Elisa Magni

To determine the influence of mechanical properties of resin-based composites on the microtensile bond strength to dentin of all-in-one adhesives. Microtensile bond strengths were measured with the non-trimming technique for the experimental groups: 1) Bond Force/Estelite Σ (Tokuyama); 2) G-Bond Plus (GC)/Estelite Σ; 3) Bond Force/Gradia Direct Anterior (GC);4) G-Bond Plus/Gradia Direct Anterior; 5) Bond Force/Gradia Direct LoFlo (GC); 6) G-Bond Plus/Gradia Direct LoFlo. The following mechanical properties of the resin-based composites were assessed: tensile strength, flexural strength, tensile elastic modulus, shear elastic modulus, Poisson's ratio, Vicker's hardness, contraction stress. Three-dimensional models of microtensile beams were created for finite element analysis of the first principal stress values and distribution in the adhesive layer during microtensile testing. Statistical tests were applied to microtensile bond strength values (two-way ANOVA) and to data from mechanical tests (one-way ANOVA). In all the analyses, the level of significance was set at p < 0.05. While the adhesive did not significantly influence microtensile bond strength, the composite was a significant factor. Regardless of the adhesive, Estelite Σ yielded significantly higher bond strengths than Gradia Direct Anterior and Gradia Direct LoFlo, that were comparable. Adhesive-composite interactions were not statistically significant. Estelite Σ had the highest Vicker's hardness, the highest tensile and shear elastic moduli, the lowest and closest to dentin Poisson's ratio. A more favorable stress distribution in the adhesive layer occurred in the Estelite Σ model. When comparing the bonding potential of several adhesives with the microtensile technique, the same resin composite should be used in all the experimental groups for building up the coronal portion.

To evaluate the effect of gasiform ozone on the repair strength of ormocer-based and silorane-based composites. 160 cavities were created in methacrylate cylinders. Half of the cavities were filled with a silorane-based composite, whereas the other half was filled with an ormocer-based composite. After storage (1 week, deionized water, 37 degrees C) the specimens of each restorative material were divided into two main experimental groups: in Group 1 the specimens were subjected to a 60-second ozone gas application; in Group 2 no pretreatment was performed (control). The corresponding adhesive of each restorative material was applied as the intermediate repair agent in both groups. Repair cylinders were then built up with the homologous material. Half of the specimens in each group were subjected to thermocycling (5,000 cycles, 5 degrees C-55 degrees C, dwell time 30 seconds, transfer time 5 seconds) prior to testing, whereas the other specimens were immediately tested. The repair strength was assessed with a shear test. The two-way ANOVA with pretreatment and thermocycling as the main factors was used to analyze the shear bond strength data within each restorative material. The pretreatment, the thermocycling and their interaction did not significantly affect the repair strength of either tested materials (P > 0.05). The ozone treatment did not significantly affect the repair strength. The silorane-based composite showed lower repair strengths compared to those of the ormocer-based composite. The immediate repair strengths in the ozone-treated and control groups were respectively, 28.1 (13.8) MPa and 28.8 (8.8) MPa for the silorane-based composite and 31.5 (9.3) MPa and 35.6 (10.6) MPa for the ormocer-based composite. After thermocycling, the repair strengths in the ozone-treated and control groups were 27.7 (9.7) MPa and 29.5 (11.1 ) MPa for the silorane-based composite and 31.4 (6.0) MPa and 34.2 (4.5) MPa for the ormocer-based composite. Mixed failures occurred most frequently in all experimental groups. In conclusion, ozone did not affect the repair strength of the tested silorane-based and ormocer-based composites.

The study evaluated the effect of ozone application on the composite-to-composite bond. Three hundred and twenty cylindrical composite specimens were divided into two groups: group 1 was subjected to a 60 s ozone application, whereas group 2 remained untreated. Four subgroups were obtained from each group according to the intermediate repair agent: an adhesive, a silane, silane/adhesive combination, or flowable composite. Repair composite cylinders were built-up. The composite repair strength was tested after 24 h and after thermocycling with a shear test. Additionally, 4 mm × 4 mm × 2 mm composite specimens were prepared and stored 24 h in deionized water. Half of the specimens were subjected to ozone application and the other served as control. The elastic modulus (E) and the Vicker’s hardness (VH) of the composite surfaces were tested immediately and after thermocycling. Significant differences among the experimental groups were detected (p < 0.001). The composite repair strength was affected by the pretreatment and by the intermediate agent, whereas, the thermocycling was not significant. The partial eta-squared statistics showed that the intermediate agent was the main factor affecting the composite repair strength, whereas the pretreatment played a minor role. No differences were observed between ozone and control groups when the same intermediate agent and the same aging conditions were applied. Repairing with flowable composite tended to achieve higher bond strengths (20.7 and 26.5 MPa in ozone and control groups, respectively, after 24 h). The use of silane coupling agent showed the lowest composite repair strengths. Ozone did not affect E and VH (p > 0.05) and the thermocycling affected only E (p < 0.05). In conclusion, the application of ozone does not impair the composite-to-composite bond.

To evaluate the cement thickness around oval and circular posts luted in oval post spaces prepared with different drills/tips. Extracted premolars were endodontically treated and obturated, then randomly divided into three groups (n = 5) according to the tips/drills used for post-space preparation and to the type of fiber post luted: medium grit oval tip + oval posts, fine grit oval tip + oval posts, Mtwo Post File drill + circular posts. The specimens were sectioned in horizontal slices; one slice per canal third was chosen for each post-space, resulting in three slices for each specimen. The distances between the canal wall and the post perimeter were measured on SEM images of each slice. The fine grit tip + oval post group obtained statistically significant lower cement thicknesses than the other groups (P < 0.05), in particular in the apical third. The MtwoPF + circular post group showed the highest cement thickness, comparable to that of the medium tip + oval post group. A good post fitting in oval-shaped canals can be obtained using a fine grit oval tip combined with oval posts.

Adhesives and lining/base materials should relieve the stresses concentrated at the tooth/restoration interface. The study aimed at comparing the mechanical properties of eight adhesives and six glass-ionomer cements (GICs). The adhesives were applied on dentin disks, whereas 2 mm × 3 mm × 2 mm GICs specimens were prepared in a teflon mold. Vicker’s hardness (VH), elastic modulus (E), creep (Cr) and elastic work (We/Wtot) were measured with a micro hardness indenter. One-way ANOVA and Tukey’s test were used to compare the mechanical properties within each materials’ type and among the materials’ classes. Enamel and dentin were used as references. Significant differences were detected within each materials’ type and among the materials’ classes and enamel and dentin. GICs were superior to adhesives in VH and E and showed a VH similar to dentin. GICs presented mechanical properties more similar to enamel and dentin than adhesives.

The aim of this in vivo study was to clarify how blistering formation occurs along intraradicular dentin bonded interfaces. Patients were selected and post space was prepared in vivo in endodontically treated teeth. Post space was etched, dried with ethanol, and bonded with one of the following adhesive systems: All Bond 2, XP-Bond, Clearfil SE Bond, Xeno III. The four adhesives were considered as representative of each bonding system class. An additional group was prepared with phosphoric acid treatment + application of Pre-Bond unfilled resin of All Bond 2, without the use of the primer agent. Etching was avoided for self-etching materials. Replicas of the post space were taken (1) after post space preparation; (2) after etching, rinsing, and drying; (3) after ethanol drying, and (4) after adhesive application. Replicas were analyzed with SEM and blisters were counted by independent observers. Statistical analysis was performed with Kruskal-Wallis ANOVA and Dunn's multiple comparison tests at p = 0.05. No blister formation occurred on replicas taken prior to adhesive application, while blister formation was evident in all replicas of bonded interfaces, irrespective of the adhesive system. No statistical difference in the number of droplets was found between All Bond 2, XP-Bond, and Clearfil SE Bond. Xeno III exhibited the highest number of blisters. Specimens bonded with Pre-Bond unfilled resin of All Bond 2 without primer application showed no blister formation. This study revealed that blister formation occurs only if the priming agent of the adhesive system was applied, thus supporting the hypothesis that blistering occurs due to adhesive phase separation or insufficient solvent evaporation.

To evaluate the effect of different curing modes of dual-curing luting systems and root regions on the push-out strength of fiber posts to intraradicular dentin. Forty-two extracted premolars with a single root canal were sectioned at the cementoenamel junction and the roots were endodontically treated. The roots were divided into two groups according to two dual-curing luting systems: (1) XP BOND-Dual Cure/Calibra resin cement; (2) XP BOND-Dual Cure/FluoroCore 2. For each luting system, three different curing modes were applied to the dentin adhesive and resin cement: "Self-cure and Self-cure (SC&SC)", "Self-cure and Dual-cure (SC&DC)", and "Dual-cure and Dual-cure (DC&DC)". Translucent Easy fiber posts (Dentsply Maillefer) were luted in the roots. A thin-slice push-out test was performed, and the data of push-out strength were analyzed using three-way ANOVA with luting system, curing mode, and root region (apical, middle and coronal) as factors. Tukey's test was used for post-hoc comparisons. The push-out strength of XP BOND-Dual Cure/Calibra was significantly lower when Calibra resin cement was self-cured than when it was dual-cured (SC&SC: 6.04 +/- 2.65 MPa; SC&DC: 10.69 +/- 3.01 MPa; DC&DC: 10.72 +/- 3.63 MPa; p < 0.05). The curing modes did not affect the push-out strength of XP BOND-Dual Cure/FluoroCore 2 (SC&SC: 7.90 +/- 3.94 MPa; SC&DC: 8.32 +/- 2.73 MPa; DC&DC: 9.27 +/- 4.12 MPa; p > 0.05). The coronal push-out strength was significantly higher than the apical push-out strength (p < 0.05). Retention of fiber posts in root canals was affected by the curing modes of dual-curing luting system and root regions.

To evaluate the effect of different intermediate resin agents on composite-to-composite microtensile bond strength (microTBS). Composite disks (8 x 4 mm) of Gradia Direct Anterior (N = 15) and Filtek Supreme XT (N = 15), stored in a saline solution at 37 degrees C for 1 month, were sandblasted (Microetcher, 50 microm-Al2O3), cleaned (35% H3PO4), and randomly divided into five groups (N = 3) according to the intermediate agent applied. Two flowable composites (Gradia LoFlo; Filtek Supreme XT Flow) and two adhesives (Adper Scotchbond 1XT, Scotchbond Multi-Purpose) were used. As a control, no intermediate agent was applied. Each disk was incrementally repaired (8x8 mm) with the same resin as the respective substrate. By serially cutting each repaired specimen, multiple sticks of about 0.8 mm2 in cross-section were obtained and loaded in tension until failure at a cross-head speed of 0.5 mm/minute. Data were statistically analyzed. Failure mode was examined by stereo- and scanning electron-microscopy (SEM). Additional specimens were prepared to morphologically evaluate the composite-to-composite interfacial quality by SEM analysis. Composite substrate and intermediate agent were significant factors (Two-way ANOVA, P < 0.001). Bond strengths achieved with Gradia Direct Anterior were higher than Filtek Supreme XT. The application of flowable composites resulted in statistically superior microTBS than adhesives and control (Tukey test, P < 0.001). Failure mode was predominantly cohesive (flowable composites), cohesive/adhesive (adhesives) and adhesive (no treatment). Flowable composites and adhesives showed a good interfacial quality.

(1) To evaluate the interfacial strength between FRC Postec posts and three luting agents (Multilink, Variolink II, and MultiCore Flow) following different surface treatments, and (2) to observe the effect of sandblasting (Rocatec Pre) on the surface morphology of methacrylate-based fiber posts. The posts received one of the following surface treatments: (1) sandblasting, (2) sandblasting + silanization, (3) silanization or (4) no treatment. The three luting agents were bonded to the post and the post-cement bond strength was evaluated with the microtensile test. SEM observation of sandblasted and nontreated posts was performed. Post-cement interfaces were also evaluated. Data were statistically analyzed with two-Way ANOVA with post treatment and luting agent as factors. Tukey's test was applied for post-hoc comparisons. Post treatment and the interaction between type of luting agent and type of post treatment were significant factors for bond strength (p < 0.001). The type of luting agent did not significantly influence bond strength (p = 0.07). Sandblasting + silanization performed better than sandblasting or no treatment (p < 0.001). Silanization resulted in significantly higher bond strengths than no treatment (p = 0.045). No differences were detected between sandblasting + silanization and silanization. SEM observation revealed an increased surface roughness and exposure of fibers in sandblasted posts. Silanization was confirmed to be a reliable method for improving the bond strength of resin luting agents to fiber posts. Bond strength of resin luting agents to fiber posts was not influenced by the type of luting agent. The sandblasting procedure modified the methacrylate-based post surface texture.