhesive application technique (41.1 ± 6.1 MPa for Adper Scotchbond 1XT and 38.0 ± 7.8 MPa for XP-BOND). No difference between the two adhesives was found under the same application conditions. With electricity- assisted application, TEM micrographs revealed a significant decrease in nanoleakage expression compared to the controls. Conclusion: The use of an electric current produced by ElectroBond during the application of two-step etch-and-rinse adhesives may enhance resin impregnation, thus improving dentin hybridization. Further studies should be done to confirm that this device can similarly improve adhesive application in vivo. Keywords: dentin bonding systems, electric current, TEM, microtensile, dentin

Purpose: To assess the effect of the hydrogel form of different concentrations (2.5%, 5%, and 10%) of sodium ascorbate on the shear bond strength of composite after bleaching of the enamel with 10% carbamide peroxide gel. Materials and Methods: Sixty flat buccal enamel surfaces obtained from 30 bovine incisors were divided into 6 treatment groups: group I, control (nonbleached); group II, no antioxidant treatment after bleaching; group III, 10% sodium ascorbate solution after bleaching; group IV, 2.5% sodium ascorbate hydrogel after bleaching; group V, 5% sodium ascorbate hydrogel after bleaching; group VI, 10% sodium ascorbate hydrogel after bleaching. The specimens were bonded with Clearfil SE Bond, then thermocycled and subjected to the shear test until failure. Fracture analysis of the bonded enamel surfaces was examined using a stereomicroscope. Statistical analysis was carried out using Kruskal-Wallis and the Mann-Whitney U-test. Results: While the samples that were not treated with antioxidant after bleaching (group I) demonstrated significantly lower shear bond strengths and the 10% sodium ascorbate gel group (group VI) demonstrated significantly higher bond strengths than the control group (p 0.05), no significant differences were found between the other groups and control group (p > 0.05). Among the antioxidant groups, only the groups treated with the 10% solution and the 10% hydrogel form of sodium ascorbate (group III and VI) revealed significantly higher bond strengths than the bleached group without antioxidant (group II) (p 0.05). Higher scores were obtained with 10% sodium ascorbate gel (group VI) when compared with the other antioxidant-treated groups (p 0.05). Conclusion: Within the limitations of this study, it can be concluded that the 10% hydrogel form of sodium ascorbate may be used in clinical procedures instead of its solution form. However, using sodium ascorbate hydrogel with concentrations lower than 10% may not be as reliable as using this agent in 10% concentration for reversing the compromised bond strength. Keywords: sodium ascorbate hydrogel, antioxidant, bleaching

Purpose: To investigate the effect of different surface treatments on the tensile bond strength (TBS) of immediately repaired anterior microfine hybrid restorative composite using nontrimmed hourglass-shaped specimens. Materials and Methods: Fifty-six nontrimmed hourglass composite specimens were prepared in this study. Eight specimens were used for the evaluation of the cohesive tensile strength as the control group. The remaining 48 were divided into 6 equal groups according to the method of proposed treatment. Groups IM1 and IM2: The specimens were repaired without intermediate treatment. Group IM3: A thin layer of Excite self-priming adhesive was applied to the proposed repaired area of each half-specimen. Group IM4: The repaired area was ground using an abrasive stone, each half-specimen was rinsed and dried, and the adhesive applied. Group IM5: Treatment consisted of 37% phosphoric acid etching of the proposed repair area. The adhesive was then applied. Group IM6: The repaired area was ground and acid etched before applying the adhesive. In all repaired groups except for IM2, repaired specimens were prepared and cured against a single layer of transparent polyester strip (matrix) to prevent the formation of an oxygen inhibition layer. In group IM2, specimens were cured in air without the polyester strip. Specimens were then tested for the repair tensile bond strength (TBS) in a universal testing machine at a crosshead speed of 0.5 mm/min until failure. Twelve more samples were used for SEM characterization of nontreated, ground, acid-etched, and ground/acid-etched samples. The failure mode was evaluated using a stereomicroscope at 30X magnification. All TBS data were expressed as mean and standard deviation, and were analyzed using StatsDirect 2.5.7. One-way ANOVA followed by Tukey-Kramer multiple-comparison post-hoc tests were used to compare the TBS between all tested groups. Differences were considered significant at p 0.05. Results: Groups that were cured against a matrix and received no treatment or were repaired with adhesive only had significantly lower TBS than the control group. Groups which were cured without the matrix and received no treatment or grinding/adhesive, acid etching/adhesive, and grinding/acid etching/adhesive showed no significant difference in TBS compared to the control group. SEM evaluation showed that acid etching did not change the morphology of the composite surface. The ground specimens showed a grooved pattern with smeared grinding products. Ground/acid-etched specimens showed removal of the smeared products with a less distinct grinding-groove pattern. Stereomicroscopic evaluation of the debonded surfaces for all repaired groups showed that the failure mode was predominantly adhesive for all evaluated debonded surfaces in each repair group. Conclusion: In the absence of an oxygen inhibition layer, the immediate repair bond strength was decreased. In contrast, in the presence of an oxygen inhibition layer, the immediate repair bond strength of composite was improved. The application of a thin adhesive layer did not improve the immediate repair bond strength as the other surface treatments did. When the composite was cured against a matrix, chemical and/or mechanical treatments of composite surface prior to application of the adhesive proved to be an effective method to improve the immediate repair bond strength. Keywords: immediate repair, resin composite, bonding agents, tensile bond strength

Purpose: The aim of this study was to verify the effects of sol-gel processed silica coating on the bond strength between resin cement and glass-infiltrated aluminum oxide ceramic. Materials and Methods: Silica coatings were prepared on glass-infiltrated aluminum oxide ceramic surface via the sol-gel process. Atomic Force Microscope (AFM), Fourier Transmission Infrared spectrum (FTIR), and Energy Dispersive X-ray Spectroscopy (EDS) were used for coating characterization. Forty-eight blocks of glass-infiltrated aluminum oxide ceramic were fabricated. The ceramic surfaces were polished following sandblasting. Three groups of specimens (16 for each group) with different surface treatment were prepared. Group P: no treatment; group PO: treated with silane solution; group PTO: silica coating via sol-gel process, followed by silane application. Composite cylinders were luted with resin cement to the test specimens. Half of the specimens in each group were stored in distilled water for 24 h and the other half were stored in distilled water for 30 days before shear loading in a universal testing machine until failure. Selected ceramic surfaces were analyzed to identify the failure mode using a scanning electron microscopy (SEM). Results: Nanostructured silica coatings were prepared on glass-infiltrated aluminum oxide ceramic surfaces by the sol-gel process. The silicon element on the ceramic surface increased significantly after the coating process. The mean shear bond strength values (standard deviation) before artificial aging were: group P: 1.882 ± 0.156 MPa; group PO: 2.177 ± 0.226MPa; group PTO: 3.574 ± 0.671 MPa. Statistically significant differences existed between group PTO and group P, and group PTO and groups PO. The failure mode for group P and group PO was adhesive, while group PTO was mixed. The mean shear bond strength values (standard deviation) after artificial aging were: group P: 1.594 ± 0.111 MPa; group PO: 2.120 ± 0.339 MPa; group PTO: 2.955 ± 0.113 MPa. Statistically significant differences existed between each two groups after artificial aging, group P had the lowest bond durability, and group PTO had the highest bond durability. Conclusion: The sol-gel process is an effective way to prepare silica coating on dental glass-infiltrated alumina ceramic. Sol-gel processed silica coating can improve the resin bond strength of glass-infiltrated alumina ceramic. Keywords: bond, alumina ceramics, silica coating, sol-gel

Purpose: To evaluate the effect of endodontic irrigation regimens and calcium hydroxide root canal sealer (Sealapex) on the microtensile bond strengths (µTBS) of dual-curing resin composite (Clearfil DC Core Automix) to the intrapulpal dentin. Materials and Methods: Forty standardized coronal-half root canal dentin specimens obtained from human premolars were divided into 4 groups: group A, no treatment (control); group B, Sealapex; group C, NaOCl/Sealapex; group D, EDTA/NaOCl/Sealapex. After 7 days of storage in 100% relative humidity, Sealapex was removed. Dentin surfaces were bonded with adhesives, either etch-and-rinse (Single Bond) or self-etching (Clearfil SE Bond), and built up with resin composite. The bonded specimens were trimmed into an hourglass shape with a 1-mm2 cross-sectional area for microtensile testing (n = 20). The µTBS to intrapulpal dentin was analyzed using two-way ANOVA and Dunnett's TC test. Two teeth of each group were prepared for micromorphological analysis of dentin surface. Results: The root canal sealer with or without endodontic irrigation significantly affected the bond strengths of resin composite to intrapulpal dentin compared with the control group (p 0.05). There were no significant differences in µTBS of each experimental group between etch-and-rinse and self-etching adhesives (p > 0.05). The dentin surface was covered with a mud-like material after sealer application for 7 days. Conclusion: The root canal sealer reduced the µTBS of dual-curing resin composite with etch-and-rinse and self-etching adhesive systems to intrapulpal dentin. Treatment with EDTA followed by NaOCl prior to obturation caused an additional reduction in µTBS of both adhesive systems to intrapulpal dentin. Keywords: endodontic irrigation, root canal sealer, intrapulpal dentin, microtensile bond strength

Purpose: The study evaluates the behavior of different adhesive systems and resin cements in fiber post placement, with the intent to clarify the possible role of unfilled resin as a luting material for fiber posts. Materials and Methods: Two luting agents (Dual-Link and Unfilled Resin) for cementing fiber posts into root canals were applied either with All-Bond 2 or One-Step Plus, or without an adhesive system, and challenged with the pushout test. Slices of roots restored with posts were loaded until post segment extrusion in the apical-coronal direction. Failure modes were analyzed under SEM. Results: Push-out strength was significantly influenced by the luting agent (p 0.05), but not by the bonding strategy (p > 0.05). The best results were obtained in combination with Unfilled Resin with One-Step Plus. Dual-Link groups failed mainly cohesively within the cement, while Unfilled Resin demonstrated more adhesive fracture at the post interface. Conclusion: The results of this study support the hypothesis that adhesive unfilled resin application is essential for achieving high bond strength to radicular dentin. Keywords: fiber post, unfilled resin, resin cement, push-out test, etch-and-rinse technique, retention of fiber posts

Purpose: To evaluate the clinical performance of direct Class II fiber-reinforced composite restorations on nonvital teeth. Materials and Methods: Thirty patients age 18 or older were included in this clinical trial restoring 35 molars. The inclusion criteria were: two- to four-surface restorations, replacement of composite and amalgam restorations necessary or unrestored teeth with decay reaching the pulp, teeth having homogeneous root canal fillings terminating 0 to 2 mm from the radiographic apex. Teeth with residual cavity walls less than 1 mm or with complete loss of the clinical crown were excluded. Teeth were restored using a combination of Ultra etch 35% phosphoric acid, PQ1 adhesive system, and Vit-l-escence microhybrid composite resin. The enamel peripheral shell of the restoration was built up first; a resin-impregnated piece of polyethylene ribbon fiber (Ribbond Triaxial) was covered with B1 Perma-Flo flowable composite, placed into a prepared canal, folded, and light cured; then, dentin and enamel occlusal surface stratification was completed. All 35 restorations were evaluated at 6 months and 1 year by two independent evaluators using modified USPHS criteria. Results: No failure was reported and alpha scores were recorded for all parameters. Before starting the treatment, 26 out of 35 teeth (74%) had apical periodontitis as diagnosed radiographically. At the 1-year recall, no signs of periapical lesions were detected and radiographs reported neither periodontal ligament widening nor periapical radiolucency. Conclusion: Direct fiber-reinforced composite resin restorations demonstrated excellent clinical performance at 1 year. Keywords: adhesive system, composite resin, Class II restoration, nonvital teeth, post and core, UHMWPE fiber, clinical report