Bonding performance of self-etch adhesives to enamel bleached with different peroxide concentrations.

The aim of this study was to evaluate the micro-shear bond strength (µSBS) of one and two steps self-etch adhesive systems after enamel bleaching with photo-activated bleaching systems of different hydrogen peroxide (HP) concentration. Occlusal enamel of forty intact human molars were flattened and assigned into four groups. GI Unbleached, GII, GIII, and GIV were bleached with Pyrenees (3.5% HP), GC TiON (20% HP), and Hi-Lite (35% HP) respectively. Enamel treatment with one and two steps self-etch adhesives (Clearfil S3 Bond- S3, and Clearfil SE Bond-SE) then micro-tubes were fixed on enamel and filled with AP-X composite (n=5). Bond was tested with the universal testing machine. Data were analyzed using two-way ANOVA and Tukey's tests at 5 % level of significance. The µSBS was significantly different between adhesives (F=154.46; p<0.05) and bleaching systems (F=77.33; p<0.05) with significant interaction. Specimens bonded with S3 shows a significantly lower µSBS than those bonded with SE (p<0.05) in all groups. For both adhesives the bleached groups demonstrate lower µSBS than unbleached except specimens bleached with Pyrenees and bonded with SE (p>0.05). A significant difference was observed between groups of the bleaching systems (p<0.05). Different peroxide concentrations photo-activated bleaching systems adversely affect µSBS of one and two steps self-etch adhesives. Low concentration system (Pyrenees) does not influence the bond strength of two steps adhesive.

FTIR and SEM of a novel chemical conditioning on the zirconia intaglio surface

Objectives: The aim of this study was to evaluate chemical and topographical changes in the intaglio zirconia surface induced by chemical conditioning solutions using FTIR and SEM analysis. Material and method: twelve plates for each FTIR and SEM tests from each zirconia materials (UPCERA HT White, BruxZir® Solid Zirconia, and Copran® Multilayer), milled by a Yenadent CAD/CAM system, sintered and divided randomly into a three groups. A different surface conditioning was applied to the intaglio surface of each group: 30% hydrogen peroxide, 30% citric acid and control group. Result and discussion: by using of the FTIR spectroscopy, an evidence of new bands formation appeared at 1637cm-1 and 3352cm-1 due to the high oxidizing effect of hydrogen peroxide, and at 630cm-1 and 1663cm-1 due to the chelating action of citric acid, and simultaneously, SEM assessment of the surface topography took place, to identify lines, scratches, or surface dissociation that appeared on the intaglio zirconia surface after conditioning. Conclusion: such analysis provides an enhancement of new convenient, less expensive, reliable trials to improve micro-bond strength of luting cement to Y-TZP ceramics.

Nanoleakage of current self-etch adhesives bonded to artificial carious dentin.

PURPOSE: To evaluate the nanoleakage of one- and two-step self-etch adhesives bonded to artificial carious dentin. METHODS: Deep dentin of 24 human molars was exposed and divided into four groups. One group served as control while the others were demineralized in artificial demineralization solution for 10 minutes, 6 hours, and 24 hours. Roots were sectioned and the crowns were bonded with one- and two-step self-etch adhesives (Clearfil S3 and Clearfil SE Bond) then restored with flowable composite (Estelite Flow Quick). Specimens were exposed to intrapulpal pressure through a tube connected to a barrel filled with silver nitrate solution in total darkness for 24 hours and then sectioned into two mid-slabs that were photo-developed and prepared for nanoleakage evaluation using FE-SEM and EDX. Penetration of silver into the hybrid and adhesive layers was evaluated and compared between adhesives and dentin condition. Data were statistically analyzed by Kruskal-Wallis test (alpha = .05). RESULTS: Increasing depths of demineralization were observed with increasing demineralization time. There were statistically significant differences for both adhesives (P < 0.05) and dentin demineralization (P< 0.05) in hybrid and adhesive layers. Normal dentin interfaces revealed no or slight nanoleakage regardless of adhesive. The bonded interface treated with one-step Clearfil S3 showed significant differences between normal and demineralized dentin. Also a trend towards increases in nanoleakage with the increasing of the demineralization time was demonstrated. Different patterns of nanoleakage were observed within adhesives.

Bond strength and ultimate tensile strength of resin composite filled into dentine cavity; effect of bulk and incremental filling technique.

OBJECTIVES: The aim of this study was to evaluate the relationship between micro-tensile bond strength (muTBS) and ultimate tensile strength (UTS) of resin composite restorations in cavities filled by a bulk or incremental technique using the micro-tensile test. METHODS: Class I cavities (4mm long, 3mm wide, 3mm deep) were prepared into dentine of sixteen human molars. All cavities were bonded with Clearfil SE Bond and restored with AP-X composite with either a bulk or incremental technique. After storage in water for 24h, the teeth were vertically sectioned to yield two slabs. Each slab was sectioned into three sticks. Sticks of one slab were trimmed into an hourglass of 0.7 mm2 area at resin-dentine interface for bond strength measurement while the other sticks were trimmed at the centre of the restoration for UTS measurement. Specimens were tested in tension at 1mm/min until failure. The results obtained were statistically analysed using two-way ANOVA and post hoc test (alpha=0.05). Pearson's correlation test was used to identify any correlation between muTBS and UTS for each filling method. RESULTS: Both muTBS and UTS of resin composite decreased towards the bottom of the cavity (p<0.05). The bulk technique group presented lower muTBS than the incremental technique groups at all regions (p<0.05). In bulk filled restoration, there was a strong positive linear relationship between mean values of muTBS and UTS of resin composite based on the depth (r2=.99; p<0.05), while in incremental restoration there was no relationship between the variables. CONCLUSIONS: There was a relationship between muTBS and UTS of resin composite filled into dentin cavity in bulk technique.

Effect of adhesion to cavity walls on the mechanical properties of resin composites.

OBJECTIVES: To evaluate the regional mechanical properties of resin composite under free and constrained conditions during polymerization. METHODS: Forty cavities (8mm diameter and 5mm depth) were fabricated in resin blocks. Half of the cavities were bonded and the other half left un-bonded. The cavities were bulk-filled with one of the following composites: flowable composite (Palfique Estelite LV, Unifil Lo Flo), and Universal composites (Clearfil AP-X, Palfique Estelite Sigma), followed by photo-curing for 30s. After 24h storage, each specimen was sliced parallel to the long axis to harvest three slabs. The middle slab was serially sliced to harvest five sticks, which were trimmed to an hour-glass shape for measurement of regional ultimate tensile strength (UTS). The remaining semi-circular slabs were polished for microhardness measurement (KHN). Data were analyzed using three-way ANOVA followed by Tukey's HSD test and t-test (alpha=.05). RESULTS: The KHNs of all the resin composites were not significantly different between the bonded and unbonded groups at each cavity depth (p>0.05). The Ucapital TE, CyrillicS of the bonded group of flowable composites was significantly lower than those of the un-bonded group at the upper regions (p<0.05), while for universal composites, there were no significant differences in UTS between the bonded and un-bonded groups (p>0.05), although Clearfil AP-X had a trend toward lower UTS under the constrained condition at the upper regions. SIGNIFICANCE: The UTS of resin composite decreases due to polymerization shrinkage stress when polymerized under a constrained condition, however, these effects were dependent upon regions in the cavity and the resin materials.

Effect of light irradiation time on the mechanical properties of two flowable composites with different initiation systems in bonded and unbonded cavities.

The aim of this study was to evaluate the regional mechanical properties of flowable composites with different initiation systems under free and constrained conditions. Forty cavities fabricated in resin blocks with or without bonding treatment were bulk-filled with Estelite Flow Quick (EFQ) or Palfique Estelite LV (ELV), followed by light irradiation for 10 or 30 seconds. Each specimen was sliced to three slabs parallel to the long axis. The middle slab was serially sliced from top to bottom to harvest three sticks for ultimate tensile strength (UTS) measurement. The remaining slabs were polished for microhardness (KHN) measurement. The results indicated that the UTS and KHN of both flowable composites decreased toward the bottom of the cavity and increased with prolonged light irradiation time. At the upper cavity region, UTS values of the bonded groups were significantly lower than those of the unbonded groups, except for the 10-second light irradiation group of EFQ. As for KHN, the values did not change significantly for both flowable composites between the unbonded and bonded groups.