Admira is a light polymerizing, ormocer-based restorative material. It contains three-dimensional polymerizable inorganic-organic polymer chains and aliphatic and aromatic dimethacrylate. The resin matrix of Admira consists of ormocer, Bis-GMA, UDMA, and TEGDMA. It contains 78% inorganic filler, glass ceramic, and SiO2 particles of 0.7 μm, and it polymerizes under halogen light [9]. In this study, the Admira bond is compared with the other fifth and six generation materials to demonstrate if these adhesive systems can be used as alternative adhesives to the Admira bond when depleted.
The results of this study showed that the Admira bond had the highest bond strength for both enamel and dentin followed by the Prime & Bond NT with no significant difference between the two adhesives when they were applied to enamel and with significant difference when they were applied to dentin. Prime & Bond NT is related to the Etch & rinse system and has nanofilled, fluoride-releasing character. The nanofiller may improve the adhesive strength to both enamel and dentin and sufficient film thickness from one-coat, one-cure technique. The nanofiller particles are less than one hundredth of the average diameter of dentinal tubules at enamel-dentin junction (0.8 μm), and therefore they are fully capable of entering the tubules and the demineralized zone of the dentin. The nanofiller serves as an additional cross-link and therefore strengthens the adhesive layer [10, 11]. It was concluded that nanoparticle hydroxyapatite particles, produced by hydrothermal routes, were used to infiltrate sections of human dentine. The effect of the particles in blocking the channels in dentine in order to prevent fluid motion was shown. In the long term, this approach may offer an effective means of treating sensitive teeth [12]. Particles prepared at pH 12 had a mean length of approximately 70 nm and diameter of approximately 30 nm. These showed the most promising infiltration results, with up to 90% of the tubules being fully or partially occluded [13]. In the present study, these properties explain the recorded cohesive mode of failure of the Admira bond. The viability of the SEM technique for the 3D characterization of dentine tubule structure was considered. It has shown the capability to capture the complex structure and interconnection in a porous insulating biological tissue with nanoscale resolution, but over volumes covering thousands of cubic micrometres [14].
The lowest shear bond strength was recorded for Prompt-L-Pop with both of enamel and dentin. Prompt-L-Pop is related to the self-etching, one-step adhesive system. This result may be attributed to the effectiveness of self-etching primer systems on properly etching the enamel which also reflected on the adhesive mode of failure of this type of adhesive. Etching of enamel by self-etching primer is less predictable than that of phosphoric acid etching. Removal of smear layer by a separate etching step before bonding would produce a more reliable and durable bond to dentin [15]. Excite and AdheSE exhibited an intermediate shear bond strength with significant difference from the Admira bond and Prime & Bond NT adhesives.
Admira bond is a specific formulated primer/adhesive ormocer-based, light-curing system for enamel and dentin bonding. It was reported that Admira bond contains special adhesive ormocer with calcium complexing functionality which enhances the bond strength on tooth structure. Because of the chemical affinity, Admira bond adheres firmly to both the tooth structure and the restorative material. This explains the cohesive mode of failure of the Admira adhesive system [9]. Ormocer-based composite should be used with the matching specially formulated primer/adhesive system, and the practitioner is cautioned not to indiscriminately exchange specific dentin bonding agents for nonspecific ones. This conclusion is somewhat in conflict with the results of our study which indicated that ormocer could be used with nonspecific primer/adhesive system, this may be attributed to the difference in the adhesives used. The researchers in that study used nonspecific self-etching adhesive in addition to specific primer/adhesive for studying microleakage not the bond strength [16].
The bond strength of Prime & Bond NT and that of Excite adhesive to enamel was significantly different. This result may be attributed to the chemical composition of the adhesives. Although both types of adhesives are nanofilled and alcohol based, Prime & Bond NT is acetone based while Excite is ethanol-based adhesive but Prime & Bond NT contains two different types of resins, T-Resin (small, cross-linked molecule) and D-Resin (small, mobile resin molecule). These types of resins enhance resin infiltration compared to Excite adhesive; this explains the significant difference between the bond strength obtained with Prime & Bond NT and Excite adhesives to enamel. Adhesives that use acetone as the solvent may require a moist dentin substrate to produce adequate bonding [17]. Also, these factors control the behavior of these adhesive during debonding.
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